Great video! I am curious whether the polarization rotation is correct at 3:20. Thorlabs "Polarization Handedness Convention" by Erik Gentzsch 10 July 2017, where the handedness is described by also by looking into the beam ("observer looks along the -z direction towards the light source"), suggests that the polarization rotation should be anticlockwise (left-handed). I guess my question is what does "back face" mean in the video? If I would look at the whole system (circular light and initial linear polarization) as looking towards the beam, the linear polarization would be flipped?
@user-or8vw3dh6i As you note, the rotation direction of the polarization vector depends on whether the observer is looking towards the light source or away from it. In addition, the rotation direction also depends on whether the vector is being plotted as a function of time or as a function of distance. In the “Polarization Handedness Convention” technical note, the polarization vector is plotted with respect to the distance axis (z), while in the video we are showing the polarization vector plotted with respect to time (t). To see why the rotation direction is flipped between time and distance plots, consider light travelling from a source on the left, to a destination on the right. If the light could be frozen at one instant of time, the light closer to the destination would have been emitted at an earlier time than the light closer to the source. Because of this, the corresponding polarization vectors’ effective timestamps would become earlier as distance from the source increases. The technical note plots the polarization vectors with respect to distance from the source, so the vectors farther from the plot’s origin correspond to light emitted at earlier times. Alternatively, measurements of the polarization vector might be made at only one physical position, but over some length of time. When the measured polarization vectors are plotted with respect to time, the vectors plotted closer to the plot’s origin have earlier timestamps than the vectors plotted farther away from the origin. This is the plotting approach taken in the video. Since the order of the vectors is opposite depending on whether they are plotted with respect to time or distance, it affects the apparent rotation direction. However, the plotting approach does not affect the “handedness” of the light. When looking into the source, right circularly polarized light rotates clockwise when plotted along the time axis and anti-clockwise when plotted along the z-axis. (For more information, see Polarized Light and Optical Systems, by R. A. Chipman et al., 2019, Chapter 2.10.)
These tutorials are incredible. Clear, short, and immediately applicable. I’m definitely going to use them for the incoming master’s students in my lab.
This makes us so very happy! A lot of love has gone into these videos, and we are thrilled to hear they're the helpful, straightforward, and practical demonstrations they're meant to be. Please let us know if there are any additional concepts that would be helpful for your incoming students.
Great video here ! With the circularly polarized light produced with the quarter wave plate , Is the intensity recorded after the last linear polarizer half the initial intensity with the first linear polarizer ? I am asking because the circularly polarized light should have equal components of polarization . Please let me know if there is an error
@josephokaidaafour693 You have the right idea! Half of the light output by the quarter-wave plate would ideally be lost after passing through the second linear polarizer, because the circularly polarized light includes two equal-intensity, orthogonally polarized components. In practice, however, the amount of transmitted light is actually a little less than half, since some light will be lost to optical reflections from the faces of the optics.
Thank you for the video! It is a great demonstration for polarization control. I have a follow up question concerning the QWP. Assuming we placed the QWP 45 degree to the polarizer infront, so we already got a circularly polarized light. If this circularly polarized light get reflected on some surface and remain as a circularly polarized light, and pass through the QWP on the opposite direction, what kind of light we will get? Thank you in advance for your reply.
The quick answer is that the light, after reflecting off the mirror and then passing a second time through the quarter wave plate, will be linearly polarized orthogonal (at 90 degrees) to the input linear polarization state. This occurs because the reflection from the mirror reverses the circular polarization direction of the light. Since the transmitted and reflected beams of linearly polarized light are orthogonally polarized, a polarizing beam splitter (PBS) placed on the input side of the QWP is often used to separate the reflected beam from the transmitted beam path. Please let us know if it would be helpful for us to show this in a video.
Sir .., Thank you for your demonstration... It clears most of my concept but i have a doubt...!!! Q1)What happens if we pass a Unpolarised light through quarter wave plate or half wave plate...? Does it remain Unpolarised or it gets Linearly polarized or CPL...? And also... Q2) Is there any effect on intensity of light when it passes through waveplate...? I mean will you please demonstrate same experiment twice...? 1) without 1st Polariser 2) without 2nd Polariser I know it's too much to ask sorry...!!
If the light incident on a wave plate is truly unpolarized, the light transmitted by the wave plate will remain unpolarized. When the photons pass through a wave plate, each photon is delayed by an amount that depends on its orientation with respect to the wave plate's axes. In unpolarized light, the polarization direction of each photon is random and not related to the polarization direction of any other photon in the group. When this group of photons passes through a wave plate, the delayed photons in the output light are still randomly oriented with respect to one another, so the output light is still unpolarized. A wave plate cannot organize unpolarized light into a pure polarization state, such as linear or circularly polarized light. The intensity of light output from the wave plate will be slightly less than the input intensity but not because of the phase-delay properties of the wave plate. There will be some light lost due to reflections from the front and back faces of the wave plate, and there is always some attenuation when light is transmitted through a material, even when the material is transparent. The purpose of the first linear polarizer is to ensure linearly polarized light with a stable orientation is incident on the wave plate. In this demonstration, there is an isolator attached to the output of HeNe laser. Since the light transmitted by the isolator is linearly polarized with a stable orientation direction, following the procedure after removing the first polarizer would provide a result similar to that shown in the video. The first linear polarizer was included in the setup to demonstrate a procedure that could be used even if the light source does not provide linearly polarized light. The alignment procedure we used to determine the orientation of the wave plate required the second linear polarizer in the path. The polarizer could have been removed once the wave plate was aligned, but we kept it in the path as an analyzer to also demonstrate how close we were to circular polarization after the wave plate.
Hi, thanks for the video. Are these polarizers and quarter waveplates direction sensitive? Do they have specific input/output sides or can they be used in any direction as input/out?
@naveed3619 The linear polarizers and quarter-wave plates in the video can be used with either side facing the input beam. They do not have specific input and output sides.
Thanks for the very informative video But what do you think about another faster way to get the circular polarizer, by placing the filters by the orders: Linear Polarizer_1 - QWP - Linear Polarizer_2. Rotate the QWP slowly, with every rotation step you check again the power after the LP_2 by rotating it in the full circle. If the power fluctuates minimum after LP_2 when you rotate it, then you got nearly a Circular Polarizer beam.
Thanks for pointing out a variation on the approach! We have found the technique you describe to be convenient when the second linear polarizer continuously rotates in a motorized mount, but we have felt that approach can be cumbersome when the optical mounts must be manually rotated.
Hello Sir, May I ask as the number of Quarter waveplates ( 266nm, 350-850nm) are available, which quarter wave plate should I use if I am going to use the band pass filter of 365nm? And if we are using band pass filter then can we use the arrangement like this? light source----------band pass filter----Polarizer------quarter waveplate------sample? Look forward to hearing from you soon. Thank You so much!
@kainattalat5739 Wavelength is definitely an important parameter to consider when choosing a quarter-wave plate (QWP), since the exact delay (retardance) provided by the QWP depends on the wavelength of the light. Retardance data is available for each QWP, and we recommend looking at this specification to determine the delay a particular QWP will provide over the wavelength range of your filtered light source. The retardance of the QWP can also be affected by the angle of incidence and other operating conditions. Different types of QWPs are designed for different cases. These types include true zero-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8635 ), pseudo-true zero-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7234 ), and multi-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7234 ). QWPs optimized for broader spectrums include achromatic ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=854 ) and superachromatic ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2193 ) types. The details or your application determine how to balance the different options to choose the best option for your particular setup. Our Tech Support would be happy to discuss the different options with you, as well as discuss particulars about your setup ( techsupport@thorlabs.com ).
Related science question: in demos where they shine light through two or more polarizers and turn one of them to either darken or brighten the light, they often explain it as its orientation blocks more or fewer of the light, but, maybe something subtle is going on instead... does a polarizer in reality let through 100% of light in all orientations and turning it merely changes the affected light's wavelength from visible light to some wavelength we cannot see? Are there cases where that happens?
Commonly used linear polarizers either absorb or redirect the unwanted polarization state. None that we are familiar with convert light in the unwanted polarization state to a different wavelength, unless you consider the heat radiated by an absorbing polarizer to effectively be a wavelength conversion. Absorbing polarizers' temperatures can rise when they are used, since they soak up the light polarized along one direction, but the heat they radiate will not be linearly polarized. When the unwanted (rejected) polarization state is reflected or redirected, it is possible to trace both beam paths’ output by the polarizer and confirm that their wavelength has not changed and that they are orthogonally polarized. Here's a quick overview of different polarizers and the method they use to provide a linearly polarized beam: - Wire grid polarizers transmit light polarized in one direction and reflect the light polarized in the orthogonal direction. This is illustrated by the drawing at the top of www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=5510&YVI=9 . - Film polarizers absorb the unwanted polarization state. One kind of film polarizer uses polymers ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=4984&YVI=9) and another uses nanoparticles (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=752&YVI=9 ). - Beamsplitter cubes transmit the two polarization states in perpendicular directions, as shown by the drawing in the overview of www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8095&YVI=9 . - Crystal-based polarizers separate the two polarizations by creating an angle between their propagation directions, as illustrated at the top of www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=745&YVI=9 .
@@thorlabs Wow, so those polarizers from your links look way more complex than what I had in mind haha, barely understood a lot of your words and don't buy polarizer type stuff, I usually surf for science explainer videos and had clicked on yours... which interested me in its mention of slower and faster speeds for light. Below is a sample video with the type of polarizers and effects I had in mind. At 1:30 and at 1:45 in this other video by Action Lab (m.th-cam.com/video/f0XttPQ6g9c/w-d-xo.html) he explains how manually turning a thin sheet of transparent polarizer will block more light (darken) and how inserting an extra polarizer in between two will then let through more light (re-brighten). What I was wondering is if maybe light wasn't blocked... maybe instead the 'missing' light had shifted into a wavelength we couldn't detect. (In those simpler polarizers like from the video I linked)
@@localverse The interaction between light and a linear polarizer is more complicated than the words "block" and "pass" suggest. While linear polarizers do not change the wavelength of the light, polarizers are not filters that just pass photons with the desired polarization. Instead, the interactions between the photons and polarizer can result in changes to the photons' polarization orientations, as well as to the photons' directions of propagation. The closer a photon's polarization orientation is to being parallel with the orientation of the polarizer's transmission axis, the more likely it is that interacting with the polarizer will change the photon's polarization orientation to be parallel to the polarizer's transmission axis. The light transmitted by the linear polarizer consists of photons that were changed to have, in addition to those that initially had, this polarization orientation. Malus' law is used to calculate the intensity of this transmitted light as a function of the angle between the transmission axis and the polarization orientation of the incident light. Light that is not transmitted is absorbed, reflected, or redirected.
@@thorlabs Thanks for taking the time to reply... I'll reread it a few times to grasp it better because the accuracy of your explanations feels reliable. If you have any suggestions for a source to learn how photons interacting with a polarizer can change their direction and polarized orientations, especially for the lay person, will gladly check that out!
@@localverse Unfortunately, the references we’re familiar with assume a familiarity with electromagnetic waves. For example, the book Polarized Light and Optical Systems by Russell A. Chipman, Wai-Sze Tiffany Lam, and Garam Young provides some descriptions and the background mathematics for various polarizer types. We would love to hear if you happen to come across a source that you think explains the subject well!
Thanks a lot! In addition to this video, could you explain how to measure circularly polarized light from materials of which circularly polarized light is only a few % of total amount of emitting light? If you could upload some instruction video like this, that would be helpful!
When the light is not purely linearly or circularly polarized, the light's four Stokes polarization parameters can be used to accurately and precisely describe the polarization state. These parameters can be measured, for example, using a wave plate and a linear polarizer. If you have a polarimeter, it can also provide these values. The Stokes parameters are typically labeled S0, S1, S2, and S3. The first parameter (S0) is the total intensity of the light. The others are the proportions of horizontally / vertically linearly polarized light (S1), ±45° linearly polarized light (S2), and right- and left-circularly polarized light (S3). Together they characterize the light's elliptical polarization state, which is sometimes plotted on a Poincaré sphere. The Stokes parameters also provide information about the amount of unpolarized light included in the beam. Unfortunately we cannot detail the measurement here, but we will definitely add the topic to the list of upcoming videos demonstrations!
There is now a Video Insight available that demonstrates how to measure the Stokes parameters (th-cam.com/video/pR4r7gMyN5U/w-d-xo.html)! The video also discusses the relationship between these parameters and the light's polarization state. Let us know what you think!
First, Thank you for your video. I have a question. If QWP Angle is same with first polarizer, Power is checked at minimum. That's understand because output light and second polarizer have different direction(90). But, If QWP Angle change degree(90), I don't understand why power also is checked at minimum. When I studied, I think maximum because QWP make linear polarized light. For example... Degree 0 : Horizontal Degree 0~90 : Elliptical, Circle Degree 90 : Vertical Please answer. I wait your support. Thank you.
Thank you for your question! When light passes through a wave plate, the light is delayed. The delay provided by a wave plate is special, because the amount of delay depends on the light's polarization direction. A wave plate delays light polarized parallel to the wave plate's slow axis more than light polarized parallel to the wave plate's fast axis. The difference in delay provided by the two axes determines the wave plate type. The difference in delay provided by a half wave plate is half a wavelength, which is the amount of delay required to convert light from one linear polarization to another linear polarization. The difference in delay provided by a quarter wave plate (QWP) is one quarter of a wavelength. A quarter-wave plate is not able to convert horizontally polarized light to vertically polarized light, because the delay difference it provides is too small. In addition, the direction of the input linearly polarized light needs to oriented between the wave plate's fast and slow axes in order for the wave plate to affect the light's polarization. When one axis of the QWP is parallel to (at a 0° angle to) the transmission axis of the first linear polarizer, the QWP delays all of the light by the same amount. This does not change the polarization state of the light. When the QWP is rotated by 90°, the other QWP axis is parallel to the transmission axis of the first linear polarizer and all of the light is delayed by a different amount. This does not change the polarization state either. The only time the QWP changes the polarization state is when the QWP is rotated to an angle more than 0° and less than 90°. Circularly polarized light is created when the QWP angle is 45°. Otherwise the light is elliptically polarized.
Silly question, but does adding QWP downstream of commerically available lasers (rotated by 45degrees) give a reasonable enough circularly polarized light? Or is it imperative to identify the polarization state of the laser prior to placing a QWP at 45 degree relative to this? Also, how drastic is the performance between multi order qwp as compared to zero order qwp if the intention is to use it for a single laser line? Thanks! Great set of videos!
It is possible that a linear polarizer is not needed between the laser and the QWP, but it depends on your laser's output and your application. Please contact Tech Support (techsupport@thorlabs.com) if you’d like to discuss your particular application. Note that not all commercially available lasers output linearly polarized light, and if one does, its polarization state may not be stable. In most applications, you should not see an appreciable performance difference between zero-order and multi-order wave plates, assuming the laser line is narrow and within the operating wavelength of the wave plate. A multi-order wave plate may also be preferable, since it should be more robust to handling.
*Saw this today. I am visiting china now. Can possibly send 2 samples of identical microlens arrays for an HMD that I would like to prototype? Thanks in advance!*
Please contact a member of our Sales or Technical Support teams to discuss your need. Contact information for these teams can be found on this page: www.thorlabs.com/locations.cfm .
the most funny beams are Tangentially and Radially polarized, I used to make then with a pair of lenses, specially oriented KGW crystal , retardation plates (1/2) and polarizer for selecting the polarization I like
The polarization state of light can be determined using an instrument called a polarimeter. We demonstrate how to build one using standard components in another Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ). A complete device and software package can also be purchased (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1564&YVI=9). Would you help us understand what sigma± you are referring to?
Optic axis is direction along which if a wave propagates, it suffers no double refraction. At 2:32 light is propagating along optical axis then why it's suffering double refraction, there should be either E-wave or O-wave means component either along fast axis or along slow axis should be there. In that case we should get linearly polarized light regardless of angle of incidence. Where am I wrong? Plz answer I'm so confused
@Ranbir.Bhardwaj We think that a label used in the animation that begins at 0:43 may be the source of your confusion. In the animation, we mistakenly labeled the horizontal axis “Optic Axis.” The horizontal axis should be labeled “Optical Axis,” since it describes propagation direction of the light and is not related to the birefringent properties of the wave plate. In this video, we use the labels “fast axis” and “ slow axis” exclusively to describe the wave plate’s birefringence. Please let us know if this does not help with your confusion.
@zedius24 There should not be any power loss from the transformation itself. However, there are typical losses that occur when light propagates through an optic, such as reflection losses at the front and back surfaces of the wave plate and material-related losses. These losses can generally be determined from the optic’s transmission specifications.
@Xinglin Zeng As you hint, this video demonstrates a technique for generating circularly polarized light, but whether the light is right- or left-circularly polarized is not known. One way to determine the handedness of the light is to measure its polarization state, and there is now a Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ) that describes how to make those measurements. Another approach is to identify the fast and slow axes of the waveplate, so that the quarter-wave plate can be oriented to provide the desired handedness of circularly polarized light. This technique is demonstrated in another Video Insight ( th-cam.com/video/XQwiPm5OtSk/w-d-xo.html ). We hope you find these videos useful!
Can we rotate the polarisation of light by 45 degrees (vertically polarised light to diagonally polarised light) by using half wave plated rotating 22.5 degrees from its axis?
Yes, people do use half-wave plates as linear polarization rotators. For the case you described with a linear polarization input and an ideal half waveplate, the angle between the incident linear polarization and the fast axis of the wave plate should be 22.5° (theta). Then, the angle between the incident linear polarization and the output linear polarization directions will be 45° (twice theta). This rotation occurs for elliptically as well as linearly polarized light, since an ideal half-wave plate creates a 180° (1/2 wavelength) phase delay between the two polarization components parallel to the fast and slow axes of the wave plate. Note that while linearly polarized input light will be output as linearly polarized light, the half-wave plate reverses the handedness of elliptically polarized light in addition to rotating its polarization orientation. This means right circularly polarized light incident upon a half wave plate will become left circularly polarized and vice versa. Because of this phenomena, it may be better to think about the incident polarization state flipping around the half-waveplate’s fast axis. Would it be helpful if we created a video Insight to discuss this in more detail?
Would you help us better understand your question? Which component's polarization axis are you thinking of? Are you referring to the light beam's magnetic field, which is always perpendicular to its electric field?
No sir. I was reading a research article regarding magneto optical birefringence measurement where an external magnetic field ( not light beam's magnetic field) which was in perpendicular to light direction. In that experiment they are telling to orient the optimum angle of polarization direction of the incident linearly polarized light with respect to magnetic field as 45degree and also to orient polarization direction of incident light parallel and perpendicular to magnetic field.
@@mubeenarafi3920 The alignment of the devices in this setup was performed using the plane of the table as a reference, and one possible approach for performing the work described in the paper is to also align the external magnetic field with respect to the table. This can be done by choosing a magnet that provides a field with the desired strength and shape and then orienting the magnet as required. If the table is the reference plane, then the techniques in ( th-cam.com/video/W9pALZ5Z8ms/w-d-xo.html ) can be used to align the polarizer horizontal and vertical with respect to the table and then the techniques in ( th-cam.com/video/cqLPD5dL9zY/w-d-xo.html ) can be used to align the polarizer at 45 degrees.
what will happen if i replace the output linear polarizer by a halfwave plate in this apparatus, how will the half wave plate affect the circularly polarized light?
@jishnusasidharan2165 If the light from the quarter-wave plate is circularly polarized and incident upon a perfect half-wave plate, then the light output by the half-wave plate will also be circularly polarized. However, the handedness of the circular polarization state output from the half-wave plate will be opposite the handedness of the incident circular polarization state. More specifically, the handedness of the circularly polarized light from the quarter-wave plate will be either right- or left-circularly polarized. For an observer facing the light source, we define right-circularly polarized light as having a polarization vector that rotates clockwise around the optical axis. Left-circularly polarized light has a polarization vector that rotates counterclockwise. To know the handedness of the light, the user must know the orientation of the quarter-wave plate’s fast axis with respect to the transmission axis of the input linear polarizer. Another of our Video Insights ( th-cam.com/video/XQwiPm5OtSk/w-d-xo.html ) demonstrates a method that can be used to find and distinguish the fast and slow axes of a wave plate to know the orientation. Alternatively, we have also demonstrated how to build a polarimeter in a third Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ), which could be used to measure the handedness.
If I had linearly polarized light parallel to the y-axis and a quarter wave plate with a fast axis initially parallel to y-axis and later on to x-axis , what would be the difference between those waves ? Could I say that between those two waves the first would forego the later by π/2 ?
You've got the concept! The first wave’s polarization state is parallel to the fast axis and the second wave’s polarization state is parallel to the slow axis. Ideally, a single pass through the quarter-wave plate will result in the phase of the second wave being π/2 larger than the phase of the first wave. But in practice, design and manufacturing limitations mean it is important to check the retardance plot of your wave plate to determine the exact phase difference (retardance). The retardance of physical wave plates is highly wavelength dependent, even over the wave plate's operating range. Also note that many quarter-wave plates provide a phase difference equal to the sum of π/2 and some multiple of 2π, instead of an exact π/2 difference. A zero-order wave plate is expected to provide a π/2 phase difference at the design wavelength if that is needed for your application.
In this demonstration, we performed a qualitative assessment of circularity based on how steady the detected power remained as the last linear polarizer was rotated. Adding a second quarter-wave plate to the path and taking a series of measurements would make it possible to calculate the Stokes polarization parameters, which characterize the light's degree of polarization, ellipticity, and handedness. Please let us know if you would like a follow-up video showing this analysis!
@Mahima Sharma There is now a Video Insight available (th-cam.com/video/pR4r7gMyN5U/w-d-xo.html) that demonstrates a couple of approaches to using a quarter-wave plate and linear polarizers to analyze light's polarization state. These are do-it-yourself versions of polarimeter instruments (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1564) used to measure the Stokes parameters of the light. The video also discusses the relationship between the Stokes parameters and different polarization states. We hope it is useful to you!
It is tempting to think so, but the ‘s’ in s-polarized light actually stands for ‘Senkrecht,’ which means 'perpendicular' in German. This is because s-polarized light is perpendicular to the plane of incidence, where the plane includes the incident, reflected, and transmitted light vectors.
![[Full] 4 ต่อ 4 Celebrity EP.920 | 3 พ.ย. 67 | one31](http://i.ytimg.com/vi/KwiW2M_kAg4/mqdefault.jpg)
Great video! I am curious whether the polarization rotation is correct at 3:20. Thorlabs "Polarization Handedness Convention" by Erik Gentzsch 10 July 2017, where the handedness is described by also by looking into the beam ("observer looks along the -z direction towards the light source"), suggests that the polarization rotation should be anticlockwise (left-handed). I guess my question is what does "back face" mean in the video? If I would look at the whole system (circular light and initial linear polarization) as looking towards the beam, the linear polarization would be flipped?
@user-or8vw3dh6i As you note, the rotation direction of the polarization vector depends on whether the observer is looking towards the light source or away from it. In addition, the rotation direction also depends on whether the vector is being plotted as a function of time or as a function of distance. In the “Polarization Handedness Convention” technical note, the polarization vector is plotted with respect to the distance axis (z), while in the video we are showing the polarization vector plotted with respect to time (t).
To see why the rotation direction is flipped between time and distance plots, consider light travelling from a source on the left, to a destination on the right.
If the light could be frozen at one instant of time, the light closer to the destination would have been emitted at an earlier time than the light closer to the source. Because of this, the corresponding polarization vectors’ effective timestamps would become earlier as distance from the source increases. The technical note plots the polarization vectors with respect to distance from the source, so the vectors farther from the plot’s origin correspond to light emitted at earlier times.
Alternatively, measurements of the polarization vector might be made at only one physical position, but over some length of time. When the measured polarization vectors are plotted with respect to time, the vectors plotted closer to the plot’s origin have earlier timestamps than the vectors plotted farther away from the origin. This is the plotting approach taken in the video.
Since the order of the vectors is opposite depending on whether they are plotted with respect to time or distance, it affects the apparent rotation direction. However, the plotting approach does not affect the “handedness” of the light. When looking into the source, right circularly polarized light rotates clockwise when plotted along the time axis and anti-clockwise when plotted along the z-axis. (For more information, see Polarized Light and Optical Systems, by R. A. Chipman et al., 2019, Chapter 2.10.)
These tutorials are incredible. Clear, short, and immediately applicable. I’m definitely going to use them for the incoming master’s students in my lab.
This makes us so very happy! A lot of love has gone into these videos, and we are thrilled to hear they're the helpful, straightforward, and practical demonstrations they're meant to be. Please let us know if there are any additional concepts that would be helpful for your incoming students.
Bill, this was absolutely divine. I became a doctor because of this video. I owe you my life. I love you.
so nice after watching many times to understand
Great video here ! With the circularly polarized light produced with the quarter wave plate , Is the intensity recorded after the last linear polarizer half the initial intensity with the first linear polarizer ? I am asking because the circularly polarized light should have equal components of polarization . Please let me know if there is an error
@josephokaidaafour693 You have the right idea! Half of the light output by the quarter-wave plate would ideally be lost after passing through the second linear polarizer, because the circularly polarized light includes two equal-intensity, orthogonally polarized components. In practice, however, the amount of transmitted light is actually a little less than half, since some light will be lost to optical reflections from the faces of the optics.
Thank you for the video! It is a great demonstration for polarization control. I have a follow up question concerning the QWP. Assuming we placed the QWP 45 degree to the polarizer infront, so we already got a circularly polarized light. If this circularly polarized light get reflected on some surface and remain as a circularly polarized light, and pass through the QWP on the opposite direction, what kind of light we will get? Thank you in advance for your reply.
The quick answer is that the light, after reflecting off the mirror and then passing a second time through the quarter wave plate, will be linearly polarized orthogonal (at 90 degrees) to the input linear polarization state. This occurs because the reflection from the mirror reverses the circular polarization direction of the light. Since the transmitted and reflected beams of linearly polarized light are orthogonally polarized, a polarizing beam splitter (PBS) placed on the input side of the QWP is often used to separate the reflected beam from the transmitted beam path. Please let us know if it would be helpful for us to show this in a video.
@@thorlabs thank you very much for the reply. It is very helpful. Of course, a video would be even better ;)
@@pipiche2991 You're very welcome! This topic is now on our list :)
Sir .., Thank you for your demonstration... It clears most of my concept but i have a doubt...!!!
Q1)What happens if we pass a Unpolarised light through quarter wave plate or half wave plate...? Does it remain Unpolarised or it gets Linearly polarized or CPL...? And also...
Q2) Is there any effect on intensity of light when it passes through waveplate...?
I mean will you please demonstrate same experiment twice...?
1) without 1st Polariser
2) without 2nd Polariser
I know it's too much to ask sorry...!!
If the light incident on a wave plate is truly unpolarized, the light transmitted by the wave plate will remain unpolarized.
When the photons pass through a wave plate, each photon is delayed by an amount that depends on its orientation with respect to the wave plate's axes. In unpolarized light, the polarization direction of each photon is random and not related to the polarization direction of any other photon in the group. When this group of photons passes through a wave plate, the delayed photons in the output light are still randomly oriented with respect to one another, so the output light is still unpolarized. A wave plate cannot organize unpolarized light into a pure polarization state, such as linear or circularly polarized light.
The intensity of light output from the wave plate will be slightly less than the input intensity but not because of the phase-delay properties of the wave plate. There will be some light lost due to reflections from the front and back faces of the wave plate, and there is always some attenuation when light is transmitted through a material, even when the material is transparent.
The purpose of the first linear polarizer is to ensure linearly polarized light with a stable orientation is incident on the wave plate. In this demonstration, there is an isolator attached to the output of HeNe laser. Since the light transmitted by the isolator is linearly polarized with a stable orientation direction, following the procedure after removing the first polarizer would provide a result similar to that shown in the video. The first linear polarizer was included in the setup to demonstrate a procedure that could be used even if the light source does not provide linearly polarized light.
The alignment procedure we used to determine the orientation of the wave plate required the second linear polarizer in the path. The polarizer could have been removed once the wave plate was aligned, but we kept it in the path as an analyzer to also demonstrate how close we were to circular polarization after the wave plate.
Hi, thanks for the video. Are these polarizers and quarter waveplates direction sensitive? Do they have specific input/output sides or can they be used in any direction as input/out?
@naveed3619 The linear polarizers and quarter-wave plates in the video can be used with either side facing the input beam. They do not have specific input and output sides.
Thanks for the very informative video
But what do you think about another faster way to get the circular polarizer, by placing the filters by the orders: Linear Polarizer_1 - QWP - Linear Polarizer_2. Rotate the QWP slowly, with every rotation step you check again the power after the LP_2 by rotating it in the full circle. If the power fluctuates minimum after LP_2 when you rotate it, then you got nearly a Circular Polarizer beam.
Thanks for pointing out a variation on the approach! We have found the technique you describe to be convenient when the second linear polarizer continuously rotates in a motorized mount, but we have felt that approach can be cumbersome when the optical mounts must be manually rotated.
Thank you! I'm a physics student, writing a lab report and this video made everything clear, nice work!
Thank you for your comment! We’re happy we could help!
Fascinating Bill. Thank you.
Hello Sir,
May I ask as the number of Quarter waveplates ( 266nm, 350-850nm) are available, which quarter wave plate should I use if I am going to use the band pass filter of 365nm? And if we are using band pass filter then can we use the arrangement like this?
light source----------band pass filter----Polarizer------quarter waveplate------sample?
Look forward to hearing from you soon.
Thank You so much!
@kainattalat5739 Wavelength is definitely an important parameter to consider when choosing a quarter-wave plate (QWP), since the exact delay (retardance) provided by the QWP depends on the wavelength of the light. Retardance data is available for each QWP, and we recommend looking at this specification to determine the delay a particular QWP will provide over the wavelength range of your filtered light source. The retardance of the QWP can also be affected by the angle of incidence and other operating conditions. Different types of QWPs are designed for different cases. These types include true zero-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8635 ), pseudo-true zero-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7234 ), and multi-order QWPs ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7234 ). QWPs optimized for broader spectrums include achromatic ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=854 ) and superachromatic ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2193 ) types.
The details or your application determine how to balance the different options to choose the best option for your particular setup. Our Tech Support would be happy to discuss the different options with you, as well as discuss particulars about your setup ( techsupport@thorlabs.com ).
Related science question: in demos where they shine light through two or more polarizers and turn one of them to either darken or brighten the light, they often explain it as its orientation blocks more or fewer of the light, but, maybe something subtle is going on instead... does a polarizer in reality let through 100% of light in all orientations and turning it merely changes the affected light's wavelength from visible light to some wavelength we cannot see? Are there cases where that happens?
Commonly used linear polarizers either absorb or redirect the unwanted polarization state. None that we are familiar with convert light in the unwanted polarization state to a different wavelength, unless you consider the heat radiated by an absorbing polarizer to effectively be a wavelength conversion. Absorbing polarizers' temperatures can rise when they are used, since they soak up the light polarized along one direction, but the heat they radiate will not be linearly polarized. When the unwanted (rejected) polarization state is reflected or redirected, it is possible to trace both beam paths’ output by the polarizer and confirm that their wavelength has not changed and that they are orthogonally polarized. Here's a quick overview of different polarizers and the method they use to provide a linearly polarized beam:
- Wire grid polarizers transmit light polarized in one direction and reflect the light polarized in the orthogonal direction. This is illustrated by the drawing at the top of www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=5510&YVI=9 .
- Film polarizers absorb the unwanted polarization state. One kind of film polarizer uses polymers ( www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=4984&YVI=9) and another uses nanoparticles (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=752&YVI=9 ).
- Beamsplitter cubes transmit the two polarization states in perpendicular directions, as shown by the drawing in the overview of www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8095&YVI=9 .
- Crystal-based polarizers separate the two polarizations by creating an angle between their propagation directions, as illustrated at the top of www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=745&YVI=9 .
@@thorlabs Wow, so those polarizers from your links look way more complex than what I had in mind haha, barely understood a lot of your words and don't buy polarizer type stuff, I usually surf for science explainer videos and had clicked on yours... which interested me in its mention of slower and faster speeds for light. Below is a sample video with the type of polarizers and effects I had in mind.
At 1:30 and at 1:45 in this other video by Action Lab (m.th-cam.com/video/f0XttPQ6g9c/w-d-xo.html) he explains how manually turning a thin sheet of transparent polarizer will block more light (darken) and how inserting an extra polarizer in between two will then let through more light (re-brighten).
What I was wondering is if maybe light wasn't blocked... maybe instead the 'missing' light had shifted into a wavelength we couldn't detect. (In those simpler polarizers like from the video I linked)
@@localverse The interaction between light and a linear polarizer is more complicated than the words "block" and "pass" suggest. While linear polarizers do not change the wavelength of the light, polarizers are not filters that just pass photons with the desired polarization. Instead, the interactions between the photons and polarizer can result in changes to the photons' polarization orientations, as well as to the photons' directions of propagation.
The closer a photon's polarization orientation is to being parallel with the orientation of the polarizer's transmission axis, the more likely it is that interacting with the polarizer will change the photon's polarization orientation to be parallel to the polarizer's transmission axis. The light transmitted by the linear polarizer consists of photons that were changed to have, in addition to those that initially had, this polarization orientation. Malus' law is used to calculate the intensity of this transmitted light as a function of the angle between the transmission axis and the polarization orientation of the incident light. Light that is not transmitted is absorbed, reflected, or redirected.
@@thorlabs Thanks for taking the time to reply... I'll reread it a few times to grasp it better because the accuracy of your explanations feels reliable. If you have any suggestions for a source to learn how photons interacting with a polarizer can change their direction and polarized orientations, especially for the lay person, will gladly check that out!
@@localverse Unfortunately, the references we’re familiar with assume a familiarity with electromagnetic waves. For example, the book Polarized Light and Optical Systems by Russell A. Chipman, Wai-Sze Tiffany Lam, and Garam Young provides some descriptions and the background mathematics for various polarizer types. We would love to hear if you happen to come across a source that you think explains the subject well!
Thanks a lot!
In addition to this video, could you explain how to measure circularly polarized light from materials of which circularly polarized light is only a few % of total amount of emitting light?
If you could upload some instruction video like this, that would be helpful!
When the light is not purely linearly or circularly polarized, the light's four Stokes polarization parameters can be used to accurately and precisely describe the polarization state. These parameters can be measured, for example, using a wave plate and a linear polarizer. If you have a polarimeter, it can also provide these values.
The Stokes parameters are typically labeled S0, S1, S2, and S3. The first parameter (S0) is the total intensity of the light. The others are the proportions of horizontally / vertically linearly polarized light (S1), ±45° linearly polarized light (S2), and right- and left-circularly polarized light (S3). Together they characterize the light's elliptical polarization state, which is sometimes plotted on a Poincaré sphere. The Stokes parameters also provide information about the amount of unpolarized light included in the beam.
Unfortunately we cannot detail the measurement here, but we will definitely add the topic to the list of upcoming videos demonstrations!
There is now a Video Insight available that demonstrates how to measure the Stokes parameters (th-cam.com/video/pR4r7gMyN5U/w-d-xo.html)! The video also discusses the relationship between these parameters and the light's polarization state. Let us know what you think!
First, Thank you for your video.
I have a question.
If QWP Angle is same with first polarizer, Power is checked at minimum.
That's understand because output light and second polarizer have different direction(90).
But, If QWP Angle change degree(90), I don't understand why power also is checked at minimum.
When I studied, I think maximum because QWP make linear polarized light.
For example...
Degree 0 : Horizontal
Degree 0~90 : Elliptical, Circle
Degree 90 : Vertical
Please answer.
I wait your support.
Thank you.
Thank you for your question!
When light passes through a wave plate, the light is delayed. The delay provided by a wave plate is special, because the amount of delay depends on the light's polarization direction. A wave plate delays light polarized parallel to the wave plate's slow axis more than light polarized parallel to the wave plate's fast axis. The difference in delay provided by the two axes determines the wave plate type. The difference in delay provided by a half wave plate is half a wavelength, which is the amount of delay required to convert light from one linear polarization to another linear polarization. The difference in delay provided by a quarter wave plate (QWP) is one quarter of a wavelength. A quarter-wave plate is not able to convert horizontally polarized light to vertically polarized light, because the delay difference it provides is too small.
In addition, the direction of the input linearly polarized light needs to oriented between the wave plate's fast and slow axes in order for the wave plate to affect the light's polarization. When one axis of the QWP is parallel to (at a 0° angle to) the transmission axis of the first linear polarizer, the QWP delays all of the light by the same amount. This does not change the polarization state of the light. When the QWP is rotated by 90°, the other QWP axis is parallel to the transmission axis of the first linear polarizer and all of the light is delayed by a different amount. This does not change the polarization state either. The only time the QWP changes the polarization state is when the QWP is rotated to an angle more than 0° and less than 90°. Circularly polarized light is created when the QWP angle is 45°. Otherwise the light is elliptically polarized.
Silly question, but does adding QWP downstream of commerically available lasers (rotated by 45degrees) give a reasonable enough circularly polarized light? Or is it imperative to identify the polarization state of the laser prior to placing a QWP at 45 degree relative to this? Also, how drastic is the performance between multi order qwp as compared to zero order qwp if the intention is to use it for a single laser line? Thanks! Great set of videos!
It is possible that a linear polarizer is not needed between the laser and the QWP, but it depends on your laser's output and your application. Please contact Tech Support (techsupport@thorlabs.com) if you’d like to discuss your particular application. Note that not all commercially available lasers output linearly polarized light, and if one does, its polarization state may not be stable.
In most applications, you should not see an appreciable performance difference between zero-order and multi-order wave plates, assuming the laser line is narrow and within the operating wavelength of the wave plate. A multi-order wave plate may also be preferable, since it should be more robust to handling.
Wonderful and clear explanation. Thanks a lot!
*Saw this today. I am visiting china now. Can possibly send 2 samples of identical microlens arrays for an HMD that I would like to prototype? Thanks in advance!*
Please contact a member of our Sales or Technical Support teams to discuss your need. Contact information for these teams can be found on this page: www.thorlabs.com/locations.cfm .
the most funny beams are Tangentially and Radially polarized, I used to make then with a pair of lenses, specially oriented KGW crystal , retardation plates (1/2) and polarizer for selecting the polarization I like
Very silly questions, how do we determine sigama- or sigma+ excitation? and also for the signal from sample how do we determine them?
The polarization state of light can be determined using an instrument called a polarimeter. We demonstrate how to build one using standard components in another Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ). A complete device and software package can also be purchased (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1564&YVI=9).
Would you help us understand what sigma± you are referring to?
Optic axis is direction along which if a wave propagates, it suffers no double refraction.
At 2:32 light is propagating along optical axis then why it's suffering double refraction, there should be either E-wave or O-wave means component either along fast axis or along slow axis should be there.
In that case we should get linearly polarized light regardless of angle of incidence.
Where am I wrong?
Plz answer I'm so confused
@Ranbir.Bhardwaj We think that a label used in the animation that begins at 0:43 may be the source of your confusion. In the animation, we mistakenly labeled the horizontal axis “Optic Axis.” The horizontal axis should be labeled “Optical Axis,” since it describes propagation direction of the light and is not related to the birefringent properties of the wave plate. In this video, we use the labels “fast axis” and “ slow axis” exclusively to describe the wave plate’s birefringence. Please let us know if this does not help with your confusion.
If allow tolerance of delay by adjusting pulsating rather than continuous then less mathematics involved
Are there power losses after transforming from linear to circular polarization?
@zedius24 There should not be any power loss from the transformation itself. However, there are typical losses that occur when light propagates through an optic, such as reflection losses at the front and back surfaces of the wave plate and material-related losses. These losses can generally be determined from the optic’s transmission specifications.
Thank you for this informative video!
Hi, thank you for the video, could you also teach us how to generate left-circular polarized light and right-circular polarized light?
We love to receive suggestions - thank you!
@Xinglin Zeng As you hint, this video demonstrates a technique for generating circularly polarized light, but whether the light is right- or left-circularly polarized is not known. One way to determine the handedness of the light is to measure its polarization state, and there is now a Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ) that describes how to make those measurements. Another approach is to identify the fast and slow axes of the waveplate, so that the quarter-wave plate can be oriented to provide the desired handedness of circularly polarized light. This technique is demonstrated in another Video Insight ( th-cam.com/video/XQwiPm5OtSk/w-d-xo.html ). We hope you find these videos useful!
Can we rotate the polarisation of light by 45 degrees (vertically polarised light to diagonally polarised light) by using half wave plated rotating 22.5 degrees from its axis?
Yes, people do use half-wave plates as linear polarization rotators. For the case you described with a linear polarization input and an ideal half waveplate, the angle between the incident linear polarization and the fast axis of the wave plate should be 22.5° (theta). Then, the angle between the incident linear polarization and the output linear polarization directions will be 45° (twice theta).
This rotation occurs for elliptically as well as linearly polarized light, since an ideal half-wave plate creates a 180° (1/2 wavelength) phase delay between the two polarization components parallel to the fast and slow axes of the wave plate. Note that while linearly polarized input light will be output as linearly polarized light, the half-wave plate reverses the handedness of elliptically polarized light in addition to rotating its polarization orientation. This means right circularly polarized light incident upon a half wave plate will become left circularly polarized and vice versa. Because of this phenomena, it may be better to think about the incident polarization state flipping around the half-waveplate’s fast axis.
Would it be helpful if we created a video Insight to discuss this in more detail?
Thank you so much. This video was very helpful.
Great! We're glad you found it helpful. If you think of another topic that interests you, let us know!
Sir,
How can we orient the polarization axis with respective to a perpendicular magnetic field?
Would you help us better understand your question? Which component's polarization axis are you thinking of? Are you referring to the light beam's magnetic field, which is always perpendicular to its electric field?
No sir. I was reading a research article regarding magneto optical birefringence measurement where an external magnetic field ( not light beam's magnetic field) which was in perpendicular to light direction. In that experiment they are telling to orient the optimum angle of polarization direction of the incident linearly polarized light with respect to magnetic field as 45degree and also to orient polarization direction of incident light parallel and perpendicular to magnetic field.
@@mubeenarafi3920 The alignment of the devices in this setup was performed using the plane of the table as a reference, and one possible approach for performing the work described in the paper is to also align the external magnetic field with respect to the table. This can be done by choosing a magnet that provides a field with the desired strength and shape and then orienting the magnet as required. If the table is the reference plane, then the techniques in ( th-cam.com/video/W9pALZ5Z8ms/w-d-xo.html ) can be used to align the polarizer horizontal and vertical with respect to the table and then the techniques in ( th-cam.com/video/cqLPD5dL9zY/w-d-xo.html ) can be used to align the polarizer at 45 degrees.
what will happen if i replace the output linear polarizer by a halfwave plate in this apparatus, how will the half wave plate affect the circularly polarized light?
@jishnusasidharan2165 If the light from the quarter-wave plate is circularly polarized and incident upon a perfect half-wave plate, then the light output by the half-wave plate will also be circularly polarized. However, the handedness of the circular polarization state output from the half-wave plate will be opposite the handedness of the incident circular polarization state.
More specifically, the handedness of the circularly polarized light from the quarter-wave plate will be either right- or left-circularly polarized. For an observer facing the light source, we define right-circularly polarized light as having a polarization vector that rotates clockwise around the optical axis. Left-circularly polarized light has a polarization vector that rotates counterclockwise.
To know the handedness of the light, the user must know the orientation of the quarter-wave plate’s fast axis with respect to the transmission axis of the input linear polarizer. Another of our Video Insights ( th-cam.com/video/XQwiPm5OtSk/w-d-xo.html ) demonstrates a method that can be used to find and distinguish the fast and slow axes of a wave plate to know the orientation. Alternatively, we have also demonstrated how to build a polarimeter in a third Video Insight ( th-cam.com/video/pR4r7gMyN5U/w-d-xo.html ), which could be used to measure the handedness.
If I had linearly polarized light parallel to the y-axis and a quarter wave plate with a fast axis initially parallel to y-axis and later on to x-axis , what would be the difference between those waves ? Could I say that between those two waves the first would forego the later by π/2 ?
You've got the concept! The first wave’s polarization state is parallel to the fast axis and the second wave’s polarization state is parallel to the slow axis. Ideally, a single pass through the quarter-wave plate will result in the phase of the second wave being π/2 larger than the phase of the first wave. But in practice, design and manufacturing limitations mean it is important to check the retardance plot of your wave plate to determine the exact phase difference (retardance).
The retardance of physical wave plates is highly wavelength dependent, even over the wave plate's operating range. Also note that many quarter-wave plates provide a phase difference equal to the sum of π/2 and some multiple of 2π, instead of an exact π/2 difference. A zero-order wave plate is expected to provide a π/2 phase difference at the design wavelength if that is needed for your application.
@@thorlabs Great ! Thank you for your help !!
Very helpful.....❤
Brilliant! Thanks
Hi, how do you analyze the circularly polarized light? (Using a LP and QWP arrangement)
In this demonstration, we performed a qualitative assessment of circularity based on how steady the detected power remained as the last linear polarizer was rotated. Adding a second quarter-wave plate to the path and taking a series of measurements would make it possible to calculate the Stokes polarization parameters, which characterize the light's degree of polarization, ellipticity, and handedness. Please let us know if you would like a follow-up video showing this analysis!
@@thorlabsThanks.
And yes, that would be great!
A polarimeter will be helpful aswell
Absolutely! If you have access to one, a polarimeter would be a quick and easy way to determine the polarization state.
@Mahima Sharma There is now a Video Insight available (th-cam.com/video/pR4r7gMyN5U/w-d-xo.html) that demonstrates a couple of approaches to using a quarter-wave plate and linear polarizers to analyze light's polarization state. These are do-it-yourself versions of polarimeter instruments (www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1564) used to measure the Stokes parameters of the light. The video also discusses the relationship between the Stokes parameters and different polarization states. We hope it is useful to you!
Thanks!
might be interesting to capture in HIGH SPEED VIDEO (recording the light paths)
S.. s.... slow... axis?
It is tempting to think so, but the ‘s’ in s-polarized light actually stands for ‘Senkrecht,’ which means 'perpendicular' in German. This is because s-polarized light is perpendicular to the plane of incidence, where the plane includes the incident, reflected, and transmitted light vectors.