Uhh... Why would loss in amplitude due to damping result in widening of frequency band? Only the maximum displacement is chaning, the time between two maxima (and hence, frequency) is remaining constant, isn't it?
ok i understood that 4level is better than 3leve because it requires less energy,but i still dont have a clear explanation as to why and is this the only thing better about it? perhaps im having trouble relating lifetime of exited state vs ground state vs the pump rate etc
i might say soemthing wrong but here s my best guess: in the 3 level laser the emission that produces the light happens between level 3 and level 1 ( the groudn state) usually the ground state is the state that has the most atoms there, which means it is really hard for you to create a population inversion between the ground state and another one ( because you have to pump a big number of electrons) in the 4 level laser the emission that produces light happens between level 3 and 4 level 4 is not the ground state , the ground state is level 1 here, but you pumped the atoms in the ground state to level 2 and they go down to level 3 which means level 3 has now more atoms than level 4 so the atoms in level 3 can easily go to level 4 and then to the ground state (in a very fast non radiative manner) which means that level 3 ALWAYS has more atoms than level 4 so the population inversion always exists between level 3 and 4. now u might think that i still pumped from the ground state to level 2 in both scenarios ( 3 and 4 level systems) so why is 4 level more efficient? the answer is that in the 4 level laser all the pumped atoms will emit radiation because level 4 has 0 atoms so in order to establish equilibrium between level 3 and level 4 alllll the atoms in level 3 HAVE to emit radiation so the population inversion stops to exist however in the 3 level laser the ground state can never be empty which means if we consider N as the number atoms that are still in the ground state after pumping and NP as the number of atoms pumped only (NP-N)/2 atoms will emit radiation for example if we have 12 atoms in the ground state and we manage to pump 7 of them, in level 3 we will have 8 atoms and 4 in the ground state, instead of all 8 atoms giving radiation we will have 2 atoms coming down which will lead to us having 6 atoms in each level hence equilibrium
@@ameraoun7 you said they go from 2 to 3? and then you go back n forth many times ,im sorry but this is all even more confusing and i appreciate you trying and writing all that but the more i read the more it made no sense and got confusing and perhaps you are making mistakes so i did not bother with all of it ,thx anyways
@Punyasloka Sahoo thx but these kind of explanations do not always make sense to me unless i am visualizing what you are saying because so many things happening at the same time
4 level laser have a meta stable state between two excited states, when electrons excite to top level, quickly decays to the third level, which is the metastable state, and spontaneous and stimulated emmision takes place, as the electrons move to the second level, which is also an excited state, can very fast move down to ground state, now think, in three level, ground state has many atoms and too much pumping is required to attain population inversion, but in 4 level, because the emmsion takes place b/w metastable nand excited and as the electrons don't stay in the excited for much time, very few atoms are requried for population inversion ans it helps in continuos emmision that can;t happen in 3 level laser which has bursts of populatkon inversion I hope this helps :)
Amazing explanation ( felt he was narrating a story)
thank u sir.
Too good and easily explained
Uhh... Why would loss in amplitude due to damping result in widening of frequency band? Only the maximum displacement is chaning, the time between two maxima (and hence, frequency) is remaining constant, isn't it?
really great work
Good lecture
The Nd:YAG laser was introduced in 1964. Nd:YAG = Neodymium-doped Yttrium Aluminum Garnet; this is a crystal.
ok i understood that 4level is better than 3leve because it requires less energy,but i still dont have a clear explanation as to why and is this the only thing better about it? perhaps im having trouble relating lifetime of exited state vs ground state vs the pump rate etc
i might say soemthing wrong but here s my best guess:
in the 3 level laser the emission that produces the light happens between level 3 and level 1 ( the groudn state) usually the ground state is the state that has the most atoms there, which means it is really hard for you to create a population inversion between the ground state and another one ( because you have to pump a big number of electrons)
in the 4 level laser the emission that produces light happens between level 3 and 4
level 4 is not the ground state , the ground state is level 1 here, but you pumped the atoms in the ground state to level 2 and they go down to level 3 which means level 3 has now more atoms than level 4 so the atoms in level 3 can easily go to level 4 and then to the ground state (in a very fast non radiative manner) which means that level 3 ALWAYS has more atoms than level 4 so the population inversion always exists between level 3 and 4.
now u might think that i still pumped from the ground state to level 2 in both scenarios ( 3 and 4 level systems) so why is 4 level more efficient?
the answer is that in the 4 level laser all the pumped atoms will emit radiation because level 4 has 0 atoms so in order to establish equilibrium between level 3 and level 4 alllll the atoms in level 3 HAVE to emit radiation so the population inversion stops to exist
however in the 3 level laser the ground state can never be empty which means if we consider N as the number atoms that are still in the ground state after pumping and NP as the number of atoms pumped only (NP-N)/2 atoms will emit radiation
for example if we have 12 atoms in the ground state and we manage to pump 7 of them, in level 3 we will have 8 atoms and 4 in the ground state, instead of all 8 atoms giving radiation we will have 2 atoms coming down which will lead to us having 6 atoms in each level hence equilibrium
@@ameraoun7 you said they go from 2 to 3? and then you go back n forth many times ,im sorry but this is all even more confusing and i appreciate you trying and writing all that but the more i read the more it made no sense and got confusing and perhaps you are making mistakes so i did not bother with all of it ,thx anyways
@Punyasloka Sahoo thx but these kind of explanations do not always make sense to me unless i am visualizing what you are saying because so many things happening at the same time
4 level system is much more efficient but why ?
Still it's not clear... 🤔
because its does not require much power which safe our cost and time thats why more efficient than 3 level system
4 level laser have a meta stable state between two excited states, when electrons excite to top level, quickly decays to the third level, which is the metastable state, and spontaneous and stimulated emmision takes place, as the electrons move to the second level, which is also an excited state, can very fast move down to ground state, now think, in three level, ground state has many atoms and too much pumping is required to attain population inversion, but in 4 level, because the emmsion takes place b/w metastable nand excited and as the electrons don't stay in the excited for much time, very few atoms are requried for population inversion ans it helps in continuos emmision that can;t happen in 3 level laser which has bursts of populatkon inversion
I hope this helps :)
Thank you sir.
Thanks
👍🏼
Thanks sir
Thank you sir.