Laser Physics - Stimulated Emission & Einstein Coefficients | Three Level Laser

What is the Physics behind light amplification via lasers? Lasers are synonymous with technology, but is based on a simple concept of Physics called Stimulated Emission.
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𓏬𓏬𓏬𓏬𓏬VIDEO DESCRIPTION𓏬𓏬𓏬𓏬𓏬𓏬
Lasers are devices that produce highly focused and coherent beams of light through a process known as stimulated emission. In stimulated emission, an atom in an excited state emits a photon when it encounters another photon of the same frequency, resulting in amplification of light.
Three-level lasers are a type of laser system with three energy levels: ground state, excited state, and metastable state. They utilize population inversion, where more atoms occupy the metastable state than the excited state, to achieve laser action.
Einstein coefficients are mathematical terms used to describe the probability of different processes in the interaction of light with matter. They are named after Albert Einstein, who introduced them to explain the physics of stimulated emission and absorption, which are fundamental principles underlying laser operation.
00:00 Introduction
01:46 Laser Physics - Stimulated Emission
15:30 Three Level Laser
22:15 Einstein Coefficients
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[@FortheLoveofPhysics]

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[@MichaelKingsfordGray]

It is pleasing to see an educated person writing in cursive.

[@lalitasharma6687]

I'm a chemistry student studying laser chemistry your lecture are really helpful for me sir thank you

[@kentykatele4353]

Thank you for updating another video. An still charging up and I can't wait for you to start talking about Schrodingers. Best video so far.keep up the good work

[@ushabhatia]

Wonderful explanation. All details have been discussed in a very simple & interesting way. Thanks for sharing this video.

[@maheshrocks65-df2mm]

Emversity's BSc, MLT, and OT programs foster creativity and innovation.

[@tanvir8800]

Your videos are awesome...I have a great passion on physics so I always follow your lectures...Thank you sir

[@Sciencebuff0003]

Thanks a lot sir 👍

[@pauldirac6243]

Yes, I agree. I often have a stimulated emission when I am in an excited state. Now it all makes sense!

[@raghavchannel2173]

Thank you sir please also explain non-uniform topic also and optical fiber too

[@AbdallaDaaMadowe-kn4jq]

I enjoy 😅 this beautiful explanation Nice sir

[@debanandadey6528]

Sir one of the best class ever ...thanks a lot..❤❤❤

[@abdulraheemjunejo7671]

Thank You Dear Sir❤

[@farheentaj9429]

Some questions Sir: 1. Ground, metastable and excited state are of atoms or electrons? 2. If it is of electron's, then is this state quantized? 3. what actually is a metastable state and how is it different from excited state in terms of energy? 4. Can we actually de-energize electrons in atoms to push it to the ground state? (when a photon hits the electron in metastable state it actually transfers the energy to it right? ) 5. Is there energy difference between the incident and emitted photon in laser? 6. for absorption we have photons of different frequency and for stimulated emission we have photons of different frequency, does that mean, we have 2 different energy sources or the laser is going to use the photons emitted by spontaneous emission as an input for stimulated emission?

[@Oz.....]

Here is the small attempt for your queries 1.Both atoms and electrons can be excited to higher energy levels in laser system, depending upon the material used. Like for semiconductor lasers 'it is the electrons which get excited by the external source ' 2.yes the energy is quantised which enables the stimulated emission of laser light 3.metastable is the energy state where life time of excited atoms or electrons is in the order of 10^-6 sec . Which is slightly Greater than that of excited state. And in terms of energy metastable state has lower energy than excited state and higher than the ground state 4.yes exactly.to understand that first we should know about what the photon actually is. It is a fundamental particle of light which stores the energy and momentum.and it doesn't have mass So it just transfers the energy to electron,for the stimulated emission to be taken place. 5. No , maximum they try to maintain the coherency between emitted and incident photon. Because laser emits the coherent light. Meaning there's no difference properties of incident and emitted photons 6.for absorption and emission solely photons are not responsible there are other sources like flash lamp , electric discharge and in some cases photons also.so photon has to maintain the frequency which can excite and de-excite the electrons or atoms between the desired state. Any mistakes or left out topics I will be happy to consider

[@VikramchauhanChauhan-pn5ol]

you are one of the best

[@salimburki5972]

Thanks alo Sir.

[@gammadas]

what characteristics stabilize the metastable state? I guess it involves calculating the transition probabilities? How does one predict these metastable states and come up with different types of lasers?

[@user-ms9kk5yb3s]

Sir kindly tell me why stimulated emission happens .means when we give a photo to a excited electron then this electron de excite and go to ground state.why not this electron abosrb this photon and go to another excited state or how I can understand this process that a electron de excite due to given photon .bcz in absorbtion when we give photon then the electron. Go to higher energy level so why not this phenomenon happens in that stimulated emission process. Plz clarify this

[@ihcurus4444]

I was thinking of the same thing. Have you got answer? If yes then pls share

[@praveenas4735]

Sir ,could you please make a vedio about UV and IR spectroscopy.

[@thestaggering4980]

Sir please make a video on Bell's inequality theorem

[@farheentaj9429]

Is it possible to achieve metastability more than 10^-3 seconds, by any means?

[@raghavmanchanda3345]

Sir what is a mathematical framework and how it used in theoretical physics?

[@praveenas4735]

Sir can you make a vedio about solid state Physics within this month please.Because I will have a exam next month.

[@raghavchannel2173]

R u from lu

[@mihirsaha2742]

Sir why is the transition from excited state to metastable state non radiative ? If it is possible then there should be no difference in energy between the two said levels. Please explain it

[@FortheLoveofPhysics]

Energy can be transferred via (1) radiation emission, (2) atomic/mol vibration (3) phonons in crystal lattice, etc. So energy is still lost, therefore energy levels of excited state and metastable state can't be same. It's preferable to have non-radiative transitions, although it's not always the case

[@mihirsaha2742]

Thank you very much sir.

[@gpranjan]

I tried to find out why "Stimulated Emission" gives photons, and that too at the same frequency, has the same phase in the same direction. Is there a classical or quantum mechanical theory for this? I have come across only one article on the web that tries to explain this, and it seems too mathematical.

[@FortheLoveofPhysics]

Yes, it's explained under Time dependent Perturbation Theory

[@rahulnandi9641]

❤

[@hazimahmed8713]

First comment

[@terabaapaaya1762]

Sir kitne saal tak ke PYQs karne chahiye for IIT JAM Physics ...to get into IIT...

[@FortheLoveofPhysics]

Go through atleast the last 5 years

[@mihirsaha2742]

Sir are you bengalee?

[@willthomsen7569]

Where did Einstein's brain come from? Like what planet was he from that he was so ahead of his time in the way he saw the world? What was it like to be inside his brain wtf

[@dougiev9287]

This video is the weakest in the series; a wonderful series. I do feel, on this topic though, the most important points were glossed over. First, spontaneous emission is the game changer here, not stimulated. Classically, stimulated is 'there' in Maxwell's eqns but it's the spontaneous emission that's the subtle secret sauce (of which lasers are a consequence). It's an explicit statement about nature. Matter... will spontaneously decay. My two cents, each type needs a video on its own it's such a radical departure from everything else covered in the other 19 videos in the series. That is a concept in it's own right!! And second, too skinny on the thermodynamics. In other videos this teacher brilliantly explained the physics while here the concept of thermo equilibrium was mentioned in passing almost. The key, key point is that this approach works in equilibrium, but also, when it's not so!! Plank can't touch that domain!! Population inversion needs detailed exposition. Otherwise, loved the whole 20 vids, especially the UV Catastrophe sub series; awesome!!

[@FortheLoveofPhysics]

Point noted. Actually lasers itself is a topic that requires multiple lectures to study in depth. I wanted to simply include ONE lecture to connect it to the concept of atomic transitions, and open the gate for further in-depth study.

[@pauldirac6243]

I sometimes have a spontaneous emission myself although I do prefer a stimulated emission 🙂

[@pauldirac6243]

My girlfriend, on the other hand, prefers absorption.