This professor, Dr. Bowley I believe is his name, is so gifted in teaching science. He may never see this comment, but I just started teaching labs as a graduate student and I have been constantly studying Dr. Bowley's teaching through Sixty Symbols. It is amazing.
1 Baff is the amount of work needed to bring a particle reacting to light of 671.005 nm into a state where it instead reacts to light of 671.000 nm. It is all explained in the video :D And it ffints nicely into the SI system where every unit is calibrated to basic laws of physics.
I have always wondered how that works! Also, you folks are getting better and better at editing together videos that do a good job of leading the viewer into ideas. You are excellent.
Just subscribed today and already learned something I've wanted to know. How they cool with lasers. Of course I could have googled it but for some reason never did. Keep up the videos!
This Sixty-Symbols Series is brilliant! And to a Fellow Aussie, (I think Meghan gave that away a couple of vids ago) Well done. You've made me sound smart again.
The professor is so good at explaining science because he has a humility and understanding of the lack of understanding of his audience - I wish I had had him as a lecturer at university!
On a complex science subject there exists union of a subject expert and a joyful demonstrator expert to make us understand at least partially and also realize the complexity of such systems and situations. Thanks.
Always enjoy learning something brand new, off to read-up a little on Doppler-cooling, which I guess is the whole point, so cheers. ... and Professor Roger is of course correct, nothing beats a really good sneeze.
Very good job editing. I was able to easily understand what they were talking about. If you remove 1 key scene from this video, it doesn't make any sense.Well done Brady!
I never thought it would be possible to make laser cooling sound any more complex but that guy just did it.... Bravo! not so much complex as it was long but still hahaha. Great video.
@ByakuyaZERO No it is significant: this is where the kinetic energy of the atom is lost bit by bit so that the atom loses its kinetic energy. It recoils when it absorbs the photon and goes into an excited state; then it re-emits a photon which can go in any direction so on the average there is no recoil, and some of the kinetic energy is lost. Also the entropy of the gas goes goes down as well as it cools, but the entropy (disorder) of the photons increases so all is well.
Oh WOW!! I've wondered for so long how they get stuff into such tiny temperatures. and YES i did think laser alway heated up or burned up stuff :D Thanks for clearing the misconception.
@mr0myster Yes! Also it is improper to state "degrees kelvin" Both rules are often broken. It is sufficient to state "zero kelvin" without the absolute or the degrees.
Yes, that is correct. When the photon hits the atom it does so with some momentum, this will impact the movement of the atom slightly,thus slowing it down. In doing so the photon causes an electron jump into a higher energy state, and because electrons don't like being in this state it will return to its original energy level, though the emission of energy, taking the form of a photon...
Nifty thing about this: because the nature of laser cooling is that the mass of the target atoms are directly related to their resonance, this technique can be used for (and has been adapted to) isotopic enrichment.
@IngeniousSheep the atom does absorb the photons, and later the spontaneous emission of these photons will contribute to cooling atoms, while induced emission of such photons does not help. Wiki page about "laser cooling" gives same explanation as seen in the "Doppler cooling" part.
@RupertsCrystals I think he said the energy of the photons when absorbed by the atoms turn into the "momentum" of their electrons, making the atoms change into an excited state. The professor said there's a recoil or "nudge" or "push" whenever this happens. What I want to know is: how do photons -massless- hitting an atom have an effect on its kinetic energy? Why do the lithium atoms slow down when they become excited?
does this mean, if you accidentally start with a laser frequency that's too *low*, you'd heat them up instead? since they might catch the light as they're moving away from it instead of towards it?
I have some questions: 1. If its in space or somewhere with 0 gravity, does its time to cooling off increase or no? 2. If you made a sphere of lasers would it go faster, or the time is the same even if you use just 2 mirror pointing at each other back and forth? 3. So it's affected by the Doppler effect? And what would happen if you...put your hand of an object on the middle where its cooled off? Very interesting video btw. ^.^
Mass and energy are interchangeable so you just look for the energy required for a particle to have an effective mass so great the particles individual gravity causes the escape velocity from the particle is greater than the speed of light.
I have one question. Because the atoms are absorbing I assume that the electrons of the atoms are going in to a higher energy state. I know that this increase in energy doesn't imply a temperature change (electron energy != kinetic energy). But, why don't the electrons fall back in to a lower energy state and eject a photon which would counteract the momentum change? Is it because this kind of cooling is only feasible for gasses which are receptive to photon absorption but less susceptible to ejection or is it because the photons aren't being absorbed by electrons but by some other particle (something in the nucleus maybe?)?
so you shoot a photon that has a certain amount of energy into another moving particle that has energy and and the resulting energy is less because the energy difference is stored in the particle itself by exciting an electron? is that correct? if not where does the energy go? and isnt the particle eventually going to go back into its ground state and emit a photon and thus start moving again? i hope i can get some answers! thanks for the great videos!! keep it up!!
Is it so that because of the Doppler effect, the atom emits a photon with a larger wavelength and energy than the one it initially absorbed; also does this cause the reduction in the kinetic energy of the atom (and cooling due to repetition of this process)?
I'm confused by something. So you need the right frequency for the atom to be affected, you need to change the laser light, like he said. But unless all of the atoms get hit and stay at the speed they need to be, won't some "fall off the bus," so to speak? In that if I need frequency X to slow the atoms down, and one of them doesn't get hit by any photons, and then the frequency is changed to Y which is no longer what it needs to be for those particular atoms, are they just left as they are?
@gamesbok The photon is absorbed by the atom and an electron goes to an excited state. The electron goes back to the ground state and a photon is emitted isotropically, that is all directions of emission are equally probable. On the average (the photon can be emitted in any direction) the atom loses momentum, and also a bit of its kinetic energy is taken away by the photon. Repeat the process ten thousand times and the atom slows down and nearly stops. A Nobel prize results for this idea.
...This emission is in a random direction, and carries with it its own momentum, meaning that it also affects the movement of the atom. This may be either slowing it down or speeding it up, but because of the large numbers of photons that are being shot at the atoms by the 3 lasers, and the random nature of the direction of the photon's emission, the result is a net cooling of the substance. Hope I've explained that well... If not let me know :)
It seems that one of the biggest enemies of cooling atoms to fractional Kelvin temperature scales is not so much the physics of doing so, but the amount of time it takes to do it. Some experiments involving these temperature scales can take hours, days or even months to reach their conclusion, and the amount of time it takes to do it when you get below 1K seems to vary inversely with the temperature they want to achieve.
Einstein once wondered what it would be like to travel alongside a beam of light. As I recall he pondered what the world around him would look like as he cruised along at 186,000 miles per second AND he pondered what the beam of light itself would look like as he traveled alongside it. My question is this, we have managed to slow a beam of light down to a crawl inside a Bose-Einstein Condensate. Aside from its speed, is the properties of light still the same regardless of its speed and can we study and learn things about light inside the BEC that we could only speculate about before the advent of the BEC?
So if you have a laser cooling something very cold, and a laser heating something very hot, you could create a heat-exchanger (peltier arrangement) that allows you to re-capture the energy?
If absolute zero is the absence of molecular motion, is there a corresponding opposite temperature? A point beyond which you can no longer add heat to a system? Would that be the temperature of gas molecules moving at the speed of light?
@bmbirdsong v=0 is just the vibrational quantum number. This isn't equal to T=0 or absolute zero. The reasons behind this are pretty complex, but it's due to anharmonic properties of molecular vibrations and fun things like that. Wikipedia is your friend on this. :)
@bmbirdsong There's no such thing as an 'absence of molecular motion'. Molecules will still possess a zero-point energy, and can never reach absolute zero. On the other hand vibrational energy levels go from v=0 to v=∞, so there is no maximum temperature. Or put another way, to get something to the speed of light would require infinite energy. Thus unless you can get to ∞°C you won't get an atom/electron or any particle with mass to the speed of light.
I understand mostly everything going on here with the doppler effect and the shifts which occur, but why do the photons add on once the particle matches the frequency of the laser?
Question: So the atom gets exited and gets slown down due to a "recoil".but does the atom emit an EM-wave with a higher frequentie than the incoming laser light frequentie ? because you'd otherwise be losing energy because the kinetic energy of the atom gets smaller. Hope my question is clear :p
I believe he's retired now. I think there's a video on it called "The Retired Professor." I liked any time he made an appearance on this channel too ;)
So interesting! I have 2 questions! 1- Where does the energy go? 2- Is that theory (about the mechanism of how it works) confirmed or is it just a hypothesis?
I think I found the answer to question one! The cooled atom will emmit a photon immediately. But now I have a new question! 3- How can you tweak / fine-tune the frequency of light with that precision?!
Where does the energy go, though? Don't the electrons on the atoms have to re-emit the photons to return from their energised state, regaining the momentum they lost (albeit in a random direction)?
i have a question if anyone knows the answer, now we hit the atom with photons in the opposite direction of the atom's motion to slow it down. but in this direction due to doppler shift the atom sees a frequency closer to its resonance frequency o it will absorb it. so what about its emission? i mean that it still absorb energy and re-emit it dost these collision due to compton effect that we consider this atom like a free particle that absorbs part of the photons energy and changes in its momentum ?
wait a minute. when the electron of a given atom absorbs a photon and the atom goes to an exited state it gains energy. how can you be cooling down the gas if you continuously ADD energy to it's atoms? Are these atoms all ending up at higher and higher states as they are cooled?
No expert but I found somewhere that they almost immediately release a photon afterwards in a random direction, with a tiny bit more momentum than the original photon, thus everything is conserved.
Alex is right, in fact this results in a cap to the amount of cooling you can achieve with lasers alone. This cap is called the "Doppler Limit". We can, however, cool atoms past the doppler limit by adding things like an external magnetic field as in a MOT (magneto optical trap), and polarization gradient cooling which uses polarized laser light to further cool atoms.
Laser cooling is awesome. You can call it laser compression. You're using an electric field to counter the motion of another electric field. It works, and it still has stuff to tell us.
So when the photon is absorbed, it's quickly re-emitted, right? Is it re-emitted back in the direction it came in from, or is it randomized? I realize that in either case the interaction will effectively steal momentum from the subject on average, but I'm curious.
only in the very rare event (technically impossible) that the atom re-emits the photon in exactly the opposite direction in which it was absorbed. Which is essentially just like the photon and atom not interacting at all
Basically it's a theory that states that as you pass below absolute 0, (you cannot obtain 0, itsself, either +/- temperatures) that as you make the temperature more negative, entropy decreases rather than increases. It's not quite the natural way of thinking about 'temperature'
@xXmatthdXx That seems unlikely. You need a gas or at least a liquid for this to work. On a CPU, which is opaque, you could at best shoot lasers on it from the top etc., but not from all directions, and the laser wouldn't reach into the CPU very far (or at all).
if movement of atoms mean temperature, then there have to be a maximum temperature because atoms can't move at the speed of light right? what's that temperature limit?
@anonymousbl00dlust I also am not an expert. I think, that when the photon hits it slows the atom down. Then the photon is re-emit in a random direction and will gain momentum again, but since it does this a lot of times and the direction is random it will equal out at some time and only the slowing down effect of the photon hitting will matter, because it always hits from the same direction. Someone pleas correct me if I'm wrong.
This may or may not be relevant but I think it's inverted temperature rather than actually physically bringing it down in steps below zero, so not the intuitive thought of below zero, probably something much different. I can't post a link to the article directly but google "temperature below absolute zero' and you should have some good leads.
the energy isnt disappearing its being absorbed by the atom. like when two pool balls move toward each other and hit both will stop. Thats why the atom has to be moving to the laserbeam.
Haha this professor is awesome, and I never knew molasses was an American word! Treecool? Is that what y'all call it? Haha, awesome video. And it's not sad he retired! Working your whole life and getting to retire is a glorious thing!
Doesn't photo electric emission take place when you but the Na atoms with photons of the correct frequency? Also, why are sodium or rubidium chosen for the experiment?
@anonymousbl00dlust The photon energy is actually lower than is necessary to excite the atoms electrons, but when the atoms are moving towards the photon source the doppler effect causes the atoms electrons to essentially be fooled into being exciting. The atoms slow down 3:40. To be honest I'm not an expert either.
@MainsOnTheOhmsRange The atoms absorb one frequency of light but then emit photons. I'm guessing they probably emit photons at a different frequency than they absorb leading to a net reduction in the energy of the atom.
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This professor, Dr. Bowley I believe is his name, is so gifted in teaching science. He may never see this comment, but I just started teaching labs as a graduate student and I have been constantly studying Dr. Bowley's teaching through Sixty Symbols. It is amazing.
+sigalig I 100% agree. I think that he is one of the most gifted teachers! Bless his soul!
I didn't realize scientist's had souls...i thought they removed their souls, at a young age, through the proper application of logic and experiment.
The best scientists have souls, it's the only way to think for yourself.
1 Baff should be a new SI unit of momentum
We should change everything else to fit with the baff more nicely.
eg: Units of force: *baffs per second*.
It would actually be an unit of work or impulse.
1 Baff is the amount of work needed to bring a particle reacting to light of 671.005 nm into a state where it instead reacts to light of 671.000 nm.
It is all explained in the video :D
And it ffints nicely into the SI system where every unit is calibrated to basic laws of physics.
I have always wondered how that works! Also, you folks are getting better and better at editing together videos that do a good job of leading the viewer into ideas. You are excellent.
Just subscribed today and already learned something I've wanted to know. How they cool with lasers. Of course I could have googled it but for some reason never did.
Keep up the videos!
This Sixty-Symbols Series is brilliant! And to a Fellow Aussie, (I think Meghan gave that away a couple of vids ago) Well done. You've made me sound smart again.
The professor is so good at explaining science because he has a humility and understanding of the lack of understanding of his audience - I wish I had had him as a lecturer at university!
On a complex science subject there exists union of a subject expert and a joyful demonstrator expert to make us understand at least partially and also realize the complexity of such systems and situations. Thanks.
Always enjoy learning something brand new, off to read-up a little on Doppler-cooling, which I guess is the whole point, so cheers.
... and Professor Roger is of course correct, nothing beats a really good sneeze.
What an excellent video! Less than 10 minutes and I now understand how lasers cool. Wow.
Thank you for the upload. Looking forward for more videos.
This video and explenation was brilliant! Really brilliant! Easy to understand. Thanks, Brady and CO. =)
Very good job editing.
I was able to easily understand what they were talking about. If you remove 1 key scene from this video, it doesn't make any sense.Well done Brady!
I did my practice presentation on this topic last week and its really interestin
Excellent explanation! Thank you!
How dare you put atoms in a cage?! P.E.T.A. will hear about this!
Amazing video once again!
I never thought it would be possible to make laser cooling sound any more complex but that guy just did it.... Bravo! not so much complex as it was long but still hahaha. Great video.
- How cool is to put your name on a bizarre state of matter?
+ Bose-Einstein cool
- That would be my first most enjoyable thing
@ByakuyaZERO
No it is significant: this is where the kinetic energy of the atom is lost bit by bit so that the atom loses its kinetic energy. It recoils when it absorbs the photon and goes into an excited state; then it re-emits a photon which can go in any direction so on the average there is no recoil, and some of the kinetic energy is lost.
Also the entropy of the gas goes goes down as well as it cools, but the entropy (disorder) of the photons increases so all is well.
love watching these vids!
But what is the first most enjoyable thing that you know Dr. Bowley? :-)
+P Bryce Alaska King Crab Legs is my guess. . . . .
Didn't get the vid but his last sentence stuck with me. Maybe he just wanted us all think about whats most enjoyable to us personally. So romantic!
I love this channel.
Oh WOW!! I've wondered for so long how they get stuff into such tiny temperatures. and YES i did think laser alway heated up or burned up stuff :D Thanks for clearing the misconception.
@mr0myster Yes!
Also it is improper to state "degrees kelvin"
Both rules are often broken.
It is sufficient to state "zero kelvin" without the absolute or the degrees.
Awesome explanation!! i had no idea that lasers could do that!! cool!
Yes, that is correct. When the photon hits the atom it does so with some momentum, this will impact the movement of the atom slightly,thus slowing it down. In doing so the photon causes an electron jump into a higher energy state, and because electrons don't like being in this state it will return to its original energy level, though the emission of energy, taking the form of a photon...
"getting JIGGLY with it", Dr. Bowley's favorite song :)
Nifty thing about this: because the nature of laser cooling is that the mass of the target atoms are directly related to their resonance, this technique can be used for (and has been adapted to) isotopic enrichment.
@IngeniousSheep the atom does absorb the photons, and later the spontaneous emission of these photons will contribute to cooling atoms, while induced emission of such photons does not help. Wiki page about "laser cooling" gives same explanation as seen in the "Doppler cooling" part.
@RupertsCrystals
I think he said the energy of the photons when absorbed by the atoms turn into the "momentum" of their electrons, making the atoms change into an excited state. The professor said there's a recoil or "nudge" or "push" whenever this happens.
What I want to know is: how do photons -massless- hitting an atom have an effect on its kinetic energy? Why do the lithium atoms slow down when they become excited?
does this mean, if you accidentally start with a laser frequency that's too *low*, you'd heat them up instead? since they might catch the light as they're moving away from it instead of towards it?
Professor Bowley should host popular science documentaries. He's really something else.
I have some questions:
1. If its in space or somewhere with 0 gravity, does its time to cooling off increase or no?
2. If you made a sphere of lasers would it go faster, or the time is the same even if you use just 2 mirror pointing at each other back and forth?
3. So it's affected by the Doppler effect? And what would happen if you...put your hand of an object on the middle where its cooled off?
Very interesting video btw. ^.^
Mass and energy are interchangeable so you just look for the energy required for a particle to have an effective mass so great the particles individual gravity causes the escape velocity from the particle is greater than the speed of light.
sadly he retired already :/ .. im glad we have these videos of him here :)
Oh, my favourite technique. Wrote a short extract on it. :)
Have they tried forming a condensate with rubidium to compare it to the lithium condensate?
How long 'til I can put one in my PC? :P
It's great to see someone so passionate about their work, it's a shame he's retired.
Good video thanks. Got an exam on this next week, wish me luck!
@rogerdotleethe exclusion principle doesn't apply to bosons, they have integer spin
I have one question. Because the atoms are absorbing I assume that the electrons of the atoms are going in to a higher energy state. I know that this increase in energy doesn't imply a temperature change (electron energy != kinetic energy). But, why don't the electrons fall back in to a lower energy state and eject a photon which would counteract the momentum change? Is it because this kind of cooling is only feasible for gasses which are receptive to photon absorption but less susceptible to ejection or is it because the photons aren't being absorbed by electrons but by some other particle (something in the nucleus maybe?)?
so you shoot a photon that has a certain amount of energy into another moving particle that has energy and and the resulting energy is less because the energy difference is stored in the particle itself by exciting an electron? is that correct? if not where does the energy go? and isnt the particle eventually going to go back into its ground state and emit a photon and thus start moving again? i hope i can get some answers! thanks for the great videos!! keep it up!!
I wonder if there is any sort of "feedback" or detectable effect on the laser's side from the atoms resisting the force of the laser beams?
Is it so that because of the Doppler effect, the atom emits a photon with a larger wavelength and energy than the one it initially absorbed; also does this cause the reduction in the kinetic energy of the atom (and cooling due to repetition of this process)?
I'm confused by something. So you need the right frequency for the atom to be affected, you need to change the laser light, like he said. But unless all of the atoms get hit and stay at the speed they need to be, won't some "fall off the bus," so to speak? In that if I need frequency X to slow the atoms down, and one of them doesn't get hit by any photons, and then the frequency is changed to Y which is no longer what it needs to be for those particular atoms, are they just left as they are?
That is the single coolest (heh) looking set of equipment I have ever seen.
@gamesbok
The photon is absorbed by the atom and an electron goes to an excited state. The electron goes back to the ground state and a photon is emitted isotropically, that is all directions of emission are equally probable. On the average (the photon can be emitted in any direction) the atom loses momentum, and also a bit of its kinetic energy is taken away by the photon. Repeat the process ten thousand times and the atom slows down and nearly stops. A Nobel prize results for this idea.
...This emission is in a random direction, and carries with it its own momentum, meaning that it also affects the movement of the atom. This may be either slowing it down or speeding it up, but because of the large numbers of photons that are being shot at the atoms by the 3 lasers, and the random nature of the direction of the photon's emission, the result is a net cooling of the substance. Hope I've explained that well... If not let me know :)
It seems that one of the biggest enemies of cooling atoms to fractional Kelvin temperature scales is not so much the physics of doing so, but the amount of time it takes to do it. Some experiments involving these temperature scales can take hours, days or even months to reach their conclusion, and the amount of time it takes to do it when you get below 1K seems to vary inversely with the temperature they want to achieve.
the time scale for the actual cooling is very short due to the number of photons emitted compared to the number of collision needed
Einstein once wondered what it would be like to travel alongside a beam of light. As I recall he pondered what the world around him would look like as he cruised along at 186,000 miles per second AND he pondered what the beam of light itself would look like as he traveled alongside it. My question is this, we have managed to slow a beam of light down to a crawl inside a Bose-Einstein Condensate. Aside from its speed, is the properties of light still the same regardless of its speed and can we study and learn things about light inside the BEC that we could only speculate about before the advent of the BEC?
Thanks for sharing this video it was really "cool".Vsauce is awesome. I hadn't thought about considering the black body radiation of the hot object.
So if you have a laser cooling something very cold, and a laser heating something very hot, you could create a heat-exchanger (peltier arrangement) that allows you to re-capture the energy?
shades2 Some of it. It's a cool experiment, but it won't be free energy.
LAZERS caution LAZERS caution LAZERS caution LAZERS caution
Igotthatreference.wav
Jonesmin For those who didn't get that reference, two things: Half Life 3 confirmed, and, watch the "playthrough" : Freeman's Mind - Episode 3
Such a good idea. The next step in supercooling...cool.
If absolute zero is the absence of molecular motion, is there a corresponding opposite temperature? A point beyond which you can no longer add heat to a system? Would that be the temperature of gas molecules moving at the speed of light?
Where would this be applied to help us? I pretty interesting stuff!
@RandyRedCactus The photons are absorbed by the electrons and raise them to another energy level
That's the craziest game of Khet that I've ever seen.
@bmbirdsong v=0 is just the vibrational quantum number. This isn't equal to T=0 or absolute zero. The reasons behind this are pretty complex, but it's due to anharmonic properties of molecular vibrations and fun things like that. Wikipedia is your friend on this. :)
Perhaps a nobel prize.
@bmbirdsong There's no such thing as an 'absence of molecular motion'. Molecules will still possess a zero-point energy, and can never reach absolute zero. On the other hand vibrational energy levels go from v=0 to v=∞, so there is no maximum temperature. Or put another way, to get something to the speed of light would require infinite energy. Thus unless you can get to ∞°C you won't get an atom/electron or any particle with mass to the speed of light.
I understand mostly everything going on here with the doppler effect and the shifts which occur, but why do the photons add on once the particle matches the frequency of the laser?
Question: So the atom gets exited and gets slown down due to a "recoil".but does the atom emit an EM-wave with a higher frequentie than the incoming laser light frequentie ? because you'd otherwise be losing energy because the kinetic energy of the atom gets smaller. Hope my question is clear :p
wonderful
what happened to this guy? he is great! more vids with him if he is still physicsing around please.
he IS great
I think it's pronounced "physicsanating"
I believe he's retired now. I think there's a video on it called "The Retired Professor." I liked any time he made an appearance on this channel too ;)
So interesting! I have 2 questions!
1- Where does the energy go?
2- Is that theory (about the mechanism of how it works) confirmed or is it just a hypothesis?
I think I found the answer to question one!
The cooled atom will emmit a photon immediately.
But now I have a new question!
3- How can you tweak / fine-tune the frequency of light with that precision?!
Where does the energy go, though? Don't the electrons on the atoms have to re-emit the photons to return from their energised state, regaining the momentum they lost (albeit in a random direction)?
Thanks for the comment. That was what I thought :)
i have a question if anyone knows the answer, now we hit the atom with photons in the opposite direction of the atom's motion to slow it down. but in this direction due to doppler shift the atom sees a frequency closer to its resonance frequency o it will absorb it. so what about its emission? i mean that it still absorb energy and re-emit it dost these collision due to compton effect that we consider this atom like a free particle that absorbs part of the photons energy and changes in its momentum ?
wait a minute. when the electron of a given atom absorbs a photon and the atom goes to an exited state it gains energy. how can you be cooling down the gas if you continuously ADD energy to it's atoms? Are these atoms all ending up at higher and higher states as they are cooled?
Where does the kinetic energy of the atoms go? When they absorb the laser photons doesn't it just put them into an excited state?
No expert but I found somewhere that they almost immediately release a photon afterwards in a random direction, with a tiny bit more momentum than the original photon, thus everything is conserved.
Alex is right, in fact this results in a cap to the amount of cooling you can achieve with lasers alone. This cap is called the "Doppler Limit". We can, however, cool atoms past the doppler limit by adding things like an external magnetic field as in a MOT (magneto optical trap), and polarization gradient cooling which uses polarized laser light to further cool atoms.
I'm really glad someone busted him on this most egregious offense. No one should take this man seriously. Thank you.
Laser cooling is awesome. You can call it laser compression. You're using an electric field to counter the motion of another electric field.
It works, and it still has stuff to tell us.
So when the photon is absorbed, it's quickly re-emitted, right? Is it re-emitted back in the direction it came in from, or is it randomized? I realize that in either case the interaction will effectively steal momentum from the subject on average, but I'm curious.
It is random.
only in the very rare event (technically impossible) that the atom re-emits the photon in exactly the opposite direction in which it was absorbed. Which is essentially just like the photon and atom not interacting at all
Basically it's a theory that states that as you pass below absolute 0, (you cannot obtain 0, itsself, either +/- temperatures) that as you make the temperature more negative, entropy decreases rather than increases. It's not quite the natural way of thinking about 'temperature'
@xXmatthdXx
That seems unlikely. You need a gas or at least a liquid for this to work. On a CPU, which is opaque, you could at best shoot lasers on it from the top etc., but not from all directions, and the laser wouldn't reach into the CPU very far (or at all).
@CRUK87 probably because.. the mirrors are altering the wave pattern by splitting and interference at the quantum level. :s
Are those Radiant Dyes Laser Mirror-Mounts and a Toptica Photonics Laser.
if movement of atoms mean temperature, then there have to be a maximum temperature because atoms can't move at the speed of light right?
what's that temperature limit?
@anonymousbl00dlust I also am not an expert. I think, that when the photon hits it slows the atom down. Then the photon is re-emit in a random direction and will gain momentum again, but since it does this a lot of times and the direction is random it will equal out at some time and only the slowing down effect of the photon hitting will matter, because it always hits from the same direction. Someone pleas correct me if I'm wrong.
"Besides... its the second most enjoyable thing that I know" Class Quote.
And LFZ15 one thinks that was implied.
This may or may not be relevant but I think it's inverted temperature rather than actually physically bringing it down in steps below zero, so not the intuitive thought of below zero, probably something much different. I can't post a link to the article directly but google "temperature below absolute zero' and you should have some good leads.
Yeah that's what I was wondering too.....Perhaps it doesn't re-emit the photon straight back.....
What is the most enjoyable thing?
very interesting
the energy isnt disappearing its being absorbed by the atom. like when two pool balls move toward each other and hit both will stop. Thats why the atom has to be moving to the laserbeam.
god i would love to go to that place
I don't know about the first part, but the second part I believe is because sodium and rubidium both can form Bose-Einstein condensates.
So, that guy owns.
Haha this professor is awesome, and I never knew molasses was an American word! Treecool? Is that what y'all call it? Haha, awesome video. And it's not sad he retired! Working your whole life and getting to retire is a glorious thing!
The old dude explaining the gas particles is EPIC, thumbs up if you agree xD
totally agree it kills me he is actually retired now, and only very infrequently does videos anymore.
Doesn't photo electric emission take place when you but the Na atoms with photons of the correct frequency? Also, why are sodium or rubidium chosen for the experiment?
Why is there a momentum shift in the gas particles when a photon hits it if photons have no mass?
@anonymousbl00dlust
The photon energy is actually lower than is necessary to excite the atoms electrons, but when the atoms are moving towards the photon source the doppler effect causes the atoms electrons to essentially be fooled into being exciting. The atoms slow down 3:40. To be honest I'm not an expert either.
3: 50 etc "A photon comes in and baffs me" don't know why but LOL.
Where does the energy from the heat go?
Are the atoms decreasing the wavelength of the laser as it passes through?
@MainsOnTheOhmsRange The atoms absorb one frequency of light but then emit photons. I'm guessing they probably emit photons at a different frequency than they absorb leading to a net reduction in the energy of the atom.
This old man is very lovely. His students must be very lucky