this type of research has grate important in modern communication because it's you can create tow entangled photons (signal and idler) this phenomena called spontaneous parametric down conversion (SPDC), I wish you good work in this Really attractive field with best regard Dear Daniel
thank you so much for the detailed explanation, those are some know-how that only acquire through hands on experience, people dont teach them on paper or books =(
I've always thought of frequency summation and doubling as if one was talking about a FM radio, but I only now am realizing it's about the interaction of the electromagnetic waves when they are also interacting with a third physical medium, whether it be it a heterodyne circuit or a nonlinear material , the mixing doesn't happen in free space , only upon simultaneous interaction with matter. How can light be FM modulated? What *are* nonlinear properties of matter that effect this interaction? Under what circumstances does *air* have nonlinear properties and what are they? In the case of a CO2 or nitrogen lasers (for instance), where there is an intermediate excited state that is opaque to the intended output frequency , would it be possible to opticaly pump such a laser with two other lasers who's frequencies separately can pass through the gas lasing material but their combined frequency is exactly what is needed to bump the atoms back to the desired excited state, maintaining the population inversion, therefore eliminating the need for cooling such lasers? Is there such an interaction?
Great, pls have you any about use KTP 1064/532 on high power fibre laser /200W CCW Raycus and how many is real as output? Pls is very important. Thx for your reply
There is no crystal for THG. Long story short, it cancels out (see D Débarre with E Beaurepaire about that). For different SHG wavelengths, it is the angle of the cut that changes.
very informative!! btw i work on plasmonics ans use a 780nm SLD to excited gold nanorods, the maximum power if SLD is 20mW, i was thinking of exciing the interband of nanorods, so if I use a BBO crystal can I get SHG, of sufficient power of say atleast 1 or 2mW? thanks..
Excellent video. I'm building a DPSS laser using intracavity SHG through KTP as a hobby and have seen exactly what you demonstrate (laser is CW). But I am seeing poor efficiency (~2% -- optimum for the cavity should be ~7%). The only resources I've found so far start with Maxwell's equations and build theory, but never get to tangible "engineering" level formulas. Are there simpler formulas / tables for different crystal types or is this just a "knuckle down and learn it" moment? Crystal is at optimum orientation and temperature and I suspect the waist isn't tight enough, but I'd like to calculate what size it needs to be instead of re-working the cavity at random.
Intracavity doubling a laser is difficult for several reasons. First, I think that the optimal length of the crystal depends on the size of the beam (which gives its Rayleigh range, or zₒ parameter). Second, the laser will be very noisy because the SH beam generated in the crystal will mix back with the fundamental and convert *back* to the fundamental or up from the fundamental depending on the exact phase diffference between the two when the return to the crystal. This is a known problem and is why those green Verdi and Millenia lasers are expensive (they manage it differently: the Verdi is a single longitudinal mode laser whereas the Millenia is a super-multi longitudinal mode laser). I am not sure what formula you are talking about but I would say making a stable intracavity doubled green laser is tough.
@@dccote Thanks for the reply. Yes, agreed it's a tough way to go. But hey, learning all the time and I want to see what I can do here before I change the cavity design. The types of formulas I'm looking for would allow me to calculate conversion rates given energy density in a crystal of a given type / length. But as you point out there is a lot of complicated interplay with the fundamental. Last week I received a copy of your well-reviewed book on the topic. Looking forward to reading it and learning more.
Thank you for your explanation. Very impressive video! I have a quick question about the beam shape, which looks very elliptical. Is it because the incident beam is not perfectly round? Does BiBO crystal affect the beam shape?
It is elliptical for many reasons, it is partly because it is incident at angle angle and that phase matching works well along one direction, not both. I made no efforts to obtain a nice beam.
This is an excellent demonstration here. Briefly, how would you interpret BBO crystals and biomaterials(e.g. microtubules) both exhibiting nonlinear optical properties?
They have a structure that is asymmetrical. Like a dipole. The technical term is “the are non centrosymmetric”. This makes them distort the electron oscillation a bit and create second harmonic and DC (typically THz with femtosecond pulses) at the same time.
So I’m new to this… haven’t been to school but I was diving into quantum entanglement and here I am. So from my understanding is that the experiment using BBO crystals and lasers is done to measure photons and their entanglement. Is there a way to capture a larger amount of particular even without a clear entanglement?
Very nice demonstration, Thanks. I want to frequency double 1600nm from the supercontinuum. I am thinking to use a dichroic mirror to separate the 1600nm part and frequency double it using MgO PPLN. I am wondering what specs should I focus on when ordering SHG crystal?. Is it just the crystal should be phase-matched for 1600nm or something else?. Also, how focused your beam should be (spot size focused into the crystal)?
When you order from these companies, you can simply say "I want to double 1600 nm". They will offer options. I have ordered from CASIX for as long as I remember. www.casix.com That said, I think your supercontinuum will be too low a power to get anything important. If you want a lot of power, this is not the right approach. A Ti:sapphire laser operates at 800 nm with very high powers.
Im sorry if you explained it in the video but im very new to this stuff and didnt understand all you said. But when you got the new frequency how much can that be shifted? Is it only possible to shift in one direction or is there any other limitations for the output? For example if I had a infrared light source, could it be doubled into visible light; and if so what frequencies could it have shifted to? Again sorry if my question is weirdly formulated, I dont know what Im doing 😅
The technique I showed here only "reduces" the wavelength, and with a single beam you can only double the frequency (half the wavelength) via Second Harmonic Generation. You can double the frequency if an infrared beam and move it to the blue-green visible if it is infrared in the range 800 to 1100 nm. But don't forget you need ultrashort pulses and fairly high power. Reducing the frequency requires a different strategy (optical parametric conversion), which is very inefficient and requires a cavity for amplification (optical parametric oscillation or amplification).
Very different process: it is called down-conversion, and it is very weak. Typically, these are put inside an Optical parametric Oscillator to amplify.
Thank you for the information. Please is there a max frequency limit for this crystal? In theory is it possible to put group of crystals to multiply frequency until gamma ray spectrum?
It is a bit complicated because crystals are not transparent in the UV/x-ray. You have to use a slightly different strategy, and I am no expert, but multi-harmonic generation is the way I have seen it done in the past.
Just a quick question. I’m using BBO , 1040 nm and 801 . This should work as well, right? In addition once the beams are spatial overlapped I can send them through BBO and check for SFG and play with delay? If it’s overlapped in time and space we should see blue. Am I thinking of this correct? Great video!!
Probably but it depends what angle your BBO was cut at. When you order it, you typically request "a BBO for secondharmonic at 820nm with Type I phase matching" for instance. You can tune that by rotating the crystal around the axis of polarization of the incoming fundamental. Now, if you want to do Sum Frequency, then the phase matching angle will be approximately between the SHG angle for 800 and the SHG angle for 1040: you would send both beams, make sure you get SHG from either one at the proper angle and orient the crystal approximately in between. Confirm the polarizations, because if they are not appropriate, this will not work. TYPICALLY, they would need to be parallel for o+o->e SHG and o+o->e SFG. The spatial overlap is obviously critical, so is time overlap and polarization and crystal orientation. It is easy to get one of them wrong.
Hi Professor, thanks for the insightful video, I had a question about the mount for your BBO @ 2:34, i can see the thorlabs rotating mount is crm1l but could you tell me what the piece is inside that holds the BBO? also the dimension of your crystal? thank you again for the video!
@@dccote If i use a half wave plate to rotate my input polarization to the crystal, is that effectively the same as rotating the crystal in the mount you have?
I always use the recommendation from companies: for instance, if you ask for a quote from Casix, and say: "I want to double 800 nm in BBO", they will offer the possible cuts of the crystal.
@@vaibhavchamkur1136 Nothing. You need a very intense laser if you use this type of crystal. The only way to do this with a normal laser is to use an extremely special type of crystal called a PPLN, and they are outragesouly expensive from what I understand.
Normally, a laser that propagates in any material will simply exit at the same, original frequency because the atoms or molecules oscillate a the same frequency as the laser. When the laser is intense, and the crystal is "sensitive" to the intensity (i.e. it is a "highly nonlinear crystal") and the phase matching conditions are matched, then the light that comes out is at a different frequency from the original frequency. So a nonlinear crystal is a crystal that permits the creation of new frequencies thanks to its nonlinear coefficient and its birefringence (examples: BBO, LBO, KDP, KTP, etc...)
@@dccote so the non linear crystal allows the photons to collapae and when tuned in phase and time the mixing product is such that the 2nd harmonic is maximal?
this type of research has grate important in modern communication because it's you can create tow entangled photons (signal and idler) this phenomena called spontaneous parametric down conversion (SPDC), I wish you good work in this Really attractive field with best regard Dear Daniel
Thank u sir very helpful for understanding the concept
Thank you Professor Daniel for your video, very informative!!
Magnifique.
Very helpful, thank you, and I'm also interesting in the difference-frequency generation.
Very helpful and insightful, thanks!
thank you so much for the detailed explanation, those are some know-how that only acquire through hands on experience, people dont teach them on paper or books =(
Awesome video!! It's like a expensive lego set for physicists. Like the laser sources and power supplies too.
Why do you think I became a physics professor?!? Toys. It’s all about the toys.
@@dccote That's really cool. Thank you for sharing that video.
I've always thought of frequency summation and doubling as if one was talking about a FM radio, but I only now am realizing it's about the interaction of the electromagnetic waves when they are also interacting with a third physical medium, whether it be it a heterodyne circuit or a nonlinear material , the mixing doesn't happen in free space , only upon simultaneous interaction with matter.
How can light be FM modulated?
What *are* nonlinear properties of matter that effect this interaction?
Under what circumstances does *air* have nonlinear properties and what are they?
In the case of a CO2 or nitrogen lasers (for instance), where there is an intermediate excited state that is opaque to the intended output frequency , would it be possible to opticaly pump such a laser with two other lasers who's frequencies separately can pass through the gas lasing material but their combined frequency is exactly what is needed to bump the atoms back to the desired excited state, maintaining the population inversion, therefore eliminating the need for cooling such lasers? Is there such an interaction?
Looks like you picked up some astigmatism and/or coma on that beam... doubling really accentuates the wavefront. :)
Realy interesting thanks.
Thank you it was very useful
Very helpful!
Great, pls have you any about use KTP 1064/532 on high power fibre laser /200W CCW Raycus and how many is real as output? Pls is very important. Thx for your reply
Can you do parametric downconversion in your lab? If so, could you show it? I love to see a single-photon being split in two ;-)
Hey it's a very good demonstration, do you have any material to explain how this nonlinear materials work?
specially a ktp cristal.
@@danielarias3041 Not really. I teach a nonlinear course but the material is not well organized for distribution
Great video!
What's the difference between a crystal specified as SHG @ 800 nm and THG @ 800 nm. Is the latter optimized for THG only or both?
There is no crystal for THG. Long story short, it cancels out (see D Débarre with E Beaurepaire about that).
For different SHG wavelengths, it is the angle of the cut that changes.
very informative!! btw i work on plasmonics ans use a 780nm SLD to excited gold nanorods, the maximum power if SLD is 20mW, i was thinking of exciing the interband of nanorods, so if I use a BBO crystal can I get SHG, of sufficient power of say atleast 1 or 2mW? thanks..
Such a great video, so helpful
Excellent video. I'm building a DPSS laser using intracavity SHG through KTP as a hobby and have seen exactly what you demonstrate (laser is CW). But I am seeing poor efficiency (~2% -- optimum for the cavity should be ~7%). The only resources I've found so far start with Maxwell's equations and build theory, but never get to tangible "engineering" level formulas. Are there simpler formulas / tables for different crystal types or is this just a "knuckle down and learn it" moment? Crystal is at optimum orientation and temperature and I suspect the waist isn't tight enough, but I'd like to calculate what size it needs to be instead of re-working the cavity at random.
Intracavity doubling a laser is difficult for several reasons. First, I think that the optimal length of the crystal depends on the size of the beam (which gives its Rayleigh range, or zₒ parameter). Second, the laser will be very noisy because the SH beam generated in the crystal will mix back with the fundamental and convert *back* to the fundamental or up from the fundamental depending on the exact phase diffference between the two when the return to the crystal. This is a known problem and is why those green Verdi and Millenia lasers are expensive (they manage it differently: the Verdi is a single longitudinal mode laser whereas the Millenia is a super-multi longitudinal mode laser). I am not sure what formula you are talking about but I would say making a stable intracavity doubled green laser is tough.
@@dccote Thanks for the reply. Yes, agreed it's a tough way to go. But hey, learning all the time and I want to see what I can do here before I change the cavity design. The types of formulas I'm looking for would allow me to calculate conversion rates given energy density in a crystal of a given type / length. But as you point out there is a lot of complicated interplay with the fundamental. Last week I received a copy of your well-reviewed book on the topic. Looking forward to reading it and learning more.
Thank you for your explanation. Very impressive video! I have a quick question about the beam shape, which looks very elliptical. Is it because the incident beam is not perfectly round? Does BiBO crystal affect the beam shape?
It is elliptical for many reasons, it is partly because it is incident at angle angle and that phase matching works well along one direction, not both. I made no efforts to obtain a nice beam.
can I do this experiment over Tin Oxide thin films (SnO2) has tetragonal crystal system?
This is an excellent demonstration here. Briefly, how would you interpret BBO crystals and biomaterials(e.g. microtubules) both exhibiting nonlinear optical properties?
They have a structure that is asymmetrical. Like a dipole. The technical term is “the are non centrosymmetric”. This makes them distort the electron oscillation a bit and create second harmonic and DC (typically THz with femtosecond pulses) at the same time.
@@dccote Thanks for this, keep up the good work my friend!
So I’m new to this… haven’t been to school but I was diving into quantum entanglement and here I am. So from my understanding is that the experiment using BBO crystals and lasers is done to measure photons and their entanglement. Is there a way to capture a larger amount of particular even without a clear entanglement?
Very nice demonstration, Thanks. I want to frequency double 1600nm from the supercontinuum. I am thinking to use a dichroic mirror to separate the 1600nm part and frequency double it using MgO PPLN. I am wondering what specs should I focus on when ordering SHG crystal?. Is it just the crystal should be phase-matched for 1600nm or something else?. Also, how focused your beam should be (spot size focused into the crystal)?
When you order from these companies, you can simply say "I want to double 1600 nm". They will offer options.
I have ordered from CASIX for as long as I remember.
www.casix.com
That said, I think your supercontinuum will be too low a power to get anything important. If you want a lot of power, this is not the right approach. A Ti:sapphire laser operates at 800 nm with very high powers.
@@dccote Thanks , that's very helpful !
Im sorry if you explained it in the video but im very new to this stuff and didnt understand all you said. But when you got the new frequency how much can that be shifted? Is it only possible to shift in one direction or is there any other limitations for the output?
For example if I had a infrared light source, could it be doubled into visible light; and if so what frequencies could it have shifted to?
Again sorry if my question is weirdly formulated, I dont know what Im doing 😅
The technique I showed here only "reduces" the wavelength, and with a single beam you can only double the frequency (half the wavelength) via Second Harmonic Generation. You can double the frequency if an infrared beam and move it to the blue-green visible if it is infrared in the range 800 to 1100 nm. But don't forget you need ultrashort pulses and fairly high power.
Reducing the frequency requires a different strategy (optical parametric conversion), which is very inefficient and requires a cavity for amplification (optical parametric oscillation or amplification).
How about different frequency generation using the same setup?
Very different process: it is called down-conversion, and it is very weak. Typically, these are put inside an Optical parametric Oscillator to amplify.
Great vid, curious what type of conversion efficiencies you see? Wavelength dependent?
10% is reasonable. Angle is wavelength dependent but efficiency is only mildly wavelength dependent
Thank you for the information. Please is there a max frequency limit for this crystal? In theory is it possible to put group of crystals to multiply frequency until gamma ray spectrum?
It is a bit complicated because crystals are not transparent in the UV/x-ray. You have to use a slightly different strategy, and I am no expert, but multi-harmonic generation is the way I have seen it done in the past.
Just a quick question. I’m using BBO , 1040 nm and 801 . This should work as well, right? In addition once the beams are spatial overlapped I can send them through BBO and check for SFG and play with delay? If it’s overlapped in time and space we should see blue. Am I thinking of this correct? Great video!!
Probably but it depends what angle your BBO was cut at. When you order it, you typically request "a BBO for secondharmonic at 820nm with Type I phase matching" for instance. You can tune that by rotating the crystal around the axis of polarization of the incoming fundamental.
Now, if you want to do Sum Frequency, then the phase matching angle will be approximately between the SHG angle for 800 and the SHG angle for 1040: you would send both beams, make sure you get SHG from either one at the proper angle and orient the crystal approximately in between. Confirm the polarizations, because if they are not appropriate, this will not work. TYPICALLY, they would need to be parallel for o+o->e SHG and o+o->e SFG.
The spatial overlap is obviously critical, so is time overlap and polarization and crystal orientation. It is easy to get one of them wrong.
Hi Professor, thanks for the insightful video, I had a question about the mount for your BBO @ 2:34, i can see the thorlabs rotating mount is crm1l but could you tell me what the piece is inside that holds the BBO? also the dimension of your crystal? thank you again for the video!
The BBO came mounted in this mount. It’s probably from Casix or Castix.
@@dccote If i use a half wave plate to rotate my input polarization to the crystal, is that effectively the same as rotating the crystal in the mount you have?
Great, whats the rep rate and pulse duration?
6 picosecond and 76 MHz
Can you make a video on only Cristal how it made who to cut it proper dimensions of crystal
I always use the recommendation from companies: for instance, if you ask for a quote from Casix, and say: "I want to double 800 nm in BBO", they will offer the possible cuts of the crystal.
@@dccote can I do this experiment at home with low cost ?
@@vaibhavchamkur1136 No. Impossible. You need an expensive femtosecond laser (more than 100k$ US).
@@dccote but what will happen when I do this with normal lasers
@@vaibhavchamkur1136 Nothing. You need a very intense laser if you use this type of crystal. The only way to do this with a normal laser is to use an extremely special type of crystal called a PPLN, and they are outragesouly expensive from what I understand.
please what is a non linear crystal? anyone?
Normally, a laser that propagates in any material will simply exit at the same, original frequency because the atoms or molecules oscillate a the same frequency as the laser.
When the laser is intense, and the crystal is "sensitive" to the intensity (i.e. it is a "highly nonlinear crystal") and the phase matching conditions are matched, then the light that comes out is at a different frequency from the original frequency.
So a nonlinear crystal is a crystal that permits the creation of new frequencies thanks to its nonlinear coefficient and its birefringence (examples: BBO, LBO, KDP, KTP, etc...)
@@dccote Thank you so much Daniel.
@@dccote so the non linear crystal allows the photons to collapae and when tuned in phase and time the mixing product is such that the 2nd harmonic is maximal?
can I do this experiment over Tin Oxide thin films (SnO2) has tetragonal crystal system?