For a very good explanation of Stimulated Raman Scattering (the primary nonlinear process in this video) please check out: Your Favourite TA's video on Stimulated Raman Scattering here: kzfaq.info/get/bejne/qcB1erB1v7HdgIU.html

Excellent work. It's a shame these videos have so few views, mainly because most people haven't got the slightest idea of what's going on or why the underlying phenomenon is so truly weird and extremely unusual to actually observe.

PhD student in matsci here…these videos are a joy to watch! thank you so much for all the effort in development and clear presentation! subscribed (and shared with lab mates:))

The peaks at 16:52 arise due to a process called Stimulated Raman Scattering (SRS). To understand this mechanism, consider a simple, isolated molecule like H2. The molecular bond can vibrate at a set of distinct frequencies due to quantum mechanics. If we were to shine a laser onto the molecule, a photon can "donate" some energy to the molecule by exciting vibrations. Since the photon has lost energy, its frequency has decreased by an amount corresponding to the vibrational frequency of the bond. Since the frequency has decreased, the wavelength must have increased. For an amorphous material like silica, the molecular bonds are extremely irregular compared to a simple H2 molecule. Therefore, the possible vibrational frequencies form a continuous "band" with a peak at ca. 13.2 THz and a width of around 5 THz as shown in Figure 2 in this link: www.rp-photonics.com/raman_gain.html Therefore, when shining a highly intense, coherent laser pulse with a certain carrier frequency into a silica fiber, coherent molecular vibrations will be excited. This transfers power from the carrier frequency to one that is approximately 13.2 THz lower; this is SRS! Furthermore, this lower frequency will keep "stealing" power from the carrier until it gets so intense that the process can repeat for a frequency that is an additional 13.2THz below that one (and so on in a process called "cascaded SRS"). This explains the observed "comb" structure. Considering the peaks at 16:52 labelled 497.7nm and 519.4nm (with an unlabeled one in between), we can see that the peak spacing is 10.85nm. Converting this difference in wavelength (BW_lambda) at 497.7nm (lambda_0) to a difference in optical frequency (BW_f) using BW_f = c*BW_lambda/lambda_0^2, we get 13.13 THz, which is very close to the peak frequency of the Raman gain spectrum presented in the link above. If you are interested in some of the theory behind nonlinear phenomena in optical fibers, feel free to check out my channel, where I both demonstrate these effects experimentally and simulate them numerically using custom python code: Experimental Self-Phase modulation : kzfaq.info/get/bejne/rcCplLeHudPRcp8.html Experimental supercontinuum: kzfaq.info/get/bejne/kNmKi9Sp3LCmk6s.html Numerical simulation: kzfaq.info/get/bejne/rq-Uot2G3p-ykac.html I plan on upgrading my own code to handle Raman effects in the future, but I know that others have created packages that allow for simulating SRS in optical fibers: github.com/WUST-FOG/gnlse-python This was a really awesome demonstration, great job :)

It's like a smoke ring. You push a wave through the middle of another wave of course you're gonna get self-focusing

0:56 Yooooo! 😂 and @Les' Lab that shirt is so smart. Nice GaAs reference, among other things

Excellent work building something like this. Not an easy task at all. The things required to make supercontinuum emission are high peak power, a very wide transverse mode spacing of several nanometers if possible, and a lot of fiber to allow mode mixing and stimulated raman scattering. Essentially the power from the light creates a strong electric field undulator that the longer wavelength mix with to create parametric mixing. The energy is so high it works a lot like a free electron laser. Why you are ending up with discrete bands of wavelengts is because the fiber is only allowing gain at those frequencies, but each color bunch should have the same mode spacing as your dye laser excitation beam in absolute value ie its 4nm across. The math describing it will make your brain bleed though. 😅😲🤓❤

Absolutely stunning!

Great content!

Loving the real genius reference. Now remember-I want 5MW by mid may.

fantastic work

I love everything about it ❤ Major props. Your videos always brighten my day! Thank you for making these videos. ❤

Wow!! Beautiful!!!

Fascinating stuff. BTW your audio level is a bit on the low side.

Great work! This is super interesting!

Blown away.

Very pretty! Never get tired of beam shows, and you're producing one without a set of galvos! :)

Nearly 10k subscribers, nice going brother!

This is worth gold

This is something that I would like to have a go at building. The only thing I don`t have to hand is the lens (to focus uv onto the dye) but you said in another one of your videos that you could use a lens from a laser printer, bit low on transmission but usable. When I get some time away from work, I will be giving this a try. This is one of better channels on KZfaq, you are vastly under subscribed!

Just found your channel. Very interesting stuff! It's always a treat listening to someone who really knows what he's doing. BUT the coolest thing is the absolutely perfect T-shirt for doing LASER experiments!

What a great experimentalist, I love your work and the passion with which you deliver your results deserves being a part of every Physics & Physical Chemistry undergraduate’s learning material. Some is well into postgrad PhD quality. Keep up the good work. I wish I had you as a neighbour! 👏👏👏👏👏👏

😮 beautiful

I cannot think of a better visualization of the dirac com from my signals/systems class. But this one gets created by some weird nonlinear effect, not by a dirac comb in time. Fantastic!

Absolutely Awesome ! and yeah would look good on the Floyd cover, can't help with the solution but can hardly wait for more....cheers.

I was not surprised to see the cleanliness of the beam exiting the fibre. When you couple a laser beam into the fibre it "just' travels through the fibre and gets scattered. In this case the fibre become the 'resonator' of sorts, so the actual lazing happens in the fibre for what you get at the output, hence the decoupled beam is the result of the laser cavity, eg. fibre. With destructive and constructive interference the beam 'cleans' it self up, or just lazes what is permitted or supported by the cavity.

Subscribed!!

A follow up on fiber cleaver is due I guess? Amazing work..

Liked and subscribed

Interesting video.. a few comments as I'm watching: -1GW/cm^2 pretty nice. Almost enough to drive optical parametric conversion - Beam size from your fiber: the fiber tester is extreme Multimode and the fiber piece you're using is very short, so even the biggest modes that experience high loses in the multimode fiber make it through that short bit. In the long fiber however those high orders have enough time to die out. If you can, try the tester on the long fiber and compare. Your Dye laser beam is also probably of much lower order than the fiber tester to begin with. You can also always check if reducing peak power with attenuation changes the beam size coming out of the fiber if you suspect non linear processes at work. The comb like structure is interesting. Did you try to influence it? (Push against the coupling mirror, stress the fiber...) To see if it changes in periodicity? 20% efficiency is pretty nice as well. Do you still get that with the 100m fiber? If you feel like experimenting you could take a few meters of the multimode fiber, get the good coupling efficiency and then with a torch heat a small section in the center and stretch it. It'll reduce the fiber diameter in a relatively controlled fashion. You might be able to push your efficiency and continuum bandwidth without the need for very long pieces of fiber.

Les, try to set the dye laser up as a ring dye laser optical setup, and if you have an AO, modulator set it up in the cavity as well with a variable frequency controller to the AO, and I have an Idea of using two piezoelectric disk with small first surface mirrors glued onto them , in the cavity as a beam stabilizer, inside the ring configuration, as well put a spacial beam filter in the cavity of the ring lasr then sync the pizo, frequency with the AO, then pump it into the Fiber,. Im going to try this after tge first of 2024, I have all the gear to do the experiment. However I think you might find thus very intriguing and interesting. Perhaps make the fiber bundle into a ring laser as well with a polarizing plate and a 1/2 Wave plate cavity dump. Use pizo setup in its ring cavity as well. Brain storming I sm. I am Dale Robertson

Very nice work! A few points regarding the mode profile: 1. What's the mode profile of the Dye laser beam? How does it look like after propagating through the fiber? 2. What is the bend radius of the multimode fiber? As you may know, overly tight bend radii induce loss in higher order modes. Is it possible to change the bend radius? 3. How does the mode profile look after various distances of propagation? 4. Do you know how to extract the delay from spectral interferogramm? It would be nice to see the Fourier transform of those spectra, as the spectra do look like the output of a white light interferometer. 5. You may be able to do FROG or IFRAC with your pulses in an reasonably sized interferometer since solitions maybe compressed compared to the initial pulse.

This is absolutely amazing! I wonder if the same effect could be made with a shorter length of fiber but with the output coupled back to it's input? or perhaps just reflected backwards and using the fiber as cavity of sorts?

Very awesome !!! You said Pink Floyd album cover and I looked up at my gold disc album picture and it's about the closest thing I've seen yet ! Have around five or six he/ne lasers, mostly Phillips laserdisc player units and a nice Chinese disco laser with two open tubes but now I really want a nitrogen laser and various dyes please 😎

I was waiting for this for whole week :) great work ! I can't think of a way to measure but probably there are micro pulses within your ns long pulses. Probably distance between these micro pulses are at the order of femtoseconds.

If this were down in the radio spectrum I would suggest harmonic resonance for the frequency comb. Not sure what the equivalent mechanism is for the optical spectrum.

Wow that dirac comb was dope! btw whats the pulse frequency and duration of individual pulses?

Awesome results Les; would love to see this in person, any chance you could join a crowd of like-minded individuals in Lincolnshire in March?

We want a video about laser gyroscopes , please !

Spectacular work! very inspiring! would it work to shoot the nitrogen laser directly down the fibre? the collimation many not be great but the efficiency may be higher...

Fantastic ! Can you tell us more about how you stripped the finer cleanly?

I wonder why the green flickers so much. It would be interesting to see if it's sensitive to fiber temperature or magnetic fields or something.

Hey Les and followers. I'm making good progress with my own SC system! I built and calibrated a Pi Spectrometer from your earlier video. It works amazingly well. 'I can't believe how accurate it is. I bought some coumarin-1 dye (mixed with acetone) and managed to make a dye laser and shoot it into 30 meters of 50/125 fiber (FC/UPC ends) from a used Model VSL-337ND-S Spectra Physics laser. From Thorlabs I bought an adjustable collimating lens for launching the dye laser into the fiber. I'm not sure this is ok: CFC2-A Adj. FC/PC Collimator, f = 2.0 mm, ARC: 350-700 nm. I'm a little concerned that the UPC ends can affect my coupling and also not sure if the 2mm f is ok. My question is this - I'm not really getting amazing SC yet. I get a huge peak at 446nm but not much spreading, and the light still looks blue. Any thing you might recommend?

Please make the explanation video if you find out why it produces such peaks in the spectrum)

I would assume that combing of the spectrum would vary with the length of the fibre.

Can you reduce the appearance of speckle by mechanically vibrating the coil of fibre? If you watch a recent Mike's Electric Stuff video you'll notice he does a teardown on a biology lab instrument using what I assume is a solid state green laser and it's run through a coil that's mounted to a motor with an eccentric weight. The resulting motion creates a rapidly varying set of path lengths through the fibre and reduces speckle especially on longer exposure readings.

Was the comb effect present at all in the single mode fiber? I wonder if the comb spacing is related to fiber width.

What kind of safety precautions are necessary for working super-continuum lasers? I guess regular safety glasses are of little use. Or are the powers low enough that it doesn't matter?

@17:30 the light appears more blueish even though it has red wavelength on it! 🤔

Could it be some sort of etaloning effect happening in the fiber? I know that usually happens in a CCD detector, but it might be worth investigation whether etaloning can occur in long (+50-100 m) fibers also? Cool video anyways - thanks!

What does the output of the fibre look like in the time domain? Do the pulses get spread temporally as well as spectrally?

Would it be possible to use this to create a full color hologram? The thought emporium used three colored lasers and a combining cube to get a "white" laser for creating color holograms and it worked okay, but this seems like it could capture the actual entire spectrum if it could be used.

Off topic question. Do red laser pointers like the ones you see used as cat toys emit only in the 630-670nm range or can the emit in the UV-blue as well. I know some of them even emit in Infrared. I’m having a issue with a photographic emulsion that I want to be IR sensitive. I know it is UV-Blue 300-520nm sensitive. After sensitizing With some dyes I found when I used a red laser on the emulsion with a 720nm filter. The emulsion reacted to the light. So can red laser pointers emit uv light or did I succeed in the Near infrared/red light spectrum?

Multimode fibers can demonstrate some complex behaviour. Of course I understand you wouldn't show all the testing you did in the final edited video, but If I saw a difference in mode coupling like that, the first thing I would do is play with the incoupling alignment to see if I could get the same affect for both lasers with the same length. The essential property of a multi-mode fiber is in its name, multiple modes are stable. however, higher-order modes have higher propagatino loss, which means they are attenuated more strongly, the longer the fiber. Do you see the same behavior if you connect the fault locator on the longer MMF?

does the pulse length change as part of the frequency broadening?

Try buildings an color laser interleaved tv unit

does changing the orientation of the coiled fibre change the output?

Does it look white in real life or does it still look strongly blue as shown on the camera?

It'd be an interesting project to make an interface to sync the N2 laser to the camera's shutter. I wonder if the HDMI outputs of modern cameras are synced to the shutter? Back with analog composite it would've been pretty easy to extract the sync pulse, phase shift if necessary and trigger the laser at 25 or 30Hz

I have a question. What optics are used at the input and at the output. Lens size and focal length.🤔

Is that just a 3.5" floppy disc on your scope? It seems somehow an odd size in the video.

where is styropyro

what are these attenuators you are refering to?

Hi, your videos are great, but you should work on volume levels - your speech volume level is way to quiet compared to other videos, and intro at 0:11 is way louder than your speech, you need a gain of about 20dB.

i dont see the red and yellow orange full spectrum like i seen the first video you done?

Where did the red color in some of these shots?

Hi Les, I have sent you an email that will probably end up in your `junk` folder as it contains an Ebay link for something I found while looking for supplies. You might find it useful. To help you find my mail, the word quatermass is part of the sender ID.

is that the shirt worn by chris knight in real genius?

0:00 _"I

My guess is that the modes, or "striations" you see after the reflecting diffraction grading are a result of multimoding occuring within the fiber. I believe that these discrete modes are occuring because the MM fiber allows for numerous, discrete TEM modes to propagate, whereas the single-mode fiber you used previously, did not. This is why we see the modes occur after the grating, because all of the power coupled into the fiber, exists propagating within these discrete modes in the fiber. I'd be curious to see if applying stress to the fiber causes these modes to shift, widen, vary in amplitude, transfer power between modes, etc...

since when does MM fiber come in yellow?

Can something like this be done for regular bright light? I am in need of such a bright continuous spectrum light source such as this fir mineral identifications as early experiments have demonstrated fluorescence at specific frequency combinations. Something which cod easy be achieved with this setup and proper filters however this appears anything but portable. Picture a flashlight which causes specific minerals to stand out in the dark similar to how UV reactive ones appear under blacklight. That is what i am pretty sure can be created but proper bright configurable is anything but simple.

Try gradient index Fiber

Not sure if this is a stupid question, would grade Index Fiber do this trick?

also.. maybe try to reach out to @corningcablesystems with some of your questions about whats going on with some of your experiments... if anyone knows, the optical engineers a corning should =]