Wow, this must be one of the most interesting videos I've seen in a long time. I'd heard of these but like you considered them to be very difficult and expensive to make. Absolutely fantastic job! What struck me most were the spectral variations, especially how far they extended into the red. I guess these are related to pulse energy variations, which demonstrates exactly how non-linear the process is.
Thanks! I was floored when I first got it to work! The whole process is quite weird, and seems dependent on pulse energy as you say, but also the repetition rate of the pump laser. In my system this seems to be around 32Hz any fater or slower and the continuum shrinks. Occasionally I have seen visible frequency comb in the output as well so there are probably many non-linear processes at play in the fiber, all interacting with each other.
@@LesLaboratory Have you been looking at average spectra or shot-to-shot spectra? Since 32 Hz seems in the range an CCD could easily take single shot spectra.
@@LesLaboratory Could you make a video on laser excited ceramic phosphor for rgb beam effects. Its new and what is used in the clay paky xtylos. I can't find anything about it.
@@LesLaboratory I keep coming back to this comment and wondering if (with huge losses obviously) this pulse train fed back into an identical setup could create the same amount of combing inbetween the established peaks. Creating a very fine grading, something that’s finer than any commonly available ccd sensor could establish anyway.
I had no idea any of this was possible! Really really interesting stuff! Why is the dye laser necessary rather than use n2 direct? If it's only to produce a wavelength compatible with plain glass fiber, what do you think of trying quartz fiber? Maybe it's not available in single mode?
Yeah it sounds likely that it’s just an issue with the fibre not being able to handle that UV. This also looks like a lossy method, i.e. it won’t go shorter than the input wavelength, only longer. So finding a ~400nm pulsed laser is a requirement to get a full visible rainbow. And I don’t think you can Q-switch a diode laser, though maybe it’s possible to construct a wider cavity by putting another output coupler in front of a diode laser, which you could put a saturable crystal. Maybe use a doubling crystal on a red laser? Be it naturally pulsed like a ruby, or Q-switched. I’m guessing the pulsing is needed for the high peak-powers to reach the fibre’s nonlinearity.
It's probably a UV absorption issue (or maybe it was even an accidental discovery). When you couple light in, even with a small setup like this you are right on the edge of the damage threshold (somewhere in the region of 10e9W / square cm (not a typo!)). I have generated Supercontinuum with multimode fiber, and I was hoping to get this on video too, since it is way more efficient (bright enough to see in full room light) the problem is that power densities are so high that it destroys the fiber as it runs, and this has gotten expensive fast! One of the issues seems to be that at large power levels another nonlinear effect manifests itself; self-focusing, which raises the power density to the point it blows the end off of the fiber. I have ordered a fiber cleaver to see if I can re-cleave the affected ends.
@@LesLaboratory When you mention the fibers ends blowing do you mean a fiber with a termination (like a FC-APC connector) or just the bare core floating in the air ? I've heard that the first element that will burn in a fiber termination/connector tends to be the glue around the core so by using just a bare core you can use higher power densities. It makes the fiber harder to handle and align but maybe it could be something to consider.
If you pass the output of the prism through an LCD screen with the backlight removed then through another prism to recombine the spectrum you can dial up any spectral profile of light that you want as the LCD can display spectral line masks.
I think this will destroy the spatial and temporal coherence though, which would essentially defeat the purpose of using supercontinuum light for many applications.
@@Muonium1 The proper name for the concept outlined is a pulse shaper. Usually they use gratings instead if prisms and also two focussing elements to have a LCD hit by a collimated beam, but they very much work to make essentially arbitraily shaped electrical fields with femtosecond pulses.
@@Zenodilodon Having some light scattered by diffraction means you have higher losses and potentially a uglier mode profile, but I don't see why that would be an issue? At worst, just add a mode cleaner afterwards.
@@TheTablet314 One use case is transmission spectroscopy imaging of microscope samples. You end up with a stack of images with each corresponding to the range that was not masked by the LCD.
OK, first, the name "supercontinuum laser" is a huge missed opportunity in our retro sci-fi. Second, I have no idea how I've circled the sun more than 40 times, admiring lasers for a lot of that time, and have never heard of this. Simply amazing. As an audiovisual engineer, I can't help but wonder if anyone's doing research on the optics to bring this to video projection. A projector with this kind of light source would blow any OLED TV out of the water, particularly with an ambient light-rejecting screen. Great stuff, Les. 👍
@@LesLaboratory I like your line of thinking, there! Unfortunately I'm not high enough on the chain of command to make suggestions to the vendors. Maybe one day.
Absolutely incredible. I did my master's research on self-phase modulation and suspected for a long time that supercontinuum could be generated using self-phase modulation on a budget. Keep up the good work.
Thanks! I was blown away when I first saw it. After is was discovered in the 70's supercontinuum was largely ignored for almost 20 years, and it only exploded into mainstream in the 90's with the advent of Photonic Crystal Fibers. PCF is clearly more efficient, but still...
As a dropout optics/laser engineer, I love seeing things like this pop up in my feed. As a fan of Ben at Applied Science and, er, whomever runs Breaking Taps, it's also a delight seeing them in the comments here. (I've just realized I have no idea what his name is.)
Amazing work! This is really cool, super impressive you were able to generate that right on your bench! I was reading about supercontinuum a while back in regards to optical coherence tomography, but ruled it out as a project pretty quickly due to the same financial reasons. 💸 So if I'm reading the paper correctly, this effect is generated because of the pulse duration causing self-phase modulation in the fiber, and the wavelength causing stimulated raman emission. The pump laser stimulates a bit of raman emission at a higher wavelength, and those photons go on to cause more raman scattering, etc etc leading to a series of discrete, longer wavelengths propagating in the fiber. Meanwhile, the pulse duration itself is causing self phase modulation stuff, which broadens the wavelength too. And since it's in a fiber, more length == more broadening of the continuum. Is that roughly how it works? Really cool stuff! Thanks for sharing this!
Thanks! Yes, very well summarized! In later work they call it Cascaded Raman Scattering (CRS). CRS should produce a "Frequency Comb" as well, with evenly spaced wide peaks, but the self phase modulation seems to smooth it all out considerably. In Multimode cable, CRS is dominant leading to bright frequency combs that are really nice to see as well. The problem is Multimode cable destroys itself due to to self-focussing effects. I am in the process of attempting to repair a cable just now. The authors suspect four wave mixing as well which should produce higher frequencies than the pump, but I have not observed this. Cheers!
@@LesLaboratory Neat! Thanks for the explanation/confirmation! That's a pretty cool phenomena...fiber techniques are just super cool in general, really makes you think about some of the less obvious interactions with light when it's bouncing down a kilometer of fiber 😄 Do you reckon the self-destruction aspect is the main reason why other techniques like using ultrafast lasers are more common nowadays?
Fantastic. I'm particularly impressed with the retrieval of a '75 paper (kudos to the authors for the abstract writing!), to solve a "mundane" 2022's home lab problem.
Fan FREAKING tastic Les!!! I love supercontinuims, but never thought it was achievable without a femtosecond laser. I’m so impressed by this video. Thank you for sharing!
For some reason I'm compelled to comment regarding a Rydberg receiver and spectrum analyzer, thinking you'd be the man that can probably cost effectively DIY. Maybe outside your "spectrum" and on a different "wavelength," you work with typically. 🙂 Still, I'm thinking you'd find a DIY way that'd leave us speechless.
Thanks! Black laser glasses will do it :-D Meh, all you need is careful work. Yeah, RU-vid is weird, none of my videos seem to take off, that said, those that are interested seem to really appreciate them, which is great!
Rydberg receiver: I think this is the second time I have had that mentioned in comments... I will certainly have a read. I suspect another academic archaeology expedition will be required!
@@LesLaboratory Maybe try to colab with some other Science RU-vid Channel. (AppliedScience, Plasma Channel, Tech Ingredients, Huygens Optics, TheBackyardScientist, Brainiac75) When RU-vid doesn't advertise your channel then do it you self :) Colabs are super nice 👍👍 *Your work is so awesome and absolutely deserves much more attention!*
Thanks! Oh yes, there will be more! The video was intended to be longer, but I blew the ends off of the fiber I was using for the second half. More is on order though!
Hehe, awesome use of standard fiber! As fiber is not single mode for VIS, I would expect higher modes traveling longer path in the fiber, and experiencing higher super-continuum generation.
Totally! Yes, basically 9um fiber is enormous compared to the wavelengths being coupled in and generated, so high order modes are inevitable. However, it turns out there are ways around this as well!
Thanks so much! When I was a kid, I used to read all the old stuff from Scientific American in the library. Back in the 60's and 70's truly amazing stuff happened!
Lately, Chinese scientists did it more simpler: They focus a Ti:Sapphire-Laser into a cuvette with water. Not a joke: Simply pure deionized water. Non-linearities in water causes supercontinuum radiation, that can be collimated as white light. Due to high power handling capabilities of water-cells, output power can be magnitudes higher, than in fiber optics. Sabine Hossenfelder did a video about.
If only I could afford a Ti:Sapphire Laser. the peak powers in this setup are quite low compare to Ti:Sapphire, I would be very interested in any Supercontinuum that could take place at even lower powers.
@@LesLaboratory Build it yourself. China delivers all sorts of high quality optical components. I have made very good experiences with CASIX (Fuzhou). The only things you need is a Ti:Sapphire Laser-crystal (preferably Brewster cut) two mirrors and a precision iris-aperture for Kerr effect mode coupling. Further a green cw 532nm DPSS-Laser as a pump light source. A Littrow prism can be used for tuning. When cw lasing starts, close the aperture, until the fs-pulse train appears.
It's very interesting that it doesn't actually require a PCF! I wonder if this could be pumped by a MOPA 532nm source(1064nm MOPA pulsed fiber laser and a homemade doubler). Affordable commercial units can go down as low as 1-2ns pulse length and have peak powers of around 16-20kW. Definitely going to have to try replicating this!
It turns out most things have an observable nonlinear effect, it's just a case of interaction length and peak power. Looking at the paper (and follow up work in the 70's) it should work fine with the Laser you describe. The main limitation is the amount of power that can be coupled into the fiber before it is destroyed. I have destroyed quite a few, but fortunately it is pretty cheap these days.
At first, I'm like "it's impossible to convert monochromatic into multiple wavelengths". Then I'm like "okay, perhaps they can be stretched without requiring half the entire distance of the universe". So, as long as there's less or equal to the amount of energy from the original, it should be possible. Probably not that efficient, but really "cool" 😀
It's oddly surprisingly efficient. The authors remarked that almost 100% of the energy coupled into the fiber is broadened. The bottleneck in the system is coupling efficiency 5 to 10%. With a nice clean single mode input, you would get a glorious output!
So many argon and diode lasers, but alas, no nitrogen one. Amazing results, what made it to video is cool enough, I can only imagine what it's like in person. Had the privilege of playing with some old Omnichrome white light lasers back in the early 2000s and those were unworldly.
Very interesting project. While Nonlinear optical phenomena are interesting, they usually require extensive and expensive optical setups. It's great to see someone doing Nonlinear optics at the comfort of their own homes. Keep it up👍👍
You see a donout mode from the output fiber facet because your output is multimode. BTW: try using a solid state laser for generating Supercontinuum like an Nd:YAG. Has sufficient peak power to drive a supercontinuum process.
Oddly though, if I use the same setup to generate Supercontinuum in multimode fiber the output is singlemode. I am already on it! I have recently did a product review on a Laser engraver, and the only reason I did it is because, I get to keep it, along with its diode pumped Q-Switched Nd:YAG head. I have just measured it up to build a mount for the bench, and then experimentation with begin.
Left you a comment yesterday but it looks like it's been deleted or they're still a bug with youtube. So I'll paste it here again As soon as I saw the laser video posted by rocketMan340..... I sent you a comment about 5 minutes after he originally posted it Looks like maybe he's been watching your channel 😁 which is awesome! I was always stunned at his content over the years ....more than a decade I've followed him I think. Such a shame that he doesn't do any real commentary or anything just short videos. Would be insane to hear him discuss and explain his lab and equipment. Mind-blowing stuff really. He said some of the most insane rare stuff I've ever seen
Yeah, I have lusted after his gear for ages, he built stuff for CERN and his collection is amazing. I e-mailed him, Sam Goldwasser and Jon Singer once I had something concrete. I am glad he could replicate the work! Agreed, commentary would be nice,but you can pick up a lot from looking.
Thanks Les! I'll just agree with all of the others' comments.... Wow! amazing, fascinating, mind-blowing,.... show me more! Happy New Year to everyone! 😎
Absolutely beyond fantastic and SUPERcool. I've of course been aware of this form of light for many years now, but have never seen anyone actually show exactly how its produced. I strongly suspect supercontinuum radiation will, in the very long term, ultimately supersede LEDs and diode laser/phosphor combos as sources for general illumination. But it's gonna be a loooong time. One of my favorite science experimentation channels by far.
Thanks! It is by far the coolest thing I have built for sure! Now that would be good, all it will take though is some engineer at a TV factory to say "you know what would work well as a light source...", and then they will be mass produced!
Awesome! I wonder if there is any visible effect when you apply stress or strong magnetic fields to the fibre. Might there be scope to optimise by controlling the temperature of the fibre?
Thanks Mike! Maybe! It is something I will look into, along with other stuff. From what I understand from the literature, it is possible to measure both electric and magnetic fields with fiber. At the very least, either should change polarization. I saw a paper where the authors sandwiched a fiber between metal plates and measured high voltages with it by applying HV to one plate and observing the polarization change. The ultimate infinity:1 probe? :-D
Absolutely spectacular! This is one of the most fascinating concepts I’ve seen about lasers. I wonder what sort of applications this would be useful for.
Mind blown! If you'd posted this on April 1 I would've been convinced you were having a laugh.. I've been interested in/experimenting with lasers for some 30 years and never imagined this could even be possible, let alone on a home lab budget! I've had a selection of fluorescent dyes on hand for years now, but this has convinced me to take the next step and order a quartz cuvette to delve into dye lasers. Did you have much luck with any other laser dyes?
Thanks! Some other dyes will work fine in the setup. The first Dye I tried was Coumarin-1 which is very efficient and easy to get. I just wanted a wider range hence Stilbene-3. I tried with R6G but did not observe a continuum with the setup, but admittedly this was early on and I did not try too hard.
@@LesLaboratory I don't have stilbene, I think the shortest emission wavelength dye I have is probably fluorescein at about 500nm. But in any case I have Rhodamine & Rhodamine 6G, which are good for beginner's dye lasers IIRC. First things first, finish N2 laser..
You're most likely getting the Donut mode because of the fiber you're using. For 400nm this is a low order multimode fiber and you're not filling it with a single mode laser in the first place. The first order mode also converts into the supercontinuum much faster and therefore experiences higher losses before the end of the fiber is reached. The continuum generated from that simply gets lost along the way. The second order propagates much further before being converted, so what you're getting out at the end is what's left of the supercontinuum from the second order. If you shorten the fiber you may be able to get the light from the first order conversion, but the second order is probably still Blue at that point. Self-phase-modulation, is a pretty common problem for fiber lasers. I would be curious how stable this is from shot to shot. The Thorlabs kit is definitely a different beast and hard to compare to this.
I was speaking to John Dudley, and this seems to be the consensus. There are other processes occurring as well that seem worthy of investigation. For example it is possible to feed a multimode beam, into a large diameter fiber, and get a single mode out as well. Sure Thorlabs kit will allow you to get high average powers out, and utilizes short PCF fibers. The primary mechanisms are different as well, but if all you want is a Supercontinuum on a budget, then this gets the job done.I still think there is merit and value in this old approach
Go for it! Out of all of the cable I have tried, all have exhibited spectral broadening, it is well worth the effort. When you first couple in light, start with low power and ensure the coupling is good before going wide open. A stack of microscope slide make good attenuators for Nitrogen Lasers.
So should the takeaway here be the following?: 1) Find a source emitting in a frequency higher than all others you want to include in your contiuum/spectrum (or wavelength shorter than all the others you want to emit) 2) Find the longest fiber-optic cable you are willing to buy (I believe "you get what you pay for" will translate directly here) as,: 3) Dispersion through the length of fiber will handle the rest. It's a kneejerk guess, but the dark spot you are observing on your screen could be some kind of incoherent spot of Arago. A spot of Argo is a characteristic feature of how a central obscuration will cause light to diffract around the edges. This spot will form at a distance behind the obscuration due to the wave nature of light interfering with itself (coherently, for this explanation) at a distance behind the obscuration dependant upon the wavelength of light and diameter of the obscuration. The input beam to the fiber looked pretty Gaussian to me overall, but it was certainly far from perfect as pointed out. (I'm not familiar with dye lasers, but I assume that this is a feature of the state(s) of the gain medium and resonant cavity used for amplification.) I think that this imperfect beam is propagating, and dispersing (quite messily, due to the deviation from a perfect Gaussian input profile) and could like you said: be dependant on core diameter of the fiber, which is intended for telecom, was probably for wavelengths of 1300 nm - 1650 nm. This combination of dispersion-inducing fiber coupled with an imperfect irradiance profile at the face of the fiber leads me to think the following: The 90 % of energy doesn't just disappear if it does not couple within the NA of the fiber. It likely continues to propagate within the cladding of the fiber as well. SO! My guess is you actually are coupling most of the source power into the fiber. It's just primarily propagating in the cladding. NOT the core of the fiber. This method of propagation would almost certainly give rise to the spot of Arago you are probably observing. The core of the fiber is acting as the central obscuration. This is however just my educated guess. I'm sure dye gain mediums are not cheap if they're anything like dyes used for fluorescence spectroscopy. That being said, I'd still like to see the cheapest BOM (bill of materials) that one could muster to reasonably pull this off (parts from ebay, etc.). Also: I suppose you could try using an axicon to bring that ring down to focus at a point. What you choose to do with this... well, use your imagination I guess. Sweet vids. Keep 'em coming.
Bravo. I'm headed to the Silacon Valley junk yards. Next week. I'm sure I can get a spool of fiber, I've got a N2, like yours, a super cw/pluse Dye Laser system. I wonder if I can use some C130, I have a little C120, maybe some RB, too. Laser diodes I have 450 NM, cw, a couple of watts., 1 at 440 NM. 2 watts, pluse ot cw. Exciting to study, maybe a cavity dumper polarizing plate, some 1/2 and 1/4 wave plates across the dyecell. Thanks, Les...! Cheers
Nice! If you could see the bare fiber, you would probably see a lot of light leaking out too. Not sure why the red end of the spectrum is so unstable 🤔 By the way the single mode fiber should be TEM00, gaussian. I suspect that your supercontinuum leaks into the cladding and produces the donut shape
Thanks, yes you can, I might get a reel of bare fiber just to see it. I think by the time red is generated the pulse is running out of steam. Nitrogen lasers are not very powerful pumps at all. From preliminary measurements the pulse width broadens out significantly as well as the red portion of the spectrum is reached. With femtosecond lasers I suppose this isn't a problem.
You mentioned stilbene-3 (a.k.a. stilbene-420) is a bit difficult to obtain. Would it be worth trying a related dye, 4,4′-Diamino-2,2′-stilbenedisulfonic acid ? If you still have your optical bench setup for fiber supercontinuum, a quick, fun, test would be to try a cuvette of clear liquid laundry detergent. Laundry brighteners often use 4,4′-Diamino-2,2′-stilbenedisulfonic acid. It is probably too diluted to have enough output, but who knows? Sometimes even "Jello" (tm) can be made to lase. Thank you for the best DIY science on the net!
I have a bottle of that, and I have some laundry brightener I picked up as well as some fluorescent markers. At some point we will have a "let's see if it will lase" episode! Yeah, I read about the infamous Jello Laser, should be able to pump one with a doubled YAG! Thanks!
Very interesting topic Leslie....Sorry for the very stupid question, but all the magic of supercontinuum generation happens inside the fiber waveguide ? I may have missed the explanation here, but I'd sure like to see a separate video on the subject.
I skipped it to keep the video short, but do follow the links! Sure I could do a video on the topic, its quite fascinating. In the setup I have it looks like the dominant processes are Self Phase Modulation (SPM) and Stimulated Raman Scattering (SRS).
Very impressive! I remember some time ago you mention your home-made nitrogen lasers had quite good modeprofile, so it maybe interesting to try to couple them directly into the fibers and see if that works. As for the donut: Telecom fiber is designed to be single mode for 1550 nm, if you have shorter wavelengths, you can obviously still get some higher order modes in it. For example the Thorlabs 1550BHP Fiber (single mode, non-PM, 9 um core) has a cut off wavelength of 1260 nm, i.e. and wavelength shorter than that and it may transmit some higher order mode. Edit: Upon thinking about it, that maybe the coherent superposition of the two TEM01 mode for the two polarizations you're seeing as a donut. Maybe if you hold a polarizer in the output you see a clearer shape.
It may be worth a shot, but I suspect the UV will damage the fiber. In the current setup I am right on the edge of the damage threshold, and have destroyed quite a few fibers getting to this point. That's what I figured. At 400nm 9um is a giant hole as far as the light is concerned. But counter-intuitively 50um fiber gives a very tight singlemode output, suggesting that self focussing can take place within the fiber. There is a lot of scope for experimentation with this project!
@@LesLaboratory May I ask how you destroyed the fibers? A blown off end facet can be polished off. While you are mainly using the thorlabs-style fixed lens couplers, you can of course couple to a more-or-less bare fiber directly too. The Newport F-1015 fiber couplers is style of fiber coupler that you can also reproduce at home that doesnt rely as much on patch cables and where you can easily fix a blown end facet. Of course, if you destroy fibers by color center formation in the fiber, there is nothing you can do, really. Yeah, the scope of experiments is nearly endless. Self-focussing is of course one of the mechanisms the modes in fiber can couple from one mode to another, but I'd be careful to take the changes mode-profile as evidence of self focussing. Since in long and bend and impure fibers, modes couple anyways.
@@LesLaboratory How could i forget it was a pulsed laser!!! whoops. Are you on the Photonlexicon forums? i haven't been there in almost a decade, but there were some really nice people on there with a boatload of knowledge on older lasersystems. Maybe they have experience with Pulsed sources and PCAOM's ??
@@AnthonyvanHamond I am indeed, though I have not posted in years (well, until a few days ago), it looks like femtoman is attempting to replicate the work. The crystal is quite wide in the PCAOM so I can always use an unused portion...
Thanks! Yes, there will be a follow up video on this. It was shorter then I expected it to be because I damaged some fiber, however I have ordered more!
thats so ridiculously easy... actually I also have not any clue how this frequency shifts are done, maybe some intra-fibre-rerlections in combination with a low efficiency couple-out... its outstanding. i wish i could see the laser speckles in real life. about the donought, in the past i got pretty fine calculation results from WinLens3D, i guess somewhere in coupling-out you got some interference...
It's a combination of effects, stimulated Raman scattering and self phase modulation. It sure is very nice to see, but it will go next level in the next video! The donut is because the wavelength of light is much smaller than the diameter of the fiber, and so you end up with a high order mode, however very strange things can happen at higher power densities....
This actually blew my mind! Amazing job, however I'm left to wonder why the output so perfectly centered around visible light, like it is the exact same wavelengths we are able to see with our own eyes... does it have to do with the equipment used to measure the spectra (ie. limited sensitivity in the Ir range) or is something related to the bandgaps of ther atomis in the fiber (like how we don't have x-ray emitting diodes or microwave emitting diodes because of the electronic band structure ...)
It was by design. The start wavelength is determined by the dye used, and so I selected one that lases as close to the UV as possible. The end wavelength depends on the length of the Fiber (or nonlinearity), so ultimately I ended up with 200 metres of the stuff!
Fantastic video!. I wonder how far one could push this with a 532 nm, nanosecond long pulsed laser with nice beam quality in terms of efficiency and spectrum generation. With current laser technology (the original paper is old!) could one get a better deal (also thinking in terms of the nice 1064nm lasers)
Oddly a fall-back for if this didn't work out was exactly that. I still need to pick up a cheap unit from Aliexpress though I suppose I could roll my own.
This will be a great piece of kit for analytic chemistry or spectroscopic research. My background is in optical fibre sensing and photonics, and am wondering about two two things: Firstly, the effect of path length on output spectrum, have you performed cut-back tests? and secondly, have you been able to test the effect of straining of the optical fibre? I would appreciate to hear about how these effects may or may not affect the output spectrum. Thanks for all your videos and I wish you well. 😀
Thanks! I did the opposite, I started off with 25m, then 50m, etc. 200m was calculated based on those tests. The longer the fiber the broader the spectrum. That said, I really want to delve deep into this, so last week I ordered a fiber cleaver, so do exactly that, start with a long length, measure, trim and measure again. There are other tests to be done as well to characterise this effect.
@@LesLaboratory Just another question, does the single mode fibre under test have angled ends? this will help reduce back reflections (60 dB) from the end facets. Perhaps you can find a cleaver that will create an angled cleaves? If not, you might be able to cleave the bare fibre whilst it has a slight twist. The optimum angle is approximately 7 and 8 degrees. *apologies if this you already know this... *
Wow! Super cool! It's interesting that when you remove the attenuator that it seems like the colors have to "warm up". Is that an artifact of the camera or does it really take a moment to produce the whole spectrum? and is that flickering of the final result visible IRL or is that an interference of the camera shutter rate and 100hz laser pulse?
Thanks! Yes, the "warming up" is a real phenomenon, but I am not sure what causes it, the flicker at the red end is real as well. Seemingly this effect is quite dependent on repetition rate, so somewhere between about 30 and 35Hz will be a real sweet spot no doubt. There is a lot about this that I want to measure and characterize.
Hey Les, I’d be very interested to know what is the pump threshold for supercontinuum in this setup (or the multimode setup). More specifically, how the input pump power relates to the output spectrum. Would you be able to measure this with some attenuators on the dye laser output? What I’m really wondering is if supercontiuum can be achieved with lower powers i.e. 10W and longer fiber lengths i.e. 20km (another standard telecom fiber cable length). Then a diode laser could be used to generate supercontinuum, eliminating the need for the dye laser and nitrogen laser. Let me know your thoughts on this!
At the input face of the fiber, with single-mode, you would be looking at 1kW being coupled in. When the SC laser idles in the video, a continuum is being produced (maybe 30 or 40nm wide), however the energy is too low to measure (with my equipment), so probably down in the 100's of watts (peak) range. As it so happens, I am actually in the process of investigating whether is it possible with Diode Lasers. I already have a test driver assembled, I just need a suitale fiber. Occasionally test reels of tens kilometers of cable show up on eBay, I am just waiting for something close to what I require so I can experiment with it. It might be possible to use shorter length of fiber, as well, so long as certain conditions are met. Even with the results in this video, I suspect this is only the beginning of what is possible...
I wonder how old single mode vs new single mode fibre changes things. The newer fibre is massively lower loss, obviously normally a good thing in transmission, but I wonder if that's actually worse here.
My thoughts as well. A significant loss in fibers in telecoms comes from nonlinear processes, especially when running multiple channels at high data rates down one fiber. At least one fiber I had (before I blew the ends off it!) had a poor nonlinearity I am ordering samples of various types to see what the differens are between them.
There are likely a number of factors. This is driven by a pulsed laser, and pulse-to pulse energy varies by a couple of percent. This is then amplified by the effects in the fiber. There are a couple of nonlinear processes going on in the fiber as well which are competing with each other. In a future version, I am hoping to address these issues, as well as boost the average power.
Thanks for the video Les, really fantastic. I'm trying to replicate this on even more of a budget than you, so I've been looking at DIYing a TEA or low-pressure N2 laser. However, I saw your comment that you only get full visible at 32 Hz pump, and from what (admittedly little) I've read, these simple air lasers only pulse around 2 Hz. I suspect this is a characteristic of capacitor design. Do you have any suggestions for improving the pulse rate of a TEA?
Hi yes, have a look on my channel list. I designed a nitrogen laser from scratch that can easily do upto 100Hz, and unlike traditional home made designs, doesnt break every half hour!
Could this be used in creating full color holograms with just one laser? I believe they currently involve the use of a red, green, and blue laser separately.
The first question in science is "I don't know" and I don't! My suspicion is probably not. The beam has spatial coherence, so it can be collimated into a remarkably thin beam with low divergence, however, it cannot be temporally coherent due to all the frequencies present. At this stage, I need to characterize this setup and preform some real measurements on it to determine limitations.
LOL Not a fan of heights though! The output power is under 1mW average, so you could not use it for say room lighting, but it depends what you want to illuminate...
I bought 200m of single mode cable from amazon for around $60 delivered. I did however spend $$$ on several types and lengths figuring all this out though!
@@LesLaboratory Thanks for the info. Yeah, I know prototyping is expensive. Especially if you do it like me, thinking that "this cheap part will suffice" and then end up buying the one that was too expensive in the first place.
Isn't there some point where you have eliminated all the characteristics of "laser" light and all you have left is just mundane light? If this is a true continuum spectrum doesn't that mean the coherence length is zero?
The beam has remarkable spatial coherence, so you can collimate into a needle thin beam with low divergence. As you say though the temporal coherence is very low, due to the broad spectrum of frequencies produced. It would be an interesting exercise to measure these properties.
Hi Les, I am really enjoying your videos. I have an old spectra physics 337 nm Laser (up to 30hz or 60hz in pulse mode) that I'm going to use to try this. I just ordered 30M of 50 micron telecon fiber. Would I get some sort of SC effect using a direct coupling into the fiber or do I need to use a longer wavelength setup with Dye? Also what do you use for your attenuators?
oh - I was looking at other commenters and saw that a dye is absolutely needed. Looks like I'll be building a dye setup like what you have in one of your other videos!
Ha, I was about to say. Amongst other things, I suspect fiber is too opaque at 337nm. Many dyes have been reported to work. I have tried Stilbene-3 and Coumarin-1 and they work well. My attenuator for the Nitrogen Laser was a stack of microscope slides.
but how you can be sure if this is really supercontinium laser? did you maked some experiments? I think supercontinium more than light source in VIS range
I am 100% certain! There is no linear optical phenomenon that can spectrally broaden a monochromatic light source like this. The only mechanisms that can, are non-linear. As you can see in the video the spectral broadening is extreme, 250nm wide from a 10nm wide input beam. The results have been confirmed by experts in the field, and replicated by someone who used to design Lasers for CERN.
Possibly, the output itself is quite noisy, though that could be dealt with in software perhaps. I have actually been doing a lot of work on SRS lately (upcoming video!), and I think there might be a new avenue to explore with the Supercontinuum.
why is the spot tingling? and as if blinking different colors, i understand freq doubling crystal but what exactly is ha[[ening here to be getting full spectrum when you are using violet laser?
The main process is Stimulated Raman Scattering. There is a fantastic explantion in this video here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--GDsMDpC3oA.html
@@LesLaboratory lol you must be kidding mate, maybe easy for you but the first 2 min alone i was confused by the guys raspy cutting voice and all those equations and numbers he was showing i have no idea on this stuff it is beyond my level right now i'm still just trying to understand laser action on as crude a level as i can get it, i was simply hoping to get a straightforward simplified answer on why the light appears to be tingling not all the math and physics involved
@@LesLaboratory I guess I'm struggling with how a broadband source can be "coherent" - are you saying that if you filtered the light (ex. 5 nm bandwidth) from the sun vs from this laser, you could somehow tell one from the other (based on coherence)?
There are lenses called axicons that can create ring shaped beams but that's a bit different from an actual "doughnut mode". For actual doughnut modes I'm not sure if a simple lens could create them but I know that it can be done with vortex waveplates.
@@MrBleulauneable Yes! that's the name I was thinking of! Thank you! Wait .. are you saying that such a thing as an actual "donut mode" ‽‽ I had to look up that last one, never heard of an optical vortex before, definitely took me places I didn't want to go well beyond my high school level with math..🤯 . I was always curious what would happen if you rotationally polarized light at a rate equal to or exceeding the frequency, I kind of figured it would just cancel itself out, but knew energy had to go somewhere... Apparently it goes into rotational angular momentum only in the center of beem axis... I wonder what future ideas that tidbit of knowledge will spawn....
