DIY SUPERCONTINUUM LASER on a BUDGET!!

in this episode is it really possible to build a super Continuum laser the ultimate white light Laser Source in a small lab and on a budget let's find out so what exactly is a super Continuum laser well we're very used to lasers producing very narrow line widths ordinarily or very pure colors if you like however there are classes of lasers out there that are capable of lazing over quite large portions of the spectrum for example dye lasers and titanium Sapphire lasers super Continuum lasers on the other hand are capable of lazing over a huge range of wavelengths that span from the ultraviolet well into the infrared we'll take a quick look at the encyclopedia entry on IP photonics website into what super Continuum generation is I'm just going to cover the main points real brief but I'll link this in down below for those of you that are interested in short um super Continuum generation is a non-linear process where we take a laser with a high peak power and fire it down a photonic Crystal fiber and its spectrally broadens the output for us the non-linear processes include things like four wave mixing cell phase modulation stimulated RAM and scattering and a whole plethora of others but in the end what we get is a very broad spectrum and this leads to a kind of laser rainbow it sets and if we scoot down the article we'll see a glorious image of one of these super Continuum lasers there it is so ultimately we end up with a white light output a continuous white light output that spans the visible spectrum and sometimes well into the infrared and well into the ultraviolet but we get this beautiful output and this is what I want to look at today so how might we go about generating super Continuum practically well all we need is a short length of photonic Crystal fiber and then we're away right um but let's have a look so I'm on Thor Labs website here and Thor Labs do all sorts of little bits of optical kits and they do a super Continuum generation kit who knew um and if we scoot down we've got a nice little diagram here we need a femtosecond laser a periscope an isolator and some other bits and pieces and we're done right and the kit itself though um is 13 000 pounds and in U.S money that's about 17 and a half thousand dollars uh the laser that you use to generate the super Continuum has to be a femtole second laser so a titanium Sapphire laser and they offer these on their website however there's no prices um it's one of these price on requests and as the same goes if you have to ask what the price is you can't afford it um I have had a look around on the internet and you can buy a titanium Sapphire laser from Del Mar photonics who are well known for producing uh really quite inexpensive lasers and this this will set you back about seventy seven thousand dollars if you're familiar with the rest of the content across my channel you'll realize that I am unfortunately on a very very small budget that Norway stretches anywhere near a hundred and ten thousand dollars for this kind of Kit so I went looking for some academic papers to see well where was this effect first discovered and is it something that is achievable in the home lab so I found this academic paper in Applied Physics from 1975 and I believe this is the first time a super Continuum using optical fibers was described the work was done by linen stolen and they worked for Bell Telephone Labs but we'll just read the abstract real quick and again very briefly we'll cover the main points of the paper so it says a new nanosecond Broadband Continuum source is described the Continuum is generated by non-linear processes in fiber wave guides pumped with a 20 kilowatt 10 nanosecond dilaser the Continuum has a bandwidth of about 180 nanometers indivisible with a total power of one kilowatt the new Continuum is in many aspects Superior to whatever came before that's that's basically it in a nutshell but what really piqued my interest is this diagram and so we can see here that they've got a nitrogen laser pumping a small die laser the output of which is fed into a fiber wave guide and then we have a super Continuum that's it I mean literally it couldn't be any more simple we've got a couple of prisms to split out the lights so that we can see that put on a screen and they're doing some measurements with a monochrometer and an oscilloscope unfortunately I don't have an oscilloscope capable of measuring nanoseconds or picoseconds um but yeah we can get a super Continuum out if we scoot onto page two we can see some plates unfortunately these are all in black and white but we've got what I present what appears to be a spectrum that runs from about 440 odd nanometers all the way to like 610 nanometers so from the blue to the red and this is exactly what we're after um if we take a look at the uh the other bits and pieces it says basically we've got a Dye Laser that's pumped by a nitrogen laser in a non-frequency selective cavity so no tunable Optics in here just plain mirrors right um fed into a fiber the interesting thing about this fiber is it's not a photonic Crystal fiber it's just silica core fiber optic cable that's it there's nothing special about this it's 19 and a half meters of seven Micron cable it says by proper alignment and overall couple of issues so five to ten percent is obtained which is a bit poor but we're trying to couple of multi-mod beam into a single mode fiber I mean so you can't really complain at that um yeah they tried it with a number of dies and they tried pilot 386 which is a an UltraViolet stroke Violet lazing die so they got uh what's this 392 nanometers to 537 so from The Violet to the green um they tried it with kumarin 120 and this is 434 to 614 so um from the blue through to the orange so they were generating super continuums with uh with ordinary fiber optic cable and there's a couple of other bits and pieces I mean the paper is well worth the reading I'll link in the DOI down below for people that are really interested in this kind of stuff I mean there's a couple of things you've got to bear in mind we're coupling although the although the the average power is pretty low and we're coupling in Peak powers of kilowatts into the end of fiber that was never designed to handle kilowatts and so you can damage the fiber but other than that it looks really really straightforward I mean it's ridiculously simple uh conceptually it's the simplest way I've come across generating super Continuum is it must have been said so with this Simplicity in mind I mean telecoms cable is dirt cheap so I had to buy a bunch of this stuff to try it out this is my super Continuum laser setup before we get started a little note on safety with these things um obviously you should be wearing laser safety glasses and these will do just fine for the Dye Laser and the nitrogen laser although once we generate super Continuum there are no laser safety glasses in the world that are going to protect your eyes and so you've got to make sensible use of Beam stops and cameras for this kind of work at the back here I've got a nitrogen laser to pump the Dye Laser this is actually featured in a previous video and it will produce about 15 milliwatts of ultraviolet light at 100 Hertz the output energy is 149 micro joules and this occurs in a very very small time frame about 2.4 nanoseconds and if you do the maths it works out at approximately 62 kilowatts per pulse which is more than adequate to drive a small die laser on the left here is my homemade Dye Laser and the die I'm actually using in this experiment today is still Bean 3 which lases at 426 nanometers or thereabouts way down in the Violet this was a particularly difficult die to get hold of but as we'll see shortly it's well worth it it's not the most efficient die either we'll maybe get pulse energies out of here at about 5.6 kilowatts which according to the original paper should be more than enough to pump this fiber the output from the Dye Laser is then coupled into a homemade collimator into this rather large length of fiber the original authors only used 19 and a half meters of silica fiber I've actually been experimenting with optical fiber in this setup for a number of weeks now and I wanted to get the maximum breadth of super Continuum I could possibly get out of this stuff so I actually have sat on the optical bench here some 200 meters of telecoms fiber this is single mold nine Micron for anybody who's playing along at home at the far end of the bench here I have the other end of my fiber mounted in a stable Mount and the output of that is directed towards a piece of card so that we can see the output foreign ER set up here pumping one end of the fiber optic cable the die that I'm using is still Bean 3 which is a violet emitting die and if we look at the spectrometer window real quick we can see that it's emitting light at 426.8 nanometers with a line width of approximately 10 nanometers when we're coupling light with high peak Powers into the end of fiber like this we need to make sure that our Optics are clean specifically we need to make sure that the end faces of the fibers are clean otherwise it'll blow the faces off as described in the academic paper the beam coupling efficiency of this setup is really quite poor um that you can expect a couple in between five and ten percent of the available light from the Dye Laser into the end of the fiber and the reason for this is that the beam is actually highly multi-mold if we have a look at a 3D plot of the beam profile real quick we can see all the garbage and stuff in the beam it's pretty far away from being a gaussian beam profile and we can imagine that really only the center portion of the beam is ever going to be successfully coupled into the end of the fiber I'm currently running the system at low power and the uncollinated beam is being projected against this white piece of paper we can clearly see a sort of diffuse blue spot emerging from the end of the fiber but once I removed the attenuator from the beam we'll see something really quite amazing happen look at that that is absolutely spectacular without a shadow of a doubt we're generating super Continuum here and we've got very clearly a white light output from a violet laser beam input absolutely incredible to see for whatever strange reason I'm getting this donut mold from the end of the fiber I've no idea why it is um I've been messing with the setup for hours and hours and can't get it to do anything other than a donut mold it's probably got something to do with the diameter of the fiber and the wavelength of light that we're producing if we analyze the light output with an optical spectrometer we can in fact see that we're generating a super Continuum that stretches all the way from 430 nanometers in the blue all the way up to 670 nanometers in the red this is covering almost the entire visible spectrum absolutely superb I have the end of the fiber connected up to a homemade collimator here and the collimated beam is being passed through a flint glass dispersing prism so that we can see the Spectrum projected onto a piece of kite currently the dilaser is idling and so we can see perhaps 20 or 30 nanometers of Continuum there but once I remove the attenuator you're going to see something absolutely spectacular this is absolutely magnificent we've got a super Continuum here stretching all the way from 430 nanometers in the deep blue all the way up to 670 nanometers in the red absolutely awesome one of the things that you guys won't be able to appreciate looking through the lens of a camera here is that there is a visible laser speckle across this entire Continuum as well absolutely superb the average output power from this super Continuum laser is really quite low probably significantly under a milliwatt this makes it really difficult to video The Beam through Funk so what I've got here is a long exposure photograph on the right hand side we can see the white beam emerging from the collimator hitting the diffraction grating and giving us a beautiful view of the spectrum thanks for watching this episode of Leslie's lab if you want to see more content like this don't forget to hit like And subscribe down below and I'll see you guys next time

Channel: Les' Lab

Views: 30,255

Keywords: supercontinuum generation, supercontinuum laser, white light laser, dispersing prism, laser rainbow, dye laser, nitrogen laser, four wave mixing, fiber optics, stimulated raman scattering, ultimate white light laser, nonlinear optics, white laser, prism, diffraction grating

Id: w1wSHizmbYg

Length: 11min 53sec (713 seconds)

Published: Thu Dec 29 2022