Talk:Dye laser

This article could use a little clean up and clarification

There is a lot of information that should be included about this complicated topic. The toughest thing about building a dye laser is the speed at which the molecules change from a singlet state to a triplet state. Depending on the dye and solvent used, flash pumped lasers experience this change in roughly 1 to 2 microseconds. Also the lasing threshold is extremely high, further complicating the problem. (In plain English, the flash mush have an extremely short duration, and be able to bring the dye past threshold before useful fluorescence becomes useless phosphorescence, at which point the dye becomes partialy opaque, cutting off the beam.) Continuous wave lasers solve this problem by constantly pumping the dye at very high speeds. Further complicating the situation is thermal shock from the flashlamp, causing turbulent changes in the dye's refractive index. Dye cells and flashlamps are often encased in a water cooled pumping cavity, which helps absorb IR radiation before it can reach the dye.

Another complication is that liquid dyes are extremely high-gain/high-loss lasers. The beam only needs to make a few passes through the dye for high gains in power, (therefore, the output mirror is usually only about 80% reflective), but any reflections generated by the dye cell walls will dramatic sap power from the beam.

The "Construction" section, I think, should be relabeled the "Operation" section, and expanded upon. A section named "construction" should be added which summerizes the various types of dye lasers, including but not limited to: Flash Pumped Lasers, Axial Flash Pumped Lasers, Continuious Wave Lasers, and Ring Lasers. Also, an "Application" section should be added, since the applications for dye lases are often very specialize when compared to other lasers.

The "Chemical" section should be expanded upon to include solvents, and even some slight mention of flammiblity, corrosion, and health hazards. (Solvents are often extremely flammible and can be absorbed directly through the skin or inhaled vapors, and dyes, such as Rhodamine 590 chloride, can be extremely corrosive to all metals except stainless steel, whith "undetermined" health risks).

Last, the "Ultra-Short" section should also be expanded upon. (ie: Ultra short pulses are possilbe due to the dye's short fluorecence lifetime, but usually require the use of special "Negative Group Velocity Dispersion" mirrors, and such).

For some good references on the subject see: Design and Analysis of Flashlamp Systems for Pumping Organic Dye Lasers – J. F. Holzrichter and A. L. Schawlow. Annals of the New York Academy of Sciences, or Simmer-Enhanced Flashlamp Pumped Dye Laser – T.K. Yee, B. Fan and T.K. Gustafson. Applied Optics – Vol. 18, No. 8 , or read the book "Principles of Lasers", by Orazio Svelto. More good info can be found at http://members.misty.com/don/xeguide.html#eg , or check out Sam's detailed website at http://www.repairfaq.org/sam/lasercdy.htm Zaereth (talk) 00:08, 14 November 2008 (UTC)

I think you have a lot of good ideas. Why not be bold? I only don't think your comment that ultra-short pulses have to do with the dye fluorescence time is correct, but the rest seems OK. Han-Kwang (t) 11:19, 14 November 2008 (UTC)

Thanks Han. You got me there. I've never constructed an ultra-fast laser, and so I'm probably mis-quoting something I once mis-read. I'll leave that section to people who have more experience on that subject. Give me a little time, and I'll work something up on the rest. I'm fairly new to Wikipedia. I've never made any changes to an article before. Are there any guidelins on how to cite the references I've listed? I've also found a few other articles, especially the Xenon Flash Lamp article, which needs some fixing also. Zaereth (talk) 01:02, 15 November 2008 (UTC)

For ultrashort pulses you need a large bandwidth, which I think the dye provides by coupling electronic transitions to vibrations. A side effect of the coupling might be that the fluorescence lifetime gets shorter, but a short fluorescence lifetime does not make it suitable for ultrashort pulses by itself. I'll leave general editing advice on your talk page. Han-Kwang (t) 09:11, 15 November 2008 (UTC)

Added information

I have added the information discussed above, (except for the wrong ultra fast stuff). If there is any question or comment, please leave it here. Zaereth (talk) 02:11, 6 January 2009 (UTC)

Definition of "dye"

In the context of dye lasers, what is a "dye"? How is it different from a something like the gain medium of a YAG laser? The article just says it's an "organic dye", but that doesn't sound too specific. —Ben FrantzDale (talk) 18:05, 26 August 2011 (UTC)

There are actually several questions here, so I'll try to answer them as briefly but thoroughly as possible.

The term "organic" in chemistry refers to the study of carbon based molecules. A "dye" is a substance which is soluable in a solvent, (eg: it will dissolve down to the molecular level), but will precipitate to form a colored stain on a surface. (This differs from pigments, which are insoluble particles suspended in the solution.) So an "organic dye" is a stain that is carbon based.

The big difference is the size of the particles. In an Nd:YAG crystal, the gain medium consist of very small neodymium atoms insides a yttrium aluminum garnet. In comparison, the dye molecules are extremely huge, long, and odd shaped structures, which react to the absorption and emission of light differently.

Another big difference is that nearly any organic dye will fluoresce at some wavelength. (It doesn't always have to be what we'd commonly think of as a dye either. Dye lasers have been made using food stuffs, like jello. I even got mine to produce a beautiful yellow beam with beer.) So, unlike the Nd:YAG laser, the dye can be replaced with another type of dye to get just about any color you could think of. I hope that helps answer your question. Zaereth (talk) 18:53, 26 August 2011 (UTC)

Can a dye laser be made from a foodstuff ingredient that isn't recognisable as a "dye"? I've never seen a beer laser, but I've done it with jelly (jello) and with whiskey. The jelly laser needed to be lime or tangerine, lurid green or orange colours from some appalling artificial colouring agent - more edible looking colours didn't work. The whiskey was some vile Korean "Scotty Whiskey Drink" that had been brought back from a conference by someone in the department. Whisky that had seen Scotland didn't seem to work. Andy Dingley (talk) 17:07, 22 November 2012 (UTC)

Hi Andy. Yes, you can indeed make a laser out of jello. As I recall, Theodore Hansch and Arthur Schawlow were the first to make one work, which they detailed in a 1971 IEEE article called "Laser Action of Dyes in Gelatin." I believe it works best if the dye mixed with the jello is fluorescein (a common food coloring) or rhodamine. I've tried many different liquids in my laser, just to see what would happen. As I recall, the beer I used was either Heineken or Grolsch; something that fluoresces well when you shine a green laser through it, and it seemed to work better if left saturated with CO2, rather than using it flat. I had to hit it with a really powerful, fast flash though. Other beers, such as Corona, did not work. I've heard of the whiskey laser on Sam's Laser Faq website, but I believe he says it works better with just the fumes rather than the liquid. Zaereth (talk) 22:15, 30 November 2012 (UTC)

Hmmm, fluorescence. Now there's an idea. I've just been working on an indoor sundial (uranium glass marbles in an ellipse, purple diode laser pointer, servo controlled mirror) There's a lot of fluorescence in that uranium glass, I wonder what its laser potential is like? 8-) Andy Dingley (talk) 23:41, 30 November 2012 (UTC)

You know, I've often wondered the same thing about uranium glass. Neodymium glass works better than YAG, but chromium glass doesn't work at all. (In fact, it's green, which is the opposite of the ruby-red color it would need to be.) I'll have to look into that some more, because I hadn't thought about it for years ... since my last trip to the stained-glass store. Zaereth (talk) 00:00, 1 December 2012 (UTC)

To answer your question, no, you cannot make a uranium laser with glass as the host. However, it can be done with calcium fluoride as the host. The reason is that uranium lases at 2490 nm, in the IR, and glass is typically not transparent to this wavelength. Uranium has it's highest absorption in the blue and green, so the host crystal needs to be transparent at both optical and IR wavelengths. Anyhow, we're getting a bit off topic for this article. Zaereth (talk) 02:00, 1 December 2012 (UTC)

Fluoride, yes! Ah, I was wondering about that. There's a vast sack of cheap chloride here, for dehumidification, and I was wondering if it had some obscure amorphous glassy form I was unaware of. Mind you, my modern CO2 laser seems to have lenses and mirrors made of cheap and robust stuff, compared to the fragile and hygroscopic old tat we used to have to put up with. Andy Dingley (talk) 17:51, 3 December 2012 (UTC)

Sorry about the mix-up. I often confuse the --ides and other chemical names. There may be some type of glass that will work, but I don't know what type yours is. Most CO2s I've encountered use zinc selenide as the optics, because it has high transmittance down to about 18000 nm, but its transmittance falls at shorter than 500 nm. There are actually many types of glass, but most common types seem to lose transmittance at wavelengths lower than 2000 nm. However, I believe some glasses have adequate transmittance as low as 3000 nm, such as fused silica or BK7. Crystallines like sapphire may also work. However, the host needs to transmit after doping and, like the case with chromium glass, that may not work with every substrate.

In an effort to bring this back on topic, one of the biggest differences between crystal/glass metal-doped lasers and dyes is the lasing range. The dyes can usually lase over a very broad bandwidth, whereas metals generally lase at only one line, and often with a very narrow linewidth. Zaereth (talk) 18:32, 3 December 2012 (UTC)

I'll have to look it up when I get a chance, but I seem to recall that, because the metal ions in the crystals are locked within the lattice, they are limited to vibrational energy-transitions only, whereas free atoms in a metal-vapor or gas laser are subject to both vibrational and rotational transitions. Dyes, because of the size and complexity of the molecules, are subject to even more complicated transitions where the spin can be "flipped," basically turning useful fluorescence into useless phosphorescence. In this article, we refer to this only as being a singlet or triplet state, but that really doesn't explain what it means nor how it differs from other laser mediums. I'll look through my books when I get some time, and try to add something about this to the article. Zaereth (talk) 20:17, 3 December 2012 (UTC)

I'm still double-checking the information about the absorption and emission properties of dyes, but I did run into some other interesting facts about uranium. The U³⁺:CaF₂ laser was the second solid-state laser ever constructed. It was built in 1960, the same year the ruby laser was invented. In 1963, it was the first laser to be be pumped with an LED (840 nm) producing the first true continuous-wave output from a solid-state laser. Apparently, there are a variety of host materials you could use, but they are usually fluoride based. (Not chloride.  :-) YLF is another common host, which has the benefit of being able to lase at room temperature (rather than 4 degrees Kelvin) and can be pumped with flashtube or titanium-sapphire. Zaereth (talk) 00:12, 5 December 2012 (UTC)

Significance of replacing the dye?

Moreover, the dye can be replaced by another type in order to generate an even broader range of wavelengths with the same laser, from the near-infrared to the near-ultraviolet, although this usually requires replacing other optical components in the laser as well.

What is the point of this remark? Should we view it as a further form of tunability, or just a way to take apart and rebuild a laser? 178.38.74.237 (talk) 18:40, 21 February 2015 (UTC)

It's trying to make the point that you can change the laser dye and the mirrors and get a different wavelength tuning range. See this for example: [1]. --Kkmurray (talk) 18:52, 21 February 2015 (UTC)

Exactly. A typical dielectric mirror has about 25 nm or so of good reflectivity. Broadband dielectric mirrors can get up to 50 nm, so changing the mirrors is often needed just to cover the bandwidth of a single dye. (Extremely broadband mirrors can cover as much as 100 nm, but these are rare and expensive.) Of course, this is not necessarily the case with metal-coated mirrors, like silver. which can often cover the entire visual range, but the reflectivity is not quite as high as with dielectrics. Zaereth (talk) 02:45, 22 February 2015 (UTC)

missing info

From Coumarin : Coumarin is also used as a gain medium in some dye lasers,[3][4][5] — Preceding unsigned comment added by 91.155.19.68 (talk) 23:06, 16 April 2017 (UTC)

This article mentions coumarin, as well as fluorescein, malachite green, and others, in the chemicals section. It could use more information, but rhodamines are by far the most widely used examples in many sources, so they are easier to find. (We didn't intentionally try to focus so much on it, but the sources seem to use it often too.) For the most part, they are all very similar in operation and behavior. Dyes toward the blue end of the spectrum tend to have shorter lifetimes than dyes near the red, but all-in-all they are very similar. Zaereth (talk) 23:16, 1 May 2017 (UTC)