TJIIRRS: Number 10 of an Ongoing Series;

Commercial laser dyes can cost over $100 per gram, and are out of the reach of most DIY laser builders. Furthermore, most chemical companies refuse to sell to individuals these days. This page explores dyes for DIYers, with an eye toward affordability, availability, and performance. Most of these have been tested with nitrogen laser pumping, and a few have been tested with flashlamp pumping.

Although Fluorescein is often available on eBay, it is not necessarily very pure; moreover, Fluorescein is difficult to excite with a nitrogen laser because it has relatively little absorption at 337 nm. (That however, makes it an interesting candidate for longitudinal pumping.) Rhodamine 6G is occasionally available on eBay, as well. Neither of them is usually of laser-grade purity, but that certainly doesn’t prevent them from lasing. (Personal experience.) OTOH, the Rhodamines don’t absorb much at 337 nm either, and they are difficult to pump with nitrogen lasers.

On rare occasions, some scintillator compounds are available on eBay. I have managed to acquire and lase both PPO and POPOP. Those, however, are the exceptions to the rule, and they cover only part of the spectrum, so it is important to find materials that DIYers can routinely acquire and use.

A good laser dye has high fluorescence efficiency, and absorbs pump light well. In addition to these general characteristics, a dye that is good for DIY use dissolves in solvents that are readily available and relatively nontoxic.

Dyes that are well-behaved under flashlamp pumping do not undergo intersystem crossing to any great extent, and thus do not exhibit much triplet-triplet [excited-state] absorption. This is not likely to be much of a problem with nitrogen-laser pumping, and it is also ignorable with several of the most common dyes (e.g., Rhodamine 6G, Rhodamine B, and Fluorescein). I have encountered it with one or two somewhat more exotic dyes, one of which I had to bubble argon through in order to lase it at all; but those are not of much interest to DIYers, as they are expensive, hard to get, and toxic. There are, in any case, other dyes that cover the same or overlapping wavelength ranges.

I have revised this page to start with the easiest and most tractable materials, after which I move on to those that are a bit more hassle or slightly less commonly available. At the end of the page or on a follow-up page I discuss “dyes” that are derived from natural sources. These require far more processing, and are of interest primarily for the fact that you generally don’t have to buy them from manufacturers or distributors, and you may be able to find some of them just lying around on the ground or hanging from trees; that said, relatively few of them are particularly good performers.

SPECIAL NOTE, added 2013.0430, URL updated 2022.1109: Yun Sothory has a good page about DIY dye lasers, on which he reports results with a number of markers and other suitable materials that are available in Russia, many of which are presumably common throughout Europe. He also includes some nice ways of building cuvettes for nitrogen pumping.

Special Note, added 2013.1028: Holger Jaenisch (who can be reached by sending email to lsei1 at yahoo dot [the usual 3 letters]) reports that he has lased several of the inks listed below (including M205 and Noodler’s Blue Ghost) without bothering to dilute them. I never even thought to try that! [As of 2018.0910, I have lased M205 undiluted.]

Here is a set of photos of the first one I tried, Private Reserve Highlights ink, in Chartreuse (I suspect that this is their only transparent fluorescent highlighting ink), which I bought at Bertram’s Inkwell. The first shows the bottle; as you would expect, you can see some fluorescence just from the roomlight. The second shows the fluorescence with a longwave UV LED shining into the bottle. The third shows a few drops of the ink in about 2 ml of distilled water in a fused silica cuvette, and the last shows that same mixture lasing. (The pump source for all of the fountain pen ink lasers described on this page, btw, is our PRA LN 1000 room-pressure nitrogen laser.)

           
           

Please note that I did not take the time to position the cuvette properly, and a little of the pump light appears to be passing by to the side of it. Even so, the dye is lasing quite nicely.

Adding a drop of concentrated ammonia appears to shift the fluorescence slightly toward the yellow, but I do not know whether it changes the lasing threshold or wavelength much. (The solution continues to lase, though, so the change in pH probably doesn’t seem to hurt anything.)

Diluting the ink into 99+% pure isopropanol produces a turbid solution with moderate blue fluorescence. I did not attempt to lase this solution, as I did not have time to filter or centrifuge it. It is remotely possible that there are two fluorescent components in the ink, but more likely there is a pronounced solvent effect of some sort. (Because the ink diluted well into distilled water, I have not yet tried it in 95% ethanol.) I will be looking into solvent issues further, when I have time.

(2011.0303)

The second ink I tried was Noodler’s Blue Ghost fluorescent invisible ink. [NOTE, added 2018.0910: this ink is now listed as “Bulletproof”. That very likely indicates a change in the formulation; I have not tried to lase the new version.)

Just as with the Private Reserve Chartreuse, this ink becomes turbid when I mix it into 99+% isopropanol. In 95% ethanol, however, it is transparent, and lases extremely well:

(That’s about 8 drops in ~2.5 ml of Everclear. I’m sure I could have used less.)

Blue Ghost also lases in distilled water, but I had to use about 8 or 12 drops in ~2.5 ml, and the lasing was not stable.

(This photo is much less bright than the best I saw from the dilution in water, but I had difficulty capturing a better image. The lasing decreased in intensity very rapidly, and the LN 1000 is not triggering correctly, so I could not predict when it would fire.)

Note, btw, the difference in color between the two photos. The ethanol solution fluoresces and lases a deeper blue. (Solvent effects of this sort are fairly common.)

(2011.0304)

A few days ago I was cleaning a pen that had contained Noodler’s Baystate Cranberry...

...and I noticed that the rinse water was strongly fluorescent. I tried diluting this ink into distilled water, but the result was disappointing (photo on the left), so I diluted it into Everclear instead (photo on the right). For each of these photos, btw, I added 3 small drops of ink to the solvent in the cuvette. The illumination for the fluorescence is from a near-UV LED.

           

As you can see, the fluorescence is far brighter in ethanol, and when I put the cuvette into the focused beam of the nitrogen laser it lased very nicely:

(The main beam is yellow; the green halo that you see in the photo was not at all evident to the eye, and I am not yet certain what may have caused it. Perhaps the ink contains more than one fluorescent dye, or possibly there is some particulate matter that is of the correct size to scatter green light just a little, though I would not expect either of those conditions to produce a halo that the camera picks up but the eye does not.)

(2011.0305)

I checked again, and I definitely don’t see the halo, but the camera in my telephone does:

I’m still very puzzled about what’s going on here. (Note, added later: it gets even more strange; see the addition from late 2013, below.)

(2011.0318, early AM)

Since I wrote the description above I have tried, several more times, to get this ink to lase in water. I was unsuccessful. In the course of my attempts, though, I found that it is totally incompatible with sodium lauryl sulfate: if I add SLS to Baystate Cranberry that I have diluted into distilled water, the solution becomes darker red, and loses almost all of its fluorescence:

I don’t recall ever having seen this behavior with any commercial dye, though it is certainly possible that a dye molecule could react with a detergent molecule, and there is no guarantee that the result would fluoresce particularly well. (There are other possible mechanisms; I put that one forward only as a vague guess.)

Baystate Cranberry is also incompatible with at least one other detergent; with that one it still fluoresced, but became turbid. [Note, added 2018.0910: this is in line with the fact that Nathan Tardif, the owner of Noodler’s, strongly recommends against mixing any of the Baystate inks with any other type, as they generally clot. (They do seem to mix nicely with each other.)]

Meanwhile, I decided to take another look at the green halo effect. Here is another photo, this time with two small drops of the ink in about 2.5 ml of 99.85% isopropanol:

(I suspect that even one drop would probably be enough.)

Here is what the scene looks like when I view it through a diffraction grating:

It was suggested to me that the cameras could possibly be picking up some NIR; at least the one in my phone would probably show that as blue (my previous phone definitely did pick up a bit of NIR, and equally definitely showed it as blue), which could mix with yellow to make some sort of green. (I say that with a certain amount of caution. Blue and yellow do not necessarily mix to make green. If they did, screens would not be RGB and color printing would not be CMYK.) As far as I can tell from this and several other photos, though, that does not seem to be what’s going on here.

What it begins to look like to me is that the response curves of the eye are slightly different from those of the cameras, and what I see as yellow the cameras “see” as green. This is supported by the fact that the center spot inside the green halo in each of the photos above is actually white: the sensor has been overdriven. This is even true in the spectrum of the dye fluorescence in the last photo. (It’s the lowest one.)

(Midday, same day)

The only thing for it is to run the output of the laser through the monochromator, and find out the wavelength. We actually have a small monochromator here, which seems to calibrate well to HeNe (shows it at about 633 nm), and I hope to perform this test some time soon. I may even be able to calibrate the monochromator to the sodium D lines, which are very easy to produce and which should be very close to the wavelength that this dye is putting out.

(Later that afternoon)

With both slits wide open, which makes it easier but considerably exaggerates the bandwidth, I get an uncalibrated range of 558-587 nm. This is probably closer to 568-577 nm actual uncalibrated range. (I have checked the monochromator against a green DPSSL laser, and I get a range of nearly 20 nm with the slits open, so we have to knock perhaps 10 nm off each end of the range I recorded for the dye. The center of the range is about 533 nm, so the reading is only about 1 nm high if the DPSSL is based on Nd:YAG, or about 3 nm high if it’s based on Nd:YVO₄, both of which are or at least have been typical.) These parameters suggest that the actual output range of the dye is close to 567-576 nm. I’m afraid, however, that you need to take all of this with a grain or two of salt. It was a quick handheld measurement, and not really reliable. At some point when I have time, I will redo this measurement with the slits narrowed down further, the dye laser output actually aimed into the monochromator, and the monochromator output displayed on a target.

In any case, if my initial measurement is not too far off, the color should be a slightly greenish yellow. Unfortunately, not only will the perception of this vary from person to person, but in addition the information on the Web is not as accurate as I would like. Just for example, I have seen one page that lists green as 510 nm. That’s much too short. Laser pointers that emit 532 nm are seriously green; by the time you get to wavelengths even as short as the common argon laser line at 514.5 nm, you have a color that is somewhere between cyan and blue. (To my eyes, the thallium emission line at 535.0 nm is about as green as it gets. YMMV.)

(2013.1028)

Holger Jaenisch (mentioned above) obtains very green output from this ink if he puts it in a narrow cuvette:

(I think that his example was pumped by a PRA LN-1000 TEA nitrogen laser.)

It seems (to me, at least) quite amazing to see brilliant yellow fluorescence and green lasing.

I tried diluting this ink into 91% drugstore isopropyl alcohol, and found that 6 drops into about 2 ml would not lase:

It is possible that a more concentrated solution might work, but it turns out that this ink lases well in distilled water, and I haven’t tried iso again yet.

(Note the slightly more yellowish color of the water dilution. If “Firefly” will lase in isopropanol, there is a good chance that the color of the laser light will be slightly shifted toward the blue. I may try that at some point, and if I do I will also try it in ethanol, to see whether the same is true.)

Note, added 2018.1012: I have determined that it lases, though somewhat weakly, undiluted:

6 or 7 small drops of this ink in distilled water did not lase. Notice how far the pump laser beam is penetrating:

I doubled the concentration, and was pleased to discover that it worked:

This issue is worth noting, as you are likely to encounter it again if you deal with dye lasers. It should come as no surprise that different dyes have different absorption spectra; as it happens, neither Firefly nor M205 Duo absorbs much at 337 nm. These particular inks may be better suited to flashlamp pumping, where the pump spectrum includes wavelengths that the dyes in them absorb better, or perhaps to longitudinal pumping, which takes slightly lower concentration.

[NOTE, added 2018.0910: I have now tried diluting this ink into 99.85% isopropanol, and also into regular rubbing alcohol (70% isopropanol). It becomes turbid.]

As mentioned above, Holger Jaenisch has lased undiluted M205 highlighter ink. As of 2018.0910, so have I:

(In this case, the ink was pumped by an air laser; the end of the channel is visible as a bluish or purplish glow to the left of the cylindrical lens I used to focus the laser’s output onto the cuvette.)

This ink does not dilute well into isopropanol.

It dilutes reasonably well into water, but does not absorb enough at 337nm to be suitable for nitrogen laser pumping. Oddly, when I add acid to the solution, almost all of the color disappears, and the fluorescence broadens and shifts toward the blue. Despite the fact that it then absorbs better at 405 nm (violet laser pointer), it absorbs even less well at 337 nm. (This photo provides good examples of two effects. First, the shutter in the camera of my phone was not well synchronized with the pulse from the air laser. Second, it is easy to see the pump beam traveling much too far into the cuvette.)

I did succeed in lasing it straight out of the bottle.

As soon as I saw Jake’s posting I went looking on the Web for sources. It turns out that Rit products are fairly easy to find. While performing that search, however, I came across Dharma Trading Company. They carry a liquid product that they call “Optic Whitener”, in 8-ounce bottles, and I bought one. There seems to be some detergent in it, and I found that when I added a small amount to some 99.8% pure isopropanol I got a very turbid and almost opaque result. This is not particularly surprising, as the product is actually intended for use in water; I added a bit of distilled water, and it cleared very nicely. (For perhaps 2.5 ml of isopropanol, 7 or 8 drops of distilled water seems to be enough to balance 2 small drops of “DTC”, which is what I’ve been calling this material. It is simpler, of course, to use 70% iso from the drugstore, which is already dilute enough; I mention the turbidity issue because it revealed something about the dye.)

DTC is extremely concentrated, and you will only need a tiny amount; for the following photo, I put two very small drops into a cc or so of 95% ethanol. The solution lases beautifully when I pump it with a low-pressure nitrogen laser:

Note, added on 28 October, 2007: Jarrod Kinsey found that he had no trouble with 91% isopropanol from the drugstore. I typically get turbid [cloudy] solutions when I add DTC to 91% isopropanol, and I’m not sure why Jarrod’s experience was different from mine.

I have also verified that DTC dissolves just fine in 70% isopropyl rubbing alcohol, and lases very nicely. (The cuvette in this photo contains two small drops of DTC in about 2.5 ml of rubbing alcohol. The photo was taken on 24 October, 2009, about two years after I wrote the original note.)

Further Note, added on 27 December, 2008: If you can acquire 95% ethanol (the brand I’m familiar with is “Everclear”), it also works quite well.

As of 2008 I have not yet pumped this dye with a flashlamp, so I don’t yet know what kind of concentration is appropriate for that. I am, however, confident that it will lase. [See next note.]

NOTE, added 05 January, 2010: This evening I lased Optic Whitener in 70% isopropyl rubbing alcohol from the drugstore, in a small dye laser that puts only 12 Joules into its flashlamp. That laser is covered on Page 015a of this series, where there is a photo of the blue output from this dye.

Note, added 16 November and 28 December, 2011: Dharma Trading Company now lists this material as “Uvitex BNB”. I have been unable to find spectra for BNB, but Uvitex OB is listed as having absorption max at 375 nm, fluorescence max at 437 nm, and fluorescence quantum efficiency of 0.81 in DMF. If we assume that BNB is not very different from OB, and that the quantum efficiency is about the same in 70% isopropanol as it is in DMF, this dye appears to be slightly better than 7-Diethylamino-4-Methyl-Coumarin, a classic blue laser dye.

Note, added 20 January, 2010: I begin to think that the addition of a small amount of base (NaOH, KOH, or concentrated ammonia) to the solution changes the wavelength slightly and improves the performance; but you can take that with a grain of salt, as I have only done one trial so far.

Note, added 10 March, 2011: Since I wrote this section I have found an article in which the authors tested 25 optical brightener compounds, and were able to lase the majority of them. Only two or three were really good lasers, but that is not surprising: fluorescence is not the only characteristic of a good laser dye. If I can find the article again, I will provide a citation.

This example was pumped by his LN-1000 (see link, above), and the pump beam was focused by an ordinary lens rather than a cylindrical lens. Note the fact that the dye is lasing mostly without feedback: you can tell by the tall stripe; if there is much feedback, the output pattern is a bright spot, or in some cases a bright spot superimposed on the stripe. There is only a hint of a spot in this photo.

Holger reports that at least one brand is extremely difficult to clean out of the cuvette, so you may want to be careful with this material.

(Please forgive the motion blur.)

1. Buy a yellow-green Sharpie™ “Accent” marker, a “Hi-Lighter” or other fluorescent marker. (When I went to buy an “Accent” marker I had to get a 2-pack, but that’s not a problem. They are still remarkably cheap, and it’s good to have extra dye on hand.)

   You can do this with other colors; I have had some success with the orange “Accent” markers, for example, though they are not as efficient as the yellow-green ones.
   
   

2. If you are extracting a yellow-green Sharpie™ marker, get a bottle of isopropyl alcohol at the drugstore. I used 91%, because 99% iso isn’t available in drugstores where I currently live, and I thought the higher percentage would be better; but ordinary 70% rubbing alcohol also appears to work.

   If you are extracting a yellow-green “Hi-Lighter” or a yellow-green Foray™ marker, you will want to use distilled water instead of isopropanol. Other brands and/or colors should be tested individually, but see below for some preliminary testing results.
   
   

3. Put on gloves. You can use ordinary rubber ones if you have decent manual dexterity with them on (I don’t), or disposable ones. If you’re allergic to latex, you can get nitrile or vinyl ones instead. I got mine (they’re vinyl) at the hardware store, but drugstores also have them.
   
   
4. Take the cap off the marker, and use a small pair of needle-nose pliers to pull out the point. (This leaves you an opening and some room down inside.)
   
   
5. Carefully pour alcohol into the marker until it’s about full. The level will probably go down, and you may get to add more alcohol. (The amount is not crucial.)
   
   
6. Put the cap back on, rinse off the marker in case any dye has escaped, and set the marker aside. (You can take the gloves off at this point.)
   
   
7. Ignore the marker for at least an hour. I let my first one go for considerably longer, but I doubt that it makes much difference. In fact, I extracted a “Hi-Lighter” for a few minutes and got dye that was sufficiently concentrated to use, though it had some dust in it and had to be cleaned. (More about this issue later.)
   
   
8. Put on some gloves. (In fact, you should wear gloves and probably a face mask any time you mess with organic dyes. Very few of them are nontoxic.)
   
   
9. Remove the cap from the marker, and pour the solution out into a small storage jar.

   NOTE: The solution will almost certainly be cloudy if you are working with a yellow-green “Accent” marker. Don’t worry about it — at this stage, that’s okay. With other markers, you may have to filter the dye if it is cloudy. On the other hand, the Foray™ yellow-green marker should produce a clear yellow solution with strong green fluorescence if you extract it with distilled water.
   
   

10. If the liquid is cloudy, seal the storage jar and set it aside for a day or two to see whether it settles out. With yellow-green “Accent” markers, the liquid separates into 2 clear layers. The upper layer can be used as laser dye. It works quite nicely under nitrogen laser pumping; I have tuned it from yellow-orange to blue-green without any difficulty. (I’ve posted photos on a followup page.)

    I suspect that when the level gets low you can add more alcohol, shake, and allow it to settle again. Eventually, the bottom layer should all be dissolved.

    With the Foray™ marker, the solution should be usable essentially immediately. You may want to try adding a drop or two of strong ammonia, to see if that improves the performance, but I’d try that with a very small quantity of dye at first, rather than an entire batch, in case it fails.

NOTE: I would guess that you could do several extractions from one marker, combine the results into a single batch, dilute it, and use it under flashlamp pumping, but I haven’t tried that yet.

NOTE: One easy way to test a marker is to pull the point out, drop it into a small bottle, and add the solvent you wish to try it with. Here are the Foray green and pink examples, with distilled water on the left and 91% isopropanol on the right:

Notice that the green ink is thoroughly incompatible with isopropanol.

Some colors won’t lase. This can be because they contain other dyes, which absorb the output; because they have too much “junk” in them (if the solution is cloudy, it won’t lase or won’t lase well); or because they do not fluoresce efficiently enough. With regard to cloudiness: I noticed that when my yellow-green “Accent” solution got cold it became cloudy, and I had to warm it up to get decent lasing. If a solution contains solid particles even at reasonable temperatures, you can centrifuge it or filter it (though a filter that is good enough for laser work tends to be expensive), or just let it stand for a long time and then very carefully decant the clear liquid off the top, leaving the sludge behind.

(If you want to see a demonstration of this, read my page about our Molectron laser, and note the photos a little more than halfway down the page. There are four of them in a row, and a fifth one a few lines further on; they show Fluorescein, first not quite lasing, and then lasing nicely when I add a small amount of a coumarin dye to it. Even though I didn’t have the camera aimed straight into the beam, taking the fifth photo in the set damaged the sensor. [“Do Not Look Into Laser With Remaining Camera!”] You will not be able to get a new sensor for your eye if you do this to it...)

It is possible that the dye may not absorb well at 337.1 nm, in which case a substantial fraction of the pump light just goes through it. If the beam penetrates even as far as 1 millimeter, there is very little chance that you’ll obtain lasing under nitrogen pumping in the usual transverse style unless your nitrogen laser is remarkably powerful (a megawatt or two might be enough) or you have an excimer laser at some other wavelength. It is, however, possible that you could pump such a solution longitudinally. Here are three dyes that fluoresce nicely, but will not lase with transverse nitrogen-laser pumping:

Top to bottom: Foray Violet (in iso); Sharpie “Accent” Purple (in iso); Foray Green (in water). All taken with the pump laser at full intensity.

Here, so you can see the other side of the coin, is a dye (4-Methyl-Umbelliferone, in alcohol and ammonia) that lases very nicely. In order to take these next two photos I had to attenuate the pump laser beam to a tiny fraction of its usual intensity. Even moderate beam strength was enough to lase the dye, which would have damaged the camera when I tried to take the picture on the right; and the brightness of the fluorescence would have made it impossible to get a clear view of what was happening in the one on the left.

For more photos, please see Report 10A, Report 10B, and the section about “DTC” on this page.

Fortunately I was able to get a double set of these, which gave me the chance to compare water against 91% isopropanol. Here are the results:

Marker Color	In Water	In 91% (or 70%) Isopropanol, or 95% Ethanol
Hot Pink	Cloudy	Somewhat clotty
Orange	Cloudy	Somewhat clotty
Yellow-Green	Excellent	Rather Cloudy
Green	Probably not sufficiently fluorescent	Almost entirely insoluble
Blue	No visible fluorescence	No visible fluorescence
Violet	Very Good	Excellent

The violet was the big surprise here. I didn’t actually expect fluorescence, but it looks very nice in a preliminary test. Unfortunately, as you can see from the first pair of photos, above, it will never lase under transverse nitrogen pumping on its own, because it doesn’t absorb the pump light strongly enough. My hope is that this dye and the corresponding “Accent“ dye (shown in the second pair of photos) may lase in a flashlamp-pumped dye laser.

Here is what the tests looked like in room light plus blacklight:

Each pair shows water on the left and isopropyl alcohol on the right. Order, L to R: pink, orange, yellow-green, purple, green. (I have omitted the blue here because it didn’t fluoresce.)

(Note, added on 23 October, 2007: It is not necessary to bother with detergents; see above for information about a concentrated optical brightener that is readily available and performs quite well.)

During a conversation about detergents in mid-2007, in which we were comparing results, Jarrod Kinsey mentioned dry detergent powder, which could, at least in principle, provide a more concentrated dye solution than commercial liquid detergents; but he noted that it doesn’t dissolve well, even in water. This suggested to me that I should try extracting the brightener from some dry powder detergent with isopropanol.

The no-dye, no-perfume dry powder version of Arm and Hammer® gave me a very concentrated solution that lased extremely well after I centrifuged it to remove the dust, even in a cuvette with misaligned walls. (If the walls are aligned well, the dye can use them as mirrors, so it is easier to reach threshold in a correctly aligned cuvette.) I have tested 91% isopropanol from the drugstore and also 99+% iso from an electronics supply store, both of which worked beautifully when I used a small homebrew TEA nitrogen laser as a pump. I have not yet tested 70% isopropyl rubbing alcohol, but there is a good chance that it would also work.

Note: I have, so far, done this with three brands of dry detergent. Only Arm and Hammer produced a dye solution that was concentrated enough to lase with a nitrogen-laser as the pump source. Tide® should give you a solution that you can lase with flashlamp pumping, but unless you evaporate some of the solvent to concentrate the dye, it probably won’t work with transverse nitrogen-laser pumping.

The following protocol produces enough dye solution to fill a small cuvette once or twice. It should scale up nicely if you have a flashlamp-pumped dye laser, but I have not tested that.

Protocol:

Take a small jar. (I used one about an inch in diameter and 2 inches tall.) Fill the jar about half full of dry Arm and Hammer powder. Add enough isopropanol so that after all of the detergent is wet, there is still a layer of iso on top of the powder, perhaps 1/3 of the powder depth. (You can try various amounts to find out what concentration your setup needs.) Cover the jar and shake it for 5-10 seconds, then let it settle for about half an hour. Pour the liquid off the powder, and centrifuge it to remove any powder that remains suspended. (In order to lase well, the solution needs to be very clear. Filtering can work as an alternative way of removing suspended solids from the dye, and Jarrod Kinsey reports that he has had success that way.) Pour the supernatant into a cuvette, and try pumping it. If it is clear, if your nitrogen laser is working well, and if the concentration of dye is high enough, it should lase nicely. (Photo, below.)

Here is a photo of a jar of detergent and isopropanol that has settled for several hours. At this stage it is probably still too cloudy to lase well, but should be easy to clean up. The iso in this jar was originally several millimeters deeper than you see here, btw; before I took this photo I removed some, centrifuged it, and used it to take the photo below that shows the solution lasing.

Judging from this photo, you might well be able to settle the stuff for several hours, decant it carefully into a cuvette, allow it to settle overnight, and just lase it.

If you want to use a centrifuge and you don’t have one, there are ways to make simple ones; see the January, 1998 “Amateur Scientist” column in Scientific American magazine for an example. (All of these columns are available on a CD-ROM now, and can be purchased from several sites on the Web, including The Surplus Shed and American Science and Surplus.)

Here is the extract being pumped by a small TEA nitrogen laser. You are looking from behind the cuvette and off to the side; the bright blue stripe at the right edge of the cuvette is the dye being pumped. (The bright stripe on the left side of the cuvette is a reflection.) The blue spots on the paper to the left of the cuvette are the output or, to be more precise, half of the output: the other half went off to the right, out of the picture. The camera cannot do justice to the color, which is a rich deep indigo...

There is an easier method, which is probably not quite as good but can certainly be made to work: acquire some “no-dye, no perfume” laundry detergent, the ordinary thick liquid sort. It’s probably best to use one that has as few ingredients as possible, but contains optical brightener[s]. (The best “organic” ones are not brightened, so be sure to check the label.) I have tried this with several detergents, and they all worked; but Jarrod Kinsey reports particularly good results with the 2x concentrated version of Arm and Hammer, which seems to be available in his area but not mine. (OTOH, I seem to be able to get a 3x concentrated version of All, which also works well.) In all cases, be sure that the detergent is not turbid (cloudy), and is not any color that seems to be intentional. A very pale yellow is expectable because of the absorption spectrum of the optical brightener, but blue or purple or green detergent is a lousy choice here, for fairly obvious reasons.

For pumping with a nitrogen laser, you should try the detergent or concentrate right out of the bottle. For flashlamp pumping, however, you’ll have to dilute it at least a little, as it will be much too viscous and almost certainly too concentrated. I would try very cautiously adding some distilled water. Your objective here is to add only enough water to allow the solution to flow through your system. (Once you get it to lase you can dilute it more if that seems to be appropriate, but if you dilute it too much at the outset you won’t be able to bring it to threshold.)

Because the solution gets warm when you pump it, and the refractive index changes with temperature, you may find that you get only one or two pulses with N₂ pumping, and then lasing will quit until you let the solution cool down. Detergent is so viscous that this can sometimes take several minutes. With flashlamp pumping you’ll want to flow the dye solution, and you’ll probably have to wait a short while (at least a few seconds) between pulses, so that the fresh solution has a chance to cool down the dye cell.

Note, added on 25 July, 2007: Jarrod Kinsey finds that when he pumps liquid detergents with his TEA nitrogen laser, he does not see the “fatigue” effect that I note above; the stuff just lases again and again. I am not yet sure what the difference is, though I was originally pumping with a reduced-pressure nitrogen laser rather than a TEA laser, and that may have had some influence.

Yet another method: I have tried diluting liquid detergent with alcohol, in an effort to reduce the viscosity so I can pulse it more often. This often just causes the detergent to crystallize out, which makes the stuff cloudy. If you are handy, however, you can probably use a combination of 99% isopropyl alcohol and chilling in a refrigerator or freezer to concentrate the dye by separating out the detergent from it. The objective is to add the alcohol, stir thoroughly, chill the solution and allow the detergent to crystallize out as thoroughly as possible, and then filter out the detergent crystals while holding the solution at low temperature. If this works, you may get a solution that flows well, fluoresces brightly, and is not cloudy at room temperature. Good luck — you’re probably going to need it.

Note: I have, more recently, found a 3X concentrated version of All® “Free Clear”, which seems to react differently — it gets slightly cloudy when I add isopropyl alcohol, but slowly clears again. (This takes several days, so be patient.) Even when significantly diluted it lases nicely.

On to a followup about alignment

On to a second followup, about tuning

On to a third followup, specifically about naturally occurring substances that are or may be suitable for use as laser dyes

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Previously modified: Tue Oct 23 18:04:28 EDT 2018 Last modified: Wed Nov 9 15:28:28 EST 2022