TJIIRRS: Number 10 of an Ongoing Series;

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 some have been tested with flashlamp pumping.

Commercial laser dyes can cost over $100 per gram, and are out of the reach of most DIY laser builders. Most chemical companies refuse to sell to individuals these days, in any case. 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 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 is typically of laser-grade purity, but that certainly doesn’t prevent them from lasing. On rare occasions, a few scintillators 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. A dye that is well-behaved under flashlamp pumping does not undergo intersystem crossing to any great extent, and thus does not exhibit much triplet-triplet [excited-state] absorption. This is not much of a problem with nitrogen-laser pumping, and it is also ignorable with several of the 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.

The following table suggests one or more dye sources for various parts of the spectrum. In each case, I have listed the ones that seem to provide the best performance in my testing, but as of the beginning of 2009, the column for flashlamp-pumped dyes is very iffy; I need to do more testing to verify performance. I hope to fill in more of the table over time. Where I do not specify a brand name, as for several of the fluorescent (“highlighter”) markers, several brands have been found to work, and you can try whatever is available in your area. It is a good idea to try several solvents, as there are significant differences in behavior among the various colors and brands.

KEY:

• “BH” = Blue Highlighter
  
  
• “VH” = Violet or Purple Highlighter
  
  
• “PH” = Pink Highlighter
  
  
• “OH” = Orange Highlighter (I have seen Foray^™ markers in this color)
  
  
• “SAH” = Sanford’s Sharpie^® ‘Accent’ Highlighter, yellow-green (other brands also work well)
  
  
• “FYH” = Foray yellow-green Highlighter, yellow-green (other brands also work well)
  
  
• “DTC” = Dharma Trading Company “Optic Whitener”
  
  
• “POPOP” = 1,4-bis-(5-phenyloxazole-2-yl)-benzene (A common organic scintillator; also a known laser dye. POPOP is generally considered to dissolve best in nonpolar solvents, though there is a chance that it may dissolve well enough in 99% isopropanol for use in flashlamp-pumped lasers; I haven’t had a chance to test that yet. Moreover, although POPOP has been used by a number of researchers, I was unable to lase it until 06 December, 2009, when I decided to try acetone as a solvent. Under nitrogen-laser pumping, POPOP lases very nicely in acetone.
  
  
• “PPO” = 2,5-diphenyloxazole (Another common organic scintillator; also a common laser dye. Dissolves best in nonpolar solvents, but is also sufficiently soluble in isopropanol to be pumped by a nitrogen laser. (When I have time, I will test it in acetone.)

Note: Until the questionmarks disappear, you should take some parts of this table with a grain or two of salt. (A single questionmark means that I haven’t finished testing the material yet; a double questionmark means that I’m not quite sure how to test it yet.)

Color	N2 Laser	Flashlamp
Near-IR		BH??
Far Red
Red
Red-Orange	PH	PH
Orange	PH; OH	PH; OH
Yellow-Orange	PH; OH; SAH; FYH?	PH; OH; SAH; FYH?
Yellow	OH?; FYH?; SAH	OH?; FYH?; SAH
Yellow-Green	SAH; FYH?	SAH; FYH?
Green	SAH; FYH?	SAH; FYH?
Blue-Green
Blue	DTC?; POPOP	DTC?
Indigo (“Deep Blue”)	DTC; POPOP?	DTC
Violet	DTC?; POPOP?	DTC?; POPOP?
Near-UV	POPOP?; PPO	POPOP?; PPO

Note: Under nitrogen laser pumping, the Sharpie “Accent” highlighter and Dharma Trading Company’s “Optic Whitener” are the best performers I have seen so far. DTC will dissolve in ordinary drugstore rubbing alcohol (70% isopropyl) or 95% ethanol (the common brand where I live is “Everclear”), and a lifetime supply costs only about $3.59 plus shipping. Two drops is enough for a small cuvette.

1. Buy a yellow-green Sharpie™ “Accent” marker, a “Hi-Lighter” or other fluorescent marker. (When I went to buy “Accent” ones 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 also possible that the dye may have insufficient extinction at 337.1 nm, in which case the pump light just goes through it. If the beam goes even as far as 1 millimeter in, there is very little chance that you’ll obtain lasing under nitrogen pumping in the usual transverse style, though it is possible that you could pump longitudinally. Here are three dyes that fluoresce nicely, but simply won’t 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 that lases very nicely (4-Methyl-Umbelliferone, in alcohol and ammonia). 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 see what was going on in the one on the left.

For more photos, please see Report 10A, Report 10B, and the detergent and brightener section that is further down 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 below 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 don’t, 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.

For pumping with a nitrogen laser, you should try the detergent straight out of the bottle. For flashlamp pumping, however, you’ll almost certainly have to dilute it at least a little; 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 lasing 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 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 take several minutes. With flashlamp pumping you’ll want to flow the dye solution, and you’ll probably have to wait a short while between pulses, so that the flow of dye solution can 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 (about 1 part isopropanol to 2 or 3 parts concentrate), it lases quite nicely.

In a discussion on the LASERS mailinglist a week or two back, Jacob Thomas pointed out that Rit makes an “Optical Whitener and Brightener” product, which he has since lased. The Rit product appears to consist of brightener, table salt, and some sort of powder that does not dissolve in alcohol. You can extract the brightener from this mixture with isopropyl alcohol the same way you can extract powdered laundry detergent; the difference is that it is much more concentrated.

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, which carries a liquid “Optic Whitener” product in 8-ounce bottles, so 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 completely opaque result. This is not particularly surprising, as the product is actually intended for use in water, so I just added some, and it cleared very nicely. (For a 3 ml cuvette, 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 it.)

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 under nitrogen pumping:

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, so I tend not to use it with this dye, though I do use it with many others.

I have also verified that DTC dissolves just fine in 70% isopropyl rubbing alcohol, and lases very nicely. (The cuvette in that photo contains two small drops of DTC in about 2.5 cc 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), that 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.

[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, and there is a photo of the blue output from this dye.]

As of 08 January, 2010, I think I may have identified the dye in this material. I am not fully certain, so you can take these spectra with a grain or two of salt. Absorption and emission are given in arbitrary units.

[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.]

...at a local Grand Mart (a big Asian supermarket). You should also be able to find it at larger Latino markets. As you can see, there isn’t much Cinchona bark (misspelled on the label) in the package, but I don’t think it was particularly pricy. If you extract the quinine from this material you will have to purify it somehow, which should be an interesting exercise. (If I do it, I’ll report it here, and I will provide some sort of method, or at least some suggestions.)

C: Other Materials

Although most organic materials fluoresce at least a little, there are very few naturally-occurring compounds with quantum efficiency above 0.5 or so. I am looking into a couple of these, and will report results as I obtain them.

There may also be relatively easy and nontoxic ways to improve some of the compounds that have lower efficiency or are difficult to dissolve, but this gets into actual chemistry, and may be difficult for DIYers because of the difficulties involved in acquiring materials and equipment.

On to a followup about alignment

On to a second followup, about tuning

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To a page specifically about naturally occurring substances that may be suitable for use as laser dyes

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Contact Information:

My email address is a@b.com, where a is my first name (jon, only 3 letters, no “h”), and b is joss.

My phone number is +1 240 604 4495.

Last modified: Wed Feb 3 19:20:52 EST 2010