Lasers

A Joss Research Institute Web Report: 4-Methyl-Umbelliferone (“4-MU”)

A Joss Research Institute Report on
4-Methyl-Umbelliferone,

A Laser Dye with Extremely Wide Tuning Range

…Under Certain Circumstances

(11 October, 2007)

The first coumarin in wide use was 7-Diethylamino-4-Methyl-Coumarin, often called Coumarin 1. (Exciton lists it as Coumarin 460.) It lases in the indigo and blue, with a tuning range of about 437 nm to 485 nm, depending on the pump source. Since Coumarin 1 was discovered, quite a few other Coumarin compounds have been found to be good laser dyes; the most common ones offer good performance across a significant portion of the visible spectrum, roughly 420-620 nm. Many (if not most) of these dyes are amino-substituted, but there are also hydroxy-substituted coumarins that can be lased. This page describes the best-known member of that group. (More specifically, the Umbelliferones, which have a hydroxyl group at position 7.)

7-Hydroxy-4-Methyl-Coumarin, usually called 4-Methyl-Umbelliferone (I will refer to it here as 4-MU, for brevity) dissolves well in ethanol and isopropanol, but is not easy to lase in neutral or acid solutions. Two main characteristics distinguish this dye. The first is the fact that it has the widest tuning range of any ordinary laser dye: from 370 to 580 nm (!), in

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A Joss Research Institute Report: A Simple Nitrogen-Pumped Tunable Dye Laser

Joss Research: A Simple “Breadboard” Dye Laser for Nitrogen Pumping

(2004 Jan 31)

Here’s a dye laser, assembled on the bench; the nitrogen laser (upper right, first photo) reflects from the large mirror at left, which focuses it into the [homebrew] dye cell in the middle. (In this photo, it contains Rhodamine 6G in 95% ethanol.) The prism lets me tune the output.

   

The entrance window of the dye cuvette is a fused silica Brewster plate that I’ve had lying around for a while; the end windows are pieces of microscope slide. I find that although most microscope slides are made of rather green glass, a few are extremely clear and uncolored. I reserved a few of those to use as end windows, because I don’t have enough fused silica. I suspect that I could use the same material as a front window, but I haven’t actually tried it yet. (Alternatively, if you can assemble the cuvette without breaking it, a cover slip should work as the front window — it’s thin enough that it probably won’t absorb much of the pump pulse.) The base and back are pieces of ordinary microscope slide. I’ve used aquarium-grade silicone caulk material to

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Joss Research: Lasers: Dye: A Blue Update

A Joss Research Institute Web Report:
Tuning 7-Diethylamino-4-Methyl-Coumarin in a
Flashlamp-Pumped Organic Dye Laser

(December 17, 2003)

Here are some photos of output from 7-Diethylamino-4-Methyl-Coumarin, running in our surplus Candela SLL250 dye laser. I was unable to tune all the way into the violet because I reached the limit stop on the tuner, but I got pretty close.

           

Sorry these are somewhat blurry. At some point, if I have time, I will update the page with better ones.


This work is supported by
the Joss Research Institute
19 Main St.
Laurel  MD  20707-4303   USA


Contact Information:

Email: a@b.com, where you can replace a with my first name (jon, only 3 letters, no “h”) and b with joss.

Phone: +1 240 604 4495.

Last modified: Fri Dec 22 20:20:05 EST 2006

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Joss Research Institute Projects: Restoring a Commercial Excimer Laser

A Joss Research Institute Report:
The Questek Impulse 4530 Excimer Laser

(04 June, 2004)

Beginnings

Today we took delivery of a Questek excimer laser, which was actually manufactured by Visx. (If I’ve capitalized that incorrectly, please forgive me; if I find out that it’s wrong, I’ll try to correct it.) I believe that this box was made in 1993; it is much heftier and more solidly made than the room-pressure nitrogen laser that I’ve been working on lately. In fact, this thing must weigh a good 500 lbs. It is rated for the usual excimers (F2, ArF, KrF, XeF, Br2 perhaps, XeCl, probably XeI, and maybe one or two others that are far less commonly used), and for both N2 and CO2, with pulsewidths from 5 ns (N2) up to 1 microsecond (CO2??) and pulse energy up to 4 Joules (I’ll believe it when I see it). I don’t know what kind of optics it has in it, but I’m sure I’ll find out.

(Note, added in proof: Milan Karakas suggests that 98% He / 2% N2 would be an appropriate mix for running this as a nitrogen laser. That sounds about right; but of course the design is not

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A Joss Research Institute Page: The Avco-Everett C5000 Nitrogen Laser

Restoring a Damaged Avco-Everett C5000 Head

Part 1: Initial Exploration and Reconstruction

Preliminary notes:

This is the first of three (as of late 2004) pages I’ve devoted to this laser. I’ve had a ton of fun getting it running (this page), rebuilding it to replace the main store when that gave up the ghost, and then rebuilding it again during the last few months, to see whether I can get higher output from it.

Note, added 27 December, 2008: I have just rebuilt this laser again, and it is performing extremely well. If you are more interested in performance than history, you can probably just skip ahead to that page.

Photos, this page: With very few exceptions (one of which is the schematic diagram just below), I have uploaded several sizes of each image. If you click one of the bitty ones, get the medium-sized one, and decide that you want something larger, change the “.lg.” in the filename to either “.vl.” (generally 800×600 px), or “.xl.” (generally 1280×960). The exceptions are cropped images, which will typically have “.c1.” or something similar in their filenames and won’t be available in the largest size(s), and “portrait”- oriented images, which will be

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Continuing the Restoration of the C5000: Page 2

 

Next Phase: New Topology, New Dumper Cap

 

 

Preliminary note:

(30 December, 2003)

This is a followon to the page in which I describe my effort to resuscitate a rather dead nitrogen laser that we acquired on eBay a while ago.

I recently brought up a commercial dye laser (also found on eBay), and discovered that although it is a fine device, there are some limitations to what I can run through it. It isn’t particularly suitable for some of the dyes I’d like to test, so I’ve returned to the Avco head, to see whether I can bring it back on line.

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Continuing the Restoration of the C5000: Page 3

Rebuilding (Again) the C5000 Nitrogen Laser Head

Next Phase: New Peaker Caps, New Dumper Cap, New Switch

Preliminary note:

(07 July, 2004)

As I say on the previous page, it has been some time since I worked on this laser. We acquired a room-pressure nitrogen laser on eBay, and I was busy with that for a while; then we acquired a Questek excimer laser, and I’ve been fussing with that, as well. (It is being a real pig, and I have been unable to find any documentation on it.)

Lately I’ve been thinking about low-pressure nitrogen lasers, though, and as part of that project set I’ve decided to rebuild the C5000 head again. This time I expect to use Barium Titanate “doorknob” caps in the peaker section, which means it will have somewhat higher capacitance than it did in previous incarnations; I am also thinking about using a 30-nf Maxwell for the dumper / main store. This is still in flux, and I haven’t yet decided whether to use a spark gap or a thyratron as the switch this time. I think, though, that I will put the cap on the distribution bus and the switch outboard. (This will make

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Continuing the Restoration of the C5000: Page 4

Rebuilding (Yet Again) the C5000 Nitrogen Laser Head

This Phase: Doorknobs, Version 2

Preliminary notes:

(06 December, 2008)

This version is a reprise of the one on the second page of this set, and as I said on that page it has been quite a while since I worked on this laser. I have, however, thought about it a fair amount, and I have decided that it is time to try again. (Every time I rebuild this thing I learn something from it, even when it doesn’t work as well as I might like.)

Here’s the topology I am using for this rebuild:

I haven’t shown the chokes in the + and – HV lines, which keep the EMP from destroying the power supply and also help mitigate the effect of shorting the output of the power supply every time I fire the laser. I should also point out that I have not bothered with the small starting capacitor that I usually put across the spark gap, because the main store is small enough and fast enough that it didn’t seem necessary. The bleeder resistor, which is part of the original design, prevents you from getting a nasty shock if

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Joss Research Institute Web Report: A Doorknob-Cap Nitrogen Laser for Do-It-Yourselfers

A Simple Nitrogen Laser

Using “Doorknob” Capacitors
in an LC-Inversion Circuit,
and Semiconductor Preionization
Primarily Intended for Do-it-Yourself Laser Hobbyists

Abstract:

This page presents the design of a nitrogen laser that is intended for DIY construction; it operates with a mixture of helium and nitrogen at room pressure, and uses a mildly novel semiconductor preionization method adapted from other types of laser. Where possible, it uses parts and materials that can be purchased at a hardware store. The device has active length of about 17″, and overall length of about 24″.

The laser operates at voltages of roughly 12 to 20 kV or perhaps a bit higher; does not require a vacuum pump; and puts out, at full voltage, more than half a millijoule in a pulse that is 5 or 6 nsec long FWHM (Full Width at Half Maximum).

The design is not hard-and-fast, nor is it restrictive. It can be modified at need, or upon desire. It may be scalable, for example, to higher capacitance and/or a longer channel. It may also be possible to switch this laser with a thyratron; thyratrons have much longer turn-on time than spark gaps (several dozen nsec as opposed to 5-15 or

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