What diode specs are essential?

On: Sun, Apr 14, 02 07:53:37 PM

DJ Mathson wrote:

Iīm thinking of buying a more powerful laser diode than my current <5 mW laser pointer, but when I look at all the diodes on the market today I get very confused. How do I know if the diode is suitable for making holograms with? There is a lot of information in the specs and I donīt know what it stands for and what is relevant to me. Can anyone please tell me what properties in a laser diode that are essential for hologram production? Or is it only by trial and error you can tell if a diode is suitable or not? The same goes with the driver. What properties should the diode driver have? Thanks


Tom B. - Mon, Apr 15, 02 03:17:06 AM

There is a wealth of information on diode lasers and drivers in Sam's Laser Faq at http://misty.com/people/don/lasersam.htm If you browse this (sipping from the firehose), you'll eventually find a table of contents for laser diodes: http://misty.com/people/don/laserdio.htm#diotoc and a short section on holography with cheap diode lasers: http://misty.com/people/don/laserlia.htm#liahol4

Colin Kaminski - Mon, Apr 15, 02 01:43:09 PM

What diodes have people tried? I have used the Mitsubishi 35mw diode. I have heard reports of the 50mw Panosonic diode working. Are there others people have tried? I know Frank tried many but I don't think he published his results anywhere.

DJ Mathson - Mon, Apr 15, 02 04:34:36 PM

Wouldnīt it be great to do a list of laser diodes that people have been able to do holograms with?

Tom B. - Tue, Apr 16, 02 01:48:47 AM

(May 22nd, 10:28 PST) Re the original question, I'm afraid that it is still a matter of trial and error, with the added complication that diodes that worked for others might not work for you. It could be that there is variation from batch to batch and from diode to diode because coherence length is not tested or controlled by the manufacturer. I wonder if one of the uncontrolled variables might be the orientation and distance of the diode emitting facet from the glass window, since back-reflections can have major (usually bad) effects on coherence. I didn't have much luck with the Mitsubishi 1016R 35 mW due to apparent multiline operation (producing contoured or "sliced bread" holograms. I will soon be trying the LNCQ05 and a couple of 5 & 10 mW Sharp 635 nm diodes and will report my conclusions. It occurs to me that I have another 1016R that I have not tried yet, too. It would be worth checking to see if it behaves the same way.

Colin - Tue, Apr 16, 02 09:49:08 PM

I wonder if the power level has something to do with the sliced bread holograms. Did you try to adjust the power levels? What were you using for a heat sink? I find the 35mw diode can be made to do all sorts of crazy things with a change in temperature. 5/16 6:53

Tom B. - Wed, Apr 17, 02 03:12:55 AM

Yes, though I only went up to about 25 mW. I noticed that fringes looked better below 15 mW output, but contrast was never very good. Heatsink was an Optima LDM1100. Ambient (basement) temp was stable, probably about 16C. I'll probably want to try other temperature/drive current combinations when I get my temperature controller (Hytek) going. Did some preliminary interferometer checks of a Panasonic LNCQ05 and a Sanyo DL3148-011 and both look promising, showing fringes out to at least 6" (the limit of my setup). The Sanyo seems more temperature sensitive, but once it settled down, it ran with stable fringes and no mode hops. I noticed that the photodiode on the LNCQ05 is very sensitive to back-reflections, which could cause problems if an APC driver was used. Did not check the photodiode on the Sanyo.

Colin - Wed, Apr 17, 02 05:15:50 PM

Frank claims the D&S to be at least 27mw. You might have better luck if you go to higher power. I have used 3 diodes now and found them all to be usable as long as you are no unlucky enough to go through a instability zone. On the 5mw laser from Integraf the diode housing is insulated with a layer of heatshrink. I assume it is to keep air currents from changing the temperature but it could be simply to shield the housing from the power supply ground. I guess this would sacrifice diode life by allowing the diode to heat up but since they are cheap it is probably a good solution.

Tom B. - Wed, Apr 17, 02 07:53:36 PM

Just made a couple of nice bright holograms with the 635 nm Sanyo DL3148-011. I wanted to try this out first since I'm experimenting with PFG03M and JD4 and had been finding it not as quite as sensitive as I had hoped with longer wavelength lasers. From the Slavich data I could see that the spectral sensitivity falls off pretty quickly from the 633 nm peak to maybe 50% at 660 nm (estimated from the log sensitivity chart). Noticed that, in common with other windowed diode lasers I've tried, this one showed fine (faint) parallel lines in the uncollimated beam, perpendicular to the long axis. I suspect that the window is somehow causing this. I'd been having problems with the softness of PFG03 emulsion - even with the gentlest treatment the image showed many blemishes which looked like they were due to gloopy emulsion. Decided to try a post bleach hardening bath - 1% acetic acid (white vinegar cut 4 to 1 with distilled water) and 15 grams per liter Alum (drugstore variety). Method tried was to bleach, rinse for a minute or so in distilled water, place in hardening bath for couple minutes, then back in the rinse bath (all with moderate agitation), then dry. In an A/B test with two identically exposed plates, the hardened hologram showed far fewer post drying defects than the non-hardened one. There were no apparent ill effects on the brightness of the image.

Colin - Thu, Apr 18, 02 12:39:09 AM

Is post hardening preformed after the bleach step? Does it help with printout?

Tom B. - Thu, Apr 18, 02 03:25:04 AM

(May 18/02 12:26 PM) Yes, after bleach - this seemed the safest. Didn't want to risk interfering with the bleach chemistry, and it seemed most of the defects were happening in the drying phase. Just made another hologram, and this time I even was able to use a squeegee with no problems - a previous attempt at squeegeeing this emulsion without hardening resulted in a complete gooey mess. The acetic acid in the hardener (recipe by the way is from Ansel Adams) probably helps reduce printout, but I rinsed afterwards because I was worried about leaving alum in the emulsion. This may not matter. For printout prevention, 1% acetic acid in the FINAL rinse is recommended to leave the emulsion in an mild acidic state. I did a 1-2 hour sunlight experiment which convinced me that it does drastically reduce printout, but I don't remember exactly what I did and will have to repeat it, taking notes this time :)

Colin - Wed, Jun 12, 02 02:47:16 AM

Here are a list of laser diodes that produce greater than 3M of coherence length. The power is after the collimating optics and run at max. stable power. nm Power 635 4 635 8 635 17 645 4 650 4 655 4 658 28 This is probably the Mitsubishi ML1016R 660 40 This is probably the Panosonic LNCQ05PS 670 4 670 8 675 8 685 28 785 30 785 48 785 56 830 80 Can anyone identify the others?

Colin - Wed, Jun 12, 02 02:51:17 AM

Could the 635nm 17mw be the DL4038-026?

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