Higher power laser diodes for holography.

Ted Park · Post by **Ted Park** » Thu May 13, 2004 4:32 pm

I am looking to purchase another laser diode for holographic work. Where did you go to purchase your diodes, and how did you determine if they were satisfactory? I tried a few shots with a relatively cheap diode that I had purchased, however I get bands on everything, even after I give it a 15 minute warm up period. Shots with my lower powered diode work OK, suggesting that perhaps there are some frequency stability issues.

Thanks for any help you can provide on this.

--Ted.

Anonymous · Post by **Anonymous** » Fri May 14, 2004 1:48 am

Are you talking about bare diodes or modules? For bare diodes, I usually buy from Optima ( http://www.optima-optics.com ). I have had good results with the 50 mW Panasonic LNCQ05 using a lab power supply lash-up. (not generally recommended) You would typically want a proper driver for the diode (Thorlabs and others sell laser diode drivers) and would also definitely need a calibrated laser power meter (~ $300) to set the output power. Some means of temperature stabilization too. And some mechanical and electronics wiring skills, plus a fair helping of luck.

Most likely you want a module. I have not had much experience with these, though I did purchase a nice 25 mW 660 nm module from Midwest laser which turned out to be unsuitable for holography. It produced the so called "sliced-bread" effect in holograms - contour lines much like what you described. Some diodes just do this - I think due to very closely spaced lines in the spectrum i.e. multimode behavior. Others have reported good results with modules - I think Kris Meerlo was happy with a module purchased from Roithner Lasertechnic. And Colin I think got one made to spec from Power Technology. And one good report on the Analog Technologies module (and one disappointment). You could try the archive search feature on this site for details on these.

Anyone else have any comments on higher power laser modules?

Wishfull · Post by **Wishfull** » Sat May 15, 2004 1:29 pm

If I had some of that $1,000,000 that Danny mentioned, I'd try a laser from Crystal Laser.

Ted Park · Post by **Ted Park** » Mon May 17, 2004 4:37 pm

Thanks for the info. I think I may try and cobble together a system with a diode and driver. I haven't had much luck with the higher powered modules that I've purchased through ebay, so probably I'm better off biting the bullet and building a proper laser system. What kind of coherence length did you get out of the LNCQ05?

Tom B. · Post by **Tom B.** » Tue May 18, 2004 3:39 am

I haven't checked max coherence length, but judging from unwanted background objects that sometimes show up in my holos if I'm not careful about light blocking, it must be at least a few feet.

Ted Park · Post by **Ted Park** » Wed May 19, 2004 11:09 am

That's good to know. It seems as though the "real" laser diodes are quite good then.

There are a lot of higher powered modules/diodes that I see on ebay - what are these devices typically used for? DVD-R and CDRW type systems?

Colin Kaminski · Post by **Colin Kaminski** » Wed May 19, 2004 11:24 am

A diode's output power changes with temperature. To keep the diodes from frying most of these modules use APC. (Automatic Power Control). I have found APC to be harder to make work than constant current. You might want to experiment with a diode, variable resistor and a battery. Make sure to set the output power with a good light meter so you don't destroy the diode. If you are happy with the results, then you can replace the battery with a lab grade power supply.

JohnFP · Post by **JohnFP** » Wed May 19, 2004 12:02 pm

I bet you couldn't get any of the surplus dealers to tell you!

I believe they are coming out of digital copiers. And if you go to Coherent's web page and read the write up about their Compass laser diodes it mentions "printing and reprographics market" market.

http://www.coherentinc.com/products/ind ... D=DPSS0005

I have been keeping my eye out for a surplus digital copier and if I find one that has a decent laser diode in it I will tell all.

bruce · Post by **bruce** » Wed May 19, 2004 12:41 pm

Just for the sake of clarity, the Coherent Compass mentioned is a diode pumped Nd:YAG, frequency doubled laser( outputting in the green wavelength). I was told that a great many of these used lasers currently on the market came from the AGFA CO. where they were used in Litho plate production. Apparently AGFA is moving their production facilities back to Europe, therefore liquidating their tooling.

Bruce

Ted Park · Post by **Ted Park** » Wed May 19, 2004 1:35 pm

Ahh - I had always thought that laser diodes required complex electronics to prevent the device from being destroyed, but I suspect that is only true when the device is being run close to its power limit. I've tried two different higher powered modules. The first was a 635nm, 15 mw module - the thing was a sealed, prefocused item, so I fed the beam through a diverging lens. I let it warm up for an hour (tests with the interferometer appeared to show stabilization after 20 mins, but I figured I'd be safe) but the holograms produced with this laser all showed bands. A 25mw, 655nm laser gave the sliced bread effect as well. Shots done with the "know good" lasers during the same session were fine (none of the objects in the setup were moved) so I suspect the problem lies with the lasers.

As an experiment I'm going to try making some holograms with the diode from a $2.50 laser pointer. The pointer faded after being on for a bit, but I removed the diode assembly, put some arctic silver on the back, soldered it to a piece of silver, and hooked the wires up to it. Coherence length on this diode is at least 40cm (I didn't check it past that)