HeCd lasers for holography?

baja · Post by **baja** » Wed Jan 19, 2011 8:30 pm

I've been shopping on ebay for various things and I keep seeing accessories
for HeCd lasers but I never see the lasers themselves. Some commercial
sellers list a coherence length of 20cm, at both 405nm and 315nm. I
think a 315nm laser would be pretty cool. Anybody have any experience
with buying/selling HeCd lasers for home holography?

Johnfp · Post by **Johnfp** » Thu Jan 20, 2011 7:24 am

20cm? That seems longer then most HeCd's I have worked with.

HeCd is a good laser but usually in the low mw's of power. What film do you plan on using?

BobH · Post by **BobH** » Thu Jan 20, 2011 11:25 am

I think the days of He-Cd are nearing an end because of the long coherence of the 445nm diode lasers when run just above threshold. 50mW is about all the He-Cd lasers would give anyway. And with He-Cd, the tube lifetime is always going to be shorter than you wished. You'll pay more for shipping the a new tube to you (if you could get one) than you'll pay for the diode system.

baja · Post by **baja** » Thu Jan 20, 2011 10:31 pm

BobH wrote:I think the days of He-Cd are nearing an end because of the long coherence of the 445nm diode lasers when run just above threshold. 50mW is about all the He-Cd lasers would give anyway. And with He-Cd, the tube lifetime is always going to be shorter than you wished. You'll pay more for shipping the a new tube to you (if you could get one) than you'll pay for the diode system.

Well that is astonishing, because I just checked ebay for 445nm diodes and found some very nice units, including this one that claims to be single spatial mode. Are you saying that if this laser were to be powered just above threshold it might produce SLM? Because that would be awesome! Its TEC cooled too so the SLM might last long enough for a hologram. Its been a while since I checked out laser diodes and I'm really amazed at how cheap 1W visible light diodes are, though they are probably mostly only good for playback.

Here's the TEC laser module:

http://cgi.ebay.com/600mW-445nm-Laser-D ... 20b6360eca

Jem · Post by **Jem** » Fri Jan 21, 2011 5:50 am

Not sure whether that module is good quality or not. However, be careful with regard to the following line...

'Otherwise we will send you the module with TTL modulation'

You would need analogue modulation so you can control the output and find a SLM sweetspot. TTL modulation is either full on or off, this wouldn't allow you any control over the output.

Might be better to do a search on Photonlexicon.com as loads of folks there are building 445nm modules from the readily available diodes harvested from the C*sio projectors.

Incidentally, whereabouts in the World are you? I have a Kimmon HeCd sitting on my bench here, not had a chance to try making a hologram with it yet though

Cheers

Jem

Viking · Post by **Viking** » Fri Jan 21, 2011 11:24 am

"Beam profile: Near TEM00"
This sounds strange to me. Doesn't this mean that there are black lines in the beam spot so to speak if it is not actually TEM00?

BobH · Post by **BobH** » Fri Jan 21, 2011 11:35 am

Yes, be careful with the choice of 445nm blue diode. Buy from Holomaker (aka Dave) or Phil from here, or as Jem says from someone credible at PL. And I don't mean to dismiss He-Cd, which is just fine for making holograms albeit with short coherence length. Just don't leave it running unless you're using it, as the lifetime is always going to be an issue and the cost to replace the tube probably prohibitive.

holorefugee · Post by **holorefugee** » Fri Jan 21, 2011 12:05 pm

Anyone interested in the blue diodes should read this thread:

http://holoforum.org/oldforum/viewtopic ... 5827fe9cc0

And read wler's laser projects page:

http://redlum.xohp.pagesperso-orange.fr/argonlaser.html

Jeffrey Weil · Post by **Jeffrey Weil** » Sat Jan 22, 2011 10:23 am

Hello Everyone,

I don't think the blue diode is quite there yet. You can only get about 50mw from them at slm. A he/cd will give you up to 200mw, which is barely enough. Most blue materials are pretty photon hungry.

But the big problem with the diodes is the beam shape and divergence. Sure for single beam stuff it's great, really great, but for serious work where you need to split the beam and steer it around for many feet, pass it through spatial filters and still have enough power to do high level work I don't think it'll replace the he/cd.

Maybe the next blue diode will, but most likely the solution for the he/cd is a dpss. Most diodes just don't have the right beam shape.

Jeff Weil
NorthBeach Holography Inc.

BobH · Post by **BobH** » Sat Jan 22, 2011 11:55 am

Great points, Jeff! What He-Cd is 200mW?!? What's its coherence length?