Green laser modules: HELP!
Phil Pilgrim (PhiPi)
Posts: 23,514
Green laser modules are driving me nuts right now. I need them to project spots on the bottom of the seabed to a depth of up to ten feet for photometry purposes. I've tried two so far, with limited success:
and a 5mW unit from InstaPark. The Sparkfun module went out of stock almost immediately after I bought it. I chose it because it had an operational rating down to 32F. To test that theory, I put it in the fridge to cool then powered it up. Nothing -- until I warmed it to nearly room temp. What a crock! From a mechanical standpoint, though, I liked it because the front end is threaded (10mm x 0.5mm -- just happened to have a tap on hand), which makes it easy to mount rigidly.
The InstaPark module had somewhat better low-temp performance, even though it's only rated from 68-86F. But it's not threaded. I thought a press-fit would be the way to go. But when I measured the brass barrels of the two modules I bought, they differed by more than 0.005".
Moreover, both modules lack an IR filter. This is an important omission, since they use a frequency-doubling crystal to convert 1064nm IR to 523nm green. But a lot of IR gets through, which is an eye-safety issue that I cannot ignore, given the classroom environment these will be used in. (I was able to scavenge some IR filters from some CCTV lenses I have on hand, but this is not a good long-term solution.
Neither module provides good axial alignment. This is important because the two beams projected to the bottom have to remain parallel. Nonetheless, I know how to fab an angular-adjustment mount, so that's not a huge deal.
Anyway, without boring my fellow forumistas with further sordid details, I need a good, economical (i.e. not direct green laser diode) source of modules with a built-in IR filter and a threaded (preferably 10mm x 0.5mm) barrel. Anybody got recommendations? Domestic sources are best, but offshore is okay if delivery time is not excessive.
Thanks!
-Phil
and a 5mW unit from InstaPark. The Sparkfun module went out of stock almost immediately after I bought it. I chose it because it had an operational rating down to 32F. To test that theory, I put it in the fridge to cool then powered it up. Nothing -- until I warmed it to nearly room temp. What a crock! From a mechanical standpoint, though, I liked it because the front end is threaded (10mm x 0.5mm -- just happened to have a tap on hand), which makes it easy to mount rigidly.
The InstaPark module had somewhat better low-temp performance, even though it's only rated from 68-86F. But it's not threaded. I thought a press-fit would be the way to go. But when I measured the brass barrels of the two modules I bought, they differed by more than 0.005".
Moreover, both modules lack an IR filter. This is an important omission, since they use a frequency-doubling crystal to convert 1064nm IR to 523nm green. But a lot of IR gets through, which is an eye-safety issue that I cannot ignore, given the classroom environment these will be used in. (I was able to scavenge some IR filters from some CCTV lenses I have on hand, but this is not a good long-term solution.
Neither module provides good axial alignment. This is important because the two beams projected to the bottom have to remain parallel. Nonetheless, I know how to fab an angular-adjustment mount, so that's not a huge deal.
Anyway, without boring my fellow forumistas with further sordid details, I need a good, economical (i.e. not direct green laser diode) source of modules with a built-in IR filter and a threaded (preferably 10mm x 0.5mm) barrel. Anybody got recommendations? Domestic sources are best, but offshore is okay if delivery time is not excessive.
Thanks!
-Phil
Comments
And there are many "30 mW" units which look similar: http://www.ebay.com/itm/532nm-30mw-Green-Laser-Diode-Module-DIY-Lab-Astronomy/181217494478
This one says filter, but $28: http://www.ebay.com/itm/Super-stable-5mw-532nm-green-laser-module-with-PD-feedback-Filter-lenses-/231038170799?pt=LH_DefaultDomain_0&hash=item35caf2b6af
http://news.yahoo.com/lethal-laser-could-cripple-isis-140000754.html
On the other hand, it looks like the transmission band of pure water skews towards the Blue end of visible light. http://i.stack.imgur.com/ZUCzw.gif Have you tried using blue or blue-green laser modules? Should be a lot lower power and wider temperature range, and may even reach deeper underwater than the green laser modules.
Marty
P.S. Here's a high end green module if your budget will stand it. http://www.thorlabs.com/thorproduct.cfm?partnumber=DJ532-10
-Phil
BTW, in checking the spectral response curves of typical solid-state sensors, 405 nm is definitely out in the fringes.
-Phil
Huh? 505nm is Cyan according to Google. Royal blue is ~450nm. I can certainly take pictures of blue stuff with my camera. So while sensitivity is down vs 850nm, it's still quite useful. I'd expect the most trouble would be from the UV-IR filters in the camera. (or the color filter array of a color sensor) For example, I often work with light at 1064nm. I've yet to find a commodity camera the won't see 1064nm after the UV-IR filter has been removed. (most also have useful sensitivity even with the UV-IR filter in place)
Have you considered adding a colored glass filter to cut down on background light? i.e. something like http://www.thorlabs.com/thorproduct.cfm?partnumber=FGB39 or http://www.omegafilters.com/bg39-1680.html Some 450nm diodes and a small GB39 color glass filter is likely cheaper than a quartet of 515nm diodes. If the BG39 glass does not suppress enough background light, a band-pass dielectric filter can suppress >10x more background light but costs more.
Oh and btw, you can drive a laser diode just like an LED if you stay well within it's ratings. (Apparently laser diodes are prone to thermal run-away if pushed when driven with a low resistance voltage source) So raw diodes and some case/lens sets off e-bay are an option for experimentation.
Marty
-Phil