Faulty DPSS Green Laser?

[dexters_lab]

I just removed a lab laser from a bit of kit and have some questions that hopefully someone here can answer?

the laser is a green DPSS made by B&W Tek, it dates from 2001, the model i am sure is BWTF-OEM-15M-AX and has a maximum output power of 20mW as far as i'm aware

i have noticed along side the main beam are several other bright spots and that if i tilt the laser head four of the spots will move in relation to the other spots and the main beam, the laser head also seems to have a rattle so i'm guessing something is loose inside

the laser owes me nothing, so i dont mind trying to open it and see what the issue might be

there is a short video with me rotating the head around the beam axis, you can see 4 spots (circled in red) move when it's rotated, i'm blocking the main beam with my finger



any thoughts?

[rrinker]

 Scratch or something on the lens causing a deflection? Can't imagine the laser itself would be generating multiple beams, it almost certainly is something in the optics.
 Just remember - do not look into laser again with remaining eye!

[dexters_lab]

the main beam seems to be fine, i'm wondering if it might be the feedback diode thats mounted in the aperture on the end piece... maybe its loose and causing reflections?

[PA0PBZ]

I see another teardown coming!   

[ajb]

That's an odd pattern, but yeah, lasers shouldn't rattle, and you've clearly got something out of alignment.  The fact that you seem to get decent output from it otherwise suggest that the actual laser and frequency doubling components are in okay shape, so it's probably from some correction or filtering element(s) that are loose/misaligned. 

Before you decide to open it, be aware that 532nm DPSS lasers an 808nm diode to pump YAG which emits at 1064nm, which is then frequency doubled to get the 532nm output.  You can't see 808nm or 1064nm, and these will be at substantially higher power levels than the 20mW output rating.  Opening up the head and exposing the invisible hazardous IR requires substantially more precaution than just playing with a visible laser.  It's also worth noting that even the 532nm output can contain a substantial amount of IR, particularly if the construction and materials are shoddy and the manufacturer didn't bother to fit an IR filter.  If this came out of a lab system it's probably okay, but DPSS lasers of unknown provenance should always be treated with a bit of extra caution until you know what you're actually dealing with.

[Kleinstein]

The laser part itself must be still working - no green light unless suficient high IR intensity.

Be carefull with possible IR emissions - the part foating around might be the IR filter.

[LaserSteve]

One, CNI/BW TEK  barely covers the IR emissions from the pump diode at 808 nm IR in those things. Thus be careful, and Danger, Class IIIB Infrared Diode Laser, Avoid Direct and Specular Reflections. Wear OD4 (optical density four) or greater IR safety goggles designed for 808 nm light  if working on the unit cover off/power on.
You should spot the problem with the power off, no problem. Most CCD based cameras can see the 808 IR, unless they have a blocking filter in the lens..

Two, CNI glues down optics on bits of aluminum and indium foil for alignment. A slight bump with cover off,  and the internal cavity optics will be misaligned. The factory aligns using an autocollimator, thus recovering lasing if you bump an optic can be well nigh impossible for a beginner. CNI has never heard of and never will spend the money for good adjustable intracavity mirror mounts..,,,, Everything is glued down or held with simple clamps. I am in no way shocked that you have a loose optic in one of those.

Three, with the cover off, the way CNI mounts the pump diode, makes it susceptable to ESD.... Be careful not to get near the pump diode assembly.

My bet is you have a loose light sensor pickoff beamsplitter or loose IR filter...

[dexters_lab]

Three, with the cover off, the way CNI mounts the pump diode, makes it susceptable to ESD.... Be careful not to get near the pump diode assembly.

My bet is you have a loose light sensor pickoff beamsplitter or loose IR filter...

great advice from everyone, thanks

LaserSteve, thanks for the specific info about these, i was aware they are delicate inside so have not attempted anything yet, and i probably wont be tempted to power it with the case open, i was just thinking  to open it up and try and see what might be loose

i dont suppose you have any pictures of the inside?

i could do with knowing how the boxed part and the front cylinder separate before i try and open it. Would all the lasing parts be contained within the boxed section? the way it's screwed together kind of implies that

[dexters_lab]

so i went and opened the end of this laser and found the problem

the feedback pickup is just attached to the end of the output cylindery thing with three small grub screws, had to order in a imperial Allen key 0.035" to open it!

in the feedback head there seems to be a square shaped filter / crystal about 6mm long or so glued into the aluminium where its been machined out, there seems to be sensors on two of the sides

The source of the rattle was found, there is a small retaining disk screwed into the end of the laser head which was just loose, so that was nipped up, behind it looked like some filters but i didn't go any deeper.

tried the laser with and without the pickup on the end, the beam quality improves and all those spots around the main beam disappear when the feedback pickup is not in place so they look like they are internal reflections off the pickup

The spots that moved were probably reflections off the filters that were rattling behind the retaining disk

i didn't open the main assembly

So it's all back together, spots are still there but it doesn't rattle any more