Advice needed: Focus issues with laserbtb LP 515 20mW

[Streamtronics]

Hello everyone.

I'm not 100% sure if this is the right sub-category, maybe this belongs into "laser companies" but I hope it doesn't need to get moved. I'm quite new to this board.

In July I bought a 515nm 20mW laser pointer (the pen-sized LP host) from laserbtb. Unfortunately it recently developed some focus issues.

tl;dr:
Laser divergence suddenly depending on temperature, laserbtb support says it's normal behavior

When I first got the laser the beam divergence was below 1.5 mRad, I didn't really measure it but it really wasn't bad. Probably around 1 mRad like my green DPSS. Just the angle at which the beam exits the host was off (see crappy pic I attached). It actually still is off like that, it even hits the side of the exit hole, giving quite a spill from the reflective housing. Anyway, I was tempted to ask the btb support for help about the angle issue but never really got around to do so.
Now however my unit seems to have a focus issue/increased divergence which greatly depends on temperature for some reason. It kinda... just broke over night. Did not drop it or did anything else to it that might have damaged the internal gluing of the lens or such. I calculated the divergence at 2.5 mRad which is definitely out of spec (<2 mRad).
The laser dot grows while using it, probably due to it warming up in my hand. I let it cool down to about 10°C, at that temperature the divergence seemed almost normal (normal being the ~1-1.5 mRad it had when it arrived). The dot grows until the host reaches my hand/body temperature.

I e-mailed laserbtb about the issue, sending a pic of the laser dot with it. The first reply I got basically looked like this:

-- a 515nm 20mW laser this is diode laser, temperature-sensitive.
-- a 515nm 20mW laser this is diode laser, when the light emitting from the diode,that is not strict stright.

EVEN if to get a replacement unit ,may be the same performance.

to which I replied that I'm pretty sure this is not normal behavior as it did have great divergence when it arrived (and that was in summer at 30°C+ so I'd have noticed a larger laser spot). The divergence definitely didn't change when it was working properly. I also sent a pic showing the beam angle being off with that mail. This was the response I got:

About power,Diode lasers are quite stable compared to DPSS,

The pic I can see the beam angle

I prefer to refund you,
I do not know if a new unit will meet your demands or not.

Well, these replies really leave me puzzled about laserbtb's quality standards. I know their other hosts are mostly fine but if they can not guarantee me a laser unit that does not break after some months and if they can't guarantee me that the beam exits the laser pointer straight why did I buy their laser in the first place... Instead they are telling me the light doesn't always exit the diode straight? I don't get it.

Even if the other units might have a divergence close to 2 mRad, I'm sure they aren't that dependent on temperature. I mean I can literally watch the laser dot grow on the wall while I'm holding it. I have never seen any laser do that before, at least not a diode laser in the temperature range 10 to 30 °C.

I'd just like to hear your opinion, you guys are the experts.
Do I really have to expect that from a $70 laser pointer? I did not reply to Kevin from laserbtb yet, do you think I have a chance getting a properly working laser from them instead of a refund? I'm usually a perfectionist but these are fundamental issues with the laser, my unit/the host has other flaws that I don't want to bring up in the first place. I just want a straight, stable beam.
If I'd get a refund I suppose I need to send back the laser, so what after that? I really want a nice 515/520 nm, preferably in a pen-host.
I guess there's not really anything I can do to get the focus right as the host is glued together.

Any ideas, brain-farts and any advice is welcome. Thank you very much for reading :3

 

[Atomicrox]

Can you make a video of the divergence expanding with temperature? I've never heard of or seen such a thing.

 

[gozert]

I don't know whether this is normal or not, but are you using the laser for a longer time than the recommended duty cycle? Also, on that picture the beam seems to come out really askew, or is it just the picture?

 

[mortuus]

wow if the picture is not broken in any way that to me looks like a faulty laser, and compared to dpss lasers a diode shouldnt be that temperature sensitive but what do i know.. To me this looks like a broken laser somehow, maybe its the combination of 520 diode and the tiny pen host that is the issue? not like lasers cant go broken during shipping also or when they produced it, you should ask them if you can send it back so they can test it.

If you really want a 520 laser do like me and get the HL host instead, seems way better then those pens, they arent the best quality really i have one 532 pen that i bought just for fun.. i would say their pens are not up to quality for the HL or even Pl hosts we are talking day and night difference..

 

[Streamtronics]

Can you make a video of the divergence expanding with temperature? I've never heard of or seen such a thing.

I sure can: http://youtu.be/UlJL-ze_V0w
It's at 4x speed. Yes, I left it on for like 3 minutes even though btb recommends a duty cycle of 100s on, 30s off. This hasn't been a issue before though, it's just a 20mW pointer after all. As I said, this is not about the general specs of this laser (which have been very good when I got it), this is about it suddenly being defocused... I started the video with the laser at like 10 °C. It never got warmer than my hand (I had my hand on the laser to warm it up).
Attached to this post is a pic with a ruler I took right after I stopped the video. It's quite hard to expose correctly on a laser dot but in the pic I tried to expose just so it looks close to what I saw with my eyes. The distance is about 12m.
Edit: It's a centimeter ruler obviously ^.^

Also, on that picture the beam seems to come out really askew, or is it just the picture?

Of course I took the pic at an angle so you can see it quite well - if I took the photo from the side you wouldn't notice it immediately. But we all like looking down a laser beam in the fog, don't we? If you look down the beam this is exactly what you see. It's "only" a few degrees off probably. Maybe I should measure it but whatever.

and compared to dpss lasers a diode shouldnt be that temperature sensitive but what do i know..

That's what I thought, and that's what their website says, too. And I'm using it in the 10-30 °C range they recommend. Still I can understand if the laser isn't stable or mode-hops (although I never saw a diode laser mode-hop, but I guess it can happen?) but what I can't live with is a varying divergence.

OT: Am I writing too much btw? Not sure how lazy users are on this board xD happy you guys responded though. Thanks for that.

 

[Streamtronics]

I probably should add that I can notice a change in beam divergence even when not leaving the laser on. As in: Use it for a few seconds when the laser is "cold" >> just hold it in hand for a minute >> turn it on again >> notice larger laser dot.

 

[crazyspaz]

I would accept the refund if I were you. That is really odd behavior for a direct diode laser, though.

 

[mortuus]

yeah accept the refund, if using indoors its hardly normal behavious id say.

 

[Streamtronics]

mmmh, I thought so. I've seen lasers with bad divergence before but none where the divergence changes like this.
The issue I have right now is that I'd actually really like this model, but a working one. One where the beam exits straight and one where the divergence is as good as it was when I got this unit. I'd probably end up buying a laserbtb LP again. I like the pen size format and I like the direct diode green, I'm not sure how easily DPSS pens break when you accidentally drop them on a carpet or something. I could imagine the crystals can easily shift out of place?
I'm still kinda shaking my head over the fact laserbtb can't guarantee their lasers have a stable divergence (even a bad one, as long as it's stable) and a straight beam. What kind of high-quality brand does that xD or is that just me being a German having high quality standards isn't anyone else thinking this is an absolute no-go for a company? It's like a car company offering you a refund for a car that can't drive straight forward saying they can't guarantee you that a replacement car has properly working steering.

 

[Atomicrox]

That's very strange. It does look like the laser is slowly hopping to a higher TEM, but I've never seen that happen with a diode laser.

The fact you're running a pen for that long is probably making it worse. Remember that diode was one of the first direct greens and it's very inefficient - it will dissipate a lot of heat despite the low output power. The pen is probably not getting hot because it's holding the heat in the module, which is even worse for the diode (that might - or might not - be a design issue with the pen host they use).

If you want to keep it on for a long time I'd go for a bulkier host.

Edit: are you sure this is a diode and not a 532nm laser? (pictures aren't very good for identifying laser WL's)

 

[Streamtronics]

The fact you're running a pen for that long is probably making it worse.

yeah, I usually really just use it as a pointer. So I usually don't leave it on more than a few seconds but also then don't really leave it off for 30 sec either. I guess I might use it for like 5 min or so, and during those 5 min I constantly turn it on and off (it has a momentary switch after all). So it doesn't stay on the whole 5 min... but as I said, the divergence changes even if I don't leave the laser on watching the dot grow. I can just turn it on after a minute in my hand and notice a way bigger dot.
I assume that's my hand temperature doing that to the laser (I actually suspect this to be a lens issue more than an issue with the diode itself. But then again I'm not an expert.)

Edit: are you sure this is a diode and not a 532nm laser? (pictures aren't very good for identifying laser WL's)

Oh yeah, absolutely.

It's way more blue-ish than my 532nm DPSS, noticed that from the first second I turned it on. Definitely not 532nm, can't really tell if it's 510 or 520 nm or whatever of course.

It's also weird that it did definitely not do this divergence changing when I got it, just the beam angle was off already back then. You're right, it looks a little like it's in a weird mode in the picture with the ruler I posted. I only saw my 532 DPSS mode-hop before, it was quite an amazing thing to see ("yeah, science, bitch!"). But not sure how mode hopping looks with diode lasers. This doesn't look at all like the very defined areas I saw with my DPSS. It also looks more like that on the photo than it does in real life. Looked at it through laser goggles, it's just kinda smeared, not really a different mode I guess. The smear might come from the wider beam hitting more of the wall of the hole at the laser exit? I don't know.

 

[Atomicrox]

Do you have a magnifying glass? Try pointing it through one, it should make it clear if the diode is mode hopping or not (note that mode hopping doesn't always produce two clear-cut beams, but it doesn't just smear the output either).

 

[mortuus]

Yes the 520 in my HL host gets alot warmer then my 405 in the same host its weird they both 100mW but the green feels like its double that atleast considering how fast it heats up but according to laserbtb mail the runtime is 3 min if iremember correctly, i asume the 520 diode just heats up way faster so having that in a pen isnt ideal, could explain your problem.

 

[Streamtronics]

The magnifying glass was a good idea, should have thought of that ^^ and it doesn't seem like it's mode hopping. In fact I'm very sure it doesn't but then again I never saw a diode laser mode hop. The dot just "smears out" a little and mainly gets larger. I guess it's just the typical diode beam shape? There's a phone pic in the attachments.

And yeah I get that 515 diodes might be quite inefficient... But if you say it gets warm, I guess you can feel the host getting warm? You don't measure the die of the laser diode I suppose. My unit runs at only 20mW and it doesn't really get warm on its own. Not within the 100 sec duty cycle anyway. Again, it's not a self-heating issue, even just picking it up from a cold room the warmth of my hand is enough to make the dot grow. And even if it heated up a little on its own... it shouldn't show that kind of behavior. My cheap multimode red O-like laser gets quite hot after a few minutes of on-time and the beam shape doesn't change at all. Not really sure how comparable those are though.
If I'd have a guess I'd say the internal lens kinda detached and is now moving a little when the host gets up to body temperature... Or do you guys really think it's the laser diode? How would you explain it did not do that when I first got it in July?

 

[Atomicrox]

That unfocused dot seems normal/single mode.

My 520nm 30mW pen gets hot very quickly. IMHO even 1 minute is too much for the it...

If your host isn't getting hot it might be a poor thermal connection between diode/module and host. Which is actually worse for the diode.

Yeah, I've never seen a diode do that either, it's not normal at all. I guess the only way to find out the culprit is to disassemble the laser, but bear in mind it might be tricky...

Perhaps someone with more experience with those hosts will show up and give you some advice

 

[mortuus]

Nah just send it back, those pens and their hosts are a pain to take apart i hear, not like you can fix this yourself if they offered a refund i would gladly take it and send it back.