greenie weirdness

[DakotaDaNative]

i got a 50mw 532nm green from laserlands and its awesome but lately ive gotten some weird like spurts of green shooting out at a 45 from the beam :wtf:you usually get. anybody ever get this? i dont get it all the time and to fix it i just turn the laser on and off a couple of times. :thinking:

 

[Morgan]

This sounds like a, "Mode Hopping", incident. The technicalities of which I am unable to explain but it should give you an avenue to search down. Try Sam's FAQs or do a search here.

I must admit I haven't heard of, "Mode Hopping", for a while now. Must be improvements in manufacturing etc.? Anybody have any other thoughts?

M

 

[HIMNL9]

Uhmm , sorry, are you sure ? ..... mode hopping happens, but i don't think it cause beams coming out at 45 degrees, as the OP said (if i've understood correctly).....

Something rattling inside the module ? ..... front lens chipped ? .....

 

[daguin]

Sometimes defects in the crystal or lens will cause this.

Peace,
dave

 

[Morgan]

Uhmm , sorry, are you sure ? ..... mode hopping happens, but i don't think it cause beams coming out at 45 degrees, as the OP said (if i've understood correctly).....

Something rattling inside the module ? ..... front lens chipped ? .....

That proves my point. Thanks HIMNL9, I said the technicalities were beyond me but thought it was a starting point for a search.

M

 

[photonaholic]

Sometimes defects in the crystal or lens will cause this.

Peace,
dave

I like this answer best, manufacturing inexpensive crystals rapidly will produce many that are "less than perfect"

 

[DakotaDaNative]

i also immediately thought lens issues or defects but i dont see how it can happen periodically. after that i thought maybe power issues im running it off a lm317 circuit. ill have to check with my meter tonight cant right now its over my friends house on my spirograph :yabbem: also takin some pictures of it tonight in a freinds basement with smoke ill have to see if the problem continues.

 

[RA_pierce]

This sounds like mode hopping to me.
If the beam switches modes, part of the beam may get reflected off of the aperture or the edge of the lens which could produce artifacts as you described.

I have seen this before.

Try out the laser with different temperatures.
In some cases, using your laser in the optimal temperature range is all that is needed to fix a mode switching laser.

The other possibility, which is a bit less likely, is that a component in the laser is loose and partially blocks the beam when the laser is rotated to a certain position.

 

[DakotaDaNative]

is it possible that im cooling it too much? without a heat sink when i bought it at first it would dim after 3 min operating and be warm. with my heat sink i have yet to reach a max operating time. i also have it sitting on top of a fan gettin pretty frosty. i would like to attach a picture but i have no idea how cuz im new on here :undecided:

 

[JLSE]

DPSS has many oddities and are much more noticeable in cheaper quality lasers. The angle you are seeing can happen when the 532 output changes modes.

A slight variation in the position exiting the crystal set then becomes emphasized as it passes through the expanding lens on the output side of the crystal.

It is the same as if you had broken loose the crystal set and changed the alignment. The now off center beam hits the collimator closer to the side and reflects off anything it hits. This is most likely where your anomaly is coming from.

You may notice that it stops happening if you replace the battery with a lower voltage, ie 3v lithium.

Or you could turn down the current fed to the LD via the trimpot. You could think of this as a 'kink' that goes away at either lower or higher current being fed to the LD.

Even if this behavior wasnt an issue for the first 10mins of use and then started happening.. Its just luck of the draw with low QC lasers.

 

[mfo]

My guess, it has something to do with the crystals. I doubt it's the lens, because that would be constant. I doubt it's mode hopping, because I've never heard of 45 degree angled beams. Sounds like the crystals act weird when they get warmed up from use.

Long story short, I'd get an exchange or a refund if I were you because obviously something definitely isn't right with it.

 

[DakotaDaNative]

im running it off of a lm317 to supply 2.9 volts when adjusted to the driver already on the diode and the driver has a pot on it. should i lower the current to the driver or trim the pot. and its not a crazy like vibrant 45 beam coming off of it but when it shines on the wall you can see the shadow of my fans im gunna run it tonight and see if it still happens and if it does you bet ill take some pics.

 

[JLSE]

Im had a similar problem with a 532nm module I put together. The crystal set is low grade and also hits a kink where the alignment goes out over a range of 15mA. If I go higher or lower in mA, the problem goes away. Now I use this module for lining up, but it cant be modulated under its mid range or the shifting begins.

Mode shifting occurs behind the expanding lens, when this happens, it does not always just show a change in beam shape, but position as well.

If the position changes it will change how the beam enters the expander. For those who have tried to align a 532nm by hand, you will know where im coming from...

What you are most likely seeing is a 'split' beam, with one of the 2 beams hitting something behind the aperture, or something to that effect.

If it was a defect in the crystal set such as a crack, it would be a permanent fixture in the beam, such as a line or 'splash'.

If the input side of the crystal set gets burned either it wont work, or you will also see 'splash' in the output beam.

I just shot this clip. You can see as the laser comes to operating current, it begins to act up. I also raise and lower the current, and you can see it responding to the 'kink'.




Edit


Did you overdrive this module at any time? Also did you take note of what the OEM driver was set to in mA?

*Double Edit..

I think RA_pierce hit this one on the head.. Think the fan may be overkill.

This sounds like mode hopping to me.
If the beam switches modes, part of the beam may get reflected off of the aperture or the edge of the lens which could produce artifacts as you described.

I have seen this before.

Try out the laser with different temperatures.
In some cases, using your laser in the optimal temperature range is all that is needed to fix a mode switching laser.

The other possibility, which is a bit less likely, is that a component in the laser is loose and partially blocks the beam when the laser is rotated to a certain position.

is it possible that im cooling it too much? without a heat sink when i bought it at first it would dim after 3 min operating and be warm. with my heat sink i have yet to reach a max operating time. i also have it sitting on top of a fan gettin pretty frosty. i would like to attach a picture but i have no idea how cuz im new on here :undecided:

 

[DakotaDaNative]

thanks for posting the vid your very helpfull i am seeing some of the "kink" if i understand it right. do you think that my current isnt steady? or that i should make it steadier? how? also isnt the colder the better and longer life? ill see if i can get mine up here by tonight to show you.

 

[Benm]

This sounds like mode hopping to me.
If the beam switches modes, part of the beam may get reflected off of the aperture or the edge of the lens which could produce artifacts as you described.

This sounds feasible. Mode hopping by itself will never cause deflections to 45 degrees - you get 2 or more beams spaced in the order of the divergence in TEM00, so you're talking mrads there.

It can be enough to just graze an aperture though, and from there reflect to any unpredictable angle.

 

[JLSE]

thanks for posting the vid your very helpfull i am seeing some of the "kink" if i understand it right. do you think that my current isnt steady? or that i should make it steadier? how? also isnt the colder the better and longer life? ill see if i can get mine up here by tonight to show you.

The LM317 should have a rock solid current, and wont be the issue.

If you are in fact running a fan on top of a large heatsink, it is probably the temp that is causing your issue.

Like RA_pierce suggested, try warming the heatsink first, and dont run the fan.

If this doesn't fix it, then worry about the current.

I don't think ive ever seen a 532 laser either that isn't problematic at cool temps..