Strange problem with O-like modules ..... any other had the same ?

Hi, i got recently some o-like green modules, for a work, and a pair of them (but NOT all) have a strange problem

One of the 10mW, and one of the 30mW, when powered, works good for approximatively 40 to 60 seconds, then the "shape" (don't know how to explain it better) of the dot change for a second, maximum two, then the dot change again and the power decrease to 1/4 or less, and remain so.

i have no way for get pics, cause at the dot my cam get saturated ..... done a draw for try to give an idea ..... the first shape, the dark green is the usual center beam, and the light green is the usual halo, all is approx, 3 mm diameter, at 2 meters of distance ..... the second shape, the center of the dot increase the luminosity, almost double, and the out ring decrease a bit ..... the third shape, all the spot faint down to 3 / 4 mW, with the center that look a little bit as an unfocused diode (but it's impossible, being a DPSS module), and the total light is the same of the halo, very low.



( the powers measured from the 10 mW one, the 30 mW one have the same proportions, with 35 mW of maximum out, and 8 / 9 mW when dimmed ..... and before someone ask, NO, I HAVE NOT POT MODDED THEM )

if i turn it off, wait a pair of seconds, then turn it on again, the modules do a flash of a second at the right intensity, then do the same thing ..... again and again.

if i left it cool for a minute or so, the module restart to work for other 40 / 60 seconds, then do again the problem.

i thought the temperature can be the guilty, so made some measures ..... the module itself pass from 28 C (ambient temperature) to 35 C, before that the problem starts, but when i left it cool, also if the module temperature go down to 29 / 30 C, need to wait the same at least 1 minute, for get it work again correctly.

For the opposite, the driver module, and specifically the driving transistor, go very hot ( 58 C ) in 5 / 6 seconds, then stay at this temperature for the rest of the working cycle (that imho is a bit too much), and the IC part, instead, gradually rise from 28 to 40 C in 30 / 35 seconds, then stay at this level, more or less ..... anyway, when i turn it off, the transistor cool to 30 C in 5 or 6 seconds, and the IC in 10 or 12 seconds, so they are not responsible for the working bad of the module (times don't match)

Anyway, i don't have any way for measure the inside temperature of the crystal assembly or the diode itself without dismantle the modules, and i had no time in these days for do that ..... maybe in the next days i try and check also this, but not now.

anyone had the same problems, or have any idea about why it happens ?

mode hopping ? (in a 10 mW unit ? ..... ..... other than this, the beam don't shift nor disalign, it remain centered and aligned, also when it faint :thinking

defective crystals ? ..... or diodes ? :wtf:

It's probably mode hopping, it looks like TEM10 or TEM01

http://www.nationmaster.com/wikimir...a.org/wikipedia/en/9/97/Laguerre-gaussian.png

^ page not found (these pages are generated on-the-fly, for prevent linking

no problems.

Just wondering if it's due to the crystal, i feel a bit improbable that it's due to the diode.

Without having any practical green experience, I think you're right. The IR pump diodes are probably as simple and foolproof as a laser diode can get, but the crystals are a quite different matter from what I've read so far, and very finicky with regards to their optimum temperature.

You have not stated what you are using to power your modules...
Batteries... Bench Power Supply...Power Adapter... or even at what
Voltage your Input Voltage is....:thinking:

BTW... what type of LPM are you using to check the Laser Power

Jerry

^ sorry, you're right ..... lab power supply (very stable and compensated), at 3,8 volt, for simulate a li-ion battery, and as LPM, it's difficult to describe, cause it's a prototype that i made when i was working for an industrial maker some years ago (i was on R&D / prototyping dep ..... or, being more precise, i was, practically alone, the R&D / prototyping dep, LOL ..... when they closed for failed investments, they had not enough money for pay all the bills, so i got some of their electronic instruments, in place of some of the money, evaluated at 10% / 15% of the market price ..... 2 oscilloscopes, frequency counter, waveform generators, multimeters, a soldering / desoldering weller station, and some other thing, including this one) ..... analog/digital, can use thermopiles or diodes, i'm using it actually with a 2 W max hybrid air cooled thermopile (the other one i have is a 50 W one, too big) ..... last time i checked calibration, it was december 2003, with a molectron 5200 LPM, from a friend.

The link worked for me. It was this picture:

Classic mode-hopping. Most likely yours is the result of temperature changes, since it takes at least few seconds for it to happen and it happens over and over. There is nothing exact about cheap DPSS modules so the fact that the times and temps are not the same each time means nothing. No two DPSS laser are exactly alike and consequently they all behave differently. It could be caused by a bad driver providing unstable power, but the truth is that while Suzie's modules are usually quite stable they have the potential to become unstable given the right conditions.. I have yet to see a cheap pointer module over 5mW that remained at TEM00 under all conditions (temp, voltage, etc.). Lab-style DPSS lasers tend to be a lot more stable, but even they can go unstable under modulation.

If I'm not mistaken... I believe the O-Like modules are rated as follows:

under 40mW at 3.0 Volts
40-50 mW at 3.0V to 3.6V
90-150mW at 3.0V to 4.2V

Not sure if it makes a big difference but the extra Voltage could heat
things up a little faster...

Jerry

The other question that comes to mind, is whether or not the modules are heatsinked?

The modules are much better with a heatsink on there...
Jay

@ maxh: thanks for the pic.

Then, perhaps it go from 00 to 01 for a pair of seconds, then fade back to 00, but with 1/4 of the original power ..... strange, anyway ..... luckily i had buyed one more module for each type (Murphy's law defeating technique, LOL), so i still can complete my prototype, when i get the holders.

Yes, it's due to crystal temperature, i opened it, and put a mini heat sensor on the crystal, and it change temp in different curve than the rest of the module ..... perhaps it don't transfer the heat with efficency to the brass holder, for some reasons ..... anyway, i don't have enough tools for unglue and realign it, at the moment ..... wondering if adding some thermal glue can help, but this is a one-time test, cause then it's impossible to take it away, if wrong

I also tried with only 3 V, and it do the same, just change a little bit the time, but not too much ..... other than this, i have other modules that rise til 45 C and over, without any hopping, so are just these 2 that, for some reasons, are extremely sensitive to temp.

And no, no heatsink, i was testing them in the worse conditions, right for see if i can use them ..... normal work environment is underwater, so the holders are always cooled (freezed, almost ..... at under 100 meters of depth, here the water is constantly at 2 C, also in full summer, and this one can go til 360 meters ) ..... but, due to the impossibility to intervent on it, in working conditions, i want to test them til stress limits, before use them, so i was testing them "bare" state ..... just surprised that they go in this mode when the brass part reach only 35 C.

Guess there is just nothing to do ..... ah, well.

Anyway, thanks all for all the info

If you'll be using DPSS technology at 2C.... Well, let's just say you won't be using DPSS technology at 2C unless you heat the module. At 2C all you'll get is a faint glow if that. Most likely the unit won't even lase at all.

Uhm, right, thanks for the reminder ..... i need to check also LOW temp, then ..... but the diodes can be took turned on for a lot of time, if needed ..... in fact, they remain turned on for the 99% of the time, and they turn them off only when made vid parts for a service (for not see the beams in the vid, if unwanted)

The water temp at the surface can go from 18 / 20 C to 4 / 5 C (they work also in winter, if needed) ..... going deep, it decrease ..... and i need also to invent something as an interlock for avoid in any way that the lasers can turn on when the ROV is not underwater (is not safe, having 4 lasers turned on in front of a ROV hanged on a rope, that wave and scroll here and there randomly, being pulled onboard or putted in water from a boat ..... especially if they are all 100 mW units ) ..... need to check if this is enough as self-heating, for make them work.

Or, also, what about turning on them after they gone to low temp for inactivity ? ..... IR diode can heat them enough for make them work, after a little time, but someone know if in the meantime the crystal can get damaged ? ..... another thing to check

Also, it use 2 100mw red and 2 100mW green ..... red ones must have no problems, being bare diodes, but can't substitute the green ones with any other thing ..... maybe filling the host with thermal conductive silicone, for convect also the heat generated from driver to the holder, can help .....

Damn, how much things to keep in consideration, doing something that none done before

You could rely on the pump to heat the module.. I couldn't begin to guess how long it would take to heat up enough to lase well. Convection would help as well. My suggestion is to use a TEC in reverse to gently heat the module. You'd need an environment that is around 2C to set the TEC (you could use a walk-in refrigerator in a restaurant if you know someone who will let you), but once you've set it it should continue to work indefinitely.

Unfortunately, i can't do it on the final product (using a TEC, i mean) ..... the modules are hosted in tubes that have an inside diameter of 13mm (just the space for the alignment, before the impregnation with thermally conductive silicone ..... like in the draw, bad as usual ), so no space at all, for a TEC .....

Can always try a thing, anyway ..... a layer of Kapton tape on the brass module, some turn of ni-cr wire, another layer of Kapton tape ..... with thermal silicone inside, for fill air gaps ..... and a thermistor glued on the brass part, with a little thermostatic circuit, can build it small enough, that use part of the laser power supply for heat the module with the ni-cr wire, and automatically disconnect when the temp is over 15 C ..... i think i can fit the wire in the space between the module and the holder, anyway, must be easy enough.

Nothing wrong with that idea, so long as your protection circuitry doesn't allow the module to exceed 50C MAX.