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odd 532nm module behavior

Traveller

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Hi2all,

I have three "modestly-powered" 532nm lasers.

The first one (80mW constant) is a perfectly round, low-divergence (1.2mrad) IR-filtered beam emanating from a high-quality LP (module type & characteristics unknown). The second one (150-130mW) is a "classic" O-Like module (Mar. '09) which also has a perfectly round, albeit slightly less divergent (2.0mrad) and non-filtered beam.

The third (125mW-80mw) & main topic of this post is one of those newer "DX-style", shorter, non-filtered modules. This guy's a real mess. At start-up (cold start), there is not one, but two points, which after 30s or so, merge into one. At this point the module has dropped to it's lowest o/p level (80mW). I'm guessing TEM01, for lack of better definition. The next odd characteristic is that when seen through 532nm googles, one point is a dull yellow (as are all my other 532nm lasers) & the second one is... green!!! :eek: Thirdly, it has the worst divergence by far, maybe 5mrad, but has a pinpoint spot at a short distance (~10cm) which "burns" better than even my 130mW module... :confused:


So what are we talking about here, a misalignment of the IR diode & crystals? Why does it burn so well - due to the selected focusing point or maybe a more powerful (& focused) IR output? FWIW, placing an IR filter in front of the beam did not change it's appearance (shape, color, etc.).


I'm not really interested in 532nm lasers for burning; I have enough 650nm & 405nm lasers for that purpose. I'd just assume have a clean, powerful beam with low divergence towards infinity. But what is it if these cheap DX modules are "configured" to burn at close distances to impress the casual LP owner?


All theories / suggestions welcomed :beer:
 



Greenmechanic

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Thirdly, it has the worst divergence by far, maybe 5mrad, but has a pinpoint spot at a short distance (~10cm) which "burns" better than even my 130mW module...


So what are we talking about here, a misalignment of the IR diode & crystals? Why does it burn so well - due to the selected focusing point or maybe a more powerful (& focused) IR output? FWIW, placing an IR filter in front of the beam did not change it's appearance (shape, color, etc.)
Multimode lasers always have more power then single mode.
In single mode they are basically "cutting"off the other modes.
By allowing them through, you get the power of both of them. ( or the power of 3,6,8 different modes) you get the idea.

So what are we talking about here, a misalignment of the IR diode & crystals?
You guessed it!
 

Traveller

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Thx for the info. No, I can't say I really understand "multi-mode" or how one can cancel all others. Having said that, I'm looking forward to improving my knowledge on this subject with a visit to SAM's FAQ, which I once started to read, but quickly got in over my head :p

But that was over a year ago & hopefully my time spent at LPF will make SAM's less frightening this time around ;)

Btw, what's your take on the short focal point?

EDIT: Speaking of which, I just came across this interesting bit:

"The thermal management is very critical with Nd:YVO4, for example, cooling a cheap pulsed pointer at the diode-end with a can of component cooler easily results in a doubling of the output power. In general, you want to heat the KTP, cool the Nd:YVO4 and temperature tune the diode so that its wavelength, which varies greatly with temperature, matches the peak adsorption of the lasing medium. I had one reject that did 100 uW or so of green at room temperature, take it down 15 °C and it did 3 mW. The alignment did not need to be changed, it was already picked well for both temperatures. The caveat is that just because power comes up, it does not mean mode quality goes up. As you chill a cheap DPSS laser, all sorts of stray beams show up and the divergence broadens. "
 
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LarryDFW

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Traveller;

The focus is not correct.

Most greenies are adjusted for focus @ infinity.

Yours is focused to a closer distance,
which gives you better burning at that point.

With some smoke or fog, you should be able to see the beam focusing to that point.

A slight adjustment of the lens should correct the beam.

LarryDFW
 

Traveller

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Yours is focused to a closer distance,
which gives you better burning at that point.
Larry,

thanks - that's what I figured. The real question is if I order another DX module if it will also be "configured" to burn (instead of properly focused for distance)... :-/

I've read about thje trials and tribulations of having to dissolve / break the glued-in-place collimator and it doesn't sound like a lot of fun... :undecided:
 

RA_pierce

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Multimode lasers always have more power then single mode.
In single mode they are basically "cutting"off the other modes.
By allowing them through, you get the power of both of them. ( or the power of 3,6,8 different modes) you get the idea.

This is true. More modes = more power...
However, lasers designed and intended to operate in one mode (TEM00) will drop in power with a mode switch.

IMO, if a mode switch results in a decrease in output power and makes the laser ill suited for it's intended use, it is "defective."

My PGL operates in multiple modes, but it does not result in decreased output (actually the opposite), the beam maintains a round profile with low divergence("near TEM00"), and the multimode operation does not interfere with its use (pointing out stars, etc.)... so I do not consider it a defect... more like a "personality."

With a module at a "modest" output power rating, it should not behave the way you described. I would get a refund or exchange if possible.
 

Traveller

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...lasers designed and intended to operate in one mode (TEM00) will drop in power with a mode switch ... it should not behave the way you described. I would get a refund or exchange if possible
Well there you go, it's starts as a TEM01 at roughly 130mW and drops to TEM00 @80mW.... .

No, it's a bad apple but it was my third attempt with the same vendor and as you can imagine, shipping stuff back & forth to mainland CN starts to get old really quick... :banghead: To make things worse, this didn't come from DX and I paid approx $80 for it... oh well, c'est la vie, n'est-ce pas?
 

BKarim

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non je pense que l'alignement est bon puisqu'ils utilisent des cristaux compsites.
par contre ils doivent utiliser des cristaux, des diodes et des lentilles pas chères...
tu peux essayer de réduire le potentiomètre ça fera peut-être un bon module de 10mW.

tu l'as acheté où ce module?
 
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Traveller

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non je pense que l'alignement est bon puisqu'ils utilisent des cristaux compsites.
Salut,

I think that English is the preferred language on the LPF boards so I will quote you in English:

"I do not believe it is a question of misalignment as we are dealing with composite crystals here."

Alors... I do not quite understand what you mean by "composite crystals". Are not all DPSS lasers built in the same way?

Pump 808nm IR Diode --> Nd:YVO4 --> KTP

Aside from glass (lenses, OC mirror), I don't know of any other crystals involved, so that all 532 DPSS lasers should work the same*.

Please elaborate, thx :)


*Correction: I guess there are simplfied and complex varieties, as clarifed on Sam's FAQ...
 

BKarim

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lab lasers have high quality separated crystals and mirrors (and very hard to alignate)
tiny modules have glued (composite) crystals of poorer quality but that are well alignated and with integrated mirrors
(pump diode and lenses don't need to be perfectly alignated to have decent beam assuming they are quality made)
that's why many pointers have an inclinated beam but the beam itself is decent (for amator use)

DPM Crystals - Casix


where did you buy this module?
 
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Traveller

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lab lasers have high quality separated crystals and mirrors ... tiny modules have glued (composite) crystals of poorer quality but that are well alignated and with integrated mirrors...

Merci... this explains a lot :beer:

Given the price (not to mention it's size of 12x50mm incl. driver...) it is certainly of the el cheapo kind... . But regardless, I have a few non-professional DPSS modules / LPs with much better characteristics, so I think this one's just a bad buy.

I got it as a "test" sample (but a paid-for sample...) but the module's external characteristics are 1-1 with the inexpensive, short-bodied "new" DX 532 modules.
 

BKarim

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from all what i've heard, you never know what you'll get at DX and other cheap prices chinese resellers
 

Traveller

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f...you never know what you'll get at DX and other cheap ... resellers
True-true, sigh...
Say... do you know of a good vendor in the EU for 532nm modules? Worse is the fact that I really do need to keep it short (~50mm incl. driver)... :rolleyes:

Thx :beer:
 

Traveller

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Thanks :)

Roithner Lasertechnik is located 20mins from me :D however they don't sell 12mm DPSS modules; only lab and/or the actual components to build your own...

The other link you supplied though was quite interesting. In fact, I found the exact same DX modules, rated at 80~100mW and tested by them... for 42GBP... . Getting a "pre-tested" module is indeed a step forwards, but IgorT once mentioned to me that the driver used is total junk... and these guys use the very same one... :undecided:

But thanks all the same, I'll look around a bit more and/or give them a call to see what makes their better then DXes ;)
 




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