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FrozenGate by Avery

External pumping of a ex-pointer. Not exactly working.

R

Riff42

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Ok all, I'm new to DPSS, not lasers. I was around reading Sam's back in the 90s, and build two N2 lasers, rebuilt a few HeNes, fixed a 300w CO2 at work, ran a light show company in college with Ar and Kr heads as well, among others, and just a pure love of lasers.


SO, I found some nice 1watt 808nm pigtailed diodes on Ebay, and have gotten slightly bored with them. I started looking into green pointers, and found out they are pumped with 808nm diodes normally, and are low power, but there are several high power systems.
I bought a cheapo green pointer, took it apart to be able to pump it with my pigtail laser. However, it has not worked as expected.
1: the pointer diode was open faced, with the doubler module pressed against the laser die, with a lens on the far side, and then the focusing lens set a few mm down.
2: I have only gotten ANY green light out, when I have the KTP module against the fiber pigtail, but that was finicky to say the least, and now, it will not work at all.
3: I can not get any green out when focusing the IR from my pigtail onto the KTP module. Nor when it's unfocused (converging and emerging focuses from the beam waist)
4: I can position the KTP module ascrew on the pointer diode, and see green light.
5: I have since then, taken off the lens that was on the KTP module off, and I can still get green light when I put the pieces back on the pointer diode, even without the lens.

So...what the hell? Is there a cavity effect that I am missing with using the pigtail pump diode? But wouldn't I negate that effect when I mis-place all the original crystals/lens back on the diode? It's NOT aligned well anymore.
What am I missing here? I thought that I should be getting green light from the KTP module when it is pumped with 808nm. Is the KTP module giving up due to the MUCH higher pump power?
 





Depending on the source of the diode you bought, it may not be exactly 808nm. Any significant deviance from that wavelength will kill conversion efficiency greatly.
 
had a similar issue with some of these 9mm "808nm" diodes. Some of them aren't close to 808nm and are somewhere beyond 940nm (guess used to fed fiber cables for communication?). To easily measure them you need a diffraction mirror (CD etc.) and a photo camery capable to catch IR. If you measure the distance of two maxima on both diodes it has to be the same distance = similar wavelength.

The small crystals out of <200mW laser pointer/modules are bonded Nd:YVO4 and KTP. The outer surfaces build up the cavity. There's no other lens etc. required. The build-in lenses are required to expand the very thin beam produced by the crystals to ~1mm (lower divergence).
 
I guess I need to find someone in the EE dept around here and see if they have a power/freq meter!!
It's just weird that I got some green output, but not always, and now nothing. I would hope that the pigtail laser wouldn't drift that much since it is an industrial laser, and they would have more stringent specs compared to a laser pointer.
Well, back to the drawing board :)
 
IR and red diodes actually tend to drift more than blue and violet laser diodes, you can actually get a noticeable color shift from a red laser diode by cooling it with dry ice and even more with liquid nitrogen.
 
So, back to this topic.

I recently starting looking back into my setup, and found that I can get green output from the KTP module with I place it against the fiber end itself. A little moving it around, changes the output dramatic. Sometimes a tiny beam, sometimes a strong bright one. I'm guessing, since the KTP module is mirrored on the output side, it forms a resonating cavity with the fiber end, vs. normally the stock IR diode's face.

Here is the weird kicker. It forms a slightly divergent beam. With NO extra optics!!! I can get a 1cm dot 10ft away.
Now this one confuses me. I would not expect the KTP module to be lensed in anyway, so how in the world is it creating a beam? The beam out of the pigtail seems to be about a 90deg spread on it's own.
 
Could be a combination of thermal lensing and TEM00 beam mode. TEM00 output has the lowest natural divergence of any mode regardless of the shape and structure of the cavity. Another factor is the distance between mirror coatings in the cavity. The longer the cavity, the lower the natural divergence. Even though your cavity is very short, it's still likely long enough that a fairly nice beam is created when the laser is running in TEM00. This is all speculation though, without seeing things firsthand that's all that is possible.

http://www.physik.unibe.ch/content/...e6254/ThermalLensinginanNdYAGLaserRod_ger.pdf
 
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