How not to treat your thermopiles

[Meatball]

So, this one is a 2006 Ophir head paired to an Ophir LPM. 3W max I believe. It got around 4 years of service and hasn't been touched for 2 years or so, and you can see why. The paint has been cleanly ablated off by our YAG, and the sensor portion has many-a craters drilled in.

They tell me it still works, but what do they know, they're nano-engineering students. I'm a laser forum member dammit. I know better...

Anywho, I laughed when I saw this and Trevor told me to post it so here it is.

Its been under the beam of many CO2s (probably way too much power for it > 1kW), Argons, a couple Excimers, a Ti:S, an OPO, and a FHG Nd:YAG, SHG Nd:YAG, and a THG Nd:YAG.

It served well and it served hard. Unfortunately, this little guy is not alone. All over the world, these Israeli-born thermopiles are exposed to hundreds of thousands of CW, nS, pS, and fS beams and pulses from all varieties of cavities and q-switches. Many are damaged and are becoming useless like this one.

Fortunately, there is hope.

STOP focusing your damn lasers on the sensors.

Post your LPM damages. And yes, everyone knows you have these damages already. You too lasersbee.

Lets see 'em.

[mixedgas]

I drilled a competing product on the first shot. Unfocused large diameter ruby beam, from a oscillator/amplifier E/O q-switched ruby. The manufacturer swore up and down to the professor that it could take the hit. Along comes poor Steve, volunteering to help with holographic breast cancer detection. Steve determines that the laser, setting on a carpet soaked with its own coolant, needs serious help. So he adds clamps to all the water hoses to stop the leaks, and sets down to the serious steps of tuning the master oscillator and the two multi-pass amplifiers. I mean, I should have known when I was getting sparks off of the diamond pinholes, but they said it could take the fluence. Oh, I tuned it. It took two days of tweeking, so big are the cap banks, that we're talking one shot a minute. Then when I was satisfied with the scope shots, I metered it.

Those who know properly tuned ultra-fast ruby will tell you, its nearly silent when properly adjusted. It goes Click-Bang! when the timing is off. I achieved near perfect silence. Then I metered it. First shot went half way through the metal behind the carbon. Second shot is when I noticed the Joule-meter was reading funny.

So they refused to honor the warranty. I came up with a solution. I re-coated the face with carbon black, filled in the holes, and hooked the detector head to a Tek scope. The piezo part worked just fine with a 50 ohm load. The beam was then spread with a lens. The Prof was so pissed, that the 4,000$ Joulemeter got returned, it was purchased on a credit card. Head and readout purchased not as a set. So we could force the return of the one, and he DID.

So that's the condensed story of the day the Booby Ruby did a Mega Gillette*

*Before Joulemeters were accurate, Gillette razor blades were a good test. They were in the lab because a stack of them on edge, made a great termination for hot beams.

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Before someone dogs me for being politically incorrect, I was never in the room when the patients were exposed. I also was the only laser technician within 150 miles who would even look at the unit. I helped them save 3000 bad exposures by changing the readout wavelength to one of the first DPSS greens, and rebuilt their large frame readout HENE, which went from 250 uWatts to 25-27 mW. Since the pink ribbon folks now use "Save the TATAs" as a bumper sticker around here, Booby Ruby seems sorta appropriate. I never billed them a dollar.

In defense of the Grad student involved, she was on her first job out of school. A first year student. No one should expect her to know about buying hose clamps and holo film shrinkage. Even though she was a straight "A" biomedical engineering student. She had the difficult job of getting patients who were getting mammograms to volunteer to be exposed to a pulsed laser. When I got there, the apparatus looked scary to the patient. When I got done, it looked like medical gear. I think I can even forgive her for using second surface mirrors (NOT!) on all the large optics. I replaced those as well.

Steve

[andythemechanic]

Here is my power sensor:



Left sensor, right laser, me in the middle. In the photo it runs happy at 11kW CW. Until now I was not able to destroy it, but when I focus that beam onto it the water behind the absorber boils a bit.

Andreas

Edit: The beam is IR at 980nm and the camera blocks it well, that is why you can't see it.

[dar303]

Nice glasses, must be blocking a fair bit...

[andythemechanic]

Yes I prefer to hide behind it for safety reasons.

[Meatball]

That's an excellent story Steve, thanks for writing that!

No more LPM accidents?

[mixedgas]

I oughta take a pic of the 210 head here at work before I throw it away. I didn't abuse it, people who were here before me did. Not only did they blast the sensor, they blasted the shell. Maybe this afternoon.

Steve

[Meatball]

I didn't abuse it, people who were here before me did. Not only did they blast the sensor, they blasted the shell. Maybe this afternoon.

Steve

Sure. Sure they did. It was them. They (those other people I never knew) are the ones that did it.

[krazer]

I don't have the sensor handy anymore for pictures, but I had a PM-10 joulemeter sensor that I was using for tuning my yag, I had the pulse rate set for about 50Hz, and was getting about 10mJ pulses, which was all nice and dandy for the sensor, until the q-switch driver overheated and shutdown. The laser switched to running CW, and was putting out ~50W, the sensor survived for about a second while I was wondering why the laser stopped pulsing, before the detector exploded and sent shards of smoking hot piezo materal across the lab.