My red dichro reflects green

[buffo]

Steve-O;

Funny you should mention that "poor man's power meter" trick. I recently had the opportunity to experience that first hand.

I've often heard people complain that their 50 mw laser will burn the back of their wrist, or that their 100 mw laser will burn the back of their hand... Even Astroguy said that he could make an *educated* guess about the power of a laser by how fast it started to burn on his skin.

But honestly, whenever I put my hand into the beam, I never felt any burning. I've got two 100 mw DPSS green lasers, and a 120-ish mw red laser, and NONE of these have ever burned my skin with the raw beam. (I'm not stupid enough to focus it through a lens onto my skin; I know that would start cooking my flesh right quick!)

Well, the other night I was messing around with my old projector housing (the one that used to run off the Alphalight). I was playing around with the settings in Pangolin (that projector is running off the QM-32 now) and I happened to put my arm down into the beam path to pick up a tool off the chair next to me. It was warm in the house (I didn't have the air conditioning on at the time) and I was sweating a little.

Suddenly, it felt like my arm was being bitten by fire ants! (If you've never been bitten by fire ants, the closest thing I can give as an analogy would be holding your hand over a candle flame until it hurts, except that the pain is immediate and doesn't go away.) My damn laser was burning my arm! OUCH! (insert the expletive of your choice here)

That's the first time it ever happened to me. So naturally, being an inquisitive fellow (that is to say, "being a guy"), I naturally had to do it again to be sure it really was the laser and not something else. (insert drumroll here...) OUCH! (insert second expletive of your choice here) It did it again!

So, after carefull experimentation under controlled conditions, I can state with certainty that a 100 mw laser *CAN* burn you, especially if your skin is moist with sweat. (Now where in the hell is that bottle of Solarcane?)

Adam

[steve-o]

Ahhh fireants
Yep I know 'em well
Living in south Florida in the late 80s I had the brilliant idea of using sand instead of cat litter..(its free down there ya know) ..It was dark out, so I went out and stuck my hand right in the middle of a large nest, scooped up the sand/ants and felt a burning unlike any other. Me thinks i dont do that again

[buffo]

Just think how upset your cat would have been!

Adam

[yaddatrance]

A little interesting tidbit which some of ya'll might not know is that the "poor man's power meter" trick is actually used by a lot of old hands on lasers up to about 6 watts. (and by certified nutjobs on anything >15W)

The key thing that makes it ghettotasically scientific-ish is you measure the power based on how fast you have to keep moving your hand to keep it "comfortably warm"...

Between 500mW and 5W you can make a solid guess (within 100mW from dead reckoning)... and more accurately if you've recently "calibrated" yourself recently while tuning a system using a power meter... at around 6W is where you have to move it a little too vigorously and beyond that is the "old-timer voodoo" point where they can give a good guess based on a swipe but where mortals such as you and I will merely give ourselves 3rd degree burns.

Not that I can in good faith recommend this practice... Your mileage may vary.

[carmangary]

Seems like it would make more sense to shine it on a thermistor or something.

[steve-o]

Just think how upset your cat would have been!

Hehehe
Yeah.. she would have been pretty pissed off

[buffo]

you measure the power based on how fast you have to keep moving your hand to keep it "comfortably warm"...

Hey Yadda!

When I first read this I couldn't decide if it was funny or scarry. I eventually decided that it's both!

But you won't see me waving my hand in front of a big frame ion laser. I have visions of a cauterized hole through my palm... (yuck! Can you imagine the smell?)

Adam

[steve-o]

mmm ..palm de flaumbe