Power meter question

[mophead]

Well, I snagged a laserbee meter from someone. Seems like a well built piece of kit and got it well worth the money. Have a question though.

In another thread we were discussing the (possibility) inflated reading from my Laserwave 200mw 532. It was measured at FLEM with Adam's Coherent pen, which after some explanation, i understand why a small amount of IR could throw the reading WAY off.

I set off to measure said laser with said laserbee. I measured 334mw (avarage) with the thermopile ~3.5" from the head--straight on. Pretty good for a 200mw laser i thought, but what about the IR?



I decided to see what kind of loss came from the front surface mirror that came out of an old laser copier... It seems the reading is higher --~370mw.



I realize that optics LOOSE power, not gain. Where is my mistake in taking measurements to figure optical loss?

I also tried through a reflect green dichro..... Came up with ~20mw waste beam (which I figured IR + dichro coating) and 313mw reflected.

What the hell is up with the mirror?

d.

[mixedgas]

Did you set the zero each time? That is the usual thermal type error.

Steve

[mophead]

No, I didn't. I simply assumed that when the mirror was gone, reading returned to what it was before, so it was correct.

Makes sense though.