I've been working on a research project here at Virginia Tech - I met with a Coherent representative earlier this semester. They donated a 641nm 100mW-rated CUBE laser to me. It is brand new,
perfectly calibrated, and is computer controllable.
A few weeks ago a user came to me when he was experiencing vastly different readings on his Kenomter USB vs. his Laserbee 2.5W - lasers were reading around 15% higher on the Kenometer USB. I sent him the Kenometer USB firmware update and gave him a new version of Luminosity. The issue persisted.
For the sake of science, I decided to test my four Ophir sensors. I set my CUBE to output 80mW. The results were as follows:
- 10.7% LOW
- 5.4% LOW
- 4.1% LOW
- 8.3% LOW
I was rather dismayed. This opened up the possibility of the LaserBee 2.5W LPM's to be incorrect. If we thought the Ophir sensors were reading high but they are actually reading low, then it means the LaserBees are probably reading
very low.
This was rather distressing. Jerry calibrates his LPM's against a Newport LPM. They should be accurate and we assume them to be accurate. I went back and found a graph on PL that showed them to be accurate. If they are not accurate, it could mean that a lot of our benchmarks and fundamental assumptions regarding laser diodes (output in millwatts being less than input in milliamps, efficiency, etc).
However, I had not tested the user's Ophir sensor. So he shipped it to me. I once again set my CUBE to output 80mW.
I fired up my Apex LPM with his Ophir sensor attached. It read 3.5mW with no power input. I moved the laser over to the sensor surface, expecting to see a high reading.
83.5mW. 3.5mW + 80mW = 83.5mW. That was NOT supposed to happen. This is BAD.
I shipped the Ophir sensor back to the user, intending to test his LaserBee next.
Last Thursday (after I'd been covering the shooting for the student paper), I got a call from him. He'd gone to test some of his lasers at a nearby university and had gotten numbers that were effectively the same as the LaserBee's.
Trevor