Power Meter Calibration and Comparison

Yeah, I think it's a good bet that it'll do.

After measuring one of my own lasers, though, I need to do some reading and checking on things. I put my latest build on it today, a PHR running on a Rkcstr 100mA fixed driver. This PHR had its can window knocked loose, so I know that will affect it some (it has lived this long at least) and it's an Aixiz acrylic (back opened up) lens. But with just a quick'n dirty test, it peaked at around 62 mW, which I was expecting at least a little bit higher peak. The loose can window could very well be doing it, but I'm going to look into it none-the-less. Also, I need to look into the recommended positioning of the laser relative to the detector, and the focus that will work best. It's a 1 cm^2 round detector, and should be extremely accurate no matter the position on the detector, but when I removed the aixiz lens, the power wouldn't get up above around 40mW, so the light wasn't getting to where it needed to the way I was holding it apparently.

The whole thing is on an air table, so vibrations and sitting it flat won't be too much of a problem I think. I'll get it worked out though, because it's certainly doable now.

pullbangdead said:

I put my latest build on it today, a PHR running on a Rkcstr 100mA fixed driver.  This PHR had its can window knocked loose, so I know that will affect it some (it has lived this long at least) and it's an Aixiz acrylic (back opened up) lens.  But with just a quick'n dirty test, it peaked at around 62 mW, which I was expecting at least a little bit higher peak.

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You know what. When i realized you are talking about optical meters i got a little worried, as even an expensive ThorLabs optical meter Climbak has, is showing way too much for 405nm, even tho it has a calibrate 405nm seting.


But i don't think your reading is off. At 109mA i got almost every number between 68 and 98mW.. The weakest diode would do ~60mW at 98.7mA (Rkcstr's 100mA driver = 98.7mA if i remember correctly)..

That doesn't mean, that you got the least efficient diode, since the window is partially the cause. It's just that most people expect more, simply because Lava got lucky with the diode he graphed. Only the very best diodes can do 80mW at 90mA....


I almost finished testing of another large batch of diodes, and i did it at more currents this time.  I will post the result in the batch testing thread when i'm done. The average diodes need 109mA to reach 80-87mW... When i get >80 at 109mA, i consider it a good diode.

I don't know how accurate my meter is of course... Glenn's meter shows 7% more, while two of Daedal's thermal sensors are spot on with mine. But even if the actual power should be 7% more, it would be 86-93mW at 109mA...


It wouldn't hurt to have at least one accurate thermal meter in all this, but i think the optical meters in your lab are actually good. And they should be, considering what they are used for.. The university probably pays a lot of money, just to keep them calibrated properly.

I think it would also be a good idea to send it to electron regardless of his participation financially. His Coherent is also a high dollar unit and freshly recieved from coherent, As well as psuedo, and possibly senkat. but again those are going to have to be willing participants to get some good potentially stable readings from some BRAND NEW meters.

We should definitelly try to gather several accurate thermal readings. I was hoping on a thermal meter baseline from their average..
If they agree with pullbangdead's university's optical meters, so much better.


Optical meter wavelength dependancy can be a problem, even when they have a preciselly calibrated setting, because the PHR diodes vary in wavelength a little.. Not much, but enough to be noticable. I had two similar power PHR lasers, where the 149mW looked brighter, than the 159mW!

Phenol told me today, he shined a PHR and a 6x through a yellow filter glass, and the 6x was blocked completelly, while some of the PHR beam came through.



I sure hope the expensive thermal meter owners join the experiment.. They might want to know how their meters compare anyway..

IgorT said:

We should definitelly try to gather several accurate thermal readings. I was hoping on a thermal meter baseline from their average..
If they agree with pullbangdead's university's optical meters, so much better.


Optical meter wavelength dependancy can be a problem, even when they have a preciselly calibrated setting, because the PHR diodes vary in wavelength a little.. Not much, but enough to be noticable. I had two similar power PHR lasers, where the 149mW looked brighter, than the 159mW!

Phenol told me today, he shined a PHR and a 6x through a yellow filter glass, and the 6x was blocked completelly, while some of the PHR beam came through.

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I too, have noticed that there are some slight differences in the 803T diodes. Not that I have a way to measure the wavelength or anything. But with two beams or dots, side by side, you can see a slight difference in some. Enough difference, so that the ones that are 'more blue', are visually brighter....even if it measures less on the power meter!
Jay

Ya know it's not that hard to determine the wavelength of your lasers. I'll post a link to how to do it, and all it takes is a simple diffraction grating.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/gratcal.html

Kenom said:

Ya know it's not that hard to determine the wavelength of your lasers.  I'll post a link to how to do it, and all it takes is a simple diffraction grating.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/gratcal.html

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Nice link! I'll file that one away for a rainy day...
Thanks,
Jay

jayrob said:

I too, have noticed that there are some slight differences in the 803T diodes. Not that I have a way to measure the wavelength or anything. But with two beams or dots, side by side, you can see a slight difference is some. Enough difference, so that the ones that are 'more blue', are visually brighter....even if it measures less on the power meter!

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Yeah, isn't it interesting.. I couldnd't understand it at first, but i actually saw the entire beam as brighter.

I mean, the wavelength climbs a little with heat, and with blu rays, that would actually mean "brighter". But i doubt that would be noticable. Besides if two are powered up for the same time, the shift should be the same with both, so the diodes have to vary in wavelength from the start..

Kenom said:

Ya know it's not that hard to determine the wavelength of your lasers.  I'll post a link to how to do it, and all it takes is a simple diffraction grating.

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That's very usefull. It makes sense, but i would never think of it..

If you make the distance large enough, and the measurements precise, the result would be quite accurate...

Unfortunately I don't have a diffraction rating with known lines width. I do have some transparent cd's (CD-R with coating ripped off) but they can be either 1.6um or 1.48um depending on if it was a 74min or 80min CD. I'll try if I can distinguish between those two with a known (approximately) 650nm laser and a 45 degree projection setup.

I just realized something we have not discussed yet. Some meters have multiple settings, which may each be calibrated separately. I suggest that all or some of those ranges be tested separately using the protocol. I just read about some Scientech lasers which have ranges far below these, which will overflow when presented with 100mW. These ranges are of course excluded from the process.

At first I would recommend testing any range you are using frequently (common laser ranges). You should also try to calibrate any other range which you might want to use in the future. On the other hand it might be confusing to have both calibrated and uncalibrated ranges and it's prone to error. Should we recommend calibrating all (possible) ranges, or some?

Maybe we should also change the setting for the lasers to all be 90mW, as not to overload meters with a 100mW max range?

Zom-B said:

Unfortunately I don't have a diffraction rating with known lines width.

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Don't you have a thermal meter?

Zom-B said:

Maybe we should also change the setting for the lasers to all be 90mW, as not to overload meters with a 100mW max range?

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That would help with the analog Scientech meters.. Since they could use the whole scale in the 100mW range, the reading would be more precise in this range. In higher ranges and on digital meters, it would be a little less precise.

How many people have an analog Scientech meter as their main meter?



I heard of some professional meters with a 100mW max range, but does anyone here have a 100mW limit on their meter?
Because in that case, when attenuators are used, the results can be horribly inaccurate.

IgorT said:

[quote author=Zom-B link=1217029972/180#184 date=1217675612]Unfortunately I don't have a diffraction rating with known lines width.

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Don't you have a thermal meter?[/quote]
What has that have to do with diffraction gratings?

Zom-B said:

What has that have to do with diffraction gratings?

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Umm, i thought we were talking about diffraction gratings because of the wavelength dependancy of optical meters..

You can add "electron" to the list of participants in the tests.

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