Power Meter Calibration and Comparison

Yeah, that will work. The low end will be somewhere around 16-20mA and high end should stay about the same (~150mA). And power dissipation should be within limits for the violet range, assuming the small pot is 1/10W rated (actual peak dissipation should be 1/20W), FYI

I'm glad to see that there is progress. I was starting to get worried.

Ok, I got everything put together but for some reason the max current I can get is pretty pathetic. I'm not going to guestimate at what's causeing the low current but it's set at 75mw exactly. so it should be enough to still do what we hope. I am contemplating not glueing the head back on with gorilla glue as it was a BEAR to get off there. Bah. I'll do it anyway. So as of monday this will go back into the mail directly to pseudo to test it. considering the accuracy of the red, I'm confident the bluray is going to be pretty doggone close too.

Try replacing the 2210 (221 ohm) resistor with an 18 ohm or so, this way the minimum current will increase significantly (to about 80 mA), and it might increase the maximum current too.

[edit]You might also want to change (or remove, and short) the resistor in series with the pot.

What kind of current was it putting out? I don't see why the max would decrease greatly unless the pot has a unusually high minimum current. Adding a smaller resistance in parallel with the pot (replacing the 221 ohm resistor with lower resistance) would decrease that value, possibly increasing the max current and increasing the low end current, as Zom-B suggested.

I don't see any reason for doing so when 75mw is sufficient for our needs. Or at least it's my opinion that it's sufficient.

Oh, ok... if you have it set where you want it, then no need to make any changes

75mW is good, let's get this going!

It's on it's way to pseudo already. Should see some results here pretty soon.

I had some time today (rare lately) so I ran some tests on the Kryton BluRay & Daguin BluRay I recently purchased from them, and did some comparisons on the Coherent LabMax, and then again on the LPM-1 set for 473nm ND.

I come up with 2.9x for a correction factor that brings me to within 4mw's of what is actually being measured on the LabMax for both BluRays.

Glass ND filter or plastic?

Wish you were getting in on this meter comparison...
Jay

I bought the complete LPM-1 package directly from Tony @ Andover Holography, it has the Glass ND8 filter calibrated to 5% accuracy.

Sorry about not being able to participate at this time, it looks like my schedule won't lighten up until mid-Nov  :-?

What I have been finding lately, is that there is a huge potential for inaccuracy with the 405nm measurements using the LPM-1 and a correction factor.

Example: I have two blu-ray lasers that I just tested. One is measuring 107mW's and the other is at 110mW's on my Coherent PowerMax 5200.

When I measure them on my LPM-1 at the 473nm ND setting, the 107mW laser is more powerful than the 110mW laser??
I am assuming that it is because of slight differences in wavelength. The 107mW laser is just as bright (visually) as my 155mW 6X blu-ray!

So the optical meter is not going to be accurate for blu-ray, because it was not calibrated for it...especially with a multiplier!
I am sure that you will find that your multiplier will vary, from laser to laser. Especially if you compare blu-ray lasers with large differences in power.

The LPM-1 seems to be pretty accurate with the wavelengths that it has been calibrated for though.

If anybody else has made similar comparisons, please post!
Jay

The 2 BluRays I have so far are similiar in power and visually look the same, using the correction factor I came up with, one of them is a few mw's over what I measured on the labmax, while the other is a few mw's under what I got on the labmax; so far 4mw's +/-.

I have another coming to me that is visually brighter than a "normal" bluray I'm told at it's given power level and the builder using filters to view it, believes it is of a higher wavelength, we are both anxious to see what I get for a reading.

I heard that the correction factor for the LPM-1 doesn't always work for 405nm, not being calibrated for that wavelength. But even if it was and then you measure a wavelength of say 407nm, the measurement then would still be inaccurate.  So I could be wrong, but I don't think it's the correction factor method that is the problem, rather the different wavelengths that look the same to us, but really are different.

The LPM-1 does seem to be pretty accurate for the wavelengths that it is calibrated for.  While I'm pleased with the LPM-1, I really don't count on it anymore, I'm only doing comparisons with it; LabMax is my meter of choice.

So far I've decided I'm probably going to just keep the LPM-1 around because I can easily put it in my pocket or something and get a quick reading being mobile.  I like to use it when I go outside with a Beam-Expander on my RPL for example and measure it's power long-range.  The LabMax though does have an internal battery pack that I can take it on the road, and it came with a carry case......but I'm keeping it strictly as a bench meter, the meter & senor are covered when not in use; handled with tender loving care.

I'll let you know how the measurement goes with the other bluray in-route.

The two blu-rays in my sig are the same PHR diodes, and the power difference is 3. Yet the more powerful one looks visually around 10 times brighter, and still the visual intensity when fluorescing things is only 3 times more.

I also agree that using a correction ratio for optical (photodiode) meters is impossible. When you look at this picture (from Sam's laser faq), you can see that with a red laser, the response varies no more than 4% in the ±10nm range, but with a 405nm laser that varies -5%+10%, as they do, the response varies as much as 25%. And I'm not even including that all photodiodes are very different.

Still waiting anxiously for the completion of the initial comarison by pseudo and then the passing of the lasers to the first on the list (daguin)