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cheap Chinese ebay LPMs vs Coherent LaserCheck vs LaserBee

runcyclexcski

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I have a team-shared Coherent Field Mate PM10 (which is great, but is not always available), and a personal LaserBee recommended here . The latter was $200 and worked for 488, 532 and 633 at 200 mW, but could not probe a 730nm beam at 16 mW. The 730 nm beam is what I am after now. The measurements are relative, i.e. I need to know the power drop after bouncing off ~10 mirrors, preferentially having enough accuracy to detect 1-5% drop downstream from every mirror (i.e. <1 mW resolution). Something between $200 and $2K which would not require holding the probe for 1 min for the reading to stabilize would be good (PM10 takes ~<1 sec for this beam).

There is the Coherent LaserCheck for about $500 which claims an 8% accuracy (barely) and <1 sec response time.

Then I just found this chinese unit on ebay for $150 claiming 3% and 1 mW resolution. Has anyone tried it? It does not look like I can post links, but there is only one hit on ebay under " Mini Laser Power Meter Pocket 390~1024nm "

BTW, if anyone has a used working LaerCheck unit they need to unload, let me know!

Cheers!
 



Cyparagon

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Can you tell us more about your project please? Your issue may be entirely unrelated to power meters.
 

runcyclexcski

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I need to measure the power of a 730 nm TEM00 laser beam that reaches a target after bouncing off 10 consecutive mirrors. Previously the mirrors had a rating of 90% reflectivity; I have replaced them with ones that have a rating of 99%. I want to verify this, and, if not the case, identify another source of power loss (there are other optics in the path where the power can be lost, 2 beam expanders and 1 beam splitter, but these are more expensive to replace).
 

runcyclexcski

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Are these front surface? (FSMs)

Yes -- Thorlabs EE02 coating. Previous ones were protected silver (1/2 the price)

I suppose I could rig a 1/2" CCD or CMOS sensor together (have a few lying around) and integrate the pixels to get relative measurements upstream/downstream of the mirrors. I could put in an NDF to avoid saturation. But then I am not sure how homogeneous pixels are in cheap CCDs. Smartphone camera sensors are useless. So I was wondering if the chinese item is basically that (would save me time). I am willing to DIY for a weekend to save $500, but not for $100...
 
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hakzaw1

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dont double post please-- go back and do edit-and combine 5 and 6.
You CAN double ('legally') if the older post is very old and you have new info to add. (update)
in that case if you combine those following the thread will not know of the additions --so DO double post in that case. TY
 

gazer101

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runcyclexcski

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This is what I was hoping for (that someone has bought this unit and could give feedback). I am now leaning towards getting a basic monochrome USB CMOS cam from Edmund (e.g. their 14-857, abt $300), put in NDF, and profile the beam that way. Quantum yield of the sensor is cited at 30% at 730 nm, and is still useful down to 800 nm -- not bad at all (unlike smartphone cams). This cam can be re-purposed for other things (web cam etc). Too bad sensors on these basic cams are really small :(. The one I mentioned is only ~4x3 mm, pixel size 5 micron. Oh well.
 

gazer101

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This is what I was hoping for (that someone has bought this unit and could give feedback). I am now leaning towards getting a basic monochrome USB CMOS cam from Edmund (e.g. their 14-857, abt $300), put in NDF, and profile the beam that way. Quantum yield of the sensor is cited at 30% at 730 nm, and is still useful down to 800 nm -- not bad at all (unlike smartphone cams). This cam can be re-purposed for other things (web cam etc). Too bad sensors on these basic cams are really small :(. The one I mentioned is only ~4x3 mm, pixel size 5 micron. Oh well.
Maybe see this thread: https://laserpointerforums.com/threads/review-on-laserpointerstores-pocket-lpm.103099/
 

runcyclexcski

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Many thanks! This looks exactly like the box I saw on ebay :) I even started thinking to get a used body of a mirror-less camera; but realized that they may not even power up w/o the lens attached.
 

Cyparagon

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I need to measure the power of a 730 nm TEM00 laser beam that reaches a target after bouncing off 10 consecutive mirrors.

That's not the whole project, is it? That would be stupid and pointless on its own. WHY do you need this measurement?
 

runcyclexcski

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The target is a microscope slide, with fluorescent molecules on it; the laser makes them glow; I image them with a camera. 730 nm is a somewhat exotic line. The power of available good-quality laser sources (e.g. Coherent) is limited at 30 mW at TEM00, and I get about 20 mW out of the fiber. 20mW is barely enough for making the molecules glow (at 760 nm). Thus, I need to make sure I get every mW I can to the target, and do not lose 1/2 of it on the way just to mirror coatings.

I think what I've learned is that low-cost LPMs cannot be used to measure the effects of individual optics (1-2 mW power loss), but can detect the cumulative drop of 5-10 mirrors in series. So, as a sanity-check, they are OK, but are not sensitive enough to identify a single problematic source of power loss. Also, for sensitive LPMs, I learned that one needs to hold the probe via a temperature-insulated holder, and make sure it's not near trivial sources of heat, like a beam chopper (which was warm to the touch, and affected readings when the probe was 1/2 inch away). So, I am not sure how integrated units like the Coherent LaserCheck and the chinese ebay unit deal with thermal issues.
 
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Buffo

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I've had a Coherent Lasercheck for quite a while. It is reasonably accurate, although you do need to be sure you set the wavelength before you measure as the sensor has a complicated calibration curve that changes based on wavelength.

If you buy a Lasercheck wand, be sure to crack it open as soon as you receive it and cut off the bleed resistor that they have soldered across the battery. If you don't do this the battery will fail in about 3 years (even if you never use it). And once the battery dies you lose the factory calibration, so even if you buy a new battery and solder it in place you will still need to send the whole thing back to Coherent for calibration.

The resistor is nothing more than a planned obsolescence device; it does nothing to improve the operation of the meter. It's only purpose is to slowly kill the battery. (Bastards)

Adam
 

runcyclexcski

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If you buy a Lasercheck wand, be sure to crack it open as soon as you receive it and cut off the bleed resistor that they have soldered across the battery. If you don't do this the battery will fail in about 3 years (even if you never use it). And once the battery dies you lose the factory calibration, so even if you buy a new battery and solder it in place you will still need to send the whole thing back to Coherent for calibration.
Many thanks, Adam! Exactly the type of unique DIY insight I love this forum for :)

May I ask if you found any thermal issues with the unit? I suppose, they placed the sensor far away from the battery, so, probably, it's not too bad of an issue. If I had to build something similar, I would probably use that arrangement, too (unlike the compact LaserPointerSource box)
 

Buffo

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I didn't experience any thermal issues, no. Bear in mind it is only rated up to 1 watt though. Mostly I use it for the low-end stuff. I have two other power meters, one that tops out at 6.5 watts and one that goes to 15 watts, so most of the time the Lasercheck is seeing Class 3B stuff only.

But it's a solid device that is surprisingly accurate and consistent. Just make sure you clip that damned resistor off as soon as you get it. Otherwise you'll have a dead unit in about 3 years, even if it's been sitting on a shelf the entire time...

Adam
 

runcyclexcski

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I see that it might be easier to probe higher power lasers (more heat?). My application deals with lower powers (up to 200 mW), and is more about the stability and resolution (1-3%). I believe, all things equal, higher accuracy and sensitivity would be better to have than being able to deal with high powers: if the power is high, I use a small reflective NDF of OD 1 and 2 to cut the power 10x or 100x, and then back-multiply the number.
 




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