Coherent LaserCheck LPM with 445nm.

leukoplast · Aug 19, 2010

I have had a Coherent LaserCheck for a few years now. It works great with greens and reds. But it is absolutely abysmal with 405nm, with 30% or more inaccuracy.

I am going to be starting my first 445nm build tomorrow if the parts show up, and I am wondering how accurate my LPM is going to be with this wavelength.

Anybody who owns a Coherent LC and some other quality LPM (as well as a 445nm laser), could you possibly run a few tests to see your LC is accurate or not? I am hoping it should be fairly accurate since the Coherent LC only goes down to 400nm, which is probably why is sucks so much with 405nm. But seeing as 445 is a good 45nm above the lowest setting, I hope it will read correctly. But I would like to know for sure.

I really appreciate any help with this!

lasersbee · Aug 19, 2010

I just did a quick check at 500mW of 445nm...
Our Newport 1825C with Thermopile head meaures 500mW
and the LaserCheck set at 445nm.. measures 329mW to 315mW
depending on the heat accumulated on the Optical Sensor...

Still sucks... IMO

Jerry

ShaOwned · Aug 19, 2010

I've also noticed significant differences between a Coherent Fieldmaster and a Newport.

ff-racer · Aug 19, 2010

leukoplast

I have this LPM. I have never had a problem with this meter until we begun to reach it's limit of 1 watt. (1000mw)
With my latest 445nm build at 900mw + the readings are not reliable IMO.
I have even gotten reading such as 010 that I assume is a rollover.

Doug

leukoplast · Aug 19, 2010

Thank you for the responses! I guess the CLC is pretty inaccurate with 445nm too. laserbee's readings with the LC were much worse than I would have hoped.

@ff-racer - I plan on taking readings 400mW and below with mine. For my first build I want to put it in the range of 150mW or less.

@lasersbee - Sorry to bother you with this again, and not even sure if it makes difference or not. But could you try taking readings with a lower output? Like 150mW?

bootleg2go · Aug 19, 2010

ShaOwned said:
I've also noticed significant differences between a Coherent Fieldmaster and a Newport.

If both meters have thermal heads and are measuring beams within their wavelength and power range, they should be within a couple of percent of each other provided they are also both within 1 year of their last NIST calibration as shown by the date on the NIST calibration label on the meter.
If the calibration is expired on one or both of them all bets are off and the longer since the NIST calibration, the more they will drift and more inaccurate they will be.

lasersbee · Aug 19, 2010

leukoplast said:
@lasersbee - Sorry to bother you with this again, and not even sure if it makes difference or not. But could you try taking readings with a lower output? Like 150mW?

I'll try that tomorrow once I back in the Shop after a day
of Service calls..

bootleg2go said:
If both meters have thermal heads and are measuring beams within their wavelength and power range, they should be within a couple of percent of each other provided they are also both within 1 year of their last NIST calibration as shown by the date on the NIST calibration label on the meter.
If the calibration is expired on one or both of them all bets are off and the longer since the NIST calibration, the more they will drift and more inaccurate they will be.

You'd be surprised at how little a good LPM actually drifts..
We have 4 different LPMs by 3 different manufacturers besides
the LaserBees that we use as a reference and we constantly
compare one to the other to make sure there is no drift...

Jerry

leukoplast · Aug 20, 2010

Here is a little update with my own findings (which isn't much). I got my parts and am testing the laser. The 445nm diode is connected using a rkcstr driver set to it's max output (440mA).

When I tested it, the Lasercheck read 472mW set at 445nm. I tested it a second time, and read 502mW. Third time was back to 472mW. Given that the diode is getting 440mA, obviously these readings are probably wrong, unless I managed to get a incredibly efficient diode. But at least it's not reading horribly low like Laserbee's was.

Although it's possible my diode is a higher wavelength than 445, maybe 450. Because I know with my 405nm lasers, if I set the LPM to 400nm (as low as it gets) it gave a higher mW rating than when it was set at 405nm.

Also this thing is BLUE. To me it looks just about as blue as a 473nm laser. So I probably got a higher wavelength diode (yay!)

GMH · Aug 21, 2010

I got a max reading of 550mw on a lasercheck for 445 running 950ma. I think mines off by like 40-50%. Im savin for a better LPM.

Cyparagon · Sep 17, 2010

I got my 445 diodes today. I've got a thermal head (Gentec) and a lasercheck. The lasercheck is off by quite a bit... up to 100 percent difference

HOWEVER, I've found through trial and error that if I set the wavelength setting to 415 instead of 445, I get a very accurate measurement throughout the whole span of 40mW to 900mW. Less than 2% difference from thermal readings.

Benm · Sep 17, 2010

I think this is a firmware error in the lasercheck, and its somewhat understandable. I'm sure coherent will have checked the conversion factors for lasers that were commonly available at the time of design, but those didnt include 445, and probably not even 405.

I can imagine they took the sensitivy data from the sensor manufacturer and put that in a conversion table, without checking it across the entire spectrum.

Its a limtation of optical sensors really, and they become even worse for dpss systems that leak 808 or 1064 along with the 532 you are trying to measure. A thermal meter will 'count' the infrared in such cases, but it will do so properly. An optical sensor might under or over estimate total power depening on what wavelength you set it for.

LSRFAQ · Sep 17, 2010

Having used one for years, 1, what serial number do you have, and did you set the wavelength? I've bounced mine off NIST tracable meters for years with no glaring errors at wavelengths down to 450.

Hecad is at 442, and I assure you coherent knew about HeCads. I'ved used mine at 175 mW of Hecad, and it was just fine against a thermal meter.

Steve

Cyparagon · Sep 18, 2010

I don't see any serial number on the device or with the documentation that came with it, but the date of manufacture was sept. 10, 2007.

And yes, I set the wavelength.

ludwigfan · Oct 14, 2010

Mine's pretty accurate. Maybe some of you forgot to set the wavelength or have low batteries in the LC. Or perhaps an older model.

At first I got a reading of 300mW with my 1W 445nm, but quickly realized I still had it set to 532nm! Once I set it to 445 it seems to be fine. Granted I do not have another LPM to check it against but it certainly isn't off by 50-100%!

lasersbee · Oct 14, 2010

ludwigfan said:
Mine's pretty accurate. Maybe some of you forgot to set the wavelength or have low batteries in the LC. Or perhaps an older model.

At first I got a reading of 300mW with my 1W 445nm, but quickly realized I still had it set to 532nm! Once I set it to 445 it seems to be fine. Granted I do not have another LPM to check it against but it certainly isn't off by 50-100%!

All the members above had set the wavelength to 445 and even tested
other settings...

If you don't have calibrated Thermal Laser Power meter to compare
the LC readings to... your stated "accuracy" comes into question...
The human eye is a bad judge of accurate Laser power... else we
wouldn't need LPMs...

Jerry

ludwigfan · Oct 14, 2010

lasersbee said:
All the members above had set the wavelength to 445 and even tested
other settings...

If you don't have calibrated Thermal Laser Power meter to compare
the LC readings to... your stated "accuracy" comes into question...
The human eye is a bad judge of accurate Laser power... else we
wouldn't need LPMs...

Jerry

I may not have one but I believe Yobresal's stated 1-1.2W claim. He built this particular laser. My Lasercheck measures it at 939mW, I measured the current at 860mA. Batteries might not be at full charge though, so I'll be testing again once I charge them all the way. Just got this laser 2 days ago.

I'm not saying the LC is accurate compared to a Thermopile LPM, just that mine does not seem to be off by 50-100% as some in this thread's LC are.

Coherent LaserCheck LPM with 445nm.

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