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About Average and peak laser measurements

yobresal

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A lot of time on this forum I see people mistakenly posting a peak output for their laser when indeed that is more likely to be the average output. Let me explain.
Many of the cheap power meters we all use have a little thermophile sensor. This sensor take a little bit of time in order to get the lasers reading accurate. You will notice with the more expensive meters the laser output is read out almost immediately while with these meters is appears that the laser take 20 or so seconds to reach full power. This is not reflecting the lasers actual output while the meter climbs. In actuality the laser is most likely already at the peak measurement the entire time. See after you measure the laser and shut it off how the output steadily climbs down. This does not mean that your laser is slowly powering off. Get it? My suggestion is for you to measure your laser and once the peak power is reached see if it maintains that power. If it does you can safely say that your laser has an average output around there. /


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Bluefan

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A smooth exponentially curve like that is a dead giveaway that the lpm used has a slower risetime. Fluctuations in power on a short timescale won't be picked up but they're fine for average power measurments and monitoring long term laser behaviour. You get what you pay for, and not everybody needs a high performance lpm.
 

lasersbee

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A lot of time on this forum I see people mistakenly posting a peak output for their laser when indeed that is more likely to be the average output. Let me explain.
Many of the cheap power meters we all use have a little thermophile sensor. This sensor take a little bit of time in order to get the lasers reading accurate. You will notice with the more expensive meters the laser output is read out almost immediately while with these meters is appears that the laser take 20 or so seconds to reach full power. This is not reflecting the lasers actual output while the meter climbs. In actuality the laser is most likely already at the peak measurement the entire time. See after you measure the laser and shut it off how the output steadily climbs down. This does not mean that your laser is slowly powering off. Get it? My suggestion is for you to measure your laser and once the peak power is reached see if it maintains that power. If it does you can safely say that your laser has an average output around there. /


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I see a run time of about 25 seconds... The User Instructions state
a stable response time of 40-50 seconds for your ( I assume) LaserBee
2.5W USB LPM...(not sue of which LaserBee you are using now..;))

I can also see that the last reading was not zeroed...(again assuming
you are using the LB-USB).

If you had turned off your laser at 10 seconds you would only get
a reading of 608mW peak... even more inaccurate since the Sensor
has not yet been heated enough by the Laser to reach equilibrium.

A peak reading does not necessarily happen when a laser is
first turned on... It may happen (as in DPSS Lasers) a while
after they are turned on.

I agree that the budget LPMs will give you a more average reading
than a faster response LPM.


Jerry
 
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yobresal

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Yes this was a laserbee 2.5. I also have another laserbee with faster response time but it maxes out at 1050mW. I love them both. This one for its easy data logging and that one for its is of use at the workbench.
Yeah I wasn't trying to get an accurate reading with this screenshot. I just wanted a picture to show the exponential rising and falling curve to demonstrate my point.
 
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What I tend to do sometimes is just shine the laser on my LPM before I even start it.
 

DTR

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You could use a different laser to "prime the pump" so to say and then switch over to the laser you want to test. I have not had to deal with that myself as my Laserbee II is pretty quick and my Ophir head is almost instant.:beer:
 

Arayan

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Not only the LPMs, but many measurement tools may have similar problems. The important thing is to measure different lasers in the same way, as if there is some kind of absolute error, it will be present in all measurements and then you can always compare the different powers.
 

Ablaze

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Not only the LPMs, but many measurement tools may have similar problems. The important thing is to measure different lasers in the same way, as if there is some kind of absolute error, it will be present in all measurements and then you can always compare the different powers.
Only the different powers that you personally measure. Your readings would mean nothing when compared to, say, your customer's readings when they receive the laser.
 

lasersbee

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Only the different powers that you personally measure. Your readings would mean nothing when compared to, say, your customer's readings when they receive the laser.
If the LPMs that are being used by the Seller and Buyer are
calibrated and used in the same conditions there is no reason
for the two reading to be very different..


Jerry
 

Arayan

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Only the different powers that you personally measure. Your readings would mean nothing when compared to, say, your customer's readings when they receive the laser.
I disagree, all you need is a single measurement made by the seller to a bought laser, to establish a coefficient of difference and subsequently apply it to all other lasers!
 

rhd

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What I tend to do sometimes is just shine the laser on my LPM before I even start it.
You could use a different laser to "prime the pump" so to say and then switch over to the laser you want to test. I have not had to deal with that myself as my Laserbee II is pretty quick and my Ophir head is almost instant.:beer:
Jerry / Yob / Others - can you comment on whether this approach is *ok* ?

It seems logical in my mind, and it would make sense to me as a decent approach, as long as leave the laser you're actually trying to measure on the sensor for long enough to establish that you're not just reading residual power from the previous beam.

That said, I would feel icky using this approach with my lasers, unless there was some consensus that it was okay/honest/accurate.
 

lasersbee

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I still can't see any need to not wait for the readings to stabilize
from a zero start or any problems doing so... Maybe I'm missing
something...:thinking:

If someone is in a big hurry to get a reading I would suggest a
faster response time LPM like a LaserBee IX or LaserBee II or
any quality LPM that uses a non modified OPHIR head... :beer:


Jerry
 

rhd

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I still can't see any need to not wait for the readings to stabilize
from a zero start or any problems doing so... Maybe I'm missing
something...:thinking:

If someone is in a big hurry to get a reading I would suggest a
faster response time LPM like a LaserBee IX or LaserBee II or
any quality LPM that uses a non modified OPHIR head... :beer:
The reason is that you might have a laser with a peak that you want to measure, that occurs in the first 45 seconds.

For example, my "Zero DC" build can really only sustain about a 30 second run time. Luckily, I have an Ophir. But if I was trying to capture the peak power on my LaserBee, I couldn't.
 
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ok i dont own a LPM btw

but this a question more towards jerry say i run a 1 minute test right? part of that is the warming up. so how much could that affect the average displayed?
 

Jaseth

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This is why I love the Kenometer Pro. You can just set a minimum power it has to reach before it begins graphing. Combined with the quick response time, this makes the interval between the graphing limit and the first local maximum of the graph an almost negligible difference to the average.
 
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