Old 02-23-2010, 06:20 PM #1
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Default Power Estimation

Heya, folks--
I'm trying to figure out an as-reliable-as-possible method for estimating the milli-wattage of a laser without a meter. I eventually intend to build one (though from what I've been reading, homebuilt power meters tend to be quite inaccurate), but in the meantime, I wonder if there are perhaps some rules of thumb or benchmarks that could give me at least a very general indication of my laser's power output.

Has anyone developed a metric based on a laser's ability to burn different materials, for instance? Or an apparent brightness comparison, as a function of its wavelength?


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Old 02-23-2010, 07:22 PM #2
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Default Re: Power Estimation

Quote:
Originally Posted by Dvorhagen View Post
Heya, folks--
I'm trying to figure out an as-reliable-as-possible method for estimating the milli-wattage of a laser without a meter. I eventually intend to build one (though from what I've been reading, homebuilt power meters tend to be quite inaccurate), but in the meantime, I wonder if there are perhaps some rules of thumb or benchmarks that could give me at least a very general indication of my laser's power output.

Has anyone developed a metric based on a laser's ability to burn different materials, for instance? Or an apparent brightness comparison, as a function of its wavelength?
You can NOT measure a laser's power accurately with anything other than a calibrated LPM.

You can estimate within ~10% using the current your little diode is run at, but efficiency from diode to diode varies. The lens is also a contributing factor to total output power.

If you want a cheap power meter, look for Lasersbee's sales threads (in the pro shop section). He is selling 200mW meters for ~$50.
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Old 02-23-2010, 07:33 PM #3
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Default Re: Power Estimation

Actually, I didn't think you'd be able to get as accurate as 10%, just doing the math. I figured the driver circuit and LD would be too lossy to get a good estimation that way. I'm going to look into building/buying a laser meter once my bank account recovers from this latest laser-splurge
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Old 02-23-2010, 07:48 PM #4
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Default Re: Power Estimation

Dvorhagen,
I can give you (very) ballpark figures according to your lasers burning abilities.
What wavelength is your diode?
650nm?
532nm?
405nm?
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Old 02-23-2010, 07:56 PM #5
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Default Re: Power Estimation

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Originally Posted by Dvorhagen View Post
Actually, I didn't think you'd be able to get as accurate as 10%, just doing the math. I figured the driver circuit and LD would be too lossy to get a good estimation that way. I'm going to look into building/buying a laser meter once my bank account recovers from this latest laser-splurge
That's if you're calculating current draw from batteries.
If you calculate current across the diode, you can get a much more accurate guesstimate.

Compare your diode to this:
http://hacylon.case.edu/laser/diode_blu_roundup.PNG

~110mW at 120mA with acrylic lens is typical for a PHR.

From your signature, I am assuming your diode is a PHR driven at 125mA.
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Old 02-28-2010, 08:05 AM #6
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Default Re: Power Estimation

Is it safe to take a mA reading across the cap/diode (which I have very closely connected)? I notice the diode dims when I try, and I'm afraid of accidentally shorting the cap through the LD...
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Old 02-28-2010, 04:48 PM #7
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Default Re: Power Estimation

NO..... You CAN NOT take Current readings ACROSS the diode...

What you have done is create a high amperage shunt/short across your
LD that could possibly damage your Driver or even the LD with a surge as
you remove that meter shunt...

Take your reading in series with your batteries... The LD driver only uses
a minimal amount of current and you will still get good readings of the
current the LD is driven to...

Jerry
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Old 02-28-2010, 05:11 PM #8
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Default Re: Power Estimation

Multimeter 101........

Gee I wonder how many amps this here outlet on my wall is putting out??

So hmm, I will set my meter as high as it can go and stick these here probes in that there outlet...

Wow smoke just came out of my meter and the breaker just tripped, what did I do wrong???

To measure current, you MUST connect in a series with your load, NOT parallel.
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Old 02-28-2010, 06:12 PM #9
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Default Re: Power Estimation

Thanks for the advice -- I guess I'm lucky I didn't kill my diode!
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Old 02-28-2010, 06:47 PM #10
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Default Re: Power Estimation

I just got a PM from a member, so here is the basic hook up.

It is highly recommended to use a test load rather than your diode, but this should get the point across.

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