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# Working out laser power output.

#### mike666

##### New member
Is there a way to work out the output of a laser beam using some sort of formula or does the beam have to be messured using one of those thermopile based meter thingys?

For instance, if you made a laser yourself using a diode taken out of an old DVD RW or something similar, how could you measure the beam power if you don't have a thermopile based meter thingy?

Thanks.

#### lasersbee

##### Well-known member
You can't... You can only guestimate

#### wesdaman14

##### New member
lasersbee said:
You can't... You can only guesstimate
And you can really only guesstimate, if you have another laser that is high power and you know the power of it, so u can say if its more power or less.

#### Oxymorphone

##### New member
and what if you would have taken a thermometer, paint it's bulb with black permanent marker, point your laser at it, and note how temp changes with time? then calculate LD power.

#### Jimmymcjimthejim

##### New member
That probably wouldn't work.
Different wavelengths would work differently, and I think that it would work differently depending on ambient temperature.

#### mike666

##### New member
Oh right.

I thought that maybe there was some sort of formula to work it out.
Something like...
Laser Diode rating x current running thru it + the voltage from power supply / Pi + ((square root off 354.3453) - 466) x speed of light +(3.14245 / 6833 squared) blah, blah, blah  = power output.

;D

#### Montana64

##### New member
mike666 said:
Oh right.

I thought that maybe there was some sort of formula to work it out.
Something like...
Laser Diode rating x current running thru it + the voltage from power supply / Pi + ((square root off 354.3453) - 466) x speed of light +(3.14245 / 6833 squared) blah, blah, blah  = power output.

;D
Well theres your problem! you forgot to figure in the gravitational pull of the black hole and multiply the mass and velocity and divide by infinity. : ;D

Ted

#### mike666

##### New member
My Maths was always crap :

#### lasersbee

##### Well-known member
Oxymorphone said:
and what if you would have taken a thermometer, paint it's bulb with black permanent marker, point your laser at it, and note how temp changes with time? then calculate LD power.
Sure that could work... but what temperature = what mW... you would need to get it calibrated...
With out calibration... you would still be guessing but would know which laser was more powerful.
and using it like a thermal detector... wavelength would not be a big problem..
Also... it would need to be a very sensitive thermometer...
And as "Jimmymcjimthejim" stated... you need to figure in Ambient Temperature..

Jerry

#### lasersbee

##### Well-known member
Montana64 said:
[quote author=mike666 link=1226453245/0#5 date=1226501494]Oh right.

I thought that maybe there was some sort of formula to work it out.
Something like...
Laser Diode rating x current running thru it + the voltage from power supply / Pi + ((square root off 354.3453) - 466) x speed of light +(3.14245 / 6833 squared) blah, blah, blah  = power output.

;D
Well theres your problem!  you forgot to figure in the gravitational pull of the black hole and multiply the mass and velocity and divide by infinity.   : ;D

Ted
[/quote]

;D ;D ;D... ROFL... ;D ;D ;D ;D ;D

#### Montana64

##### New member
Oxymorphone said:
and what if you would have taken a thermometer, paint it's bulb with black permanent marker, point your laser at it, and note how temp changes with time? then calculate LD power.
Not sure this would work on a glass thermometer. Focusing a "hot spot" on glass, especially painted black to absorb them maximum amt of heat, could cause the glass to fracture.

Ted

#### john_lawson

##### New member
Montana64 said:
[quote author=Oxymorphone link=1226453245/0#3 date=1226469060]and what if you would have taken a thermometer, paint it's bulb with black permanent marker, point your laser at it, and note how temp changes with time? then calculate LD power.
Not sure this would work on a glass thermometer.  Focusing a "hot spot" on glass, especially painted black to absorb them maximum amt of heat, could cause the glass to fracture.

Ted
[/quote]
only if your using gus's promethius

#### Montana64

##### New member
john_lawson said:
only if your using gus's promethius
promethius? thats more like a plasma torch! ;D ;D

#### ElektroFreak

##### New member
One way that I have found to 'guesstimate' laser power is to observe its destructiveness on certain objects.

For Example: (These figures are without focusing, just a collimated beam)

At 20mW or less you'll get no destructive power whatsoever.

At 50mW you'll start to be able to burn/cut black electrical tape and other thin black plastic sheets.

Around 75mW you'll start to be able to feel it sting your skin and pop black balloons.

~100mW will light matches (particularly black ones.)

~150mW will light any match, melt thicker black plastic.

~200mW will melt through 1mm thick black plastic.

~250mW will do all of the above plus light fireworks and cigarettes.

~300mW will burn through cardboard and some thick plastics.

This is definitely NOT a completely accurate way to tell, due to the fact that all lasers have their own characteristics that can either add to or detract from their ability to burn.

Using this chart will allow you to put your laser in a power class, but as far as an exact measurement, you'll need a power meter.