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# laser power conversion needed...

#### dtvonly

##### New member
Hi. I am using a light meter with a sensor head that can detect from 200 to 1000nm wavelength. However, the meter has a unit of mW/cm2. The laser that I am trying to measure is around 5mW with the beam diameter of a bout 3/4 to 1mm. Do I just multiply the display power (mW/cm2) with the cross sectional area of the laser beam? This is strange because the reading from the meter is "nearly" correct but in mW/cm2; i.e. meter read 4.7mW/cm2. Please advice. Thanks.

#### ARG

##### Well-known member
Do I just multiply the display power (mW/cm2) with the cross sectional area of the laser beam?

Yup, that sounds right.

#### dtvonly

##### New member
Yup, that sounds right.

The "gold" unit I am using has a known power of 3.5mW. The meter I am using reads around 3.47mW/cm2. If I multiply 3.47mW/cm2 by the diameter of the laser beam (1mm = 0.1cm = 0.01cm2), the new/converted laser reading would be 3.47 * .01 = .0347mW.

#### ARG

##### Well-known member
The math looks correct. I'm going to take a guess that your reading is off? Have you tried expanding the beam on the sensor?

What meter are you using? Most that come with a power density feature can also do regular power measurements.

#### dtvonly

##### New member
The math looks correct. I'm going to take a guess that your reading is off? Have you tried expanding the beam on the sensor?

What meter are you using? Most that come with a power density feature can also do regular power measurements.

I am using the ILT 1400-A with the SED (SEL) 033 silicon detector (head). The laser beam is fixed. Please advise. Thank you.

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#### Cyparagon

##### Well-known member
Your device is meant for lighting intensity, and isn't directly translatable to total power. You're going to need the sensor area, the laser's wavelenth, and this table. What does the meter read with the known laser?

Be aware the sensor is only rated for 11mW max at 980nm, and 6mW max at 650nm.

#### dtvonly

##### New member
Your device is meant for lighting intensity, and isn't directly translatable to total power. You're going to need the sensor area, the laser's wavelenth, and this table. What does the meter read with the known laser?

Be aware the sensor is only rated for 11mW max at 980nm, and 6mW max at 650nm.

Hi. My laser specs: 635nm at desired power of 5mW. As stated previously, when I shine my (known gold) laser at the sensor head, the ILT-1400-a reads 3.47mW/cm2.