How to calculate laser power on photodiode?

Hallo everyone,

I am completely lost calculating the power of a laser diode and hope, that someone could help me.

Here is my setup:

OSRAM PL 520 (Type B1 = 50mW) Green Laser Diode
OSRAM SFH 203 Photodiode

The laser diode projects a laser beam on a photodiode with a distance of around 1,5m from laser diode to photodiode.

How can I calculate the current output of the photodiode based on the data provided in the datasheets?

Thanks to everyone for the help!
PL 520_EN.pdf (856.3 KB)
Osram - SFH 203.pdf (480.0 KB)

Measure the current instead. Easier and vastly more accurate.

I did, its around 26µA.

But isn't there a way to calculate the current instead of measuring it?

Not with any useful accuracy. If you are happy with "order of magnitude" estimates, possibly.

What is the real question?

I want to calculate the power of the laser beam in W at my surface and want to use that data for further measurements in a more scientific way when I use different sensors + transimpedance amplifier. Of course I can test out different resistors in the TIA circuit, but my supervisor prefers a more theoretical approach.

My thoughts were:

  1. Use the SFH 203 Photodiode, measure the current with a known resistor -> 26µA for a 5k resistor.
  2. Calculate the laser power
  3. Use a different photodiode, calculate the value of the feedback resistor in the TIA circuit to get a specific current with the previous calculated laser power. For that, use spectral sensitivity of the photodiode.

I am stuck at #2.

Thanks for your help!

If you know the quantum yield of the photodiode, the short-circuit or reverse bias current will report the number of photons/second absorbed by the diode itself. (The current through a 5K resistor will not).

To work out the laser output power, you also need the area of the photodiode, the beam area and the wavelength distribution.

The problem is that semiconductor devices are extremely difficult to manufacture to specifications, and are characterized by the manufacturer either individually (at your expense) or statistically, for the device data sheet. So the data sheet will tell you only how the typical photodiode performs.

Buy a photodiode-based laser power meter from a reputable manufacturer, where they do all the hard calibration work for you. Or, calibrate the photodiode yourself using a laser of known output power.

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