# 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.