If you need a low accuracy qualitative power meter, for either standard or laser light, or if you need to sample a light source for it’s speed/frequency, you can do so using a $5 electronic component called a phototransistor. Basically a phototransistor acts in a similar manner as a standard transistor, but instead of allowing current to flow from collector to emitter based on an input signal, the phototransistor does so when light enters it’s diode. This means that as more light is collected by the diode, more current, or more voltage (depending on the configuration) will flow from the base to the emitter.
I needed a high speed measurement of a laser which was scanning, so I bought an NTE3037 and connected an oscilloscope positive lead to the emitter, and negative lead to the base. If used for simple power measurements you can connect a multimeter to these leads instead of a scope. Using this setup I could get high frequency measurements of my system down to 2uS. This is quite fast for a $5 investment. Here’s an example of a scope read using this assembly.
Without amplification, the output from this setup is in the millivolt range, but most multimeters can measure these smaller signals, so for many users no amplification is needed. If amplification is needed you can hook up a voltage source to the base, and allow the transistor type function to drive the larger signal from the base to the collector as more light enters the collection diode.
I was quite surprised how well this worked using my basic setup. I hope you’ll find it helpful as well!
-Austin