Measuring the timing of light pulses

This page describes a cheap and simple device that can be attached to an oscilloscope (or patch rig, etc) to record the timing of light pulses. It won't measure quantitative mW accurately, but it can measure the timing of pulses really accurately.

It uses a BPW34 photodiode (~$2 each, widely available) connected directly to a BNC plug, with a 1KOhm resistor across the pins.

Soldering photos here:

You can also enclose it in a tasty case :) (TinkerCAD designs here)

To use, attach the device to an oscilloscope with a BNC cable, and shine your patch cord at the BPW34 photodiode.

Configure the ossciloscope range and scale to show your pulse. Here, we are capturing 1ms pulses from an Arduino in the blue channel, and recording light power from the BPW34 on the yellow channel. Don't worry about the amplitude - that's not accurate, but the timing of the shape is!

From this, we learned that ThorLabs LEDs can produce 1ms pulses with high fidelity, but they have ~50us delay. They also can't produce 0.1ms pulses accurately (or we can't measure them but either way use caution and validate if trying to make trains with sub-ms pulse widths!).