I'm constantly amazed at the level of technology we have available at our fingertips.

After watching an Alpha Phoenix video on building a 2 billion frame per second camera I realised I'd be able to measure the speed of light with just a few extra parts - a sensor and a laser.

The key part is the fast laser driver. It has a rise time of 4ns, and results in a very sharp rise time on the sensor.

The sensor is a SiPM - Silicon Photo Multiplier. Like a photomultiplier tube, but solid state, less fragile and easier to drive.

A bench PSU provides 15V for the laser and 26v bias for the SiPM. A signal generator creates 10ns pulses at 100Hz for the laser.

The mirror is setup 0.5m away (1m total distance) and the pulse is stored as a reference waveform (brown).

The mirror is moved to 1.5m away (3m total distance) and the pulse captured.

The delta distance is 2m. The delta time is 6.88ns.

So the speed of light is calculated:

2m / 6.88ns = 290,700,000 m/s