I'm using a Raspberry PI as my driver for the laser's PWM input. This allows me to control the total power in the beam. Ds triggers my oscilloscope while Df my photo detector is connected to the second channel.
I thought this would be good enough to get started if it were not for some lazy characteristics of the laser itself.
First problem is the delay in the laser. Once the PWM goes high, as seen by the yellow trace, it takes about 3.8us before the beam comes out and gets detected. I tested this by placing Df at the laser.
Replacing the laser with an off the shelve LED shows a significantly faster response.
Now the delay in the laser would not be a problem so long as it were consistent... of course it's not! Looking closely at the jitter on Df. again with the detector hard against the laser. All the fuzzy stuff is the +-95ns error between when I tell the laser to turn on and it actually does.
Given the distance I'm working at is about 18 metres (60ns ToF) the jitter we are getting is a killer.
In the second setup we'll see how a beamsplitter and second detector is used to exclude this error from the system.
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