Scafir

Hey! Really not my cup of tea, but here’s a few comments:

• what are the input outputs? Are you powering 6 lasers at the same time? Why hook it up to an arduino? How are the lasers connected? What is a good representative load for your laser (probably resistive, but maybe inductive or capacitive?)
• Looking at the driving circuit, there’s something fishy about them. Having a variable Vi and static ADJ pin is not what I would have expected, nor what the datasheet suggests
• how about providing a fixed, appropriate voltage on the + terminal of your laser and have low side switching through a mosfet?
• components seem pretty basic, you could probably simulate this throught spice to get a better idea of what’s happening (you can prob do this directly in kicad). Be careful about choosing models for stuff outside the PCB like the lasers. Long cables can have significant capacitive load for example.

EDIT: I think the gist of the problem is that (1) the LM317 is powered on and off continusly, causing transients, power on delays,… (2) the adjust pin depends on the voltage on the output pin, potentially causing more resonance/weird transients. I would: stick to the suggested circuit in the datasheet of the lm317, and move the switching transistor between the lm317 and the laser.