Driving a laser diode with a simple current mirror

[PythonGuython]

I need to drive a laser diode whose optical intensity matches a square wave input up to around 3 kHz (It needs to switch on/off very quickly as I am trying to reproduce the rolling shutter effect). It turns out driving a laser is not trivial. Best practices say that I need to be mindful of transients, over-voltage, over-current, temperature, ESD, and more - all without getting laser in my eyes. Here's the thing, I just need to get this project working for a weekend. I don't care about maintaining a precise optical intensity, or running this for long periods of time. I need a quick and dirty solution.


Let's say I need to run the LD at 125 mA, which creates a forward voltage of 6.9V. Someone tell me why I can't just put the laser diode in a current mirror if my MOSFET's are matched closely, given I manage to get my LD wired up without frying it with ESD.

[twospoons]

BJTs might be faster. And Vbe is ~0.7V vs ~1.5 VGth for the mosfet.  Also if your matching isn't great adding small emitter or source resistors can improve matters a bit.  Make sure your bjt's or mosfets are in close thermal contact, ideally in the same package, better still on the same die. Aim for the same dissipation in both devices - or the thermal transients will screw it up.  Look at using a Wilson current mirror too (see attached). The power handling gets offloaded to the upper devices, letting the lower devices do the current mirroring with lower thermal loading, more constant collector voltages.

I'd be inclined to power the LD off dc, and add a second current setting resistor off DC to set the idle current of the LD just below lasing threshold - unless the small amount of light that will result is going to be a problem for you.
Other than that - go for it. The idea seems reasonable to me.