Powering an IR + RED laser with an Arduino
Usually, a photodiode (PD) is used to
monitor the power. The signal from the
PD will be fed back to the current source
to maintain the output power from LD at a
constant level.
Depending on the application type, LD
driving current source should be selected,
from the viewpoints of maximum current,
maximum voltage, and with or without
modulation and APC function.
REF
Read about it.
CC regulator designs are easily found. Use the PD current to detect laser power using the PD current converted to voltage in a load resistor of your choice with an Op AMp and FET with a stable reference voltage.
The reason for this is although the forward voltage rises with current, it falls with higher temps quickly so overvoltage and thus overcurrent can more easily damage the LASER diode than an LED due to additional nonlinear lasing effects and component tolerances with thermal cooling required.