Schottky diode part of a laser power supply enable circuit
Q2 also pulls down the left side input voltage, which sets the laser current, through the right-facing 1N4148 diode. The Schottky diode keeps these two functions separate.

Without the Schottky, a low voltage output from A1 could pull the current control input low, limiting the input voltage to some value that depends on the laser's forward voltage. There would also be a positive feedback path which could lead to oscillation.