Diodes are current hungry and as they heat up their internal resistance is lowered causing them to want to draw more current. Don't attempt to connect the diode directly to a fixed voltage source like a battery. You must use a "constant current" power source like a current limiting driver or variable current power supply with the current limited to no more than 1.8A or you diode will suffer thermal runaway and die. For more info on the reason for a constant current driver see this thread.
Testing Osram 1.6W PLTB450B 450nm Laser Diode
Power test done with a G-2 glass lens
Not recommended to go past 1.8A. Pictures are for testing t