Although "TTL" is a specific logic family, it's is sort-of shorthand for "5V logic" and the Arduino is TTL compatible.
So IF your laser has a TTL/PWM dimming input is should be as easy as [u]dimming an LED[/u].
Many (most?) laser power supplies are designed with feedback for constant-controlled light output and they are not dimmable... They will "fight you" if you try to dim them.