This is a Truglo Laser known as the Micro-Tac, model TG7630G.
The Truglo Micro Tac laser is a next generation" high-efficiency superconductor laser diode. It features a powerful 520nm green laser and easy ambidextrous push-button activation for left and right handed users.
Features:
Recessed on/off buttons
Automatic shut off after 5 minutes
Mounts to Picatinny or Weaver-style rails