AR coated Fabry-Perot Laser 

Gain Chips are modified Fabry-Perot Laser Diodes with an excellent AR coated output facet. While not self-lasing they are intended to be operated in External Cavity Diode Laser setups (ECDL), such as in Littman or Littrow configuration. With external feedback they reveal narrow single frequency operation in combination with superior tuning capabilities.