The TFP Interferometers require a low reference laser intensity (about 1-2 mW) for stabilization purposes. The Brewster Attenuator is a convenient way to provide this intensity. 

The device is placed near the laser source and when oriented parallel to the polarization of the laser will transmit nearly 100% of the laser intensity. A slight rotation of the head allows a small amount of light to couple into an optical fiber which is directly attached to the TFP to provide the reference intensity. 

The fiber coupling accepts FC/PC fiber optics patch cables and includes a suitable patch fiber cord.