The NTE3102 Interrupter Module is a single channel switch consisting of a gallium arsenide infrared emitting diode and an NPN silicon photo transistor mounted in a polycarbonate housing. The package is designed to optimize the mechanical resolution, coupling efficiency, ambient light rejection, cost, and reliability. Operating on the principle that objects opaque to infrared will interrupt the transmission of light between an infrared emitting diode and a photo sensor switching the output from an “ON” into an “OFF” state.
 
Full spec sheet:
https://www.nteinc.com/specs/3100to3199/pdf/nte3102.pdf