HP 81524A InGaAs Optical head
The HP 81524A is an optical head that connects to the 81533A or 81533B which is a plug-in module that fits the 8153A and 8163 and 8166 Agilent/HP series mainframe. The 81524A optical head is made of a 5mm InGaAs sensor element and covers the range of 800-1650 nm wavelengths in a range of +3 to -90dBm. Various connector interfaces are available for that head.
Click the PDF Specification for further information.