  We present a cryogenic configurable slit unit (CSU) for a multi object
infrared spectrograph with an effective field of view of 9.1 arcmin x 9.1
arcmin that was completely conceived and designed in the laboratory at TIFR.
Several components of the CSU including the controller for the commercially
procured piezo-walkers, controlled loop position sensing mechanism using
digital slide callipers and a cryogenic test facility for the assembled
prototype were also developed in-house. The principle of the CSU involves
division of the field of view of the spectrometer into contiguous and parallel
spatial bands, each one associated with two opposite sliding metal bars that
can be positioned to create a slit needed to make spectroscopic observations of
one astronomical object. A three-slit prototype of the newly designed CSU was
built and tested extensively at ambient and cryogenic temperatures. The
performance of the CSU was found to be as per specifications.
