IRCS grism system efficiency
Grism observations shortward of 2.5Ám are made by selecting different orders of the light reflected from a single grism.
Observations in the thermal-infrared are made with a different grism.
The efficiencies of the new JH and HK low-resolution grisms are as follows:
The appropriate order is selected by means of order sorting filters. The transmission curves for these filters was measured at ~90K, and there is a slight shift when they are cooled to 65K.