Optical & Radiometric Conceptual Design of EMAS Thermal Port Upgrade Kickoff Meeting June 29, 2010 Roy W. Esplin

Optics and Radiometry Overview of E-MAS Cooled Optical Bench (COB) The COB will replace the current thermal ports 3 and 4 The COB will contain a12-channel LWIR spectrometer and a single channel MWIR radiometer with space available to convert the MWIR radiometer to a 12-channel MWIR spectrometer in the future SDL will design the LWIR spectrometer, specify and purchase its components, fabricate and test it SDL will design the MWIR radiometer, specify its components, fabricate mechanical hardware and test it SDL anticipates that the government will furnish the MWIR/LWIR dichroic, the MWIR lens, and the MWIR detector and preamplifier 2

COB Optical Layout with Panels Removed 3 LWIR Beam MWIR Beam

LWIR Spectrometer Optical Components Fold Mirror Grating Lens Detector Array with Cold shield 4

Cold Shield and Cold Optics Aperture Cold shield with cover removed Cold optics aperture mounted to cold shield 5

Parametric model used to compute area of warm bench seen by detectors parameter d deg = 7.5 mrad Afocal magnification = 6 (7.5 mrad)/6 =1.25 mrad FOV = 2*1.25mrad = 2.5 mrad Cross-hatched, crescent-shaped area is the warm area of bench that is seen by detectors 6

Background Reduction Factor of COB 7

Background Change to Signal for 10K Warm Bench Temperature Change for Channel 12 and 300K Signal 8

Signal-To-Noise Ratio Improvement Factor 9

Temperature Stability Requirements The cold optical bench can change more than 10K with no significant change in the detector output The cryo-cooler temperature is controlled to 0.1K Thus, the detector temperature is controlled to ~0.1K The detector responsivity changes ~0.14% for a 0.1K detector temperature change The signal change due to a 0.1K detector temperature change will be dominated by warm bench temperature changes A warm bench temperature change of only K produces a 0.14% change in detector output As a point of reference the temperature control of the SABER focal plane, which uses the same type detectors, is ~0.1K 10

LWIR Detector Array Solid Model Increasing wavelength Section View Linear Variable Filter (LVF) 11

LWIR Detector Array Dimensions To meet budget we need to reduce number of detector widths from 3 to 2 Based on Linear dispersion of mm/µm Detector array length may be too long for F/1 lens 12

LWIR Spectrometer with F/1 Lens Grating 64.7 line-pairs/mm Fold Mirror F/1 Lens 13

Polarization of LWIR Same As Current Design, MWIR will be rotated 90 Degrees 14

Conclusions SDL is already working with Teledyne Judson Technologies to finalized detector array specifications Effects of field stop width on spectral purity not yet modeled Dispersion may need to be reduced or F/number increased to make LWIR lens practical We need to decide if dispersion of MWIR orthogonal to LWIR is an issue The Cooled Optical Bench (COB) will significantly reduce measurement errors due to background emissions 15