LWIR FPA Mirror Image Problem & Recovery April 11, 2011 Roy W. Esplin Dave McLain

LWIR FPA Mirror Image Problem EMAS_Port4_V5g_Cold.ZMX ray trace As-Built FPA EMAS_Port4_V5g_Cold.ZMX ray trace footprint on detectors. View from back side of detectors X Y FPA was rotated 180º to put wavelengths on correct side, but we overlooked the fact that this converted smile into a frown. Problem discovered April 4, 2011 during final checking of LWIR Detector/Lens Assembly Dwg

LWIR FPA Mirror Image Solution As-Built FPA EMAS_Port4_V6a_Cold.ZMX ray trace footprint on detectors. View from back side of detectors Solution: Modify optical design to match “as-built” LWIR FPA. New optical design maintains same EMAS performance. EMAS_Port4_V6a_Cold.ZMX ray trace X Y 3

Changes Required Optical prescription changed from EMAS_Port4_V5h_Cold to EMAS_Port4_V6a_Cold with the following changes Changed diffraction order from +1 to -1 Reversed sign on alpha tilt angle of grating Rotated grating 180 degrees to maintain blaze efficiency One part of the grating mount has to be remade Rough machining and first thermal cycle have been completed. Some paint on cold bench has to be removed to mount this remade part. The clocking angle of the FPA must be changed by 180 degrees Requires 3 new holes in LWIR lens cell. Model and drawing already modified. Length of thermal strap must be increased approximately 3 inches. Work on strap had just begun, so only rework is fabrication of 2 copper blocks. Requires 2 new holes and covers for clearance of screws bolting thermal strap to FPA Part of a rib in the thermal shroud must be removed to provide clearance for thermal link. This is not a strength issue because partial rib is similar to other ribs in shroud. Some paint on cold bench must be removed to mount thermal strap. FPA connector must be rotated 180 degrees No changes to LWIR FPA or EMAS performance 4

Revised Optical-Mechanical Configuration New grating mounting part (Shown in blue) FPA rotated 180º from its previous orientation Thermal strap ~3 in. longer. FPA unchanged. 5

Location of Spectral Band Images Relative to Lens and FPA for Revised Configuration L1 Image L12 Image 6

Relative Orientation of FPA and Lens for Revised Configuration 7

L1 Band Rays Now aligned with FPA 8

Field-Stop Spectral Images Now Aligned with Detectors (Slide 1 of 2) 9

Field-Stop Spectral Images Now Aligned with Detectors (Slide 2 of 2) 10

Revised Thermal Strap The FPA is now rotated 180º from its previous orientation, so the thermal strap connection is now on the left rather than on the right. Location of FPA thermal strap connection for previous configuration Thermal strap connection to FPA Paint on cold bench under this part of strap needs to be removed FPA electrical connector rotated l80º from previous orientation 11

Revised Configuration Fits Within Existing Thermal Shroud Thermal Shroud 12

Repositioned Grating and Thermal Link Fit Within the Existing Thermal Shroud New Grating Mount Thermal Shroud Thermal Link Thermal Shroud Part of shroud rib removed for clearance Heads of screws mounting thermal strap to FPA. Holes cut in shroud to provide clearance. Thermal Strap 13

Two Clearance Holes Cut in Thermal Shroud Two holes cut in thermal shroud to provide clearance for Screws bolting thermal strap to FPA. This holes will have to be covered to prevent the cold bench from seeing the warm enclosure. Location of holesVacuum enclosureThermal shroud 14

Orientation of Grating in Revised Configuration Grating spacing has been increased in this figure to make the grating facets visible 15

Geometry Used To Verify 15.27º Blaze Angle for Revised Configuration (Slide 1 or 2) Z-axis is the grating normal for revised configuration of EMAS_Port4_V6a_Cold Incident Gut Ray Diffracted Gut Ray for 9.730μm wavelength The blue line is the bisector of the angle determined by the incident and diffracted rays. This blue line defines the direction of the normal to the grating facets for a grating blazed for maximum efficiency at a wavelength of 9.730µm because the incident ray is reflected from this facet in the direction of the diffracted ray. Grating spacing has been increased in this figure to make the grating facets visible This yellow plane is normal to blue bisector line This yellow plane contains the incident and diffracted gut rays for 9.730mm wavelength 16

Geometry Used To Verify 15.27º Blaze Angle for Revised Configuration (Slide 2 or 2) Incident Gut Ray Diffracted Gut Ray for 9.730μm wavelength This yellow plane is normal to blue bisector line The blue line is the bisector of the angle determined by the incident and diffracted rays. This blue line defines the direction of the normal to the grating facets for a grating blazed for maximum efficiency at a wavelength of 9.730µm because the incident ray is reflected from this facet in the direction of the diffracted ray. The angle between the incident and diffracted rays appears much smaller than it really is because of the viewing direction 17