Optical AlignmentNov. 15, 2010

Roy W. Esplin

Dave McLain

Alignment Plan Outline

Verify vacuum system and cryogenic system are operational

Fit check all optical components

Align optics to internal optical bench

Align internal optical bench to vacuum enclosure

Transfer boresight from internal optical bench to alignment cube on exterior of vacuum shell

Iterate to final alignment by adjusting focus and clocking of focal plane assemblies (FPAs) over several thermal cycles

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Alignment of optics to internal benchInstall mirrors and lens at positions determined by precise machining

Install LWIR grating and MWIR grating replacement mirror at nominal locations

Mount unexpanded, 633-nm laser on XY stage; set angle using flat F1 (SDL’s)

Translate laser until beam strikes center of mirror M1 (dichroic not installed)

Measure distance from face of internal optical bench to laser beam (optical axis)

Center laser beam on grating by translating grating

Adjust grating angles until 15th order is reflected straight back by lens L1 and line of dispersed orders is perpendicular to internal bench.

Increment grating angles to put 15.3 order at lens L1 center.

Install dichroic and adjust its mount for best centering of laser beam on mirrors M2 and M3

Translate & tilt M4 to center laser beam on M3 and lens L2

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M1

M2Dichroic

F1

M3

L1GratingL2

M2

Align Internal Optical Bench to Vacuum Enclosure and Map Boresight into Cube

Align surface 1 on internal optical bench parallel to surface 2 on exterior of vacuum enclosure and translate internal optical bench so optical axis is at correct location on the window using a Coordinate Measuring Machine (CMM)

Map boresight angles into alignment cube using CMM

Measure any angular changes in the cube when vacuum pulled on enclosure using theodolite

4 SDL Alignment cube

Surface 1

Surface 2

Window

FPA AlignmentInitial FPA location and orientation set using Judson’s measurements of FPA detector locations relative to package

XY coordinates of FPA origin relative to holes at 12, 3, 6 and 9 o’clock on FPA package

Detector Z location relative to mounting flange

Clocking of FPA in package relative to holes as well as vertical members on both sides of printed circuit board

Focus shim between lens housing and FPA sets focus

Shims between FPA package and shimming fixture used to get controlled translation and clocking adjustment of FPA.

Iterate to best alignment Functional Test setup described on next slide

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Shimming fixture

Translation shims

Rotational shims

Functional Test Setup

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COB 12-Ch. A/D Computer

Detectors and dispersed image of point source

12 spectra (one for each detector)

Poor Focus

Good Focus

Area Within Dashed Lines Purged with LN2

0 10 20 30 40 50 60 70 80 900

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0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

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Poor Focus

Good Focus

Wavelength (um)

Interferometer

OAP

Steering Mirror

Pinhole

Translatable Platform

Lens

Simulated Telescope Exit Pupil (Exit pupil is only 1-inch in diameter)

Use of Metrics From Functional Test to Align FPA

Iterate to best lateral location of FPA by measuring spectral location of 50% points

Iterate lateral FPA adjustment iterate to best FPA clocking using steering mirror to move dispersed spectrum off the top and bottom of the detectors

Iterate to best focus by maximizing both the spectral slope and rate that response falls off as dispersed spectrum is moved off top and bottom of detectors

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