1. Extended Scene Shack-Hartmann
A Wavefront sensing and control testbed was built to develop wavefront sensing and control technique for active optics
Phase Retrieval Camera (PRC)
Shack-Hartman Camera (SHC)
CCD camera
10k+ subapertures
Slower update rate ~12sec
Source module provides a point source and extended scene source for the testbed
Point source: narrow band or broadband
Extended scene: broadband, 5 scenes
Shack-Hartmann sensor
Centroid based WFS for point source
Image correlation based WFS for extended scene targets
Using one subaperture image as reference image for correlation

2. Simplified Testbed Description
Optical Bench DM
Accelerometers
Thermal sensors
Calib. Mirr.
BS1
BS2
FSM
Source BS
DFS
Source
Module
PRC
SHC

3. SHC Sub-aperture Images PRC Image (Full Aperture High Res Image
Extended Scene #4
SHC Sub-aperture Images
PRC Image (Full Aperture High Res Image
Scene #4: USAF 1951, coarse pattern, 100% contrast, negative, Groups -1 through -2
Negative of like this

4. ESHC Sensing Accuracy and Robustness
Using a poked DM actuator to test ESHC sensing accuracy. Plot shows the result from an actuator poking with voltages between -1 and +1 volt
Net DM poke WFE (difference between poked and flat)
ESHC measures the subaperture WF slops which then convert to OPDs. (see PRC DM setup slide)
OPD area is cropped around the actuator poke for more meaning full RMS and P-V calculations
For ESHC robustness testing the extended scene target intensity is varied from 25%, 50%, 75% and 100% to the full well exposure. RMS WFE scattering is less than 0.6 nm
DM Zygo calibration measures the gain of actuator WFE ~13.6 nm/V – matching ESHC’s measurement
ESHC WFE Gain = 14 nm/V

5. ESHC Sensitivity Map #1 Map #2 Map #3 Map #4 Map #5 Map #6
Using a small poked DM actuators to test ESHC sensitivity
6 DM poke maps with different poke values as well as both positive and negative DM pokes – see DM actuator map and tables blow for poke actuator location and poke values
The results shown is from extended scene target #4
The results show that ESHC can sense WFE as small as 1.4 nm P-V
DM Poke Map #1 & #2:
Act #51: DPoke = ±0.05 V = ± 7.0 nm (P-V)
Act #27: DPoke = ± 0.02 V = ± 2.8 nm (P-V)
Act #47: DPoke = ± 0.01 V = ± 1.4 nm (P-V)
Act #71: DPoke = ± V = ± 0.7 nm (P-V)
DM Poke Map #3 & #4:
Act #51: DPoke = ± 0.1 V = ± 14 nm (P-V)
Act #27: DPoke = ± 0.04 V = ± 5.6 nm (P-V)
Act #47: DPoke = ± 0.02 V = ± 2.8 nm (P-V)
Act #71: DPoke = ± 0.01 V = ± 1.4 nm (P-V)
DM Poke Map #5 & #6:
Act #51: DPoke = ± 0.5 V = ± 70 nm (P-V)
Act #27: DPoke = ± 0.2 V = ± 28 nm (P-V)
Act #47: DPoke = ± 0.1 V = ± 14 nm (P-V)
Act #71: DPoke = ± 0.05 V = ± 7 nm (P-V)
Map #1
Map #2
Map #3
Map #4
Map #5
Map #6

6. Compared to Point Source SHC Sensitivity
The results shown is from point source SHC
The results show that ESHC can sense WFE as small as 1.4 nm P-V
ESHC and Point Source SHC sensitivities are comparable
DM Poke Map #1 & #2:
Act #51: DPoke = ±0.05 V = ± 7.0 nm (P-V)
Act #27: DPoke = ± 0.02 V = ± 2.8 nm (P-V)
Act #47: DPoke = ± 0.01 V = ± 1.4 nm (P-V)
Act #71: DPoke = ± V = ± 0.7 nm (P-V)
DM Poke Map #3 & #4:
Act #51: DPoke = ± 0.1 V = ± 14 nm (P-V)
Act #27: DPoke = ± 0.04 V = ± 5.6 nm (P-V)
Act #47: DPoke = ± 0.02 V = ± 2.8 nm (P-V)
Act #71: DPoke = ± 0.01 V = ± 1.4 nm (P-V)
DM Poke Map #5 & #6:
Act #51: DPoke = ± 0.5 V = ± 70 nm (P-V)
Act #27: DPoke = ± 0.2 V = ± 28 nm (P-V)
Act #47: DPoke = ± 0.1 V = ± 14 nm (P-V)
Act #71: DPoke = ± 0.05 V = ± 7 nm (P-V)
Map #1
Map #2
Map #3
Map #4
Map #5
Map #6

7. ESHC In-Vac Repeatability Test
ESHC is repeated measuring the WFE with Spherical Mirror in
The RMS OPD variation (left plot) has shown that ESHC repeatability is less than 2.8 nm
Point source SHC shows similar repeatability
ESHC Repeatability Measurement of a Static WF
RMS OPD Deviation from the Mean OPD