# Presentation: 710682

## First Laboratory Demonstration ofAnti-Halo Apodization (AHA):  A coronagraph “afterburner”

- Johanan L. Codona

*JPL/TPF Coronagraph Workshop*
*Sept. 28-29, 2006*
*Pasadena, CA*

*Steward Observatory**University of Arizona *
*Tucson, AZ, USA*

## Scope of this work

- We are developing new focal-plane wavefront sensing techniques that can drive active halo suppression devices.
- We have demonstrated interferometric measurement of the complex halo using a Focal Plane Interferometer (FPI).
- We have used this focal plane information with a Pupil DM (PDM) to suppress the halo in closed loop.
- We have now also built an AHA antihalo modulator and used it to suppress a coronagraphic halo.

## Focal Plane Interferometer: FPI

**Focal Plane Interferometer: FPI**

**Uses discarded starlight**
- Core forms reference beam to probe halo.
- Halo processed as usual.
- Must capture both 0O and 180O phases for photon efficiency.
- Gives an estimate of the halo phase from minimum number of photons.
- Allows measurement of halo phase in presence of bright incoherent background by using a much brighter reference beam.

## FPI in Action

- Intensity Pattern

- Complex Halo

**Airy Pattern**
*(with DM print-through diffraction artifacts)*

**Speckle Halo**
*(phase and amplitude screen in pupil plane)*

## Using the FPI to drive a Pupil DM (PDM)

**Using the FPI to drive a Pupil DM (PDM)**

- Using a simple speckle-steering algorithm, we used the FPI complex amplitude measurements to suppress the halo in closed loop.

**Intensity Halo**

** ****Halo Phase re core**

**Suppressed 90****O**** sector**

**When fully suppressed, phase will become completely random.  This simple system could have gone another 1-1.5 decades fainter.**

## Using the FPI to drive a Pupil DM (PDM)

**180****O ****ROI**

**90****O ****ROI**

## Anti-Halo Apodization for 360 degree suppression - AHA

- Use AHA complex spatial light modulator to directly imprint a detailed “anti-halo” which  interferes destructively with the star's halo

## AHA Operation with FPI

- Example Halo

- Complex Halo (FPI)

- Average over DM Actuator size

- Halo+AntiHalo

- Compute DM displacements

*Real FPI Data used to model the effect of AHA*

## Complex Antihalo Control

- FPI *Measured*  Complex Halo (=3)

-  Halo intensity suppression proportional to local density of points.
-  Overall scale set with ND filter.
-  0.1 radian permits 100x improvement in halo intensity.

- Complex AntiHalo values addressable by prototype AHA modulator

- Complex Halo Distribution

## Effect of AHA Illumination

- AHA Modulator
**too bright**

**Antihalo level set by an ND filter setting the fraction of core starlight used by the AHA modulator.**

*Antihalo density is lower:**Can't suppress halo as far.*

- AHA Modulator
**too faint**

*AHA can't suppress these speckles*

- AHA Modulator
**too faint**

- AHA Modulator
**just right**

## Basic FPI/PDM/AHA Lab Design

- Three beams:
- Halo and Reference paths same as in FPI design.
- AHA path uses part of core starlight to feed two DMs in a Michelson to give complete complex field control.
- Uses segmented BMC 140-element MEMS DMs.
- Driven with IrisAO SmartDriver high-resolution electronics
- Linux-based control system.

- Reference Path

- Halo Path

- Lyot Stop 2.2

- Spatial Filter

- Spatial Filter

- Pupil=3.3

- Laser

- DM=3.3

- Beam Dump

- Detector

- AHA Modulator

## AHA Operation with a 12x12 modulator

## First AHA Lab Results

**AHA in Action:**
- Suppressed test rectangle

**Test**
**Halo**

**Halo + (unset) Anti-halo**

**DM Settings**

## First AHA Lab Results

## Comments:

**AHA Works!**
- Combined with an FPI, AHA should provide 2-3 decades of improved halo suppression for any coronagraph design.
- Antihalo level set using ND filter, not super accurate control.
- 0.1 radian phase control gives 100x additional halo suppression – from _*any*_ starting point.
- Works better with smaller pixels (actuators).
- Works over entire focal plane (with larger DMs).