# Presentation: 279041

## Progress in deep broadband interferometric nulling with the adaptive nuller

- Robert D. Peters
- Oliver P. Lay, Muthu Jeganathan
- Jet Propulsion Laboratory
- California Institute of Technology
- June 26, 2008

## Outline

- Background
- How it works
- Development activities
- Results
- Summary

## Nulling in TPF-I

- For deep null require electric fields with
- equal amplitudes
- opposite phases
- simultaneously at each wavelength and polarization
- Single-mode filter makes it easier
- Removes all spatial effects

- 

- Single mode filter

*A(****,pol)*

***(****,pol)*

## Why Do Adaptive Nulling

- Include a compensator to actively control amplitude and phase for each polarization and wavelength at low bandwidth

## Parallel high-order compensator design

- Parabolic mirror
- ~ 10 x 14 cm

- Uncompensated
- beam in (~4 cm)

- Dispersive element
- splits wavelengths

- Birefringent element
- splits polarizations

- Pupil
- Stop

- Compensated
- beam out (~4 cm)

- Pupil
- Stop

- Birefringent element
- re-combines
- polarizations

- Dispersive element
- re-combines
- wavelengths

- S-polarization

- Deformable
- mirror

- P-polarization

## Phase and Amplitude Control

- Deformable mirror allows independent control of piston and tilt at each wavelength and polarization

- * Side view, shown for single wavelength & polarization

## Outline

- Background
- How it works
- Development activities
- Results
- Summary

## Development activates

- Proof-of-concept experiment ( = 0.8 to 0.9 μm)
- Less expensive optics and detectors
- Relaxed/scaled requirements
- Demonstrate feasibility of the design
- Gain experience with the control system
- Status: Complete – all requirements met/exceeded.
- Results presented at SPIE 05 Annual Meeting, San Diego.
- Mid-IR experiment ( ≈ 8 to 12 μm)
- Demonstration of phase and intensity control only
- Requirements traceable to flight needs for phase and intensity control
- Demonstrate to functionality of the design
- Status: Complete – all requirements met.
- TPF Milestone 1 Report
- (_[http://planetquest.jpl.nasa.gov/TPF-I/adaptiveNullerTestbed.cfm](http://planetquest.jpl.nasa.gov/TPF-I/adaptiveNullerTestbed.cfm)_)
- Applied Optics Paper http://ao.osa.org/upcoming_pdf.cfm?id=94240
- Mid-IR Nulling experiment ( ≈ 8 to 12 μm)
- Demonstrate nulling at the required TPF level of 100,000:1
- 3 runs of > 6 hours with and RMS null of 100,000:1 at least 3 days apart
- Status: In progress – complete by end of September, 2008
- Requirements detailed on PlanetQuest site in TPF-I Milestone #3 Whitepaper.

## What goes into a 100,000:1 null?

- Nuller

- Intensity Balance < 0.12%

- OPD < 8nm

- Phase Dispersion < 5nm

- 100,000:1

## Schematic Experimental Setup

- Mach-Zehnder type interferometer
- Reference is a “fixed” version of the adaptive nuller.
- Laser metrology to maintain a stable difference between the two arms.
- Bandwidth = 3.2μm FWHM.

**Single Pixel**
**Detector**

**Flipper**
**Mirror**

## Outline

- Background
- How it works
- Development activities
- Results
- Summary

## Recent Results

## Ongoing Work

- Some more improvements to the testbed
- Full enclosure
- Fully fix the metrology system to increase bandwidth
- Interferometer “EKG” system installed
- Measure environmental parameters to see if we are taking “good” data.
- More photons!
- If we still can’t get to 100,000:1
- Filters to narrow the bandwidth
- Wire-grid polarizers
- Pinhole on fiber output
- ???

## Summary

- Mid-IR experiments in progress
- Metrology problems that have slowed us are understood.
- At least one null ~90,000:1 has been achieved and was shown to be stable over 2 hours
- Identified key upgrades to be done within the next month.
- Identified potential “fixes” if it still doesn’t work.
- Many more measurements to take before we can declare victory
- Null ~80,000:1 many months ago (Applied Optics)
- Null ~70,000:1 month ago (w/ flaky metrology)
- Null ~90,000:1 week ago

## Thank you for your time.

- This work was performed by the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space administration.

- Thanks to Peter Lawson!

## BACKUP 

- SLIDES

## Deformable Mirror

- Tilting every other actuator
- 8 actuators to control the spectrum

- MEMS deformable mirror from Boston Micromachines.
- 140 actuators (12x12 – 4 corners)
- 3mm square continuous membrane
- ~1.8μm travel per actuator

## Mid-IR components

- Using ceramic heater as source
- Transmissive optics replaced with appropriate materials (ZnSe)
- Wollaston prism tested separately.
- CdSe is the only birefringent material
- Manufactured by Cleveland Crystals
- Cost ~ $27k each.
- Test sample had good agreement with our Zemax model.
- Mid-IR spectrometer
- Grating and single pixel mercury cadmium telluride detector on a computer controlled translation stage

## Lab Setup