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 Horizontal polarization Vertical polarization 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 Perfectly matched beamtrain optics Fully symmetric, high performance beam combiner Single-mode spatial filter Realistic beamtrain optics Simple asymmetric beam combiner Single-mode spatial filter Compensator

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 Phase control with piston*:Amplitude control with tilt*: * 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 ( Applied Optics Paper 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 < 8nmPhase Dispersion < 5nm 100,000:1 PolarizationSingle Mode Fiber Leakage...Other effects

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 Data RMS = 93,000:1 ~2 Hours Metrology off Shutters Closed Noise Floor

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 cant 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 doesnt 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 Source Reference Arm Adaptive Nuller Arm DM Shutter Dispersing Wedges Flat Mirror