TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 7
Improvements to the DM oven are underway. The chamber’s thermal control system is
currently inadequate to prevent the chamber from tracking changes in room temperature;
elimination of this behavior will reduce the temperature variation of all testbed
components. If sensitivity analysis and stability experiments dictate, thermal control can
also be added to individual optical mounts and the optical bench.
• Improved calibration and algorithm efficiency, which will reduce the time required for an
experiment and lessen the impact of testbed instability.
• Recoating the optics will reduce the stray-light level due to obvious contamination on the
mirrors.
• Polarization of the input beam, which will improve performance when polarization
becomes a limiting error source. A polarization analysis will be conducted for the testbed
optical design.
7.2.2 Milestone 2: Broadband Starlight Suppression on the HCIT
Planned Completion Date: Q3 FY06
Milestone #2 will extend the technology demonstration of Milestone #1 to white light, using an
optical bandwidth of 60 nm of the required bandwidth and to a level within an order of
magnitude of the required TPF-C contrast at the required angle necessary to distinguish a planet
signal from its star.
The current performance for white light (40 nm bandpass centered at 800 nm) is 5 × 10 -9
contrast, within a factor of 5 of the milestone. The current limiting error source may be red-light
leak in the filters or thermal stability of the components.
In addition to the plans discussed in the previous section, broadband performance will be
improved by the following testbed modifications:
• Improved filters with reduced red leak (already installed in the HCIT).
• A brighter white light source. A supercontinuum source, which uses a nonlinear fiber to
convert Nd:Yag laser pulses to pulsed broadband light (covering 500-1500 nm), is
nearing completion. Preliminary testing suggests that this pseudo white-light source will
provide greater than 100 times as much power as our current xenon lamp, cutting
exposure times from 10s of minutes to 10 seconds.
• Enhanced white-light efficiency via design of an improved illumination system inside the
testbed. The simple optical system used to image the fiber onto a pinhole will be replaced
with a more advanced design, incorporating achromatic lenses, selectable (fixed)
polarization, and finer, remote adjustment of fiber to pinhole alignment in vacuum.
• Improved optics. This will reduce phase-induced amplitude variation, which will reduce
the chromatic effects of amplitude compensation. Improved coatings would also reduce
these effects. Preliminary modeling suggests that the current HCIT optics are adequate to
achieve 10 -9 broadband contrast, so improved optics will probably not be procured until
Phase A.
Other error sources uncovered during error budget development or experimentation will be
addressed when needed. Diagnostic hardware will be designed and implemented when
necessary to support contrast experiments and model validation.
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