This PDF file contains the front matter associated with SPIE Proceedings Volume 6693, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The New Worlds Observer (NWO) is a mission concept for the detection and characterization of extra-solar planets. It employs an external starshade and a space telescope. The starshade suppressed the parent star's light making detection of the extrasolar planet possible. This paper reviews the proposed requirements for the Terrestrial Planet Finding (TPF) mission. Using current understanding of the performance and trades inherent in the NWO architecture it is shown how to construct the allowed design space for a NWO mission.

One of the major goals in astronomy today is the detection and characterization of extra-solar planets. There are currently many exciting new concepts on the horizon that have the capability to vastly increase our knowledge of extrasolar planets, particularly, planets like our own. The Terrestrial Planet Finder (TPF) program spans several different mission concepts that are all capable of detecting and characterizing Earth-like planets. One such concept under study consists of a telescope spacecraft and separate occulter spacecraft. The external occulters (EO) will be tens of meters in diameter and will be located thousands of kilometers away. This arrangement allows the mission to observe companion planets with a ~4 m telescope by extinguishing on-axis starlight. The operational efficiency of external occulters is constrained by the large separation between the telescope and the occulter spacecraft. Slewing between target stars will consume maneuvering fuel and time. Thus, the efficiency of any single EO mission may be greatly improved by using two or more occulters and optimizing the mission scenario. We explore the design of different size occulters for different objectives in the TPF mission. In one approach, a smaller occulter performs a "survey" function, while a large occulter performs follow-up searches on prospective planets and fainter celestial objects. The small occulter would have more maneuverability, but have a large inner working angle. The optimized combination of two such occulters may provide the best compromise in the mission's ability to search and characterize extra-solar planets. This paper discusses several potential TPF mission scenarios involving two occulters (one large, one small) and explores the optimization of different scenarios for detection and characterization of Earth-like planets.

One of the proposed methods for directly imaging extrasolar planets is via a free-flying occulter for blocking the starlight. The occulter would fly between a conventional telescope and the target star. It has long been known that a solid occulting disk does not produce a deep shadow; diffraction effects result in a bright spot in the center that would mask a planet. However, utilizing recent results in shaped pupil optimization, we have developed designs for an occulter with a shape that does effectively block the light from the star, allowing the planet light to be seen even at a small angular separation. The shadow created by the occulter is wavelength-dependent and quite sensitive to the shape of the outer edge. We present an optimization approach for producing these occulter designs to meet contrast requirements over multiple wavelengths and also discuss tolerancing requirements on the shade manufacture and control.

We present laboratory studies of scaled occulting starshades for the New Worlds Observer (NWO). A deep reactive ion etched silicon starshade has been fabricated by NIST, designed to cover the same number of Fresnel zones as in the proposed mission. The broadband shadow is mapped with a photometer in a dark vacuum tunnel fed by a heliostat at HAO. CCD images provide direct contrast measurements of different features around the starshade. Preliminary measurements reach 5x10^-6 suppression in the center of the shadow at the focal plane. The two-dimensional structure of the starshade diffraction pattern is compared to that produced by the Fresnel integral.

For a planet-finding external occulter system applicable to Terrestrial Planet Finder, acquiring and maintaining collinearity of the telescope, occulter (starshade), and star can be a substantial challenge. The principal difficulty is the angular sensitivity and accuracy, and the telescope-starshade distance (20-100 megameters) is a significant complication. We discuss some sensor concepts as well as operations that support initial acquisition of a star, observations, slewing, and reacquisition. Among these concepts is one so simple that we can argue there is no enabling required in the alignment area.

Initial high-fidelity, flight-like ground demonstrations of precision formation flying spacecraft are presented. In these demonstrations, maneuvers required for distributed spacecraft interferometry, such as for the Terrestrial Planet Finder Interferometer, were performed to near-flight precision. Synchronized formation rotations for "on-the-fly" observations require the highest precision. For this maneuver, ground demonstration performance requirements are 5 cm in relative position and 6 arc minutes in attitude. These requirements have been met for initial demonstrations of formation-keeping and synchronized formation rotations. The maneuvers were demonstrated in the Formation Control Testbed (FCT). The FCT currently consists of two, five degree-of-freedom, air bearing-levitated robots. The final sixth degree-of-freedom is being added in August 2007. Each robot has a suite of flight-like avionics and actuators, including a star tracker, fiber-optic gyroscopes, reaction wheels, cold-gas thrusters, inter-robot communication, and on-board computers that run the Formation and Attitude Control System (FACS) software. The FCT robots and testbed environment are described in detail. Then several initial demonstrations results are presented, including (i) a sub-millimeter formation sensor, (ii) an algorithm for synchronizing control cycles across multiple vehicles, (iii) formation keeping, (iv) reactive collision avoidance, and (iv) synchronized formation rotations.

This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized. The current interferometer architecture, design trades, and the viability of possible reduced-scope mission concepts are also presented.

A novel space interferometer design originating in Europe has been studied. The interferometer uses the technique of starlight nulling to enable detection of earth-like planets orbiting nearby stars. A set of four telescope spacecraft flying in formation with a fifth, beam-combiner spacecraft forms the interferometer. This particular concept shows potential for reducing the mission cost when compared with previous concepts by greatly reducing the complexity of the telescope spacecraft. These spacecraft have no major deployable systems, have simplified propulsion and a more rugged construction. The formation flying geometry provides for greater average separation between the spacecraft with commensurate risk reduction. Key aspects of the design have been studied at the Jet Propulsion Laboratory with a view to collaborations between NASA and the European Space Agency. An overview of the design study is presented with some comparisons with the TPF-FFI concept.

The NASA Terrestrial Planet Finder Interferometer (TPF-I) and ESA Darwin missions are designed to directly detect mid-infrared photons from earth-like planets around nearby stars. Until recently, the baseline TPF-I design was the planar stretched X-Array, in which the four collectors spacecraft lie on the corners of a rectangle with the combiner spacecraft at the center, all in the plane normal to the direction to the target star. The stretched X-Array has two major advantages over other configurations: the angular resolution is very high, and the ability to eliminate instability noise. A direct consequence of the latter is that the null depth requirement is relaxed from 10^-6 to 10^-5. Implementation of the planar configuration requires a significant number of deployments, however, including large sunshades and secondary mirror supports. ESA had been pursuing a non-planar configuration with 3 collector telescopes. Dubbed the 'Emma' architecture (after the wife of Charles Darwin), this approach brings the combiner spacecraft up out of the plane of the collectors, and offers significant simplifications in the collector design with minimal deployments. The Emma X-Array combines the best aspects of each design, bringing together the 4-collector stretched X-Array collector configuration with the out-of-plane combiner of the Emma geometry. Both the TPF-I and Darwin missions have now adopted the Emma X-Array as the baseline design, moving a step closer to a single, joint TPF/Darwin mission. In this paper we assess the planet-finding performance of the Emma X-Array. An optimized completeness algorithm is used to estimate the number of Earths that can be found as a function of collector diameter. Other key parameters − the inner and outer working angles and the angular resolution − are also addressed.

The space Corot telescope has been developed by Thales Alenia Space Cannes (previously named Alcatel Alenia Space) and has been delivered to the French Space agency (CNES. The satelllite has veen successfully launched from Baïkonour the 27th of December 2006. This telescope is a very precise and stable imaging instrument that is pointed towards fixed areas in the sky for periods of at least 5 month, in order to carry out two kinds of missions: (i) Stellar seismology, (ii) Search for exoplanets (by transit detection). Corot is likely to be the first space instrument capable of detecting Earth like planets orbiting around other stars and providing accurate stellar data in relation with their internal constitution. The target stars will have visible magnitudes lower than 9 for the seismology mission, and lower than 13 for the detection of Earth-like planets. COROT is a low cost mission and has a polar circular orbit with an altitude around 800 Km (unfortunately not at L2 orbit). In order to comply with the above objectives, the instrument shall deliver a very stable signal from a stable source. More particularly, this stringent stability requirement implies: (i) a high level of straylight (coming from earth) rejection, (ii) a high pointing stability, (iii) a high level of performance for the thermal control subsystem in term of temperature and gradient stability associated with the use of hyper stable materials. On the other hand, this instrument is carried by a low size satellite associated with the use of hyper stable materials. On the other hand, this instrument is carried by a low size satellite of the PROTEUS family, allowing a faster and cheaper development. This paper focuses on the proposed opto mechanical design for the telescope, its baffling cancept and its performance which are now demonstrated in flight.

SIM is a space astrometric interferometer capable of better than one-microarcsecond ( as) single measurement accuracy, providing the capability to detect stellar "wobble" resulting from planets in orbit around nearby stars. While a search for exoplanets can be optimized in a variety of ways, a SIM five-year search optimized to detect Earth analogs (0.3 to 10 Earth masses) in the middle of the habitable zone (HZ) of nearby stars would yield the masses, without M*sin(i) ambiguity, and three-dimensional orbital parameters for planets around ~70 stars, including those in the HZ and further away from those same stars. With >200 known planets outside our solar system, astrophysical theorists have built numerical models of planet formation that match the distribution of Jovian planets discovered to date and those models predict that the number of terrestrial planets (< 10 M₍₊₎ ) would far exceed the number of more massive Jovian planets. Even so, not every star will have an Earth analog in the middle of its HZ. This paper describes the relationship between SIM and other planet detection methods, the SIM planet observing program, expected results, and the state of technical readiness for the SIM mission.

Optical interferometry will open new vistas for astronomy over the next decade. The Space Interferometry Mission (SIM-PlanetQuest), operating unfettered by the Earth's atmosphere, will offer unprecedented astrometric precision that promises the discovery of Earth-analog extra-solar planets as well as a wealth of important astrophysics. Results from SIM will permit the determination of stellar masses to accuracies of 2% or better for objects ranging from brown dwarfs through main sequence stars to evolved white dwarfs, neutron stars, and black holes. Studies of star clusters will yield age determinations and internal dynamics. Microlensing measurements will present the mass spectrum of the Milky Way internal to the Sun while proper motion surveys will show the Sun's orbital radius and speed. Studies of the Galaxy's halo component and companion dwarf galaxies permit the determination of the Milky Way's mass distribution, including its Dark Matter component and the mass distribution and Dark Matter component of the Local Group. Cosmology benefits from precision (1-2%) determination of distances to Cepheid and RR Lyrae standard candles. The emission mechanism of supermassive black holes will be investigated. Finally, radio and optical celestial reference frames will be tied together by an improvement of two orders of magnitude. Optical interferometers present severe technological challenges. The Jet Propulsion Laboratory, with the support of Lockheed Martin Advanced Technology Center (LM ATC) and Northrop Grumman Space Technology (NGST), has addressed these challenges with a technology development program that is now complete. The requirements for SIM have been satisfied, based on outside peer review, using a series of laboratory tests and appropriate computer simulations: laser metrology systems perform with 10 picometer precision; mechanical vibrations have been controlled to nanometers, demonstrating orders of magnitude disturbance rejection; and knowledge of component positions throughout the whole test assembly has been demonstrated to the required picometer level. Technology transfer to the SIM flight team is now well along.

Precision white light interferometry performed at the picometer class level is an extremely challenging endeavor. Over the past several years a combination of analysis, experiment, and reconciliation of the two has yielded continued improvements and refinements of the process to bring this technology to fruition. This paper provides an overview of several of the refinements of the interference models and algorithms developed for calibration and fringe estimation that have evolved over this period.

The near-infrared camera (NIRCam) on the James Webb Space Telescope (JWST) will incorporate 2 identical grisms in each of its 2 long wavelength channels. These transmission gratings have been added to assist with the coarse phasing of the JWST telescope, but they will also be used for slitless wide-field scientific observations over selectable regions of the λ = 2.4 − 5.0 μm wavelength range at spectroscopic resolution R ≡ λ/δλ ≃ 2000. We describe the grism design details and their expected performance in NIRCam. The grisms will provide point-source continuum sensitivity of approximately AB = 23 mag in 10,000 s exposures with S/N = 5 when binned to R = 1000. This is approximately a factor of 3 worse than expected for the JWST NIRSpec instrument, but the NIRCam grisms provide better spatial resolution, better spectrophotometric precision, and complete field coverage. The grisms will be especially useful for high precision spectrophotometric observations of transiting exoplanets. We expect that R = 500 spectra of the primary transits and secondary eclipses of Jupiter-sized exoplanets can be acquired at moderate or high signal-to-noise for stars as faint as M = 10 − 12 mag in 1000 s of integration time, and even bright stars (V = 5 mag) should be observable without saturation. We also discuss briefly how these observations will open up new areas of exoplanet science and suggest other unique scientific applications of the grisms.

The expected stable point spread function, wide field of view, and sensitivity of the NIRCam instrument on the James Webb Space Telescope (JWST) will allow a simple, classical Lyot coronagraph to detect warm Jovian-mass companions orbiting young stars within 150 pc as well as cool Jupiters around the nearest low-mass stars. The coronagraph can also be used to study protostellar and debris disks. At λ = 4.5 μm, where young planets are particularly bright relative to their stars, and at separations beyond ~0.5 arcseconds, the low space background gives JWST significant advantages over ground-based telescopes equipped with adaptive optics. We discuss the scientific capabilities of the NIRCam coronagraph, describe the technical features of the instrument, and present end-to-end simulations of coronagraphic observations of planets and circumstellar disks.

We present the status of the development of a coronagraph for the Space Infrared telescope for Cosmology and Astrophysics (SPICA). SPICA is the next generation of infrared space-borne telescope missions following to AKARI, led by Japan. SPICA will carry a telescope that has a 3.5 m diameter monolithic primary mirror and the whole telescope will be cooled to 4.5 K. It is planned to launch SPICA into the sun-earth L2 libration halo orbit using H II-A rocket in the middle of the 2010s and execute infrared observations at wavelengths mainly between 5 and 200 micron. The SPICA mission gives us a unique opportunity for coronagraph observations, because of the large telescope aperture, the simple pupil shape, the capability of infrared observations from space, and the early launch. We have started development of the SPICA coronagraph in which the primary target is direct observation of extra-solar Jovian planets. The main wavelengths of observation, the required contrast and the inner working angle (IWA) of the SPICA coronagraph instrument are set to be 5-27 micron, 10^-6, and a few λ/D (and as small as possible), respectively, in which λ is the observation wavelength and D is the diameter of the telescope aperture (3.5m). We focused on a coronagraph with a binary shaped pupil mask as the primary candidate for SPICA because of its feasibility. Nano-fabrication technology using electron beam lithography was applied to manufacture a high precision mask and a laboratory experiment with a He-Ne laser (λ=632.8nm) was performed in air without active wavefront control. The raw contrast derived from the average measured in the dark region reached 6.7×10^-8. On the other hand, a study of Phase Induced Amplitude Apodization (PIAA) was started in an attempt to achieve higher performance, i.e., smaller IWA and higher throughput. A hybrid solution using PIAA and a shaped pupil mask was proposed. A laboratory experiment was performed using a He- Ne laser with active wavefront control via a 32×32 channel deformable mirror. A raw contrast of 6.5×10^-7 was achieved. Designs of binary shaped pupil mask are presented for the actual SPICA pupil which is obstructed by the telescope's secondary mirror and its support. Subtraction of point spread function (PSF) was also evaluated.

The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission to image planetary systems of nearby stars simultaneously in a few wide spectral bands covering the visible light (0.4-0.9 μm). It achieves its power by combining a high accuracy wavefront control system with a highly efficient Phase-Induced Amplitude Apodization (PIAA) coronagraph which provides strong suppression very close to the star (within 2 λ/D). The PIAA coronagraphic technique opens the possibility of imaging Earthlike planets in visible light with a smaller telescope than previously supposed. If sized at 1.2-m, TOPS would image and characterize many Jupiter-sized planets, and discover 2 RE rocky planets within habitable zones of the ≈10 most favorable stars. With a larger 2-m aperture, TOPS would have the sensitivity to reveal Earth-like planets in the habitable zone around ≈20 stars, and to characterize any found with low resolution spectroscopy. Unless the occurrence of Earth-like planets is very low (η_⊕ <~ 0.2), a useful fraction of the TPF-C scientific program would be possible with aperture much smaller than the baselined 8 by 3.5m for TPF, with its more conventional coronagraph. An ongoing laboratory experiment has successfully demonstrated high contrast coronagraphic imaging within 2 λ/d with the PIAA coronagraph / focal plane wavefront sensing scheme envisioned for TOPS.

This paper reports the results of a design study for an exoplanet imaging system. The design team consisted of the students in the "Electromagnetic Sensing for Space-Bourne Imaging" class taught by the principal author in the Spring, 2005 semester. The design challenge was to devise a space system capable of forming 10X10 pixel images of terrestrial-class planets out to 10 parsecs, observing in the 9.0 to 17.0 microns range. It was presumed that this system would operate after the Terrestrial Planet Finder had been deployed and had identified a number of planetary systems for more detailed imaging. The design team evaluated a large number of tradeoffs, starting with the use of a single monolithic telescope, versus a truss-mounted sparse aperture, versus a formation of free-flying telescopes. Having selected the free-flyer option, the team studied a variety of sensing technologies, including amplitude interferometry, intensity correlation imaging (ICI, based on the Brown-Twiss effect and phase retrieval), heterodyne interferometry and direct electric field reconstruction. Intensity correlation imaging was found to have several advantages. It does not require combiner spacecraft, nor nanometer-level control of the relative positions, nor diffraction-limited optics. Orbit design, telescope design, spacecraft structural design, thermal management and communications architecture trades were also addressed. A six spacecraft design involving non-repeating baselines was selected. By varying the overall scale of the baselines it was found possible to unambiguously characterize an entire multi-planet system, to image the parent star and, for the largest base scales, to determine 10X10 pixel images of individual planets.

We present the design of a new testbed experiment to demonstrate nulling interferometry using polarization properties. This three-beam set-up is perfectly symmetric with respect to the number of reflections and transmissions and should therefore allow a high rejection ratio in a wide spectral band.

In previous work, we explored the possibility of using intensity correlation techniques, based upon the Hanbury Brown-Twiss effect to perform fine resolution imaging in the service of exoplanet astronomy. Here we consider a multi-spectral variant of the Hanbury Brown-Twiss technique. At each of a number of independent, light-gathering telescopes photodetection data encompassing each of a set of frequency channels are obtained and then are communicated to some convenient computational station. At the computational station, the correlations among the photodetections in each of the frequency bands are time averaged and then further averaged over the various frequency channels to arrive at measurements of the mutual coherence magnitude for each pair of telescopes. From these statistics, imaging data are, in turn, computed via phase retrieval techniques. Here, within a modern quantum optics framework, we examine the signal-to-noise characteristics of the coherence estimates obtained in this way under a variety of non-ideal conditions. We provide step-by-step derivations of the statistical quantities needed in a largely self-contained treatment. In particular, we examine the effects of partial coherence on a scene typical of exoplanet imaging and show how partial coherence can be used to greatly attenuate the parent star. We find that the multispectral version of intensity interferometry greatly improves the signal-to-noise ratio in general and dramatically so for exoplanet detection. The results also extend the analysis of signal-to-noise to a wider variety of practical conditions and provide the basis for multispectral intensity correlation imaging system design.

For the past several years NASA has been developing the Terrestrial Planet Finder Coronagraph (TPF-C), a space based telescope mission to look for Earth-like extra-solar planets. By evaluating the cumulative number of habitable zones observable with a given observation sequence (completeness) we test the relative merits of the baseline 8-m telescope design and smaller (2.5 - 4 m), less capable TPF-C designs based on various coronagraph technologies as well as external occulters.

Pupil mapping (a.k.a. Phase-Induced Amplitude Apodization, or PIAA) is a promising technique in high-dynamic range stellar coronagraphy that obtains higher throughput and better inner working angle than any other known approach. As with any coronagraph, the optical surface requirements and the diameter of the controllable region in the image plane are tied to the wavefront control system and optical bandpass. For example, in a monochromatic bandpass, a single ideal deformable mirror (DM) can create a dark hole with a diameter limited by its Nyquist frequency, even for highly aberrated optics. In broadband light, the depth of the dark hole is linked to the wavelength dependence of aberrations, their spatial frequency content, and their propagation through the system. We derive requirements on the surface height and reflectivity power spectral densities for optics in the PIAA system and describe a sequential-DM architecture that will achieve high-contrast over a large optical bandwidth.

ESA's Darwin mission is devoted to direct detection and spectroscopic characterisation of Earth-like planets in the thermal infrared domain by nulling interferometry in space. This technique requires deep and stable starlight rejection to an efficiency around 106 over the whole spectral band. Darwin is a major target for Thales Alenia Space, and is considered as a strategic part of its programme roadmap. In this paper we present the main outcomes of the Darwin mission study conducted by Thales Alenia Space from Oct. 2005 to Jul. 2007. Studying this mission in depth, our proposed most promising configuration features spacecraft in non planar arrangement (called Emma). It offers the best science return in terms of number of stars detected and sky accessibility while staying compliant with mass and volume constraints of a single Ariane 5 launch. Our solution dramatically alleviates engineering constraints thanks to a fully non deployable concept. As compared to the more conventional planar arrangement (called Charles), Emma suppresses Single Point Failures and spurious flexible modes, thus maximising both the system reliability and the stability of the dynamical environment. Emma is fully compatible with either 3 or 4 collectors.

The missions DARWIN and TPF-I (Terrestrial Planet Finder-Interferometer) aim at the search and analysis of terrestrial exo-planets orbiting nearby stars. The major technical challenge is the huge contrast ratio and the small angular separation between star and planet. The observational method to be applied is nulling interferometry. It allows for extinguishing the star light by several orders of magnitude and, at the same time, for resolving the faint planet. The fundamental performance of the nulling interferometer is determined by the aperture configuration, the effective performance is driven by the actual instrument implementation. The x-Array, an aperture configuration with 4 telescopes allowing for phase chopping and decoupling of the nulling and imaging properties, provides highest instrument performance. The scientific goals necessitate an instrument setup of high efficiency and utmost symmetry between the beams concerning optical path length, beam profile and state of polarization. Non-planar spacecraft formations allow for a simpler spacecraft design which comes at the cost of inherent constellation and beam asymmetry, of increased complexity of the beam relay optics and of instrumental errors synchronous to the planet signal demodulation frequency. Planar formations allow for perfect efficiency and symmetry but need deployable structures for the secondary mirror and the sunshield due to launcher accommodation constraints. We present a discussion of planar and non-planar implementations of the x-Array aperture configuration and identify for both the critical items and design drivers. We compare the achievable instrument performance and point out the constraints for each spacecraft formation.

The TEDI (TripleSpec Exoplanet Discovery Instrument) will be the first instrument fielded specifically for finding low-mass stellar companions. The instrument is a near infra-red interferometric spectrometer used as a radial velocimeter. TEDI joins Externally Dispersed Interferometery (EDI) with an efficient, medium-resolution, near IR (0.9 - 2.4 micron) echelle spectrometer, TripleSpec, at the Palomar 200 telescope. We describe the instrument and its radial velocimetry demonstration program to observe cool stars.

Space coronagraphy is a promising method for direct imaging of planetary systems orbiting the nearby stars. The High Contrast Imaging Testbed is a laboratory facility at JPL that integrates the essential hardware and control algorithms needed for suppression of diffracted and scattered light near a target star that would otherwise obscure an associated exo-planetary system. Stable suppression of starlight by a factor of 5×10⁻¹⁰ has been demonstrated consistently in narrowband light over fields of view as close as four Airy radii from the star. Recent progress includes the extension of spectral bandwidths to 10% at contrast levels of 2×10⁻⁹, with work in progress to further improve contrast levels, bandwidth, and instrument throughput. We summarize recent laboratory results and outline future directions. This laboratory experience is used to refine computational models, leading to performance and tolerance predictions for future space mission architectures.

The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton for detection of extra-solar earthlike planets. It is designed to achieve 10^-10 contrast at an inner working angle of 4λ/D in broadband light. A critical requirement in attaining this contrast level in practice is the ability to control wavefront phase and amplitude aberrations to at least λ/10⁴ in rms phase and 1/1000 rms amplitude, respectively. Furthermore, this has to be maintained over a large spectral band. The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab (JPL) is a state-of-the-art facility for studying such high contrast imaging systems and wavefront control methods. It consists of a vacuum chamber containing a configurable coronagraph setup with a Xinetics deformable mirror. Previously, we demonstrated 4x10^-8 contrast with the SPC at HCIT in 10% broadband light. The limiting factors were subsequently identified as (1) manufacturing defects due to minimal feature size constraints on our shaped pupil masks and (2) the inefficiency of the wavefront correction algorithm we used (classical speckle nulling) to correct for these defects. In this paper, we demonstrate the solutions to both of these problems. In particular, we present a method to design masks with practical minimal feature sizes and show new manufactured masks with few defects. These masks were installed at HCIT and tested using more sophisticated wavefront control algorithms based on energy minimization of light in the dark zone. We present the results of these experiments, notably a record 2.4×10^-9 contrast in 10% broadband light.

Some common metals and alloys have been identified as potential candidates with optical properties applicable to image plane masks for terrestrial planet finder (TPF) coronagraph especially for broad band performance in the visible spectrum. Thin films of these materials exhibit thickness dependence of refractive index and extinction coefficient which vary with wavelength and consequently the intensity and phase of transmitted light. We report on the fabrication and measurement of thickness-dependent optical properties of thin films of Ni, Pt and Inconel alloys to enable optimum design of image plane masks for Lyot coronagraphs to operate in the 500 to 800 nm band. We discuss the potential and limitations of practical masks with such materials.

The optical vortex coronagraph is a promising scheme for achieving high contrast low loss imaging of exoplanets as close as 2λ/D from the parent star. We describe results using a high precision vortex lens that was fabricated using electron-beam lithography. We also report demonstrations of the coronagraph on a telescope employing a tip-tilt corrector.

High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require excellent wavefront control and diffraction suppression. At the Laboratory for Adaptive Optics on the Extreme Adaptive Optics testbed, we have already demonstrated wavefront control of better than 1 nm rms within controllable spatial frequencies. Corresponding contrast measurements, however, are limited by amplitude variations, including those introduced by the micro-electrical-mechanical-systems (MEMS) deformable mirror. Results from experimental measurements and wave optic simulations of amplitude variations on the ExAO testbed are presented. We find systematic intensity variations of about 2% rms, and intensity variations with the MEMS to be 6%. Some errors are introduced by phase and amplitude mixing because the MEMS is not conjugate to the pupil, but independent measurements of MEMS reflectivity suggest that some error is introduced by small non-uniformities in the reflectivity.

TOPS (Telescope to Observe Planetary Systems) is the first coronagraphic telescope concept designed specifically to take advantage of Guyon's method of Phase Induced Amplitude Apodization PIAA).¹ The TOPS primary mirror may incorporates active figure control to help achieve the desired wavefront control to approximately 1 angstrom RMS accurate across the spectral bandwidth. Direct correction of the primary figure avoids the need for a separate small deformable mirror. Because of Fresnel propagation, correction at a separate surface can introduce serious chromatic errors unless it is precisely conjugated to the primary. Active primary control also reduces complexity and mass and increases system throughput, and will likely enable a full system test to the 10-10 level in the 1 g environment before launch. We plan to use thermal actuators with no mechanical disturbance, using radiative heating or cooling fingers distributed inside the cells of a honeycomb mirror. The glass would have very small but finite coefficient of expansion of ~ 5x10^-8/C. Low order modes would be controlled by front-to-back gradients and high order modes by local rib expansion and contraction. Finite element models indicate that for a mirror with n cells up to n Zernike modes can be corrected to better than 90% fidelity, with still higher accuracy for the lower modes. An initial demonstration has been made with a borosilicate honeycomb mirror. Interferometric measurements show a single cell influence function with 300 nm stroke and ~5 minute time constant.

Direct imaging of exo-planets requires that an effcient starlight suppression system and wavefront compensator work together to achieve a stable null whose contrast level is deep enough. The performances of several con- figurations for these two sub-systems have been extensively studied over the past few years, with particular attention being paid to the following four quantities and their relationship: throughput, contrast level, Inner Working Angle and bandwidth. In this paper we propose a new approach that considers starlight suppression and wavefront correction as a unique integrated component that is the association of a shaped-pupil and two sequential deformable mirrors that operate simultaneously as a short stroke pupil mapping device and a wavefront compensator. To do so we first develop a new method based on Huygens wavelets to explain the contrast limits of pupil mapping due to propagation, and study the hybrid associations of PIAA systems and shaped pupils that have been introduced in order to mitigate these effects. Then, since two cascaded deformable mirrors are also a wavelength independent amplitude actuator, we argue that they could be used in conjunction with shaped pupils to carry some of the apodisation load and thus increase the throughput of the new hybrid system.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phase of the beams that are being combined. We have tested a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength across the bandwidth of 8 to 12 microns wavelength. This paper will cover the results of the adaptive nuller tests performed in the mid-IR.

Direct detection and characterization of a planet around a star by nulling interferometry, must be efficient in a large wavelength domain in order to detect simultaneously the infrared bio-tracers CO₂, O₃ and H₂O. This condition requires that an achromatic phase shift of π be implemented, with an accuracy sufficient for achieving a deep nulling at all considered wavelengths. Several solutions have been presented. We present here a new concept for designing such an achromatic phase shifter. It is based on two cellular mirrors (alternatively, transparent plates can be used) where cells have thickness which are respectively odd and even multiples of a quarter of the central wavelength. Each cell introduces then a phase shift of (2k + 1)π or of 2kπ, on the fraction of the wave it reflects. Each mirror is introduced in the collimated beam issued from one or the other telescopes. Because of the odd/even distribution, a destructive interference is obviously produced on axis for the central wavelength when recombining the two beams. The trick to obtain a quasi-achromatisation is to distribute the thickness of the cells, so that the nulling is also efficient for a wavelength not too far from the central wavelength. We show that if the thicknesses are distributed according to the Pascal triangle, a fair quasi-achromatism is reached. This effect is the more efficient that the number of cells is large. For instance, with 256 × 256 cells, where phase shift range is between -6π and +6π one shows that the nulling reaches 10^-6 on the wavelength range [0.7λ₀, 1.3λ₀] which corresponds roughly to the DARWIN specification. In a second step, we study the optimum way to distribute the cells in the plane of the pupil. The most important criterion is the isolation of the planet image from the residual image of the star. Several efficient configurations are presented. Finally we consider some practical aspects on a device belonging to the real world and on the bench we are developing. The major interest of this solution is that it allows a compact, simple and fully symmetric design, with essentially no ajustable sub-systems ; extension to multi-telescopes interferometers with phase shift other than π can also be envisioned.

In the context of the ESA-Darwin mission, Thales Alenia Space has developed a nulling breadboard for ESA. The Multi Aperture Imaging Interferometer (MAII) first demonstrated deep nulling in both integrated optics and multi-axial combination schemes. More recently, Thales Alenia Space and Observatoire de la Côte d'Azur have been improving the nulling performance of MAII. The work was focused on polarization and the bench was upgraded consequently. Unpolarized and polarized nulling ratios are now quite similar at N ≈ 10^-5 over a 5% relative bandwidth, stable over more than one hour. In this paper, we report on the improvements we have implemented in MAII and present our latest results.

Infrared interferometric nulling is a promising technology for exoplanet detection. Nulling research for the Terrestrial Planet Finder Interferometer has explored several interferometer architectures at the Jet Propulsion Laboratory (JPL). The most recent efforts have focused on an architecture which employs a geometric field flip to achieve the necessary π phase delay in the interferometer. The periscope design currently in use allows for a completely achromatic phase flip. Deep interferometric nulling requires optical path stability, precision optical alignment, intensity balancing, and dispersion correction. This paper will discuss recent efforts to implement a precision optical alignment, stabilize the interferometer environment, implement optical path metrology, control intensity balance, and compensate for dispersion introduced by beamsplitter mismatch.

We show the theoretical limitations of a multi-axial nulling interferometer with respect to longitudinal polarization. We furthermore analyze the filtering capabilities of a single-mode fiber in this case.

We have carried out some investigation to optimize the broadband performance of the high-contrast imaging testbed (HCIT) at JPL through optical modeling and simulations. The analytical tool is an optical simulation algorithm developed by combining the HCIT's optical model with a speckle-nulling algorithm that operates directly on coronagraphic images, an algorithm very similar to the one that has been used on the HCIT. We have experimented in our simulations with different designs for the occulting mask and the Lyot Stop, and also tried several different speckle-nulling approaches. Some results predicted by our simulations agree well with the results measured on the HCIT. In this paper we describe the details of our simulations and present our results.

Practical image-plane occulting masks required by high-contrast imaging systems such as the TPF-Coronagraph introduce phase errors into the transmitting beam, or, equivalently, diffract the residual starlight into the area of the final image plane used for detecting exo-planets. Our group at JPL has recently proposed spatially profiled metal masks that can be designed to have zero parasitic phases at the center wavelength of the incoming broadband light with small amounts of OD and phase dispersions at other wavelengths. Work is currently underway to design, fabricate and characterize such image-plane masks. In order to gain some understanding on the behaviors of these new imperfect band-limited occulting masks and clarify how such masks utilizing different metals or alloys compare with each other, we carried out some modeling and simulations on the contrast performance of the high-contrast imaging testbed (HCIT) at JPL. In this paper we describe the details of our simulations and present our results.

The shape of an exoplanet lightcurve is usually obtained by averaging the noise over multiple datasets. Fractal analysis has been demonstrated to be an effective tool for the detection of exoplanet transits using lightcurves summed over all wavelengths sensitive to the detector (G. Tremberger, Jr et. al, 2006 Proc SPIE Vol 6265). The detection of spectral features would depend on the extent to which the signal was buried in the noise. Different noise sources would have different fractal characteristics. Also, the signal strength could be discontinuous in time depending on the exoplanet's local atmospheric environment. Such a discontinuity is unlikely to be detected with time integrated data. The lightcurve noise and shape information were characterized with fractal dimension analysis of a noise buried time series signal. Computer simulation revealed that when the noise is three times that of the signal, the fractal algorithm could detect the signal at about the 87% confidence level. Application to noise buried time series datasets (HD 209458b lightcurve, HD149026b lightcurve) detected discontinuities consistent with the results obtained by averaging datasets. Extension to individual wavelength lightcurves would establish a detection limit for the existence of spectral features at wavelengths important for exoplanet study. Other applications such as pre-implantation genetic screening spectroscopy and spatially varied aneuploidy bio-data could use the same analysis principle as well.

This paper explores and quantifies the sources and effects of light scattering from the New Worlds Observer Starshade into the observing telescope. We will discuss the calculation of the scattered light level and its effect on extra-solar planet detection. We consider light scattered off the starshade from the Sun, the Earth, the Moon, the solarsystem planets, zodiacal dust, and the galactic background. We will treat holes caused by micrometeorites and other orbital debris as a separated case.

Practical band-limited occulting masks used in visible-light Lyot coronagraphs, such as those proposed for the Terrestrial Planet Finder Coronagraph (TPF-C), will exhibit some non-band-limited transmission errors that may limit their observing contrast ratios to unacceptable levels. The complex (both phase and amplitude) transmission profiles of these masks exhibit large dynamic ranges over small spatial scales, which are difficult to probe using ordinary optical microscopes and interferometers. We describe here a technique for making these complex transmission measurements with the mask in-place in a Lyot coronagraph, using point-source images taken in the focal and pupil planes, with the Lyot stop removed. We also present measurements taken from the High-Contrast Imaging Testbed (HCIT) at JPL.

High resolution spectroscopy is the foundation for many of the most challenging and productive of all astronomical observations. A highly precise, repeatable and stable wavelength calibration is especially essential for long term RV observations. The two wavelength references in wide use for visible wavelengths, iodine absorption cells and thorium/argon lamps, each have fundamental limitations which restrict their ultimate utility. We are exploring the possibility of adapting emerging laser frequency comb technology in development at the National Institute of Standards and Technology in Boulder, Colorado, to the needs of high resolution, high stability astronomical spectroscopy. This technology has the potential to extend the two current wavelength standards both in terms of spectral coverage and in terms of long term precision, ultimately enabling better than 10 cm/s astronomical radial velocity determination.

The Space Interferometry Mission is an unique interferometer capable of performing narrow and wide angle astrometry on a few thousands of stars, distributed all over the Galaxy. It will be designed to achieve a single epoch precision of 10 micro arc seconds and an end of mission accuracy of 4 micro arc seconds in position and a similar accuracy in parallax and proper motions. The presence of confusing background and foreground stars might impose a limitation on the astrometric accuracy. We estimate the expected single measurement position uncertainty of the targets, owing to the presence of the confusing stars, from the knowledge of the dispositions and the spectral energy distributions (SEDs) of the stars within and just outside the field-of-view (FOV) of SIM. Our model also includes details of the instrumental parameters and the measurement process. The estimated uncertainties can in turn be used to correct the bias in the single measurement astrometric delay and, thus the final astrometric accuracy can be improved. We estimate the offsets from the zero delay position of the instrument and the projected separation of the components of binary stars in an elemental observation, following an one-dimensional synthesis imaging approach and a model fit to the absolute visibility data. These simulations help us to explore the strategies that can be followed to extract the details of the field through suitable model parameters in future.

Coronagraph focal-plane occulting masks have generally been described as attenuation profiles free of any phase shift. However, phase shifts are expected and observed in physical occulting masks, and they can impose significant limitations on coronagraph contrast at the billion-to-one level in spectrally broad light, as required for the direct imaging of planetary systems orbiting the nearby stars. Here we explore design options for a physically realizable occulting mask composed of a metallic and a dielectric thin film, each profiled in thickness and superimposed on a glass substrate. We show that such hybrid masks, together with a deformable mirror for control of wavefront phase, offer contrast performance better than 10^-9 over spectral bandwidths up to 30% with Lyot coronagraph throughput efficiencies of 66% or more.

One of the most critical units of nulling interferometers is the Achromatic Phase Shifter. The concept we propose here is based on optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection induces a phase shift between the polarization components of the incident light. We present the principles, the current status of the prototype manufacturing and testing operations, as well as preliminary experiments on a ZnSe Fresnel rhomb in the visible that have led to a first error source assessment study. Thanks to these first experimental results using a simple polarimeter arrangement, we have identified the bulk scattering as being the main error source. Fortunately, we have experimentally verified that the scattering can be mitigated using spatial filters and does not decrease the phase shifting capabilities of the ZnSe Fresnel rhomb.

The Annular Groove Phase Mask coronagraph (AGPM) is an intrinsically achromatic vectorial vortex. It consists of integrated subwavelength optical elements whose space-variant polarization properties can be engineered and optimized to synthesize one of the theoretically most efficient coronagraphs. This paper briefly recalls the principles of the AGPM, presents the benefit of its implementation inside a polarimetric differential imager, realistic numerical simulations assessing its performances, as well as the current status of the near-infrared and visible prototype manufacturing operations.

The Darwin and TPF-I space missions will be able to study the atmosphere of distant worlds similar to the Earth. Flying these space-based interferometers will however be an extraordinary technological challenge and a first step could be taken by a smaller mission. Several proposals have already been made in this context, using the simplest nulling scheme composed of two collectors, i.e., the original Bracewell interferometer. Two of these projects, viz. Pegase and the Fourier-Kelvin Space Interferometer, show very good perspectives for the characterisation of hot extra-solar giant planets (i.e., Jupiter-size planets orbiting close to their parent star). In this paper, we build on these concepts and try to optimise a Bracewell interferometer for the detection of Earth-like planets. The major challenge is to efficiently subtract the emission of the exo-zodiacal cloud which cannot be suppressed by classical phase chopping techniques as in the case of multi-telescopes nulling interferometers. We investigate the potential performance of split-pupil configurations with phase chopping and of OPD modulation techniques, which are good candidates for such a mitigation. Finally, we give a general overview of the performance to be expected from space-based Bracewell interferometers for the detection of extra-solar planets. In particular, the prospects for known extra-solar planets are presented.