Alexander Ksendzov

Terrestrial Planet Finder Interferometer: 2007-2008 Progress and Plans

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.

Terrestrial Planet Finder Interferometer Technology Status and Plans

This paper reviews recent progress with technology being developed 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. TPF-I is in the early phase of its development. The science requirements of the mission are described along with the current design of the interferometer. The goals of the nulling and formation-flying testbeds are reviewed. Progress with TPF-I technology milestones are highlighted.

Silver halide single mode fibers for modal filtering in the middle infrared

Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers, because they can help achieve deeper interferometric nulls. Silver halide fibers of composition AgClxBr1-x(0 Astronomical Telescopes + Instrumentation AS 3 2008-06-23|2008-06-28 SPIE Astronomical Telescopes + Instrumentation AS08 796182 Marseille, France Optical and Infrared Interferometry 7013 IO and Fibers 11

Measurement of spatial filtering capabilities of single mode infrared fibers

Spatial filtering is necessary to achieve deep nulls in optical interferometer and single mode infrared fibers can serve as spatial filters. The filtering function is based on the ability of these devices to perform the mode-cleaning function: only the component of the input field that is coupled to the single bound (fundamental) mode of the device propagates to the output without substantial loss. In practical fiber devices, there are leakage channels that cause light not coupled into the fundamental mode to propagate to the output. These include propagation through the fiber cladding and by means of a leaky mode. We propose a technique for measuring the magnitude of this leakage and apply it to infrared fibers made at the Naval Research Laboratory and at Tel Aviv University. All measurements are performed at 10.5 μm wavelength.

Wedge filters for spectral imaging in the near-IR using metal grids

Linear variable filters have found increasing applicability in spectrally selective optical instruments. They serve as moderate resolution spectral discriminators in astronomical instruments and in reconnaissance equipment. They perform extremely well as sliding out-of-band blocking filters when used in conjunction with grating spectrometers.

Design of multibandwidth frequency selective surfaces for near-infrared filtering

This paper describes the design of infrared filters using methods drawn from microwave and millimeter wave filters. Special note is made of approximations made in the infrared design, and ways to improve upon these approximations. Results from the design, manufacture and test of linear wedge filters built using microlithographic techniques and used in spectral imaging applications will be presented.

Advanced Si IR detectors using molecular beam epitaxy

SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

Low power consumption lasers for next generation miniature optical spectrometers for trace gas analysis

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Air quality monitoring grows in importance as mission duration increases. Due to the small size, low power draw, and performance reliability, semiconductor laser-based instruments are viable candidates for this purpose. Achieving a minimum instrument size requires lasers with emission wavelength coinciding with the absorption of the fundamental absorption lines of the target gases, which are mostly in the 3.0-5.0 μm wavelength range. In this paper we report on our progress developing high wall plug efficiency type-I quantum-well GaSb-based diode lasers operating at room temperatures in the spectral region near 3.0-3.5 μm and quantum cascade (QC) lasers in the 4.0-5.0 μm range. These lasers will enable the development of miniature, low-power laser spectrometers for environmental monitoring of the spacecraft.

An optical fiber-based high contrast imager

Arrays of single mode fibers can be used to form segmented pupils of almost arbitrary geometry. Such pupil arrays can be used both for interferometric imaging, for example by non-redundant aperture masking or in direct imaging systems such as the phased array coronagraph. Achieving control over the optical coupling, phase and dispersion for fiber arrays of reasonable size is a technological challenge. Progress has been made using a monolithic block of single mode fibers, lens arrays and masks, and mirror arrays. On one testbed, arrays of up to 37 beamlets are being combined to form a single image. On a second testbed, control of dispersion between fibers of slightly different length is being evaluated. The combination of the techniques being demonstrated has a range of potential uses in astronomy. In this paper we discuss the initial testbed results.

Technology challenges for exoplanet detection with mid-IR interferometry

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.