Breakthroughs in Silicon Grism and Immersion Grating Technology at Penn State

New Frontiers in Stellar Interferometry

Miller

2004

Self Cite

We report results from development of a prototype extremely coherent single mode fiber optic array for the TPF visible nulling interferometer. This device is used to negate the effects of residual stellar leakage (scattering) due to imperfections in the TPF telescope optics and the visible nulling interferometer optical train. This prototype consists of 10 10 single mode fibers, V-groove arrays, two lenslet arrays (one at the front end and the other at the back end) and auxiliary mechanical components. This first development will pave a clear path for making a final coherent fiber array with ~ 1000 fibers. The final array, once fully functional, should be able to improve image contrast by another ~ 3 orders of magnitude after 6-7 orders of magnitude star light subtraction using the visible nulling interferometer to allow detection of earth-like planets as close as 0.1 arcseconds around stars at ~ 10 pc in space with a 4m size TPF. This concept combines all the advantages of a nulling interferometer with the simplicity of a modest size and modest optical quality single aperture telescope, which allows tremendous reduction of the total cost and simplicity of the operation of a visible TPF over other TPF approaches. This fiber array can also be used in the visible coronagraph for rejecting scattered light.

Section: Precision Parametersmentioning

confidence: 90%

Development of an extremely coherent single-mode fiber bundle array for high-contrast imaging of extrasolar planets with visible Terrestrial Planet Finder

New Frontiers in Stellar Interferometry

Miller

2004

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“…Our new processes should improve the grating surface quality and efficiency of the anamorphic gratings. We have also developed special tools at Penn State Nanofab for handling silicon disks with diameter up to 6 inch and thickness up to 2 inch (Ge et al, 2002b). These tools should provide an immediate step for making high resolution silicon anamorphic immersion gratings.…”

Section: Development Of a Silicon Anamorphic Immersion Gratingmentioning

confidence: 99%

Silicon anamorphic gratings for IR high-resolution spectroscopy with future giant telescopes

Bernecker

Future Giant Telescopes

et al. 2003

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Future 30m telescopes provide enormous challenges for IR high resolution spectrograph design. The spectrograph collimated beam size will reach ~ 400 mm in order to reach R ~ 25,000 under 0.4 arcsec seeing-limited images. This beam size will push an IR spectrograph volume larger than that of the giant optical echelle spectrograph at 10m telescopes, e.g. the Keck HIRES is 6 6 4 m 3 (Vogt et al. 1994). The cost would be enormous considering the entire instrument must be cooled to cryogenic temperatures to be feasible. Here we propose a new kind of IR spectrometer using silicon anamorphic immersion gratings as the main disperser. By operating silicon immersion gratings in an anamorphic immersion mode, the increase in spectral resolving power can be up to a factor of n 2 or ~12 times at Brewster's angle (Dekker 1987). Hence, to reach the same spectral resolution, the collimated beam size is reduced to ~33mm in diameter, which makes the design of the instrument relatively easy.The recent breakthrough in silicon immersion grating technology at Penn State has allowed us to routinely fabricate high quality silicon grisms and immersion gratings with sizes of up to 2 inches, <1% integrated scattered light, and diffraction-limited performance thanks to newly developed techniques. Silicon anamorphic immersion gratings with etched dimensions of ~4 inches are being developed at Penn State. The first grating will be available for testing in late 2002. Currently, industry can supply up to 12 inch diameter silicon ingots. We plan to develop a new tool to handle this large grating size in our stateof-the-art nanofabrication facility. A silicon anamorphic grating of this size can provide a seeing-limited (0.4 arcsec) spectral resolution of R ~ 30,000 or diffraction-limited spectral resolution of R ~ 750,000 at 2.2 microns. In this paper, technical issues related to the design of an anamorphic grating spectrograph are discussed.

“…Our new processes should improve the grating surface quality and efficiency of the anamorphic gratings. We have also developed special tools at Penn State Nanofab for handling silicon disks with diameter up to 6 inch and thickness up to 2 inch (Ge et al, 2002d). These tools should provide an immediate step for making high resolution silicon anamorphic immersion gratings.…”

Section: Development Of a Silicon Anamorphic Immersion Gratingmentioning

confidence: 99%

Adaptive optics high-resolution IR spectroscopy with silicon grisms and immersion gratings

Chakraborty

et al. 2003

SPIE Proceedings

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The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy when it is coupled with adaptive optics at large ground-based telescopes. Fabrication of high quality silicon grism and immersion gratings up to 2 inches in dimension, less than 1% integrated scattered light, and diffraction-limited performance becomes a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ~ 4 inches are being developed at Penn State. These immersion gratings will be able to provide a diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. Prototype silicon grisms have been successfully used in initial scientific observations at the Lick 3m telescope with adaptive optics. Complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ~ 3000 were obtained. This resolving power was achieved by using a silicon echelle grism with a 5 mm pupil diameter in an IR camera. These results represent the first scientific observations conducted by the high-resolution silicon grisms, and demonstrate the extremely high dispersing power of silicon-based gratings. New discoveries from this high spatial and spectral resolution IR spectroscopy will be reported. The future of silicon-based grating applications in ground-based AO IR instruments is promising. Silicon immersion gratings will make very high-resolution spectroscopy (R > 100,000) feasible with compact instruments for implementation on large telescopes. Silicon grisms will offer an efficient way to implement low-cost medium to high resolution IR spectroscopy (R ~ 1000-50000) through the conversion of existing cameras into spectrometers by locating a grism in the instrument's pupil location.