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J. Ge, D. Ciarlo, P. Kuzmenko, B. Macintosh, C. Alcock, K. Cook, D. Gavel, C. Max (LLNL), J. Lloyd, J. Graham, M. Liu (UCB), S. Severson (UCSC)
The world's first silicon grisms with 10x10 mm2 etched grating area and 46\circ wedge angles have been successfully developed at LLNL in 1999. The first light of one of the grisms at the Lick 3m telescope with the IRCAL near-IR camera and adaptive optics has demonstrated a diffraction-limited spectral resolution, R = 5,500 at 2.2 \mum with a pupil diameter of only 5 mm. This spectral resolution is the highest of all conventional grisms. The measured scattering light level from the grism is less than 4%. Coupled with the Lick AO system, it allows efficient IR spectroscopy at very high spatial resolution at 0.2 arcsec. Combined with a conventionally made CaF2 grism cross-disperser, it allows a complete wavelength coverage in the K band. The details of first light engineering tests and initial scientific observations will be reported.
The etched silicon gratings including grisms and immersion gratings we are developing at LLNL promise a major impact in IR spectroscopy. The silicon grisms promise a very convenient and inexpensive way to implement intermediate and high spectral resolution in any existing IR camera. The silicon immersion gratings offer high efficiency and very high spectral resolving power (R > 100,000) in the IR for the first time.
For example, a silicon grism with 40 mm clear entrance aperture and a 46\circ wedge angle can provide a diffraction-limited spectral resolution of R = 10,000 - 100,000 in ~ 1-10 \mum. The same grating working in the immersed reflection mode can provide ~ three times higher spectral resolution than in the transmission mode. Both of the silicon immersion grating and grism promise to play a critical role in space and airborne missions to significantly reduce the size and weight of spectroscopic instruments.
The silicon grism development work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
The author(s) of this abstract have provided an email address for comments about the abstract: ge1@llnl.gov