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Session 74 - Ground-Based Instruments.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We have fabricated an immersion echelle grating using silicon micromachining (chemical etching) techniques (Graf et al. 1993, Applied Optics, Vol. 33, No. 1, p. 96). The grating consists of a pattern of V-shaped grooves (25\mum spacing, 70 degree opening angle, blazed at 55 degrees) etched onto one facet of a monocrystaline silicon prism. By diffracting an IR beam inside the prism we obtain a factor of 3.47 (the refractive index of Si at 2\mum) increase in resolving power over a front surface reflection grating of the same length. This technique has the advantage that the grating can obtain equivalent spectral resolution to a front surface grating 3.47 times its size, making the immersion grating ideal for cryogenic and/or space-based platforms where spectrometer size must be minimized. We present laboratory test results which evaluate the efficiency and pattern accuracy of our immersion echelle; first as a front surface reflection grating from \lambda = 0.5\mum to 2.5\mum, and then in immersion at \lambda = 1.5\mum to 2.5\mum. Finally, we offer some conclusions and suggestions regarding the utility of such gratings in astronomical spectrometers. This work was supported by the David and Lucile Packard Foundation and by NASA Grant NAGW-4027.
