Physics – Optics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt........12t&link_type=abstract
Thesis (PhD). UNIVERSITY OF HAWAI'I, Source DAI-B 63/06, p. 2875, Dec 2002, 153 pages.
Physics
Optics
3
Scientific paper
We have designed, fabricated, and installed a coudé imaging spectrograph for use with the Advanced Electro-Optical System (AEOS) 3.7-meter telescope atop Mt. Haleakala on Maui. The spectrograph is divided into two main subsystems: a visible (˜0.5 01.0 μm) channel and an infrared (˜1.0 2.5 μm) channel, both cross-dispersed echelle spectrometers with resolutions in the 10,000 50,000 range. Several features have made this endeavor distinctive. The most important was the fact that the AEOS spectrograph was designed to have a spectral resolution sufficiently high enough to clearly resolve the atmospheric OH lines, which are the primary source of background radiation between 0.7 1.8 μm. In the infrared, achieving adequate sensitivity between the OH lines is possible only with the low read noise (5 e- rms) and dark current (1 e- min-1) of the large-format detectors the HAWAII array development program has demonstrated, thereby making the AEOS spectrograph infrared channel one of the highest resolution astronomical grating spectrometers currently in existence and unique in the science it can accomplish. The optical design of the spectrographs is based on the “white pupil” concept, where a second collimator allows placing the pupil image on both the echelle and cross-disperser gratings, thus minimizing the size and complexity of the spectrograph camera optics. The white pupil design also allows the echelles to be used very close to true Littrow configuration, thus maximizing grating efficiency. We present preliminary observations and results obtained with both spectrograph channels. Expected wavelength coverages and dispersions have been achieved. Initial estimates of the visible channel throughput show it to be approximately 6% on average over the wavelength coverage, comparable to the best high-resolution visible echelle spectrometers. The infrared channel requires further testing before accurate throughput and sensitivity characteristics can be derived. At the time of this work, the slits of the two respective channels are coaligned to within two arcseconds; upcoming installation of an adjustable dichroic will therefore increase the versatility and efficiency of the instrument even further by allowing both visible and infrared spectra to be acquired simultaneously. The AEOS spectrograph design relied in part upon previous experience at the IfA. Nevertheless, the size and unique features of the infrared spectrograph made its custom design a challenge.
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