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A New Grating for CRSP (1Sep94)
(from KPNO, NOAO Newsletter No. 39, 1 September 1994)

Due to the improved performance and larger spectral coverage of the 256  256
InSb array in CRSP, one may now obtain complete coverage of a given spectral
band with a single grating setting. This makes the 50 l/mm grating 4
redundant. The intermediate resolution grating 3 provides almost complete
coverage of the J and K bands, but its efficiency in the H band is very low
because one is operating well off the blaze.

To fill this void, we are ordering a new grating 4, which will have a 200
l/mm ruling, blazed at 3 um. In the H band (m = 2), this grating should yield
a dispersion of 0.0012 um/pixel, or a two-pixel resolving power of 670, at
much higher efficiency than possible with grating 3. As an added bonus, this
grating will provide approximately the same resolving power in the I band
(0.9-1.2 um) in 3rd order, without the order overlap problems encountered
with gratings 1, 2, and 3 in 4th order.

The grating is expected to arrive in early September and should be installed
for the fall observing season. When it is installed, the instrument manual in
the NOAO anonymous ftp area kpno/manuals will be updated appropriately.

Dick Joyce

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