Infrared camera and spectrograph for the Subaru Telescope: performance improvement with the new Aladdin-III array

We report on the significantly improved performance of the Infrared Camera and Spectrograph (IRCS) for the Subaru Telescope. The IRCS consists of the camera side for imaging and grism spectroscopy and the spectrograph side for echelle spectroscopy. Due to the low sensitivity of the previous Aladdin-II engineering grade InSb infrared array on the camera side, the capability of imaging and grism spectroscopy was reduced. Thus, we replaced the array on the camera side into the new Aladdin-III array in August 2001. The newly installed Aladdin-III array has 1.9 times higher quantum efficiency (95%), 2/3 lower read-out noise (12e(-) with 16 non-destructive-readout at 27.5K of the array temperature) and better cosmetics than the old Aladdin-II array. We have also obtained grism spectra for a comparison of performances with the old and the new arrays. The spectra with the new array show about twice better signal-to-noise for each spectral element and almost no systematic noise. Currently we have two different types of arrays: Aladdin-II array on the spectrograph side and the science grade Aladdin-III array on the camera side. We will also present dark current, read-out noise, linearity curve and the other characteristics as a function of array temperatures to summarize the current performance of both arrays. We plan to upgrade the Aladdin-II array on the spectrograph side to a new Aladdin-III array in summer 2003.