We had developed three types of large VPH grisms (110×106 mm²) for FOCAS of the 8.2 m Subaru Telescope with high efficiency, high dispersion and small wavefront error in visible region. However, it has been highly difficult to fabricate VPH gratings for longer wavelength due to thickness of the grating. In order to overcome this problem, by optimizing exposure condition and introducing active phase control technique, we had successfully developed VPH grating for optical communication wavelength (1550 nm) with diffraction efficiency over 90% (TE mode) and a high refractive index modulation of 0.047. We extend these techniques to the device for astronomical observation, aiming at the application of K band VPH gratings for MOIRCS of the Subaru Telescope. The resultant grating has attained high diffraction efficiency of 91.5%, spectral bandwidth (FWHM) 320 nm, and small wavefront error 0.03 waves in r.m.s. at 2200 nm. This VPH grism is a promising dispersion device for astronomical observation in near-infrared region.

Date Published: 9 July 2008
PDF: 11 pages
Proc. SPIE 7014, Ground-based and Airborne Instrumentation for Astronomy II, 70141Q (9 July 2008); doi: 10.1117/12.790107

Published in SPIE Proceedings Vol. 7014:
Ground-based and Airborne Instrumentation for Astronomy II
Ian S. McLean; Mark M. Casali, Editor(s)