Demonstration of a binary-optic infrared grism: a slitless spectrograph for meteor observations

We describe a grism suitable for low-resolution, slitless spectroscopy in the IR region between 3.0 and 5.0 micrometers . The grism is fabricated in silicon using a three-mask, photolithographic process, resulting in an eight-step binary approximation to the normal sawtooth grating profile. Desirable features of this approach include the ability to incorporate aberration correction in the gratin and a gentle ruing relief profile permitting a conformal anti-reflection coating for improved efficiency. To demonstrate the performance of this grism in a practical applications, we have constructed a slitless spectrograph system using an off-the-shelf InSb camera and simple, uncooled, refractive optics. This system is well suited to observing compact, bright, transient phenomena without good a priori knowledge of their positions. We present examples of present instrument performance. An upgrade currently under construction will increase sensitivity by cooling more of the optical path and increasing the aperture of the collecting optics. We plan to use the improved instrument to observe the Leonid Meteor shower in November 1998.