The JANUS X-Ray Flash Monitor

JANUS is a NASA small explorer class mission which just completed phase A and was intended for a 2013 launch date. The primary science goals of JANUS are to use high redshift (6<z<12) gamma ray bursts and quasars to explore the formation history of the first stars in the early universe and to study contributions to reionization. The X-Ray Flash Monitor (XRFM) and the Near-IR Telescope (NIRT) are the two primary instruments on JANUS. XRFM has been designed to detect bright X-ray flashes (XRFs) and gamma ray bursts (GRBs) in the 1-20 keV energy band over a wide field of view (4 steradians), thus facilitating the detection of z>6 XRFs/GRBs, which can be further studied by other instruments. XRFM would use a coded mask aperture design with hybrid CMOS Si detectors. It would be sensitive to XRFs/GRBs with flux in excess of approximately 240 mCrab. The spacecraft is designed to rapidly slew to source positions following a GRB trigger from XRFM. XRFM instrument design parameters and science goals are presented in this paper.Comment: submitted to Proc. SPIE, Vol. 7435 (2009), 7 pages, 8 figure

Haze-Free Polymer Dispersed Liquid-Crystals Utilizing Linear Polarizers

Polymer dispersed liquid crystal(PDLC) light shutters are scattering in the OFF state and transparent in the ON state for normally incident light. PDLC shutters appear hazy in the ON state when viewed at oblique angles as a result of light scattering. The haze is caused by the effective increase in the refractive index of the liquid crystal. However, only one polarization of the incident radiation is scattered. Therefore, PDLC shutters with a linearly polarized sheet on the incident surface are haze‐free for an entire viewing plane. While addition of a polarizer reduces transmission through the PDLC to less than 50%, it also offers a simple means of producing haze‐free PDLC shutters for applications where viewing is predominantly in one plane.</p