On the Feasibility of Using a Laser Guide Star Adaptive Optics System in the Daytime

Abstract

We investigate the use of ultra-narrow band interference filters to enable daytime use of sodium laser guide star adaptive optics systems. Filter performance is explored using theoretical and vendor supplied filter transmission profiles, a modeled daylight sky background, broadband measurements of the daytime sky brightness on Maunakea, and an assumed photon return from the sodium laser guide star and read noise for the wavefront sensor detector. The critical parameters are the bandpass of the filter, the out-of-band rejection, and the peak throughput at the wavelength of the laser guide star light. Importantly, a systematic trade between these parameters leads to potentially simple solutions enabling daytime observations. Finally, we simulated the Mid-Infrared Adaptive Optics (MIRAO) system planned for the Thirty Meter Telescope with an end-to-end simulation, folding in daytime sky counts. We find that MIRAO with five sodium laser guide stars, commercial off-the-shelf filters to suppress the sky background in the laser guide star wavefront sensors, and a near-infrared natural guide star ($K \le 13$) tip/tilt/focus wavefront sensor can attain daytime Strehl ratio values comparable to those at night.