  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.
