Performance modeling of a wide-field ground-layer adaptive optics system

Using five independent analytic and Monte Carlo simulation codes, we have studied the performance of wide-field ground-layer adaptive optics (GLAO), which can use a single, relatively low order deformable mirror to correct the wave-front errors from the lowest altitude turbulence. GLAO concentrates more light from a point source in a smaller area on the science detector, but unlike with traditional adaptive optics, images do not become diffraction-limited. Rather, the GLAO point-spread function (PSF) has the same functional form as a seeing-limited PSF and can be characterized by familiar performance metrics such as full width at half-maximum (FWHM). The FWHM of a GLAO PSF is reduced by 0."1 or more for optical and near-infrared wavelengths over different atmospheric conditions. For the Cerro Pachon atmospheric model, this correction is even greater when the image quality is poorest, which effectively eliminates "bad seeing" nights; the best seeing-limited image quality, available only 20% of the time, can be achieved 60% - 80% of the time with GLAO. This concentration of energy in the PSF will reduce required exposure times and improve the efficiency of an observatory up to 30% - 40%. These performance gains are relatively insensitive to a number of trade-offs, including the exact field of view of a wide-field GLAO system, the conjugate altitude and actuator density of the deformable mirror, and the number and configuration of the guide stars.