Evaluation of ground layer adaptive optics for the wide field optical spectrograph on the TMT

We arrive at a Ground Layer Adaptive Optics (GLAO) design that offers true seeing-improved performance and operation for the red and infrared wavelengths. The design requires an adaptive secondary (AM2) and that the sodium Laser Guide Star (LGS) launch telescope be able to steer four of the beams to 8.5 arcminutes off-axis. When provided with this, the proposed design is potentially the simplest, lowest cost design that can take the form of an upgrade. This is seen as a significant advantage over designs that would build an adaptive mirror into each of the four arms of WFOS. We show that the performance penalty for using one mirror instead of four to correct the entire 81 square arcminute WFOS field is minor