Introduction

The use of laser guide star (LGS) adaptive optics (AO) was pioneered at Lick Observatory in the mid-90s [1] on the Shane 3-meter telescope. The current infrared camera, IRCAL, was installed and characterized in 2000 [12]. A major system upgrade, called ShaneAO, is in the process of being tested and installed on the Shane telescope [4] with plans for first light in late 2013. This upgrade comprises:

• A new infra-red camera (called ShARCS - Shane Ao infraRed Camera and Spectrograph) based on the Teledyne HAWAII-2RG detector (the same chip is used in the MOSFIRE instrument on the Keck telescope) that has higher resolution, higher quantum efficiency and lower noise than the PICNIC array used on IRCAL. The change in detector alone promises longer exposure times before detector limits are reached (where night sky lines are not dominant).

• A dual-deformable mirror AO pipeline with a 52-actuator, high-stroke, low-frequency (spatial and temporal) ALPAO DM-52 mirror (the ``woofer'') and a 1024-actuator, low-stroke, high-frequency MEMS Boston Micromachines Kilo-DM mirror (the ``tweeter'') [3]. The Shack-Hartmann wavefront sensor camera is being upgraded to allow use of a 30$\times$30 lenslet array.

• A more efficient solid-state laser [5] (replacing the current dye laser) with projected improvements to the launch system geared towards increasing return flux so that the AO system can use more subapertures.

• A new support structure for the AO system and camera designed to reduce flexure and improve long-exposure stability. The assembly is also designed to be rotated with precision to allow for long-slit spectroscopy.

The cumulative effect of the upgrades will be to deliver diffraction-limited imaging and Nyquist-sampled point-spread functions in the $J$, $H$ and $K$ bands [4] at nearly double the Strehl ratio of the current system [6]. Nyquist-sampling in all bands is particularly desirable to measure and reconstruct the PSF reliably. The PSF varies because of atmospheric turbulence and the change in gravity vector as the telescope moves - the AO bench is to be mounted at the Cassegrain focus.

The new laser with a pulse format designed to couple better to the Sodium atoms in the upper atmosphere is expected to allow routine use of more subapertures, making better use of the tweeter's spatial frequency sampling ability. Hence, any turbulence will be better measured and corrected because subaperture spacing will be 10 cm for a 30$\times$30 lenslet array, which is a much better match to measured conditions at Lick Observatory [7]. In addition, the telescope will be usable over a greater range of the nightly and seasonal variations in mesospheric Sodium levels.

Spectroscopy will also be much improved because of the aforementioned improvements in stability. The ability to reliably rotate the instrument structure and the slit will allow stable object tracking over a longer course of time. Less object wander enables reliable co-adding to raise signal-to-noise ratio (SNR), better tracking of variability in night sky lines and minimizes the impact of hot pixels. The intent of these upgrades is to investigate fainter objects at the diffraction limit of the telescope in all bands and achieve target SNRs in less time. We present the result of modeling the emissivity and throughput of ShaneAO and conservatively predict that the new system will achieve its targets.