  Direct imaging of exoplanets allows us to measure positions and chemical
signatures of exoplanets. Given the limited resources for space observations
where the atmosphere is absent, we want to make these measurements from the
ground. However, it is difficult from the ground because it requires an
adaptive optics system to provide an extremely well corrected wavefront to
enable coronographic techniques. Currently only natural guide star AO systems
have demonstrated the necessary wavefront correction for direct imaging of
exoplanets. However, using a stellar source as the guide star for wavefront
sensing limits the number of exoplanet systems we can directly image because it
requires a relatively bright V~10 mag star. To increase the number of
observable targets, we need to push the limit of natural guide stars to fainter
magnitudes with high Strehl ratio correction. We propose to combine laser guide
star (LGS) and natural guide star (NGS) wavefront sensing to achieve the high
Strehl correction with fainter natural guide stars. We call this approach
Hybrid Atmospheric Phase Analysis (HAPA); 'hapa' in Hawaiian means 'half' or
'of mixed ethnic heritage'. The relatively bright LGS is used for higher order
correction, whereas the NGS is used for high accuracy lower order correction.
We focus on demonstrating this approach using Robo-AO-2 at the UH 2.2m
telescope on Maunakea with a UV Rayleigh laser at 355 nm. The laser focuses at
10 km altitude and has an equivalent magnitude of m_U~8. In this report
specifically, we present simulated results of HAPA employed at Robo-AO-2, with
the LGS system having a single configuration of 16x16 subaperture
Shack-Hartmann wavefront sensor and the NGS system having 6 different
configurations -- 16x16, 8x8, 5x5, 4x4, 2x2 and 1x1. We also discuss the on-sky
experiments we plan to carry out with HAPA at the UH 2.2m telescope.
