Effects of small misalignments on output beam quality in off-axis negative-branch confocal strip unstable resonator

In this paper the beam characteristics of off-axis negative branch confocal strip unstable resonator have been studied. The resonator geometric relation is derived, and the formulas of mirror geometric parameters are expressed. Numerical simulation has also been carried out for negative branch strip off-axis confocal unstable resonator by means of Fox-Li iteration method and Collins Formula. The result shows that the intensity at the optic axial is stronger than other region and the phase distribution is close to uniform distribution on the output mirror, the far field intensity angle distribution is a typical Gaussian distribution of fundamental mode with little side lobe because of the straight edge diffraction. The influence of tilted mirror with different angle on far-field light intensity distribution for both negative and positive branch also have been compared, which shows that negative-branch is far less sensitive to the misalignment of mirror than positive branch.