Lateral shearing interferometer for auto alignment beam sensing

An auto-alignment beam tracking apparatus comprising:

• objective optics configured to receive optical radiation from a viewed scene and an auto-alignment beam;
• an auto-alignment beamsplitter configured to separate the auto-alignment beam from the optical radiation;
• an optical train configured to receive at least a first portion of the auto-alignment beam from the auto-alignment beamsplitter;
• a linear detector array including a plurality of photosensitive detectors arranged side-by-side in a single row, each photosensitive detector being configured to measure intensity of electromagnetic radiation incident thereon;
• and
• a lateral shearing interferometer positioned between the optical train and the linear detector array, the optical train being configured to direct the first portion of the auto-alignment beam to the lateral shearing interferometer, the lateral shearing interferometer being configured to produce an interference pattern at the linear detector array from the first portion of the auto-alignment beam, wherein changes in the intensity measured by the plurality of photosensitive detectors over time corresponding to a lateral shift of the interference pattern on the linear detector array indicate an angular tilt of the auto-alignment beam,
• wherein the lateral shearing interferometer includes a diffraction grating configured to spatially disperse the first portion of the auto-alignment beam into at least two diffraction orders, interference between the at least two diffraction orders producing the interference pattern at the linear detector array, and wherein the diffraction grating is blazed for a 50/50 dispersion between the 0 diffraction order and the +1 diffraction order.