Double-shearing interferometer for accurate test of laser wavefront

Inter-satellite laser communications require nearly diffraction-limited laser beam, correspondingly an accurate test of laser wavefront is necessary. In this paper, an aperture-divided double lateral-shearing interferometer is developed which can be used for wavefront analysis ranged nearly from 0.1λ to λ with a simple structure and no alignment needed. The interferometer includes two Jamin plane parallel plates and four slightly wedge-shaped plates of the same size. The four wedged plates are combined into two pairs of different wedges, which are separately placed in the arms of the Jamin interferometer. The thickness of a plate leads to a beam shift, and the wedge a beam inclination, so that there appears two shearing interferogram of different background fringes in a divided aperture. Plane wavefront, perfect spherical wavefront and some types of aberration including primary spherical aberration, primary coma are simulated. It is concluded that the measurable wavefront height of laser beam reaches to better than 0.1λ. Note that the interference is from the beams of equal optical distance thus suitable for semiconductor lasers for the space application, which may be with the coherent length of millimeters.