Angle measurement by injection-detection in a laser diode

We propose a new technique to measure the angle of a remote flat surface with respect to a laser beam based on injection-detection in a LD. The surface under test acts as the remote mirror of an external cavity laser (ECL), which is made to operate in the coherent collapse regime. The power emitted by the ECL depends on the alignment of the remote surface, and this allows to measure angles with a sensitivity of 0.1 arcsec. The attained performances are comparable to those of existing autocollimators with the advantage of compactness and low cost. This make the new technique interesting for the development of a measuring instrument.