Collimation Testing and Coherence Length Measurement of Short Coherence Laser Beams Using a Compact Holographic Shearing Interferometer

A compact system using two holographic optical elements (HOEs) is designed for collimation testing as well as for coherence length measurement of beams from short coherence lasers. Collimation testing is performed by observing the rotation of interference fringes with respect to the direction of shear. Coherence length is obtained by measuring the contrast of interference fringes by varying optical path difference between the two HOEs. The collimation is achieved within the error limit of 10 μm while the coherence length of used laser diode is measured to be 1600 ± 20 μm. Realization of the system is described and its applications are discussed.