Collimation testing using coherent gradient sensing

In the present communication, an application of coherent gradient sensing (CGS) for collimation testing of an optical beam has been proposed. In the path of the beam to be tested, a set of two identical linear Ronchi gratings is introduced. The diffracted orders from the two gratings traveling in the same direction are isolated using spatial filtering arrangement. The resulting laterally sheared wavefronts carry information regarding the defocusing errors. The grating rotation mechanism has been incorporated for collimation setting. The results of experimental investigation are presented. Improved accuracy and precision has been achieved because the requirement of maintaining the grating separation to be equal to self-imaging distance as in Talbot interferometry has been alleviated.

► Improved design for collimation testing using grating based shearing interferometer is presented.
► Simple, inexpensive and flexible design of experimental set-up.
► Errors due to inaccurate grating separation minimized.
► Improved measurement accuracy and precision achieved.