Collimation testing techniques: A review

Collimation of beam is essential in long path interferometry otherwise significant measurement error may be introduced. Therefore, considerable efforts were spent in developing techniques of collimation testing (1-33). In laser interferometers, the source is effectively a point. However, its axial shift from the focus of the collimator introduces a curvature in the wave front and its lateral shift may introduce off-axis aberrations. Therefore, the objective is to place the point source at the focus of the collimator. This task is achieved by collimation testing techniques, which can be grouped under Interferometry, Shear interferometry, Talbot interferometry and Phase conjugate interferometry. We will discuss these techniques below.