Measurement of second-order coherence in a light beam using a microscope and a grating

The measurement of the complex cross-spectral density function of a light beam is discussed using a new type of shearing interferometer. This interferometer is composed principally of only an imaging lens system such as a microscope and an ordinary transparent diffraction grating replica. This interferometer is selfaligning, inexpensive, and able to introduce precise wavefront shears of the order of a few light wavelengths. A theoretical analysis of the instrument is developed giving expressions for calculating the magnitude and phase of the cross-spectral density function using observable properties of the interference pattern formed by the instrument. A simple experiment is described which demonstrates the operation of the instrument.