The use of a laser diode in a joint transform correlator (JTC) is proposed. Effects of temporal coherence, spatial coherence, astigmatism, and elliptical beams are analyzed. Laser diodes can be used in JTC, and also can be used for the correlation process in a Vander Lugt correlator and reading a hologram. Even a light-emitting diode (LED) may be used for the purposes mentioned, if its exit facet is sufficiently small. Two methods for correcting a laser diode beam using a cylindrical lens or a pair of cylindrical lenses are also reviewed. A corrected laser diode can be used in JTC to totally eliminate the effect of astigmatism.