The experimental layout for the diffraction spectrometer is shown in Fig. 1. In this setup, the laser light passes through a narrow slit, which forms the object to be imaged. This slit is located at the focal point of a spherical mirror, such that the light hitting the diffraction grating is collimated. The light then diffracts off of the grating, with different wavelengths of light diffracted at different angles. The second spherical mirror then forms an image. Different wavelengths of light will form an image of the original slit at different horizontal locations due to the different angles of diffraction from the grating. For a laser running multimode, this will produce several images of the slit, corresponding to the different wavelengths present in the laser. During the first part of the experiment, a free-running diode without optical feedback should be used. This setup provides a common apparatus for determining the wavelength of an “unknown” source in undergraduate laboratories, so much of this equipment may already be available.