Diffractive optical element external cavity diode laser

Summary form only given. The diffractive optical element (DOE) discussed here is a reflective Fresnel zone plate which has a strongly wavelength dependent focal length. The DOE is placed behind the back facet of an uncoated Fabry-Perot diode laser. Uncollimated light emerging from the Fabry-Perot diode laser is reflected off the DOE and focused back down onto the optic axis. Different wavelengths are focused to different points along the optic axis so that moving the DOE along the optic axis focuses different wavelengths onto the facet of the laser and thereby sets the wavelength of operation of the laser.