Laser beam frequency doubling system

Abstract

For separation of second and higher order second harmonics from a composite laser beam, a substrate is provided with a binary level relief structure that, in the preferred construction, consists of a regular series of parallel substantially rectangular grooves on one or both of its major surfaces. In a transmissive grating, which is traversed only once by the beam, the depth h of the grooves is chosen to be .lambda. divided by n.sub.1 -n.sub.0, where n.sub.0 is the refractive index external to the grating (assumed to be approximately unity for air), n.sub.1 is the refractive index of the substrate, and .lambda. is the wavelength that will pass directly through the grating, e.g. the second harmonic. Wavelengths greater than .lambda., e.g. the fundamental 2.lambda., will be diffracted away from the beam path. When a reflective coating is applied on the surface with the relief structure, the groove depth is chosen to be .lambda. divided by 2n.sub.0 or 2n.sub.1 depending upon whether the beam encounters the relief structure from outside the substrate or from inside, respectively. A more general formula for the value of h provides for the incident beam arriving at an inclination to the normal to the substrate surface. Also the relief structure itself can be more general in nature, consisting of elevated and unelevated portions of various shapes.