Thermally Induced Surface Relief Holograms
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Holograms on photoresist are recorded as surface relief modulations (SRH), as opposed to phase holograms which are refractive index modulations. Fabrication of SRH requires a layer 10 of resist, which is then exposed to the sinusoidal intensity distribution resulting from the interference of two mutually coherent laser beams 12, as depicted in the figure. Wet development transforms exposure variations into surface modulations in the resist, which in turn cause periodic phase changes giving rise to a diffraction pattern. Parameters that control diffraction efficiency, that is, the amount of incident illumination that is diffracted into the first order, are the wavelength-to-grating period ratio (go/d), and the ratio of modulation depth to period (h/d).