Low-noise, low-aberration, holographic optical elements

Methods for reducing the noise and aberration levels of interferometrically recorded holographic optical elements (HOEs) are developed. The work emphasizes HOE lenses and holographically blazed diffraction gratings. The techniques utilize noise-immune coherent recording configurations and novel incoherent interferometric optical systems to record HOEs in spatially and/or temporally incoherent light.; HOE lenses are frequently employed in coherent optical systems to perform beam shaping, focusing and collimating functions. HOEs are usually selected for such tasks when size or weight restrictions inhibit the use of conventional lenses. Consequently, the HOE is often required be of low f/No. to achieve compactness. A method for producing diffraction limited, nearly f/1 HOEs using only point sources is described. The technique involves recording the HOE at a shorter wavelength than that intended for use, and compensating for the aberrations introduced by the wavelength shift through appropriate choice of recording geometry. The technique is applied to produce HOEs for use in the red and near IR.; Diffraction gratings are often used for their dispersive properties in spectroscopic applications. Ruled gratings are usually made with a sawtooth or blazed groove profile which concentrates most of the diffracted light into a single order; however, ruled gratings inevitably suffer from several types of imperfections introduced by the mechanics of the ruling process. This work discusses methods for eliminating imperfections by interferometrically producing gratings using an incoherently illuminated grating interferometer. Blazing is accomplished by generating multiple beam interferences to synthesize a Fourier approximation to a sawtooth profile. This technique has several advantages. First, the fringes are formed in incoherent light, so coherent noise is largely eliminated. Second, the interferometer is capable of producing fringe fields considerably larger than the constituent gratings themselves, thus large gratings can be produced. Last, because there are few restrictions on the illuminating source, gratings can be produced using a variety of sources ranging from multimode lasers to high powered arc sources.; Finally, the results of a study on the noise suppressing capabilities of varying degrees of coherence is reported. Findings show that even small amounts of incoherence can be very beneficial.