Holographic Optical Elements for Combined Holographic and Digital Speckle Pattern Interferometry

Holographically recorded diffractive optical elements are described, which can be used to implement very simple self-aligning electronic speckle pattern interferometers (ESPI) and holographic interferometers requiring only a laser source and a CCD camera in the optical set-up. The ESPI systems can utilise transmission or reflection holographic optical elements (HOEs). The HOEs are essentially amplitude beamsplitters and recombiners which whose recording and reconstruction parameters can be adjusted to optimise the ratio of reference and object beams reconstruction so as to maximise subtraction fringe contrast. The HOEs are recorded using a 4-component photopolymer system. In addition the HOEs can be recorded at visible wavelengths but used in ESPI systems, which incorporate at diode laser. The diode can be wavelength modulated. In this way we can incorporate digital speckle pattern interferometry (DSPI) or amplitude and phase modulation of the optical path difference for time-averaged speckle interferometry.