A simple and compact electronic speckle pattern interferometry system using a reflection holographic optical element is presented. The reflection holographic optical element is recorded on an acrylamide based photopolymer formulated and prepared at the Centre for Industrial & Engineering Optics. Light intensity of 40mW/cm2 with an exposure time of 60 seconds was used in fabricating the holographic optical element. The vibration mode patterns of a 4 cm diameter thin circular sheet of brass metal attached to a 4 cm diameter paper cone loud speaker are presented.
An electronic speckle pattern interferometry (ESPI) system for detection of cracks and defects is presented. In the first stage a holographic optical element (HOE) is recorded using a photopolymer material. Since the polymerization process occurs during recording, the holograms are produced without any development/processing. In the second stage the HOE is used in an ESPI configuration for detection of cracks and defects. Due to the introduction of the HOE in the ESPI set-up, precise alignment of the optical elements is not necessary. For this reason the system is well suited for industrial applications.
This paper presents the use of an acrylamide-based photopolymer as the recording medium in holographic Interferometry. The recorded hologram can also provide a speckle reference image for out-of-plane sensitive electronic speckle pattern interferometry. This dual use of the hologram is demonstrated in the testing of thick plastic PVC pipes, which were internally pressurized. The radial strain was measured using holographic interferometry by measuring the out-of-plane motion of the object due to a known change in pressure inside the cylinder. The radial strain for the same magnitude of internal pressure change was also investigated using electronic speckle pattern interferometry (ESPI) by using the hologram stored in the photopolymer acting as a holographic optical element. A hologram was also recorded at a wavelength of 532nm and the image was reconstructed at laser diode wavelength of 784nm. The hologram was used in an ESPI system as before. As the diode can be wavelength modulated, digital phase shifting can be implemented in both interferometric techniques for detailed fringe analysis.
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 utilize transmission or reflection holographic optical elements (HOEs). The HOEs are essentially amplitude beamsplitters and recombiners whose recording and reconstruction parameters can be adjusted to optimize the ratio of reference and object beams reconstruction so as to maximize 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.
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