Simple Versatile Shearing Interferometer Suitable for Measurements on a Microscopic Scale

Microelectromechanical systems (MEMS) behave differently from massive samples. Conventional testing and inspection techniques usually fail at the microscale. Recently there has been an increasing interest in the application of optical techniques for microstructure testing, because they are high-resolution, non-contact, full-field, fast and relatively inexpensive. New interferometric systems, which are suitable for microscopic optical metrology, are of interest for engineering and industrial applications. A modified electronic speckle pattern shearing interferometer (ESPSI) with a very simple shearing device has been designed for metrology applications on the microscale. The shearing device consists of two partially reflective glass plates. The reflection coefficients of the coatings are 0.3 and 0.7 respectively. The distance and the tilt between the two glass plates control the size of the shear. A long working distance microscope objective is attached to the CCD camera to form a field of view variable over several millimetres in width. The suitability of the system for microscopic measurements is demonstrated. The capability of the system for phase-shifting is also demonstrated. The results obtained are promising for future applications of the ESPSI system for testing and characterisation of MEMS

Double-Glazing Interferometry

This note describes how white light interference fringes can be seen by observing the Moon through a double-glazed window. White light interferometric fringes are normally observed only in a well-aligned interferometer whose optical path difference is less than the coherence length of the light source, which is approximately one micrometer for white light. Obtaining such fringes in a Michelson interferometer is not a trivial task.1 The interferometer is typically illuminated with a monochromatic source and the path length difference adjusted with a wedge angle between the interferometer mirrors so that five or six vertical fringes are visible, indicating nearly equal paths. Then the mirrors are adjusted until the fringes are almost perfectly straight. Finally we use a white light source and carefully scan through the approximately equal path range until five or six white light fringes are seen to sweep rapidly by

A Simple Phase-Shifting Lateral Shearing Interferometer

A phase-shifting electronic speckle pattern shearing interferometer with a very simple shearing device is proposed. Two partially reflective glass plates are used to introduce the shear in this new interferometer. The reflection coefficients of the coatings on the two plates are 0.3 and 0.7. The distance between the two glass plates controls the size of the shear. The proposed new interferometric system is simple, flexible, and low cost

Comment on C.E. Close, M.R. Gleeson and J.T. Sheridan Monomer Diffusion Rates in Photopolymer Material Part 1. Low Spatial Frequency Holographic Gratings

COMMENT: on C. E. Close, M. R. Gleeson and J. T. Sheridan “Monomer diffusion rates in photopolymer material.Part I. Low spatial frequency holographic gratings” J. Opt. Soc. Am. B / Vol. 28, No. 4 / April 2011 pp 658- 666 [1

Implementation of Phase-only Modulation Utilizing a Twisted Nematic Liquid Crystal Spatial Light Modulator

Twisted nematic liquid crystal spatial light modulators, (SLM) are widely used for amplitude modulation of light. The technique for measuring phase and amplitude modulation introduced by a twisted nematic cell is not new but the novelty here is that after characterisation of a Holoeye LC2002 TNLC device we were able to identify specific conditions that allow for its use as a pure 180 degree or more, phase modulator with little or no amplitude modulation at 514.5 nm laser wavelength. The phase shift introduced by the SLM was measured using a Mach-Zehnder interferometer. The experimentally measured and the theoretically predicted intensity transmission and phase shift as functions of gray levels, are compared. Finally, the effects of errors in the angular settings of the polarizers and quarter waveplates on the intensity transmission and phase shift are studied

Electronic Speckle Pattern Interferometer using Holographic Optical Elements for Vibration Measurements

A simple and compact electronic speckle pattern interferometry (ESPI) built with holographic optical elements (HOEs) used for the study of out-of-plane vibration is reported. Carefully fabricated reflection and transmission HOEs provide reference and object beams in the interferometer. All the alignment difficulties in conventional ESPI systems are minimized using HOEs. The time average ESPI subtraction method is used to generate correlation fringes. The background speckle noise is removed by introducing a phase shift between sequential images. The amplitude and phase maps are obtained using path difference modulation in an unbalanced ESPI

Characterization of an Acrylamide Based Photopolymer for Fabrication of Liquid Crystal Devices

Photopolymers are increasingly interesting as new materials for the fabrication of electro optical liquid crystal devices. Photoinduced surface relief gratings in dry, self developing acrylamide based photopolymers can be used to align liquid crystals (LCs) as an alternative to the rubbing technique. These optically recorded surface relief patterns can be used to fabricate electro-optical switchable LC Bragg gratings. An investigation of the dependence of photoinduced surface relief gratings on recording intensity and thickness of the photopolymer layer is reported. The surface relief gratings were filled with E7 LCs and a switchable LC diffraction grating was fabricated

Nanoparticle Doped Photopolymer with Reduced Shrinkage for Holographic Recording

We demonstrate holographic recording with Si-MFI zeolite doped acrylamide based photopolymerfilm. The influence of silicate nanoparticles on photopolymer shrinkage has been studied and compared withshrinkage in undoped photopolymer layers The shrinkage of the material (1.03%) is significantly lower forrecording in Si-MFI zeolite nanoparticle doped samples than for undoped layers (1.77%)

Investigation of the Photoinduced Surface Relief Modulation in Acrylamide-based Photopolymer

A surface relief diffraction grating is inscribed in acrylamide photopolymer by holographic recording with spatial frequency below 300 l/mm. The periodic surface modulation appears in addition to a volume phase holographic grating. Due to the nature of the presented photopolymerisable material the gratings are induced by light only and no post-processing is required. An investigation of the dependance of the amplitude of the photoinduced relief modulation on spatial frequency of recording and on sample thickness has been carried out utilising white light interferometry. A model of the mechanism of surface relief formation is proposed on the basis of the measured dependencies. The possibility for inscription of surface relief modulation implies different applications of the photopolymer: fabrication of diffractive optical elements, recording of computer generated holograms and biosensors

Effect of Monomer Diffusion on Photoinduced Shrinkage in Photopolymer Layers Determined by Electronic Speckle Pattern Interferometry

The aim of this study is to determine the effect of monomer diffusion on the photoinduced shrinkage profile in acrylamide based photopolymer layers during holographic recording. Using phase shifting electronic speckle pattern interferometry the displacement at each pixel in the image of the layer is measured. The complete displacement profile of the layer was obtained using phase shifting technique. We observed a reduction in shrinkage as a result of monomer diffusion from unexposed regions of holographic exposure. As a result of diffusion the maximum shrinkage was reduced by 26 % from 7.18μm to 5.28μm in a photopolymer layer of thickness160 ± 3 μm after 84 seconds of recording