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

Research in Bioenergy and Other Renewable Energy Sources in Bulgaria

The interest in Renewable Energy Sources (RES) in Bulgaria reflects the changes in the field of energy policy worldwide and in Europe. The key to successful development of renewable energies in Bulgaria requires a combination of political commitment and decision making as well as support mechanisms including well-defined government targets, technological advances and public acceptance. The renewable energy sources (RES) theoretical potential in Bulgaria is considerable. It is evaluated to 14387 J/year for geothermal energy; 77156,7 J/year for solid agricultural waste; 478,4 J/year – biomass from paper waste; 9605,2 J/year –biomass from wood for heating; 79,8 J/year –biomass from natural fibers; 11381,83 J/year –liquid agricultural waste; 25766 GWh/year – big and small HPS; 1450-1500 kWh/m year – solar radiation. The geothermal and wind energy sector’s potential is considered the highest, while larger-scale utilisation of solar and biomass energy may also be attractive. The research in bioenergy and other RES in Bulgaria is carried out mainly in the following organisations in Bulgaria: National Centre of Agricultural Science (NCAS), University of Forestry Sofia, Agricultural University Plovdiv, University of Rousse, Trakia University – Stara Zagora, Technical University Sofia, Technical University Varna

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

Diacetone acrylamide-based non-toxic holographic photopolymer

A new low-toxicity diacetone acrylamide-based photopolymer is developed and characterized. The environmentally-compatible photopolymer has been modified with the inclusion of glycerol. The incorporation of glycerol results in a uniform maximum refractive index modulation for recording intensities in the range of 1-20 mW/cm2. This may be attributed to glycerol’s nature as a plasticizer, which allows for faster diffusion of un-reacted monomer within the grating during holographic recording. An optimum recording intensity of 0.5 mW/cm2 is observed for exposure energies of 20-60 mW/cm2. The modified photopolymer achieves a refractive index modulation of 2.2x10-3, with diffraction efficiencies up to 90 % in 100 µm layers. The photopolymer layers containing glycerol have improved stability and optical quality

Electronic Speckle Pattern Shearing Interferometry for Nondestructive Testing of Thermal Sprayed Alloy Coatings

Thermal sprayed coatings have wide engineering applications. There now exists a wide range of destructive and nondestructive testing (NDT) methods for surface coating inspections. This paper describes an application of Electronic Speckle Pattern Shearing Interferometry (ESPSI) for NDT of thermal sprayed surface coatings. In contrast to other conventional methods such as eddy current, ultrasonic or X-ray, ESPSI allows fast and large survey area inspection. Experimental results of shearographic measurements are presented. Thermal sprayed coatings were tested using ESPSI. Delaminations of the coatings were detected and the fringe patterns were captured using this method. It is shown that the shearography technique can be applied successfully to surface coating quality inspection and it is very effective for delamination detection

Comparison of Three Electronic Speckle Pattern Shearing Interferometers using Photopolymer Holographic Optical Elements.

Three electronic speckle pattern shearing interferometers (ESPSI) using photopolymer holographic gratings to produce the sheared image are presented. In the first ESPSI system two holographic gratings are used. The gratings are placed between the object and an imaging lens in front of the CCD camera. In the second ESPSI system one grating is used in combination with a sheet of ground glass. The sheared images on the ground glass are further imaged onto a CCD camera. In the third ESPSI system only one grating is used - it is placed in front of the object. The image and the sheared image are imaged onto the CCD camera, whose optical axis coincides with the normal to the object surface. The introduction of photopolymer holographic gratings in ESPSI systems gives the advantage of using high aperture optical elements at relatively low price. The systems are compared in terms of flexibility in their adjustment, sensitivity, suitability and limitations for different applications

Whole Field Out-of-plane Vibration Analysis with a HOE-based ESPI System

Electronic speckle pattern interferometry (ESPI) is a full-field measurement technique, capable of displaying vibrational mode shapes. A simple optical set-up for an ESPI system using a holographic optical element (HOE) is presented. The HOE is designed to create a speckled reference beam in the interferometer. A partially reflective glass plate provides illumination of the object along the normal to its surface, ensuring that the system is sensitive only to out-of-plane displacement of the object. It is demonstrated that the HOE-based system can be used for vibration measurements. Phase shifting can be implemented for fringe analysis. A big advantage of the system is its simplicity. It requires a small number of components: a coherent light source, a holographic optical element, a glass plate and a CCD camera. Introducing holographic optical elements in ESPI gives the advantage of large aperture optical elements at relatively low cost

Application of a Photopolymer Material in Speckle Pattern Shearing Interferometry

A new application of a photopolymer diffractive optical element in electronic speckle pattern shearing interferometer (ESPSI) is presented. In the first stage a holographic grating is recorded using an acrylamide based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. In the second stage the holographic grating is used to produce the two sheared images in an ESPSI configuration. A ground glass screen following the grating serves the purpose of eliminating unwanted diffraction orders. The distance between the grating and the ground glass can be used to control the amount of the shear. The sheared images on the ground glass are further imaged onto a CCD camera. The proposed system is simple and flexible