Development and implementation of automated interferometric microscope for study of MEMS inertial sensors

Microelectromechanical systems (MEMS) are quickly becoming ubiquitous in commercial and military applications. As the use of such devices increases their reliability becomes of great importance. Although there has been significant research in the areas of MEMS errors, there is a lack of work regarding long term reliability of packaged systems. Residual thermomechanical stresses might relax over time which affects physical distances within a package, ultimately influencing the performance of a device. One reason that there has not been sufficient work performed on the long-term effects on structures might be the lack of a tool capable of characterizing the effects. MEMS devices have been measured for shape and its changes using interferometric techniques for some time now. Commercially available systems are able to make high resolution measurements, however they might lack loading options. To study aging effects on components a test might need to run continuously for days or weeks, with systematic operations performed throughout the process. Such a procedure is conducive to an automated data acquisition system. A system has been developed at WPI using a Twyman-Green interferometer and a custom software suite. The abilities of this system are demonstrated through analysis performed on MEMS tuning fork gyroscope (TFG) sensors. Specifically, shape is recorded to investigate die bond relaxation as a function of time and thermal cycle. Also presented are measurements made using stroboscopic illumination on operating gyroscopes, in situ. The effect of temperature on the performance of the sensors is investigated using a customized precision rate table

Spatially multiplexed interferometric microscopy: from basic principles to advanced arrangements

La posibilidad de visualizar y analizar objetos microscópicos transparentes de una manera no invasiva ha sido uno de los principales retos de la microscopía óptica a lo largo del siglo XX. Para ello, se desarrollaron diversas técnicas de microscopía que convertían las variaciones en el índice de refracción de los objetos en variaciones de intensidad, haciendo estos objetos visibles a simple vista, entre las que destacan la microscopía de contraste de fase de Zernike o de contraste diferencial de Nomarski. Sin embargo, estas técnicas solamente proporcionan información cualitativa del objeto, por lo que su análisis se limita a la simple visualización. Por otro lado, existen otras técnicas de microscopía basadas en la interferometría, que proporcionan información cuantitativa de fase de un modo sencillo y directo. A partir de esta información de fase es posible obtener, de una manera precisa, información sobre la morfología y el índice de refracción del objeto bajo análisis. Este hecho hace que este tipo de técnicas sean muy interesantes en diversas áreas de conocimiento como la medicina, la biofotónica, o la biología, entre otras. Quizás la técnica interferométrica por excelencia para la obtención de imágenes cuantitativas de fase sea la microscopía holográfica digital. La microscopía holográfica digital surge de la combinación de holografía digital y la microscopía óptica. En los últimos años, se han llevado a cabo numerosos avances en el campo de la microscopía holográfica digital con el fin de introducir mejoras en términos de robustez, simplicidad, precisión y coste. En la misma línea de estos avances, esta tesis está centrada en el desarrollo y la mejora de una técnica llamada “microscopía interferométrica por multiplexado espacial”. Esta técnica se basa en la introducción de una serie de modificaciones sencillas en el cuerpo de un microscopio estándar de campo claro, con el objetivo de convertirlo en uno holográfico de una manera muy robusta, sencilla y económica. Todas las modificaciones realizadas están encauzadas a la implementación de un interferómetro de camino común empleando estrategias de multiplexado espacial en el microscopio. Estas modificaciones son principalmente tres: 1) la sustitución de la fuente de iluminación de banda ancha del propio microscopio por una fuente luminosa coherente que permita interferencias; 2) el multiplexado espacial del campo de visión mediante su división en dos o tres regiones para la transmisión de un haz de referencia; y 3) la inserción de un elemento interferométrico, tal como una red de difracción o un cubo divisor de haz, que produzca el patrón interferencial a registrar. Así pues, todas las técnicas desarrolladas en esta tesis están encaminados a la mejora de esta técnica en términos de: 1) ruido coherente, 2) diseño del campo de visión, 3) resolución espacial, 4) capacidad de análisis de objetos no transparentes, 5) caracterización del índice de refracción, y 6) capacidad de análisis a tiempo real. Todas las validaciones experimentales realizadas durante esta tesis demuestran que la técnica de microscopía interferométrica por multiplexado espacial es una técnica muy versátil, potente y económica que permite la obtención de imágenes cuantitativas de fase a partir de un microscopio de campo claro convencional.The possibility of visualizing and analysing transparent microscopic objects in a non-invasively manner was one of the addressed challenges in the microscopy field during 20th century. Several microscopy techniques were created for that purpose, including quantitative phase imaging. Quantitative phase imaging provides numerical information about the morphology and the refractive index of such objects, so that it can be very appealing in diverse fields of knowledge such as medicine, biophotonics or life science, just to cite a few. One of the easiest ways of achieving quantitative phase imaging is employing digital holographic microscopy techniques. Digital holographic microscopy arises from the combination of digital holography and optical microscopy. In recent years, many novel digital holographic microscopy approaches have been successfully developed in order to improve their capabilities in terms of robustness, simplicity, usability, accuracy, and price. In line with that, this thesis is focused on the development and improvement of the technique named "Spatially Multiplexed Interferometric Microscopy". This technique introduces minimal modifications in the embodiment of a conventional bright field microscope in order to convert it into a holographic one in an extremely simple, low-cost and highly-stable way. The modifications are aimed to implement a common-path interferometer by a spatially multiplexed approach in the embodiment of the microscope and are mainly three: 1) the replacement of the broadband illumination source of the microscope by a coherent one; 2) the spatial multiplexed of the input plane by dividing it into two or three regions; 3) and the insertion of an interferometric component such as a diffraction grating or a beam splitter cube. All performed arrangements and phase retrieval procedures are focused on the enhancement of such a technique regarding: 1) coherent noise; 2) spatial multiplexed input plane; 3) spatial resolution; 4) ability for reflective samples analysis; 5) refractive index characterization; and 6) real-time analysis. Experimental validations carried out during the thesis demonstrate that spatially multiplexed interferometric microscopy is a powerful, versatile, and low-cost technique for achieving quantitative phase images from a commercially available standard microscope

Phase imaging below the diffraction limit

Tato diplomová práce se zabývá konstrukcí interferenčních zařízení pro výzkum měření fáze světla na mikro-strukturách a fáze plazmonů na nano-strukturách. V první kapitole je vybudován teoretický základ pro optiku a nano-fotoniku používané v budoucích kapitolách. Následně je popsána interference vln a jejich praktické použití pro prolomení difrakčního limitu pomocí holografie plazmonů. Prvním experimentální sestavou je Machův-Zehnderův holografický mikroskop. Je popsán způsob, jak ho sestavit z běžně dostupných součástek a jak je navržen ovládací software k jeho používání. Následně jsou popsány výsledky naměřené pomocí tohoto zařízení. V poslední kapitole se zaměříme na sestavení holografického SNOM přístroje pro studování plazmonů a jejich interference. Nejdříve popíšeme základní princip a navržení softwaru pro automatizaci měření, pro zrychlení vědeckých postupů. Nakonec předložíme výsledky měření mikroskopu.This Master's thesis is focus on construction of phase imaging systems capable of studying both micro- and nano-sized objects. The first chapter lays the foundation of optics and nano-photonics. Then the interference of coherent waves and its practical application will be discussed for the use of breaking the diffraction limit and extracting information out of optical systems. First experimental setup discussed will be the Mach--Zehnder type in--line digital holographic microscope. We show a way to construct this device out of cheap materials and how to design its control software. Then the experimental results created using this device are presented. In the last chapter, we focus on how a SNOM holography can be implemented, how it was built, and how automation via software was utilized to reduce operator time waste. Finally, we will present experimental results obtained from our system.

High-sensitivity interferometry

High-sensitivity interferometric techniques are considered for non-destructive testing applications. The methods enable quantitative measurement of optical path variations, resulting from dynamic changes within the test object. [Continues.

Optical techniques applied to measurements in art

Optical diagnostic techniques are particularly attractive for the non-destructive detection of incipient damage and the evaluation of the state of surface decay. Non-contact, high precision measurements of the shape and deformation of an artifact can be performed using laser methods based on holographic and speckle interferometry. [Continues.

A New Versatile Electronic Speckle Pattern Interferometer For Vibration Measurements

Electronic speckle pattern interferometry (ESPI) has been widely used for vibration amplitude and phase measurements. Conventional ESPI systems are bulk and expensive and need careful alignment of all the optical components which is a time consuming task. To overcome these problems alternative compact ESPI systems were developed using fibre-optical components or holographic optical elements (HOEs). The fibre-optic based ESPI systems suffer from random phase fluctuations induced by environmental temperature changes. Hence HOEs can be used as more powerful alternative optical elements to design ESPI systems. The time average ESPI method is widely used for vibration studies. The time average method combined with phase stepping can be used for automatic vibration measurements. Using this technique higher vibration amplitudes cannot be measured because fringe patterns follow Bessel function intensity distribution. To overcome this problem an alternative technique can be used by modulating the phase of the reference beam in an unbalanced interferometer. This thesis reports a novel ESPI system for vibration measurements by combining use of holographic optical elements (HOEs) and optical path length modulation (reference beam phase modulation). The optical path length modulation is implemented using laser diode wavelength (frequency) modulation. Different HOE based ESPI systems are reported in this thesis using either a single HOE or dual HOE. This thesis examines performance of different HOE based ESPI systems that are sensitive to out-of-plane displacement components using laser diodes operating either in the near infrared or visible electromagnetic spectrum. Vibration modes of a circular metal plate clamped at the edges of a loud speaker and a circular metal plate driven by a piezoelectric actuator (PZT) were studied using a single RHOE based ESPI system and a hybrid (transmission HOE with a partially reflecting mirror) HOE based ESPI system respectively using a near infrared laser diode (763nm). Optical path length modulation technique was implemented using a laser diode operating in visible electromagnetic spectrum (658nm). Vibration mode patterns of a circular metal plate driven by a PZT actuator were obtained using both single RHOE and dual HOE based ESPI systems. Using optical path length modulation technique in a dual HOE based ESPI system detailed phase and amplitude maps of a circular metal plate driven by a PZT actuator are obtained. The dual HOE based ESPI system was also used for measuring roations of a circular metal plate mounted on a mirror mount. In conclusion we have developed a compact HOE based ESPI system to conduct vibration measurements. A few potential future developments are also suggested at the end of the thesis

Terahertz for subsurface imaging and metrology applications

In the area of metrology and non-destructive testing, Terahertz wavelengths have been widely researched and used. However, the lack of 2D detectors working at room temperature and high power sources prevent the widespread application of Terahertz in industry. In that context, research on the development of new Terahertz equipment is moving at a fast pace. Within the scope of this thesis, applications of newly developed Terahertz technologies were explored using the scanning of single point detectors with the objective to establish the feasibility for their full-field applications in readiness for future 2D detectors. For the first time, a frequency tuneable, all-optical Terahertz source was implemented in multi-wavelength interferometry to overcome one wavelength ambiguity in precise thickness/distance measurements with sub-millimetre resolution. Phase-shifting digital holography is another interferometry technique which allows us to reconstruct not only the amplitude of one object, but also the phase and the depth of it, using existing mathematical algorithms. Digital holography was performed successfully at Terahertz wavelengths using a multiplier/mixer Terahertz source coupled with a single point pyroelectric detector for the applications of non-destructive testing and depth measurements. The novelty is that the phase-stepping technique for digital holography was implemented in THz frequencies for the first time to remove unwanted terms in the reconstructed image in order to improve image quality compare to conventional holography. In the current experiments, recording time for one set of phase-shifting holograms (4 holograms for 4 phase-steps algorithm) was 6 hours. When the technology is ready for 2D detectors, recording time of holograms could be reduced considerably, and the technique will play an important role in full-field applications in industry metrology and/or non-destructive testing and evaluation.EPSR

Quantitative Phase Imaging: Instrumentation, Validation, and Annular Illumination

The imaging of transparent objects like biological cells and optical fibers is difficult using conventional optical microscopy. Quantitative Phase Imaging (QPI) provides a label-free, quantitative, and reliable way of imaging transparent objects. Conventionally, disk illumination has been widely used as a standard illumination type in microscopy. However, annular illumination provides a way to enhance contrast and improve resolution. In this work, the phase recovery performance of the two illumination types was compared using 2D QPI experiments performed on a standard-type phase test chart using weighted-least squares multifilter phase imaging with partially coherent light (WLS-MFPI-PC). A state-of-the-art QPI system with 2D QPI and 3D QPI capabilities was developed for performing the experiments and is described in detail. The reconstructed phase images were compared to an ideal image using spatial frequency response. Furthermore, the comparison results were found to match the theoretical predictions from MFPI-PC showing the significant advantage of annular illumination in higher spatial frequencies. Thus, the model used to describe the optics of QPI for the two illumination types was validated. A summary of the paraxial, non-paraxial, and WLS-MFPI-PC theories is also provided for the readers.M.S

Investigation of Line-Scan Dispersive Interferometry for In-Line Surface Metrology

Advanced manufacturing techniques enable ultra-precision surfaces to be fabricated with various complicated and large-area structures. For instance, the cost-effectiveness of Roll-to-Roll (R2R) manufacturing technology has been widely demonstrated in industries making high volume as well as large-area foil products and flexible electronics. Evaluation of these fine surfaces by an expensive trial-and-error approach is unadvisable due to the high scrap rate. Therefore quality control using in-line metrology of the functional surface plays an important role in the success of employing R2R technology by enabling a high product yield whilst guaranteeing high performance and a long lifespan of these multi-layer products. This thesis presents an environmentally robust line-scan dispersive interferometry (LSDI) technique that is suitable for applications in in-line surface inspection. Obtaining a surface profile in a single shot allows this interferometer to minimise the effect of external perturbations and environmental noise. Additionally, it eliminates the mechanical scanning and has an extended axial measurement range without the 2π phase ambiguity problem by dispersing the output of the spectrometer onto the camera. Benefiting from high-speed camera, general-purpose graphics processing unit and multi-core processor computing technology, the LSDI can achieve high dynamic measurement with a high signal-to-noise ratio and is effective for use on the shop floor. Two proof-of-concept prototypes aimed at different applications are implemented. The cylindrical lens based prototype has a large lateral range up to 6 mm and can be used for characterisation of additively manufactured surface texture, surface form and surface blemish. The second prototype using a 4X microscope objective with a diffraction limited lateral resolution (~ 4 µm) is aiming at characterisation of surface roughness, micro-scale defects, and other imperfections of the ultra-precision surfaces. System design, implementation, fringe analysis algorithms and system calibrations are presented in detail in this thesis. Their performances are evaluated experimentally by measuring several standard step heights as well as Al2O3 coated polyethylene naphthalate (PEN) films. The measurement results acquired using both prototypes and a commercial available instrument (Talysurf CCI 3000) align with each other acceptably. This shows that the developed metrology sensors may potentially be applied to production lines such as R2R surface inspection where only defects present on the surface are concerned in terms of quality assurance. Implementation of these prototypes offers an attractive solution to improve manufacturing processing and reliability for the products in ultra-highprecision engineering

Optoelectronic speckle shearing interferometry

This thesis describes the implementation of enhanced signal processing techniques in electronic speckle shearing interferometry, including two-wavelength slope measurement, phase stepping, and heterodyning and stroboscopic illumination in vibration analysis. All the techniques were achieved using laser diode emission wavelength modulation. Slope measurement using two-wavelength illumination can generate slope fringes in a mechanically passive manner and the fringe visibility is better compared to other illumination-shifting and object-tilting methods. Three simple geometric objects were measured using an x shear of 4 mm and AX ~ 0.45 nm. The results are in agreement with a theoretical analysis. The measurement accuracy can be further improved by calculating the simple equations of parameters in the fringe function. A novel phase stepping technique has been demonstrated using laser diode injection current modulation. An imbalanced Michelson-interferometer arrangement, with a perspex block of 25 mm thickness inserted into the longer interferometer arm to maintain equal image magnification for the two images, was used to obtain a 2n phase shift for an optical frequency change of 7.25 GHz. The technique provides an additional phase stepping method in shearography with the advantages of removing an active phase-shifting component from the interferometer and a greater linearity in the phase shifts through the diode wavelength modulation. In vibration measurement, heterodyning and stroboscopic illumination have also been successfully achieved in a mechanical passive manner. For shearing systems using a Michelson interferometer, heterodyning was originally difficult to perform. With the unbalanced optical configuration as used in the phase stepping work, heterodyning has been demonstrated to measure vibration motion ~5.5 kHz and the diode optical frequency modulation ~15 GHz. By pulsing the laser diode with an 11% duty cycle, stroboscopic illumination was performed to obtain cosine fringes along with greatly improved visibility. Phase stepping methods were then incorporated to automate the fringe analysis.Ph