Illumination plays an important role in optical microscopy. Köhler illumination, introduced more than a century ago, has been the backbone of optical microscopes. The last few decades have seen the evolution of new illumination techniques meant to improve certain imaging capabilities of the microscope. Most of them are, however, not amenable for wide-field observation and hence have restricted use in microscopy applications such as cell biology and microscale profile measurements. The method of structured illumination microscopy has been developed as a wide-field technique for achieving higher performance. Additionally, it is also compatible with existing microscopes. This method consists of modifying the illumination by superposing a well-defined pattern on either the sample itself or its image. Computational techniques are applied on the resultant images to remove the effect of the structure and to obtain the desired performance enhancement. This method has evolved over the last two decades and has emerged as a key illumination technique for optical sectioning, super-resolution imaging, surface profiling, and quantitative phase imaging of microscale objects in cell biology and engineering. In this review, we describe various structured illumination methods in optical microscopy and explain the principles and technologies involved therein.
Crystallization studies are carried out under non-isothermal conditions with samples heated at several uniform rates. The dependence of the glass transition temperature (T g), the crystalline temperature (T c) and the peak temperature of crystallization (T p) on the composition and heating rate (β β) has been studied. For a memory/switching material, the thermal stability and ease of glass formation are of crucial importance. The glass transition temperature, T g , increases slightly with the variation of Bi content. From the heating rate dependence of T g , the activation energy for glass transition (E t) has been evaluated. The results are discussed on the basis of Kissinger's approach and are interpreted using the chemically ordered network model (CONM).
Alloys of the Tex(Bi2Se3)1−x glass system, obtained using rapid quenching technique, have been characterized by calorimetric measurements and differential thermal analysis for different heating rates in this work. A systematic investigation of crystallization kinetics is carried out for the composition range in which amorphous alloys exhibit a large glass-forming ability in Se-based systems, thermal stability including in the temperature range between the glass transition temperature, Tg, and crystallization temperature, Tc, and the effect of ΔTc (=Tc − Tg) at different heating rates for the formation of an amorphous single phase is evaluated from thermal analytical data. The thermal stability of these glasses is found to provide good control for forming these glasses with ease. This analysis helps to find the suitability of an alloy for use in phase transition optical memories/switches.
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