Fluoride single crystals such as calcium fluoride (CaF2) belonging to the cubic crystal system and magnesium fluoride (MgF2) belonging to the tetragonal crystal system are utilized as optical elements in high power lithography systems. In such uses of the single crystals, birefringence is an important phenomenon that affects optical performance. Based on the papers published by the present authors, we review the birefringence of CaF2 and MgF2 single crystals. Intrinsic birefringence is dealt with in addition to stress birefringence. First of all calculation methods for stress birefringence are presented. They are the Jones calculus, an exact method, and the average stress method, an approximate method, and the relation between the two methods is given. In the stress birefringence simulations after annealing of CaF2 single crystal, the importance of time-dependent nonlinear deformation behavior of a material called creep is pointed out in calculating residual stress that induces stress birefringence. When the wavelength of light becomes down to the vacuum ultraviolet region, CaF2 single crystal shows intrinsic birefringence in addition to stress birefringence. Birefringence simulations of a CaF2 single crystal chamber window of an ArF excimer laser light source are performed by considering both stress birefringence and intrinsic birefringence to evaluate the optical performance and to obtain the optimum condition of CaF2 single crystal window. MgF2 single crystal shows intrinsic birefringence even for visible light because of its strong crystal anisotropy. The results of birefringence analyses are shown for MgF2 single crystal as an example of combining stress birefringence with intrinsic birefringence under a visible light condition.
This article describes the history of the optical microscope. The convex lens, an important component of the microscope, was already in use during the ancient era as a tool to create fire from sunlight. The quality of the lens improved in the 11th and 12th centuries and had begun to be used as a microscope component by the end of the 16th century. In the 17th century, innovation of the optical microscope accelerated the study of biological specimens. Robert Hooke designed a two-lens microscope and observed various microorganisms. He published “Micrographia” in 1665, in which the term “cell” first appeared. Another contributor to the microscope in the same period was Leeuwenhoek, who constructed a single lens microscope and discovered bacteria. In 1857, Zeiss, with the cooperation of Abbe and Schott, manufactured a stand type modern microscope that achieved a spatial resolution of 0.2 μm. Their microscope significantly contributed to subsequent discoveries in medical biology. Due to the wave nature of light, the spatial resolution of an ordinary microscope is limited to 0.2 μm. To overcome this limitation, various microscope configurations such as a two-photon laser-scanning microscope, a near-field scanning optical microscope, and a photoactivated localization microscope were developed. For the nonstaining visualization of biological specimens, optical microscopy utilizing a nonlinear optical phenomenon was proposed. Currently, the second harmonic generation microscope and the coherent Raman scattering microscope are widely used and several examples of these microscopic results are presented in this article.
The method to estimate errors included in observational data and the method to compare numerical results with observational results are investigated toward the verification and validation (V&V) of a seismic simulation. For the method to estimate errors, 144 literatures for the past 5 years (from the year 2010 to 2014) in the structure engineering field and earthquake engineering field where the description about acceleration data is frequent are surveyed. As a result, it is found that some processes to remove components regarded as errors from observational data are used in about 30% of those literatures. Errors are caused by the resolution, the linearity, the temperature coefficient for sensitivity, the temperature coefficient for zero shift, the transverse sensitivity, the seismometer property, the aliasing, and so on. Those processes can be exploited to estimate errors individually. For the method to compare numerical results with observational results, public materials of ASME V&V Symposium 2012-2015, their references, and above 144 literatures are surveyed. As a result, it is found that six methods have been mainly proposed in existing researches. Evaluating those methods using nine items, advantages and disadvantages for those methods are arranged. The method is not well established so that it is necessary to employ those methods by compensating disadvantages and/or to search for a solution to a novel method.
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