Spectroscopic imaging ellipsometry (SIE) is a powerful technique devoted to the study of optical properties and thickness of thin films by measuring the change in polarization state of light reflected from the surface. SIE measures two quantities (Ψ and Δ ), which represent the amplitude ratio and phase angle of deflection of the p-polarized light and s-polarized light reflected from the sample surface. The SIE measurement of thin film is difficult when the substrate is uniaxial anisotropic crystal for two reasons - firstly the p-polarized and s-polarized components of reflective light are coupled which makes the data processing more complex and secondly an optical model is needed for SIE data processing with the substrate optical constants as known parameters in the model, but the substrate optical constants are not unique when the plane of the optical axis changes. Hence in the measurement of thin film on an anisotropic material using generalized ellipsometry, significant errors due to the complex calculation arise. The best approach is to measure the uniaxial substrate as an isotropic material by adjusting the optical axis in the incident plane. In this paper, the crystal optical axis is determined by rotating the sample using the SIE setup and the incident light is adjusted in the optical axis plane to eliminate the effects of uniaxial substrate. A uniaxial KDP (Potassium Dihydrogen Phosphate) crystal with thin oil film and a bare KDP substrate are prepared. A scheme to determine KDP crystal optical axis is proposed. Finally, the optical constants of the KDP substrate are determined, and the oil film thickness on KDP crystal is measured when the incident light is in crystal optical axis plane.
Wire grid polarizers (WGP), are sub-wavelength gratings with applications in display projection
system due to their compact size, wide field of view and long-term stability. Measurement and testing
of these structures are important to optimize their use. This is done by first measuring the Mueller
Matrix of the WGP using a Mueller Matrix Polarimeter. Next the Finite Difference Time Domain
(FDTD) method is used to simulate a similar Mueller matrix thus providing the period and step height
of the WGP. This approach may lead to more generic determination of sub-wavelength structures
including diffractive optical structures.
Plastic optics has been widely used in different application. They have been facing birefringent effects during manufacturing or during certain application. Finite element modeling of plastic optics in CAD interface is done along with experimental and theoretical comparison of the specimen with the help of solid mechanics and image processing. Low birefringence plastic optics is chosen for the experiment and varying load is applied to observe the characteristics both in experiment and simulation. Low birefringence polariscope was used to measure the birefringence in the plastic specimen. Birefringence is caused due to many effects like stress induced birefringence temperature induced due to thermal gradient and pressure during manufacturing. Here stress is induced on low birefringence specimen by two point compression loading and is compared on the base of solid mechanics, finite element modeling and image processing. The results were found to be similar and convincing.
Birefringence affects the quality of image analysis in injection molded micro-plates. Depending upon their manufacturing / production processes and the type of material, different plates exhibit varying amounts of birefringence. This birefringence is attributed to residual stress generated during the molding process. Polarimeter is the standard tool for birefringence distribution visualization and quantification. Broad chemical resistance and high mechanical stability of the plates are the desirable properties that can be characterized by birefringence measurement. Birefringence, expressed in nm/cm is light retardance (nm) after passing through a sample with certain thickness (cm). Low or uniform birefringence plates provide high-resolution demonstrating higher performance, hence suitable for bio-chemical analysis.
Conference Committee Involvement (1)
International Conference on Experimental Mechanics(ICEM) 2014
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