High-sensitivity two-dimensional thermal- and mechanical-stress-induced birefringence measurements in a Nd:YAG rod

Review on Optical Methods Used to Characterize the Linear Birefringence of Polymer Materials for Various Applications

Optical polymers are recognized for their high transparency, raised flexibility, low cost, and good film-forming ability; hence, they introduce a multitude of benefits in a wide range of devices, such as information storage, displays, optical communications, and filters. Among the optical properties, birefringence is an essential parameter in practical cases that demand the control of the state of polarization of light. This review is focused on describing some fundamental and applicative aspects concerning the optical birefringence of the polymer materials. First, elementary notions depicting the phenomenon of light double refraction in macromolecular media are provided. Furthermore, the most relevant optical techniques to determine birefringence are reviewed by highlighting the working principle and mathematical basis for computing this parameter. Then, a series of investigations of optically birefringent polymers are described, summarizing the most utilized approaches to induce light double refraction in such materials. The selected results are analyzed in relation to the pursued applications. In the end, the future of this scientific domain is briefly presented by establishing the research paths that need further exploration. Moreover, the novel directions that could be formulated and might contribute to certain considerable advancements in the materials employed in the modern optical technologies are mentioned.

Fracture characteristics of ceramic Nd:YAG

The fracture of laser material in a ceramic Nd:YAG laser pumped by a fiber-coupled laser diode was analyzed. The fracture of the laser material was found to occur when the critical temperature difference between the center of the material and the surface exceeded 355°C. To quantitatively analyze the material fracture, the heat-generation length and heat-generation radius of the laser material were calculated and the critical pump power per unit volume was examined. Under lasing and non-lasing conditions, the fracture of laser material occurred at 24.41 kW/cm(3) and 19.53 kW/cm(3), respectively, for 2 at.% ceramic Nd:YAG and 25.57 kW/cm(3) and 20.47 kW/cm(3), respectively, for 4 at.% ceramic Nd:YAG.

Two-dimensional measurement technique for birefringence vector distributions: measurement principle

The two-dimensional measurement principle for a birefringence vector distribution in transparent materials is analyzed. The system nonuniformity that results from the system components makes the two-dimensional measurement principle quite different from that of a point-measurement method, and the measurement principle requires a two-dimensional analysis. A pulsed optical phase modulation is employed to simplify the two-dimensional mathematical analysis. As a result, concepts are proposed of the system function that characterizes the system nonuniformity that results from the system components and of the intrinsic function that is related to the birefringence vector distribution in a birefringent sample. The influence of the system nonuniformity on the two-dimensional measurement is eliminated by measurement of the intrinsic function, whereas its two values allow for the mathematical separation of the birefringence vector components. The effectiveness of the two-dimensional analysis is illustrated by measurement of a birefringence vector distribution, which is induced by an internal stress distribution in a poly(methyl methacrylate) plate, owing to the photoelastic effect.