The LCPDI: A compact and robust phase-shifting point-diffraction interferometer based on dye-doped LC technology

Point-diffraction interferometers, by design, are much less sensitive to environmental disturbances than dual-path interferometers, but, until very recently, have not been capable of phase shifting. The liquid crystal point diffraction interferometer (LCPDI) utilizes a dye-doped, liquid crystal (LC), electro-optical device that functions as both the point-diffraction source and the phase-shifting element, yielding a phase-shifting diagnostic device that is significantly more compact and robust while also using fewer optical elements than conventional dual-path interferometers. These attributes make the LCPDI of special interest for diagnostic applications in the scientific, commercial, military, and industrial sectors, where vibration insensitivity, power requirements, size, weight, and cost are critical issues. Until very recently, LCPDI devices have used a plastic microsphere embedded in the LC fluid layer as the point-diffraction source. The process for fabricating microsphere-based LCPDI devices is low-yield, labor-intensive, very "hands-on, and great care and skill are required to produce devices with adequate interference fringe contrast for diagnostic measurements. With the goal in mind of evolving the LCPDI beyond the level of a laboratory prototype, we have developed "second-generation" LCPDI devices in which the reference diffracting elements are an integral part of the substrates by depositing a suitable optical material (vapor-deposited thin films or photoresist) directly on the substrate surface. These "structured substrates eliminate many of the assembly difficulties and performance limitations of previous LCPDI devices as well as open the possibility of mass-producing LCPDI devices at low cost by the same processes used to manufacture commercial LC displays.