Two-Dimensional Dispersion Interferometer

Many applications in science, engineering, biology, and technology rely on interferometry to measure precisely the density of a plasma, gas, fluid, cellular structure, etc. Optical interferometry provides the highest sensitivity and resolution of all similar methods, yet designs are limited by mechanical vibrations, design complexity, and high maintenance. A Dispersion Interferometer (DI) alleviates these concerns, in a design that is stable, high bandwidth, and low cost. However, today’s DI systems provide only a 1-dimensional measurement, whereas a 2-dimensional measurement at cm2 transverse areas, and larger, is desired. Interferometers interfere two beams to make a measurement. Typically, separate paths are used for the reference-beam and the probe beam. In the DI both beams are co-linear, accounting for its design simplicity and high stability. DI’s presently use a continuous-wave (CW) laser to generate a primary beam that is then frequency-doubled in small, second-harmonic (SH) crystals. The resulting beam diameters are typically, ~ mm2 area. Instead, if a pulsed, high-intensity laser and beam optics were used to expand the beam to fully illuminate the sample, and then reduce it for the SH crystals, then 2-D interferometry would be feasible. However, methods must first be refined to demonstrate technical feasibility, by 1) characterizing precisely the instrument’s performance, and 2) re-constructing the phased-image data to represent accurately the sample. Extending this concept further, with a high- repetition-rate laser and fast camera, enables new imaging modalities in a 2-D cinematic recording of the sample’s evolution. The Phase I Project will assemble a 2DDI and characterize its performance in three configurations of increasing assembly: Configuration 1 is the basic instrument; Configuration 2 images a mm2 sample; Configuration 3 images a cm2 sample with beam optics. Digital methods are also needed to manipulate the phase-mapped interferometric data and allow the characteristics of the dispersive sample to be reconstructed. Feasibility demonstration is determined by successful results obtained from Configurations 1 & 2, enabling the 2DDI’s design to be scaled for larger- and smaller-size imaging applications, as a commercial product.The 2DDI is a superior approach to interferometry for measuring the characteristics of: plasma density in fusion, space physics, low-temperature physics, semiconductor processing; neutral-gas density in fluid dynamics, combustion dynamics, hydrodynamic compressors; structures at the nanometer scale, cellular function, microscopy in medicine and biology; quality-assurance testing in metrology. All of these are potential application areas for the commercial product.