2-Dimensional Second-Harmonic Dispersion-Interferometer

Interferometers are used for an incredible array of measurements in science, engineering, medicine, and technology, to quantify mass density and scale-lengths in a plasma, gas, liquid, etc. Interfer- ometers are often characterized by their high-cost, complex designs, and by the need for frequent maintenance. An interferometer lacking such downsides is appealing for many applications. Interferometers measure the phase difference between two electromagnetic beams. In transparent samples, such as plasma,gas,optical glass,the phase shift is due to chromatic dispersion thatis determined by the sample’s mass density, or similar physical quantities. A Second-Harmonic Dispersion-Interferometer (SHDI) may be used to measure the dispersive-phase shift. In the SHDI a primary beam is used to produce a second-harmonic (SH) beam both before, and after, the sam- ple. In this way all beams remain co-linear, allowing the primary beam to encode its phase directly into the second, SH beam. Thus, the phase difference between the two SH beams may be pre- cisely measured. The result is a design that is robustly stable, with fewer components, eliminating common-mode noise, and reducing routine maintenance. Until now, SHDIs have been constructed using beam diameters, d mm’s, which provides for a 1-dimensional, line-of-sight measurement. Most applications would benefit by having a 2-dimensional measurement, where the sample’s- transverse profile is imaged. This motivates the development of a 2D-SHDI, where d >> cm’s. During Phase I a 2D-SHDI prototype was assembled, using: a pulsed-high-power laser, fast- digital-cameras, and sophisticated-software algorithms. The prototype was used to measure the phase change produced in large-area samples, d cm, by increasing the beam diameter and ad- justing the laser intensity. These data verify that the 2D-SHDI’s phase coherence, image quality, and spatial resolution are suitable for 2-dimensional interferometric imaging. In Phase II the performance of the 2D-SHDI will be enhanced, then tested in collaborative experi- ments with members of the plasma-physics community, using their devices, that are representative of a broad range of existing-confinement concepts. The data produced in these collaborations will be disseminated in publications and at meetings, expositions, and trade shows. Commercialization of the instrument will focus on direct sales and licensing to established-instrumentation vendors. A 2D-SHDI is suitable for electron-density measurements in plasmas used in research, fusion en- ergy, space physics, materials processing, as well as the density of neutral gases, and for quantitative- phase microscopic imaging of structures. The 2D-SHDI provides a stable, cost-effective platform for measuring 2-dimensional phase interferometry with high-spatial and temporal resolution.