Next Generation High-Speed Microplasma Three- Dimensional Imaging

Colorado School Of Mines, Golden CO

Investigators

Abstract

The goal of this project is a first exploration of computational microscopy for the study of ionized gasses, called plasmas. Over the last century, scientists have intensely investigated macro- and microscopic systems composed of plasmas. Optical investigations of laboratory scale plasmas have been dominated by several well-known techniques for some time, and stagnation in development of new techniques has critically limited information accessible to measurements that use light as a probe. Recently, new and transformative microscopes that make images with assistance from powerful computer algorithms have led to an ever-increasing amount of information extracted from physical systems, even for the same amount of collected data. With these advances, it is now possible to image the thickness or height of objects, and their material composition all in three-dimensions using a single, short burst of light. This project will enable application of the new computational microscopy techniques to the study of microplasmas. Unlocking the power of light as a nondestructive, noninvasive probe of harsh environments like plasmas will have immediate impact on a variety of fields including material science, particle accelerators, and alternative light sources, all based on laser created plasmas. Fundamental limits of Schlieren imaging, imaging interferometry, shadowgraphy, and Zernike phase contrast imaging are well known from analytic calculations. Schlieren imaging is sensitive to a quantity that is related to the first, directional derivative of the specimen’s refractive index and shadowgraphy can produce images proportional to the second derivative of the refractive index under certain approximations. However, this information is qualitative in nature. Interferometric imaging requires a known reference, relatively small phase shifts, and is quite sensitive to vibrations; it also requires careful timing between the reference wave and the interrogating wave and is therefore more experimentally complicated. Shadowgraphy is the simplest experimental configuration but is the most complicated method to analyze; and while Zernike phase contrast imaging is an excellent technique, it is not capable of producing reference free images with simultaneous phase and amplitude. Only coherent computational imaging is capable of producing quantitative, single-shot, reference free images with simultaneous phase and amplitude contrast -- over a range of frequencies, in three-dimensions. The development of such truly quantitative simultaneous phase-and-amplitude contrast imaging technique capable of probing plasmas is expected to be transformative for both fundamental and applied studies of laboratory plasmas. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.