Super-Resolution Photoelectron Imaging with Real-Time Subpixelation by Field Programmable Gate Array and Its Application to NO and Benzene Photoionization

Abstract

We have constructed a photoelectron imaging spectrometer with super-resolution image processing and have applied it to the photoionization of nitric oxide and benzene in molecular beams. A field programmable gate array is employed for real-time subpixel centroiding calculations on hardware, providing 64 megapixel resolution (8192 x 8192 pixels). We examined eight different centroiding algorithms based on the center-of-gravity (COG) and Gaussian fitting (Gauss) methods and have found that the two-dimensional COG (2D-COG) and weighted mean of Gaussian center (w-Gauss) methods have the best performance. The excellent performance of the instrument is demonstrated by visualizing a 25 mum diameter pore structure of an MCP, indicating a spatial resolution of 0.03%. The photoelectron image in one-color (1 + 1) resonance-enhanced multiphoton ionization of nitric oxide using a nanosecond laser provided a photoelectron kinetic energy resolution of 0.2%. This resolution is currently restricted by charged-particle optics. The photoelectron energy and angular distributions in the one-color (1 + 1) resonance-enhanced multiphoton ionization of benzene via 6(1) and 6(1)1(1) vibronic levels in the S(1) state are also presented. The results demonstrate that photoelectron angular anisotropy varies with the photoelectron kinetic energy and the vibronic state of the cation.