Operating Characteristics of a GaAs Tip Fast Polarized Electron Source

Previous work from our group demonstrated that through a multiphoton emission process using a Ti:Saph oscillator, with field effects from sharp tips, it is possible to create a source of polarized electrons from GaAs without a negative electron affinity (NEA) surface [1,2].  This source is fast, i.e., the photoemitted electron pulse duration is comparable to the photon pulse duration. Here, we measured the intensity and polarization of the photoemitted electrons as a function of the voltage on the GaAs shard and the average laser power. The tip voltage and average laser power were varied between -100V and -900V and 30 mW and 120 mW, respectively. The electrons were scattered by a 20 kV Mott polarimeter with an effective Sherman function characterized based on the scattered electron energy loss [3]. We observed electron polarizations varying between 5% and 15% depending on the emitting shard-tip feature. Our results show evidence of a dominant four-photon process. In addition, we have made improvements in the source’s ease of operation as well as the scattering intensity.

[1] Brunkow, E., et. al. (2019). Appl. Phys. Lett. 114, 073502.

[2] T.J.Gay, et. al.; U.S. Patent Granted (Application No.: 16/688,544), 2021.

[3] Clayburn, N. B., et. al. (2016). Rev. Sci. Instrum. 87, 053302.