High brightness and high polarization electron source using transmission photocathode with GaAs-GaAsP superlattice layers

Abstract

Articles you may be interested in30-kV spin-polarized transmission electron microscope with GaAs-GaAsP strained superlattice photocathode Development of spin polarized electron photocathodes: GaAs-GaAsP superlattice and GaAs-AlGaAs superlattice with DBR AIP Conf.In order to produce a high brightness and high spin polarization electron beam, a pointlike emission mechanism is required for the photocathode of a GaAs polarized electron source. For this purpose, the laser spot size on the photocathode must be minimized, which is realized by changing the direction of the injection laser light from the front side to the back side of the photocathode. Based on this concept, a 20 kV gun was constructed with a transmission photocathode including an active layer of a GaAs-GaAsP superlattice layer. This system produces a laser spot diameter as small as 1.3 m for 760-810 nm laser wavelength. The brightness of the polarized electron beam was ϳ2.0ϫ 10 7 A cm −2 sr −1 , which corresponds to a reduced brightness of ϳ1.0ϫ 10 7 A m −2 sr −1 V −1 . The peak polarization of 77% was achieved up to now. A charge density lifetime of 1.8 ϫ 10 8 C cm −2 was observed for an extracted current of 3 A.

Elimination of local thickness modulation in GaAs/GaAsP strained superlattices for high spin-polarization photocathodes

“…In the GaAsP layer on the GaAs substrate, some cracks along [110] and [1][2][3][4][5][6][7][8][9][10] directions were observed as shown in Figure 3 (a). Except the cracks areas, the surface of GaAsP layer shows relatively flat.…”

“…Highly spin-polarized electron sources are intensively developed for applications in high-energy physics, atomic physics, and studies of thin film and surface magnetism [1]. A strained superlattice structures composed of a GaAs-related semiconductors are known to be most effective as photocathode of the spin-polarized electron beam [2,3].…”

Self-Standing Graphene Sheets Prepared with Chemical Vapor Deposition and Chemical Etching

“…The LEED patterns of the three surfaces exhibit sharp diffraction spots representing 1  1 atomic structures, indicating that the graphene layers are commensurate with Ni(111) substrate. The high-brightness LEEM used in this work was recently developed by Koshikawa and others; a negative electrode affinity (NEA) photocathode operating in an Extreme High Vacuum (XHV, ~10 -10 Pa) chamber achieved high brightness of 10 7 A cm -2 sr -1 Suzuki et al, 2010;Yamamoto et al, 2008). (111) system (see Shelton et al, 1974).…”

Improvement of Quantum Efficiency in Transmission-Type Spin-Polarized Photocathode

“…As a result, a high spin polarization of 90% with high QE of 0.4% was achieved. The value of the QE is 4 times higher than that of the previous transmission-type photocathodes [13]. To find a clue to improve the QE further, we investigated the SL structure using the transmission electron microscopy (TEM).…”

“…In our previous study, we developed the transmission-type GaAs/GaAsP strained SL photocathode [13,14]. In this system, a super-high brightness electron beam was achieved by illuminating a small area on the backside of the photocathode with a pump laser light that was well-focused by a short-focal-length lens.…”