Ultrafast Time-Resolution and the Beam Quality in Spin-Polarized Pulse-TEM

Makoto Kuwahara, Toru Ujihara, Hidefumi Asano, Koh Saitoh and Nobuo Tanaka

Abstract:Pulse beam emission in a spin-polarized pulse-TEM (SP-TEM) was performed using a combination of a semiconductor photocathode and an ultra-short pulse laser, which has an ability of a time-resolved measurement. The photocathode has high quantum efficiency of the order of 10^-3 comparing with other metal-type photocathode, which can realized a wide range of the pulse duration from a continuous emission to a pico-second pulse emission. The SP-TEM has several advantages of a high brightness of 3.1×10⁸ A/cm²・sr, a narrow energy width of 114 meV and a long coherence length of 150 nm. In a pulse-mode operation, a pico-second pulse duration was realized with a newly developed ultra-short pulse laser system which consists of a mode-lock Ti-Sapphire laser, a compensator of a group velocity dispersion and a pulse-duration converter. Time-resolved TEM imaging and pulsed interference fringes were also conducted successfully with a stroboscopic acquisition technique. Consequently, in spite of a high current density, the pulsed electron beam emitted from the photocathode has enough coherence to realize a time-resolved holography that can observe phase information in a temporal space.

Key words: Pulse, Spin, Photocathode, Transmission Electron Microscopy, Coherence