FEL2026 - 42nd International Free Electron Laser Conference

Improvement of KU-FEL performance by a new 1.6-cell photocathode RF gun with a semiconductor cathode

TUP23

25 Aug 2026, 16:00

2h

Poster Presentation Session 6: FEL Oscillators and Infrared FEL (IR-FEL) Tuesday Poster Session

Speaker

Heishun Zen (Kyoto University)

Description

A new 1.6-cell photocathode RF gun has been installed at the Kyoto University Free-Electron Laser (KU-FEL) facility to increase its peak power for high-harmonic generation (HHG) in gas. During the 2022 Phase I commissioning, which utilized a copper photocathode, the electron bunch charge was limited to 60 pC due to low quantum efficiency (QE). To address this, a semiconductor thin film (CsTe with a CsBr protective layer) was subsequently deposited onto the copper cathode plug to increase the QE. This upgrade increased the electron bunch charge to 550 pC and achieved an FEL micro-pulse energy of 120 micro-J at a wavelength of 5 micro-m at the KU-FEL user station #1. The achieved micro-pulse energy was 2.4 times as high as that obtained with 200-pC electron bunches from the old 4.5-cell RF gun. By focusing the FEL pulse, we could observe 3rd harmonic generation in oxygen more clearly than previous. This work was supported by MEXT Q-LEAP (JPMXS0118070271).

Funding Agency

Funding Agency: MEXT Q-LEAP (JPMXS0118070271)