Cold electron beams from cryo-cooled, alkali antimonide photocathodes

TL;DR

This paper demonstrates that cooling alkali antimonide photocathodes to cryogenic temperatures significantly reduces thermal emittance, enabling the generation of ultra-bright, cold electron beams with record low emittance.

Contribution

It provides experimental evidence that lattice cooling to 90 K lowers thermal emittance in alkali antimonide photocathodes, advancing ultra-bright electron beam technology.

Findings

Achieved a thermal emittance of 0.2 μm (rms) per mm at 90 K.

Demonstrated a quantum efficiency >7×10⁻⁵ at 690 nm wavelength.

Validated the hypothesis that lattice temperature limits thermal emittance.

Abstract

In this letter we report on the generation of cold electron beams using a Cs3Sb photocathode grown by co-deposition of Sb and Cs. By cooling the photocathode to 90 K we demonstrate a significant reduction in the mean transverse energy validating the long standing speculation that the lattice temperature contribution limits the mean transverse energy or thermal emittance near the photoemission threshold, opening new frontiers in generating ultra-bright beams. At 90 K, we achieve a record low thermal emittance of 0.2 $\mu$m (rms) per mm of laser spot diameter from an ultrafast (sub-picosecond) photocathode with quantum efficiency greater than $7\times 10^{-5}$ using a visible laser wavelength of 690 nm.