A newly-designed femtosecond KBe$_2$BO$_3$F$_2$ device with pulse duration down to 55 fs for time- and angle-resolved photoemission spectroscopy

TL;DR

This paper reports the development of a new femtosecond KBe$_2$BO$_3$F$_2$ device capable of generating 55 fs pulses, significantly improving time resolution for ultrafast spectroscopy in quantum materials research.

Contribution

A specially optimized KBBF device was designed to achieve 55 fs pulse duration, enabling high time resolution in VUV sources for ultrafast pump-probe spectroscopy.

Findings

Achieved 55 fs pulse duration with the new KBBF device.

Attained 81-95 fs time resolution in TrARPES measurements.

Extended KBBF application to ultrafast spectroscopy with high tunability.

Abstract

Developing a widely tunable vacuum ultraviolet (VUV) source with sub-100 femtoseconds (fs) pulse duration is critical for ultrafast pump-probe techniques such as time- and angle-resolved photoemission spectroscopy (TrARPES). While a tunable probe source with photon energy of 5.3 - 7.0 eV has been recently implemented for TrARPES by using a KBe$_2$BO$_3$F$_2$ (KBBF) device, the time resolution of 280 - 320 fs is still not ideal, which is mainly limited by the duration of the VUV probe pulse generated by the KBBF device. Here, by designing a new KBBF device which is specially optimized for fs applications, an optimum pulse duration of 55 fs is obtained after systematic diagnostics and optimization. More importantly, a high time resolution of 81 - 95 fs is achieved for TrARPES measurements covering the probe photon energy range of 5.3 - 7.0 eV, making it particularly useful for investigating the ultrafast dynamics of quantum materials. Our work extends the application of KBBF device to ultrafast pump-probe techniques with the advantages of both widely tunable VUV source and ultimate time resolution.