# Precision-controlled ultrafast electron microscope platforms. A case study: Multiple-order coherent phonon dynamics in 1T-TaSe2 probed at 50 fs–10 fm scales

## TL;DR

A new ultrafast electron microscope system is tested, achieving high temporal resolution to study atomic vibrations in a material.

## Contribution

A new RF controller system enables high temporal resolution and sensitivity in ultrafast electron microscopy.

## Key findings

- Temporal resolution of 50 fs and detection sensitivity better than 1% were achieved.
- Multi-terahertz coherent phonon dynamics in 1T-TaSe2 were probed effectively.
- High-precision phase-space manipulation enhances detection of low-contrast signals.

## Abstract

We report on the first detailed beam tests attesting the fundamental principle behind the development of high-current-efficiency ultrafast electron microscope systems where a radio frequency (RF) cavity is incorporated as a condenser lens in the beam delivery system. To allow for the experiment to be carried out with a sufficient resolution to probe the performance at the emittance floor, a new cascade loop RF controller system is developed to reduce the RF noise floor. Temporal resolution at 50 fs in full-width-at-half-maximum and detection sensitivity better than 1% are demonstrated on exfoliated 1T-TaSe2 system under a moderate repetition rate. To benchmark the performance, multi-terahertz edge-mode coherent phonon excitation is employed as the standard candle. The high temporal resolution and the significant visibility to very low dynamical contrast in diffraction signals via high-precision phase-space manipulation give strong support to the working principle for the new high-brightness femtosecond electron microscope systems.