LACUS (Lausanne, Switzerland)

Research highlights

Time-Resolved Spectroscopy

Time-resolved and steady-state ARPES has recently delivering new insights into

• polarons in perovskites [Phys. Rev. Lett. 124, 206402 (2020)]
• light-induced renormalization in the ZrSiSe semimetal [Phys. Rev. Lett. 125, 076401(2020)]
• the spin texture in chiral Tellurium [Phys. Rev. Lett.  (2020) in press]

UV Spectroscopy

The deep-UV lab has demonstrated femtosecond circular dichroism spectroscopy [Optica 6, 56-60 (2019)], applying it to biological chromophores [J. Phys. Chem. Lett. 10, 2700 (2019)] and unravelled for the first-time slow charge carrier relaxation in Gold nanoparticles [Wang et al., J. Phys. Chem. C (2020)]

Ultra-fast Imaging

Ultrafast imaging of skyrmions in magnetic systems was performed using Lorentz Transmission Electron Microscopy [Phys. Rev. Lett. 120, 117201 (2018)]. Using electron microscopy and the electron-light interaction mediated by nanostructures, manipulation of the quantum state of free electrons was achieved [Nat. Mater. 18, 573 (2019)].

Projects performed by external users >>

Expertise

LACUS is a consortium of ultrafast laser labs across the Faculty of Basic Sciences of the EPFL. It develops and operates a wide range of laser set-ups and associated facilities:

1. The Harmonium set-up: an HHG source providing VUV fs pulses to three beamlines for resp., steady-state and time-resolved angle-resolved photoelectron spectroscopy (ARPES) and PES and XUV absorption of liquid micro-jets
2. The LOUVRE lab: provides tuneable and continuum deep-ultraviolet pulses for ultrafast spectroscopic (transient absorption, multidimensional spectroscopy, circular dichroism) studies of various types of samples (molecular, biological, solids, nanoparticles)
3. Ultrafast imaging of magnetic systems via Lorentz Transmission Electron Microscopy.
4. Ultrafast momentum-resolved Electron Energy Loss Spectroscopy of solid materials and layered solids.
5. Ultrafast electron diffraction of solids, including low temperature ones.
6. Diagnostics of laser-induced plasmas by means of gamma-ray spectroscopy and energy filtered electron microscopy

LACUS is also deeply implanted at large scale facilities (synchrotrons and Free electron lasers) in Switzerland and worldwide, where it performs ultrafast X-ray spectroscopic and scattering experiments. In particular, it has 4 collaborators stationed at the Paul-Scherrer Institut (Villigen). Finally, LACUS contains several theory groups providing support and novel avenues to experimentalists.

Equipment offered to external users

The Harmonium facility

• Laser system
  • 1 – 15 kHz 15 W NIR source
  • high harmonic generation apparatus from 10 to 100 eV
  • EUV monochromator
  • EUV spectrometer
  • liquid microjet interaction chamber
  • differentially pumped photoelectron spectrometer.
• Wet station for PE spectroscopy
  • Produces a 25 μm-thick laminar flow liquid jet in high vacuum conditions
  • Time-resolved photoelectron spectroscopy from liquid samples
  • 30 μm XUV focal spot
  • Differentially pumped electron time-of-flight spectrometer
• TR-ARPES ultra-high vacuum station
  • Cryo-cooled sample preparation
  • ARPES detector

The LOUVRE lab

• A 20 kHz amplified femtosecond laser set-up for deep-UV spectroscopy providing tuneable pump pulses in the 260-380 nm range and white light probe continua in the 520-760 nm region and 260-280 nm ranges. This set-up is designed for 1D and 2D transient absorption studies and for Circular Dichroism studies.
• A fluorescence up-conversion set-up with broad band detection covering the range from 300 nm to the near-IR, as well as tuneable excitation down to 270 nm. The resolution is 130 fs.

Electron-based methods

• Ultrafast electron diffraction (300 fs resolution, transmission and reflection geomtry, 30 KV electrons, 20 KHz repetition rate, 800nm, 400nm pump, up to mJ/cm² fluence, possibility to implement MIR pump excitation).
• Ultrafast electron-energy-loss-spectroscopy (300 fs resolution, 0.8 eV energy resolution, electron counting mode)
• Ultrafast electron microscopy (bright and dark field imaging, 1-2 nm resolution in pump-probe, Lorentz microscopy, 500 fs time resolution)