LUXEM is a brand new laboratory for Ultrafast Imaging Science. We study structure-property relationships in functional nanomaterials and interfaces, in the ultrafast (10-15s) time domain. We do so by implementing novel experimental techniques for scattering and imaging, which integrate tabletop pulsed EUV/X-ray photons from High-Harmonic Generation (HHG) and electrons. We collaborate with Synchrotron and Free-Electron Laser large-scale facilities.
Infrastructure & Instrumentation
The laboratory is located in the basement of the Department of Physics at the University of Pavia (IT). It features a controlled temperature and humidity space with acoustic and vibration isolation, an independent thermal regulation unit, and back-up generator. The Laboratory hosts:
- A Ti:sapphire ultrafast regenerative amplifier that employs a patented cryogenically-cooled amplifier technology with tunable average pulse energy
- A tabletop EUV/soft X-ray beamline from High-Harmonic Generation for time-resolved microscopy and nanometrology
- A compact beamline for ultrafast electron diffraction and small-angle scattering, where we also develop new methods of image reconstruction and speckle detection from compact sources with partial spatial coherence
Ultrafast Laser System
The ultrafast Laser System at LUXEM is a KMLabs Ti:sapphire ultrafast regenerative amplifier that employs a patented cryogenically-cooled amplifier technology with tunable average pulse energy: >3mJ at 5kHz, >2mJ at 10kHz, >0.6mJ at 20kHz, 35fs average pulse duration. In each beamline, the amplified femtosecond laser beam is divided into two paths:
- The pump laser pulse, which initiates the sample’s dynamics and serves as a reference point in time
- The probe – in our case extreme ultraviolet/soft x-ray photons or electrons pulses, which record snapshots of the sample’s dynamics as a function of the time delay
Ultrafast EUV/soft X-ray Ptychography
Ultrafast EUV/X-ray ptychography is a powerful, general purpose, full-field imaging technique which can be customized towards imaging energy, charge, and spin transport, with nm-to-Å spatial and femtosecond (10-15s) temporal resolution on nanostructured surfaces or buried interfaces.
A train of pulses from a femtosecond driving laser will be used to generate the EUV/soft X-ray light –to image the specimen– and the pump, which photo-activates the sample to its out-of-equilibrium state(s). At each time delay, the EUV light is focused and overlapped with light pump pulses on the sample. Multiple coherent patterns from overlapping fields of view are collected in either transmission or reflection geometry. The EUV scattered light is directly collected on a detector (AXIS), without the need for image-forming optics.
In ptychography, iterative phase-retrieval algorithms are used to reconstruct the sample phase information, lost when recording only the diffraction intensity. The delay between pump photons and probing EUV light is controlled by a motorized delay-line. The dynamic response of each sample is captured by collecting stroboscopic images as a function of time delay between pump and probe pulses, acquiring snapshots of a nanoscale movie.
Ultrafast Electron Diffraction & Speckle Imaging
In this beamline, the probe beam is frequency-tripled by third harmonic generation in nonlinear crystals, to generate the probing electron bunches inside a DC gun (0-100keV, DrXworks). The electron probe pulses are directed to the sample with a system of magnetic lenses that collimates and focuses the beam at the sample, plus steering beam deflectors for beam positioning. An optical delay line allows to change the time of arrival on the sample between pump and probe pulses. The electron pulses scatter from the sample and a diffraction image is detected by an Hybrid Photon Counting detector (Dectris). It is possible to customize the transverse coherence of the electron beam to enable speckle detection and analysis with modern techniques of angular cross-correlation.
LUXEM infrastructure completion – April 2022
3D Renderings courtesy of Ing. Cristina Cecchini and Ing. Claudio Ogliari