Pump-probe
Characterisation Installation 5
The pump-probe spectroscopy infrastructure @ FORTH provides in-situ probes of the excited state of the matter, i.e. in the time/frequency domain at the fs-ps scales.
Tabletop workstations, based on fs laser sources combining wavelengths from the UV to visible to NIR and THz, can follow in time the electronic and lattice evolution, gaining thus insight in the material dynamics. Carrier transport and recombination dynamics, as well as phase transition dynamics in nanosystems, can be monitored, via their optical and near-optical signature through absorption and photoluminescence changes that are induced by ultrafast laser excitation.
The NFFA-SPRINT facility @ CNR-IOM is designed to provide pump-probe photoelectron spectroscopy (ARPES and Spin Polarimetry) experiments. The High Harmonics Generation (HHG) beamline is based on a PHAROS laser, providing 20 W, 400 mJ pulses @ 50 kHz, with a tunable repetition rate from single shot to 1 MHz and a pulse duration around 290 fs. 90% of this radiation is used to generate high harmonics in gases (Ar and Ne), covering the energy range between 17 to 76 eV, with high photons flux, up to 1012 photons/seconds @ 27 eV, 50 kHz, and allowing very good generation also @ 200 kHz. The remaining 10% can be used to pump two Optical Parametric Amplifiers (OPA), in the range 630 nm -16000 nm, used for pump-probe measurements.
The facility is connected with two end station for Time resolved-ARPES (T-ReX group) and Spin polarimetry (SPRINT). The SPRINT end station is a stand-alone spectrometer for UV and soft X-ray time-resolved photoelectron spectroscopy, readily moveable to FEL sources, but routinely available for users at NFFA-SPRINT. A Scienta SES-2002 electron spectrometer devoted to PES and ARPES is presently equipped with a phosphor detector and CCD camera and will be soon upgraded with a crossed delay-line detector (developed by Elettra Detector group) to allow pump-probe experiments. A reference statistical VUV source, a resonant HeI-II lamp, provides 21.2 eV and 40.8 eV light for reference photoemission spectra and resolution tests. Cryogenic temperature control (down to 40 K) is implemented. The samples are prepared in an annex sample preparation module that can also receive samples via a UHV shuttle.
SPRINT (Spin Polarized Research Instrument in the Nanoscale and Time Domain) @ CNR-IOM
Photoelectron spectroscopy of complex materials, secondary electron spin-polarimetry, ARPES
Dynamics of magnetization and electronic structure
Generation of High Harmonics from a Solid State Laser: the driving laser wavelength is multiplied by highly non-linear multiphoton processes triggered by extremely high laser power densities in high-pressure jet of gas; the source delivers odd multiples of the driving laser photon energy (1.2 eV) in ultrashort (300-200 fs) pulses; the flux is 2x1012 ph/s (4x107 ph/pulse) in the energy range 10-30 eV and 5x108 ph/s (1x104 ph/pulse) in the range 40-75 eV; the natural linewidth is in the tens of meV
He discharge lamp: (21.22 eV), natural linewidth < 10 meV
Solid state based:
Laser (1030 nm ) (1.2eV)
OPA (630-16000 nm)
OPA+crystals (630-200 nm) (2-6 eV)
Argon HHG (High flux):
VUV (125-40 nm) (10-30 eV) In odd harmonics separated by 4.8 eV steps
Neon HHG (High photon energy):
XUV (30-16.5 nm) (40-75 eV) In odd harmonics separated by 2.4 eV steps
Hemispherical electron analyzer Scienta SES 2002: main radius 200 mm, working distance 55 mm, aperture diameter 16 mm, variable slit width from 0.2 to 4.0 mm; angular acceptance ±3.5°; lens modes: transmission and angular; detection: Multi-Channel Plate with phosphorous screen and CCD camera
Mott detector for spin polarization of secondary electrons; vectorial analysis of the spin polarization vector; single electron counting and multi-hit detection electronics
Four degrees of freedom (x, y, z, θ)
x,y: ±10 mm, resolution 10 mm
z: ±300 mm, resolution 10 mm
θ: 360°, resolution 0.1°
Ferrovac sample-holder
Measurement temperature range: 40-900 K
Preparation temperature limits: 500 K during sputtering, 1000 K only annealing (in separated stage)
Base pressure: 1x10-10 mbar
Max magnetic field strength: 16 kA/m
Max voltage: 2 kV
Max pumping field intensity: 1 mJ per pulse (1.4 mJ/ cm2)
