Laser-excited PEEM using a fully tunable fs-laser system

Abstract

The ferroelectric domain structure on a (001) surface of a BaTiO 3 single crystal prepared under ultrahigh vacuum conditions is imaged by laser-excited photoemission electron microscopy (PEEM). The PEEM images allow for discrimination of three domain types by their different photoemission yields. To characterize the contrast between the different ferroelectric domains of BaTiO 3 (001) in the region of 4.0-4.6 eV close to the photoemission threshold, the broad wavelength tunability of the femtosecond laser system is used. The femtosecond time resolution within two-photon PEEM experiments, using two fully independently tunable laser beams, is demonstrated for the first image potential state of Ag(001). In a pump-probe setup with a cross-correlation full-width at half-maximum of 70 fs, an angle-integrated apparent lifetime of 40 fs is derived from the PEEM intensities. In contrast with energy-resolved two-photon photoemission measurements, PEEM data reveal a 17-fs shorter lifetime. This difference is discussed by considering the co-excitation of bulk states, which leads to an additional time-dependent photoelectron contribution in PEEM.

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

“…The experiments have been performed in an ultrahigh vacuum chamber equipped with a 150 mm hemispherical electron analyzer (Phoibos 150, SPECS, Berlin) with a 2D CCD detector and low-energy electron diffraction optics as described in detail elsewhere 57,58 . A broadly tunable femtosecond laser system operated at a repetition rate of 1.4 MHz with two noncollinear optical parametric amplifiers (NOPA), pumped by a 20 W fiber laser (IMPULSE, Clark-MXR, Dexter) is used for the 2PPE 57,59 . The two frequency-doubled beams of the NOPAs serve as pump-probe excitation source with typical pump-probe cross correlation widths between 70 and 100 fs (full-width-at-half-maximum).…”

Application of the Extended Kalman Filter for Denoising Movies of the Dynamics of the Dielectric Polarization

“…One technique for generating such movies is to measure the change of the transmission of the light of a laser probe pulse, resulting from the change of the dielectric polarization by the dynamics of the dielectric polarization [8]. Alternatively, the photon emission electron microscopy (PEEM) can be used [9]. At least in movies produced by the first technique the number of pixel points, i.e., the number of degrees of freedom, is also very large, so that for the use of the extended Kalman filter for denoising the movies it is absolutely necessary to use a Green's tensorial method for the calculation of the Jacobian matric.…”

Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate

“…The remaining part of the 1030 nm pump radiation is converted to its second (2 ) and third harmonic (3 ) in an all-collinear geometry for the amplification of selected spectral parts of the seed lights. Opposed to previous implementations with lower pump pulse energies [19][20][21] , in our setup a novel concept reducing twophoton absorption-induced heating in the BBO crystals is applied in order to avoid pulse energy instabilities. 34 This is the author's peer reviewed, accepted manuscript.…”