Femtosecond two-photon photoemission at 150 kHz utilizing two noncollinear optical parametric amplifiers for measuring ultrafast electron dynamics (original) (raw)
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Femtosecond single-electron pulses generated by two-photon photoemission close to the work function
New Journal of Physics, 2015
Diffraction and microscopy with ultrashort electron pulses can reveal atomic-scale motion during matter transformations. However, the spatiotemporal resolution is significantly limited by the achievable quality of the electron source. Here we report on the emission of femtosecond single/fewelectron pulses from a flat metal surface via two-photon photoemission at 50-100 kHz. As pump we use wavelength-tunable visible 40 fs pulses from a noncollinear optical parametric amplifier pumped by a picosecond thin-disk laser. We demonstrate the beneficial influence of photon energies close to the photocathode's work function for the coherence and duration of the electron pulses. The source's stability approaches the shot noise limit after removing second-order correlation with the driving laser power. Two-photon photoemission offers genuine advantages in minimizing emission duration and effective source size directly at the location of photoemission. It produces an unprecedented combination of coherent, ultrashort and ultrastable single/few-electron wave packets for timeresolving structural dynamics.
Time and angle resolved photoemission spectroscopy using femtosecond visible and high-harmonic light
Journal of Physics: Conference Series, 2009
The angle resolved photoelectron spectroscopy (ARPES) has emerged as a leading technique in identifying static key properties of complex systems such as the electronic band structure of adsorbed molecules, ultrathin quantum-well films or high temperature superconductors. We efficiently combined ARPES by using a two-dimensional analyzer for parallel energy (E) and momentum (k || ) detection with femtosecond time-resolved spectroscopies. Using time and angle resolved two photon photoemission (2PPE) with visible light pulses, the hot electron dynamics in complex electronic structures are directly accessible by means of angle resolved hot electron lifetime mapping. Furthermore, femtosecond ARPES spectra recorded with high harmonic generation (HHG) light pulses are presented, showing the potential of this technique for future investigations of surface dynamics and photo-induced phase transition processes.
Femtosecond two-photon photoemission studies of image-potential states
Chemical Physics, 2000
High-resolution two-photon photoemission studies with femtosecond time resolution permit the accurate determination of decay and dephasing processes for image-potential states. The influence of adsorbates on the respective inelastic and Ž. Ž. quasielastic scattering processes is investigated for Cu on Cu 100 and Cu 111. The results are discussed in relation to Ž. previous work for CO on Cu 100 .
AN INNOVATIVE YB-BASED ULTRAFAST DEEP ULTRAVIOLET SOURCE FOR TIME-RESOLVED PHOTOEMISSION EXPERIMENTS
Review of Scientific Instruments
Time-and angle-resolved photoemission spectroscopy is a powerful technique to study ultrafast electronic dynamics in solids. Here, an innovative optical setup based on a 100-kHz Yb laser source is presented. Exploiting non-collinear optical parametric amplification and sum-frequency generation, ultrashort pump (hν = 1.82 eV) and ultraviolet probe (hν = 6.05 eV) pulses are generated. Overall temporal and instrumental energy resolutions of, respectively, 85 fs and 50 meV are obtained. Timeand angle-resolved measurements on BiTeI semiconductor are presented to show the capabilities of the setup. ©2014AIPPublishingLLC.[http://dx.doi.org/10.1063/1.4903347\]
Methods and applications of femtosecond time-resolved photoelectron spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2000
Femtosecond time-resolved photoelectron spectroscopy is emerging as a new technique for investigating polyatomic excited state dynamics. Due to the sensitivity of photoelectron spectroscopy to both electronic configurations and vibrational dynamics, it is well suited to the study of ultrafast non-adiabatic processes such as internal conversion, often occurring on sub-picosecond time scales. We discuss technical requirements for such experiments, including laser systems, energy and angle resolved photoelectron spectrometers and new detectors for coincidence experiments. We illustrate these methods with examples from diatomic wavepacket dynamics and ultrafast non-adiabatic processes in polyatomic molecules.
Review of Scientific Instruments, 2019
Time-and angle-resolved photoelectron spectroscopy (trARPES) is a powerful method to track the ultrafast dynamics of quasiparticles and electronic bands in energy and momentum space. We present a setup for trARPES with 22.3 eV extreme-ultraviolet (XUV) femtosecond pulses at 50-kHz repetition rate, which enables fast data acquisition and access to dynamics across momentum space with high sensitivity. The design and operation of the XUV beamline, pump-probe setup, and UHV endstation are described in detail. By characterizing the effect of space-charge broadening, we determine an ultimate source-limited energy resolution of 60 meV, with typically 80-100 meV obtained at 1-2×10 10 photons/s probe flux on the sample. The instrument capabilities are demonstrated via both equilibrium and time-resolved ARPES studies of transition-metal dichalcogenides. The 50-kHz repetition rate enables sensitive measurements of quasiparticles at low excitation fluences in semiconducting MoSe 2 , with an instrumental time resolution of 65 fs. Moreover, photo-induced phase transitions can be driven with the available pump fluence, as shown by charge density wave melting in 1T-TiSe 2. The high repetition-rate setup thus provides a versatile platform for sensitive XUV trARPES, from quenching of electronic phases down to the perturbative limit.
Two-photon coherent control of femtosecond photoassociation
Faraday Discussions, 2009
Photoassociation with short laser pulses has been proposed as a technique to create ultracold ground state molecules. A broad-band excitation seems the natural choice to drive the series of excitation and deexcitation steps required to form a molecule in its vibronic ground state from two scattering atoms. First attempts at femtosecond photoassociation were, however, hampered by the requirement to eliminate the atomic excitation leading to trap depletion. On the other hand, molecular levels very close to the atomic transition are to be excited. The broad bandwidth of a femtosecond laser then appears to be rather an obstacle. To overcome the ostensible conflict of driving a narrow transition by a broad-band laser, we suggest a two-photon photoassociation scheme. In the weak-field regime, a spectral phase pattern can be employed to eliminate the atomic line. When the excitation is carried out by more than one photon, different pathways in the field can be interfered constructively or destructively. In the strong-field regime, a temporal phase can be applied to control dynamic Stark shifts. The atomic transition is suppressed by choosing a phase which keeps the levels out of resonance. We derive analytical solutions for atomic two-photon dark states in both the weak-field and strong-field regime. Two-photon excitation may thus pave the way toward coherent control of photoassociation. Ultimately, the success of such a scheme will depend on the details of the excited electronic states and transition dipole moments.
Femtosecond Two-Photon Laser Photoelectron Microscopy
The Journal of Physical Chemistry A, 1998
It is shown that high-resolution photoelectron images (with a resolution of up to 3 nm for ultrasharp silicon tips) can be obtained for practically all materials when irradiating tips made of these materials by pulses of the second harmonic of a femtosecond Ti:sapphire laser. In addition to the images, absolute values of the two-photon external photoelectric effect for these tips also can be measured using this method. The first experimental realization of this two-photon femtosecond laser projection photoelectron microscope is presented, and corresponding data for silicon, diamond, and calcium fluoride tips are analyzed. S1089-5639(97)03153-8 CCC: $15.00
Two-color photoemission produced by femtosecond laser pulses on copper
Journal of the Optical Society of America B, 1995
Single-color illumination of a copper surface by a red or an ultraviolet femtosecond laser pulse yields a threephoton (red) or a two-photon (UV) photoemission process. A multicolor, multiphoton process is generated when the red and the UV pulses overlap both in space and in time on the photocathode. It is shown that this emission process results from the absorption by an electron of one red and one UV photon. It provides a means to correlate ultrashort laser pulses of different wavelengths.
Advances in Femtosecond Optical Spectroscopy Techniques
Laser Chemistry, 1983
This paper reviews the recent advances in optical pulse measurement techniques which have made possible the investigation of ultrafast phenomena in condensed matter on a time scale of 100 femtoseconds or less. Recent results in pulse generation, amplification, white light continuum generation, and pulse compression will be discussed. In addition, applications of these pulses for measurement will be discussed.