Quantum model simulations of attosecond electron diffraction

Ultrafast diffraction with free attosecond electron pulses promises insight into the four-dimensional motion of charge density inatoms,molecules and condensed matter. Here we consider the quantum dynamics of the electron-electron scattering process on anattosecond time scale. By numerically solving the time-dependent two-electron Schrdinger equation,we investigate the interactionof an incoming keV-range electron wavepacket by the bound electron of an aligned H+2 molecule,using a one-dimensional model.Our findings reveal the ratio of elastic to inelastic contributions,the role of exchange interaction,and the influence of the molecularelectron density to diffraction. Momentum transfer during the scattering process,from the incoming to the bound electron mediatedby the nuclei,leaves the bound electron in a state of coherent oscillation with attosecond recurrences. Entanglement causes relatedstate-selective oscillations in the phase shift of the scattered electron. Two scenarios of distinguishable and indistinguishable freeand bound electrons yield equivalent results,irrespective of the electronic spins. This suggests to employ the scenario of distinguishable electrons,which is computationally less demanding. Our findings support the possibility of using electron diffraction forimaging the motion of charge density,but also suggest the application of free electron pulses for inducing attosecond dynamics.

Watt-scale super-octave mid-infrared intrapulse difference frequency generation

The development of high-power,broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications in medical diagnostics,spectroscopy,microscopy,and fundamental science.One of the major,long-standing challenges in improving the performance of these applications has been the construction of compact,broadband mid-infrared radiation sources,which unify the properties of high brightness and spatial and temporal coherence.Due to the lack of such radiation sources,several emerging applications can be addressed only with infrared(IR)-beamlines in largescale synchrotron facilities,which are limited regarding user access and only partially fulfill these properties.Here,we present a table-top,broadband,coherent mid-infrared light source that provides brightness at an unprecedented level that supersedes that of synchrotrons in the wavelength range between 3.7 and 18μm by several orders of magnitude.This result is enabled by a high-power,few-cycle Tm-doped fiber laser system,which is employed as a pump at 1.9μm wavelength for intrapulse difference frequency generation(IPDFG).IPDFG intrinsically ensures the formation of carrierenvelope-phase stable pulses,which provide ideal prerequisites for state-of-the-art spectroscopy and microscopy.

Multi-mW,few-cycle mid-infrared continuum spanning from 500 to 2250cm^(−1)

The demand for and usage of broadband coherent mid-infrared sources,such as those provided by synchrotron facilities,are growing.Since most organic molecules exhibit characteristic vibrational modes in the wavelength range between 500 and 4000 cm^(−1),such broadband coherent sources enable micro-or even nano-spectroscopic applications at or below the diffraction limit with a high signal-to-noise ratio1–3.These techniques have been applied in diverse fields ranging from life sciences,material analysis,and time-resolved spectroscopy.Here we demonstrate a broadband,coherent and intrinsically carrier-envelope-phase-stable source with a spectrum spanning from 500 to 2250 cm^(−1)(−30 dB)at an average power of 24mW and a repetition rate of 77 MHz.This performance is enabled by the first mode-locked thin-disk oscillator operating at 2μm wavelength,providing a tenfold increase in average power over femtosecond oscillators previously demonstrated in this wavelength range4.Multi-octave spectral coverage from this compact and power-scalable system opens up a range of time-and frequency-domain spectroscopic applications.