1,860 research outputs found
Polarization contrast of nanoscale waveguides in high harmonic imaging
No full textThe optical polarization response of a structured material is one of its most significant properties, carrying information about microscopic anisotropies as well as chiral features and spin orientations. Polarization analysis is therefore a key element of imaging and spectroscopy techniques throughout the entire spectrum. In the case of extreme ultraviolet (EUV) radiation, however, both the preparation and detection of well-defined polarization states remain challenging. As a result, polarization-sensitive EUV microscopy based on table-top sources has not yet been realized, despite its great potential, for example, in nanoscale magnetic imaging. Here, we demonstrate polarization contrast in coherent diffractive imaging using high harmonic radiation and investigate the polarization properties of nanoscale transmission waveguides. We quantify the achievable polarization extinction ratio for different waveguide geometries and wavelengths. Our results demonstrate the utility of slab waveguides for efficient EUV polarization control and illustrate the importance of considering polarization contrast in the imaging of nanoscale structures. (C) 2016 Optical Society of Americ
Interlocked attosecond pulse trains in slightly bi-elliptical high harmonic generation
No full textAbstractThe ellipticity of high harmonics driven by bi-chromatic (e.g. ω−2ω) co-propagating fields can be fully tuned by varying the polarization of the pump components. In order to start revealing the underlying mechanism of this control, we explore a relatively simple regime of this scheme that still gives rise to full control over the harmonics ellipticities. In this regime, the pumps are only slightly elliptical and the high harmonic radiation consists of two (different) interlocked attosecond pulse trains (APTs). We formulate a semi-analytic model that maps the high harmonic ellipticity to properties of the APTs harmonic decompositions. Utilizing this model, we reconstruct these APTs variables from measurements of the high harmonics ellipticities. This ellipticity-resolved spectroscopy of interlocked APTs may be useful for ultrafast probing of chiral degrees of freedom
Toroidal grating astigmatism of high-harmonics characterized by EUV Hartmann sensor
Full text linkThe beam transport of single high-order harmonics in a monochromator arrangement is studied. A toroidal grating combines spectral filtering and focusing in order to produce a small individual spot for each harmonic. Here, the effect of small deviations from perfect alignment is investigated. Experimentally, a Hartmann sensor monitors the EUV wavefront while the grating is subjected to an online alignment procedure. The obtained results are confirmed by a simple theoretical description employing optical matrix methods
Attosecond-precision coherent control of electron recombination in the polarization plane
No full textHigh-sensitivity extreme-ultraviolet transient absorptionspectroscopy enabled by machine learning
No full textWe present a novel denoising scheme for spectroscopy experiments employing broadband light sources and demonstrate its capabilities using transient absorption measurements with a high-harmonic source. Our scheme relies on measuring the probe spectra before and after interacting with the sample while capturing correlations between spectral components through machine learning approaches. With the present setup we achieve up to a tenfold improvement in noise suppression in XUV transient absorption spectra compared to the conventional pump on/ pump off referencing method. By utilizing strong spectral correlations in source fluctuations, the use of an artificial neural network facilitates pixel-wise noise reduction without requiring wavelength calibration of the reference spectrum. Our method can be adapted to a wide range of experiments and may be particularly advantageous for low repetition-rate systems, such as free electron lasers as well as laser-driven plasma and HHG sources. The enhanced sensitivity enables the investigation of subtle electron and lattice dynamics in the weak excitation regime, which is relevant for studying photovoltaics and photo-induced phase transitions in strongly correlated materials.Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/100005156Deutsche ForschungsgesellschaftGottfried Wilhelm Leibniz PrizeMax-Planck-Gesellschaft http://dx.doi.org/10.13039/50110000418
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