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We demonstrate a novel method to measure the temporal electric field evolution of ultrashort laser pulses. Our technique is based on the detection of transient currents in air plasma. These directional currents result from subcycle ionization of air with a short pump pulse and the steering of the released electrons with the pulse to be sampled. We assess the validity of our approach by comparing it with different state-of-the-art laser-pulse characterization techniques. Notably, our method works in ambient air and facilitates a direct measurement of the field waveform, which can be viewed in real time on an oscilloscope in a similar way as a radio frequency signal. more...

The ability to measure and control the carrier–envelope phase (CEP) of few-cycle laser pulses is of paramount importance for both frequency metrology and attosecond science. Here, we present a phase meter relying on CEP-dependent photocurrents induced by circularly polarized few-cycle pulses focused between electrodes in ambient air. The new device facilitates compact, single-shot CEP measurements under ambient conditions and promises CEP tagging at repetition rates orders of magnitude higher than most conventional CEP detection schemes, as well as straightforward implementation at longer wavelengths. more...

The study of core electron dynamics through nonlinear spectroscopy requires intense isolated attosecond extreme ultraviolet or even X-ray pulses. A robust way to produce these pulses is high-harmonic generation (HHG) in a gas medium. However, the energy upscaling of the process depends on a very demanding next-generation laser technology that provides multi-terawatt (TW) laser pulses with few-optical-cycle duration and controlled electric field. Here, we revisit the HHG process driven by 16-TW sub-two-cycle laser pulses to reach high intensity in the 100-eV spectral region and beyond. We show that the combination of above barrier-suppression intensity with a long generation medium significantly enhances the isolation of attosecond pulses compared to lower intensities and/or shorter media and this way reduces the pulse duration as well as field-stability requirements on the laser driver. This novel regime facilitates the real-time observation of electron dynamics at the attosecond timescale in atoms, molecules, and solids. more...

Nonlinear light–matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigated at free-electron laser (FEL) facilities. Yet, electron dynamics are often too fast to be captured with the femtosecond resolution of state-of-the-art FELs. Attosecond pulses from laser-driven XUV-sources offer the necessary temporal resolution. However, intense attosecond pulses supporting nonlinear processes have only been available for photon energy below 50 eV, precluding XUV-pump/XUV-probe investigation of typical inner-shell processes. Here, we surpass this limitation by demonstrating two-photon absorption from inner electronic shells of xenon at photon energies around 93 eV and 115 eV. This advance opens the door for attosecond real-time observation of nonlinear electron dynamics deep inside atoms. more...

A novel single-shot second-order autocorrelation scheme for extreme-ultraviolet radiation (XUV) is proposed. It is based on an ion-imaging technique, which provides spatial information of ionization products in the focal volume of the XUV beam. Using simple analytical and detailed numerical modeling, an evaluation toward selecting an optimum configuration has been performed. The implementation of the concept to characterize attosecond pulses is discussed, and the proposed setups are assessed. more...

Sectional views of thin films of symmetric polystyrene/polyisoprene (PS/PI) blends spin-cast from toluene (C6H5CH3) onto CH3- and COOH-terminated self-assembled monolayers (CH3−SAM and COOH−SAM) show concave- (sharp-edged) and convex-shaped (round) protrusions, respectively, while other morphology features are identical. A 3-dimensional phase domain arrangement was determined with spectroscopic techniques (profiling and mapping mode of dynamic secondary ion mass spectrometry, dSIMS, and X-ray photoelectron spectroscopy). Surface topography was examined with atomic force microscopy and monitored, during the dSIMS analysis, with secondary electrons. In addition, solvent evaporation from PS, PI, and PS/PI layers cast on CH3−SAM and COOH−SAM was determined. The collected data were used to put forward a model of morphology formation and to elucidate the role of evaporation speed dependent on substrate chemistry in this process, demonstrated here for the first time. more...

Thin polymer films with lateral structures are expected to play an important role in future applications (e.g. plastic-based electronic devices). Such structures could be formed when blend films are spun-cast onto substrates patterned with self-assembled monolayers (SAM). The spin-coating process results in composition variations accompanied by surface undulations. We have studied both phenomena for PVP/dPS and PVP/PBrS blends, composed of poly(vinylpyridine) (PVP) and deuterated (dPS)- or brominated (PBrS)-polystyrene. SAM stripes of HS(CH2)15CH3on Au substrate (‘bare’ or covered with HS(CH2)15COOH) were used as the pattern with periodicity of 4μm. Transfer of the pattern from the substrate to the film interior and to the film surface was examined with secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM) combined with selective dissolution of blend components. Characteristic size Dof the phase domains corresponding to given spin-casting conditions was determined for the blends cast on homogeneous SAM substrate. Fourier transform analysis (FTA) of topographic (AFM) and compositional (SIMS) maps was performed. FTA confirms that the pattern-directed composition variations coincide with the surface undulations. It reveals also that most effective pattern transfer is achieved for the size Dcommensurate with the pattern periodicity for the carefully adjusted polymer–substrate interactions. more...

Thin films, formed by polymer blends spun-cast from a blend/solvent solution onto a rigid substrate, are used in many practical applications (e.g. photoresist layers, dielectric coatings). Film preparation process is often accompanied by phase decomposition (PD) during the rapid evaporation of the solvent. PD is reflected in undulations formed on an air/film interface. We have studied the topography of surface undulations and the phase domain morphology in thin film blends of polystyrene (PS) and polyisoprene (PI) using atomic force microscopy combined with selective dissolution of blend components. Gold covered with self-assembled monolayers [HS(CH2)15COOH]y[HS(CH2)15CH3]1−y(SAMy) was used as a substrate. For films of PS and PI (50% by mass) cast from toluene, the PS-rich domains protrude high above the PI-rich matrix forming concave or convex islands for hydrophobic (SAM0)- or hydrophilic (SAM1)-support, respectively. Different substrates (e.g. SAM0.5and Si with a native oxide layer), solvents (CCl4, chloroform) and PS mass fractions were used to evaluate the extent of this novel effect. more...