No abstract

Near-fields of non-resonantly laser-excited nanostructures enable strong localization of ultrashort light fields and have opened novel routes to fundamentally modify and control electronic strong-field processes. Harnessing spatiotemporally tunable near-fields for the steering of sub-cycle electron dynamics may enable ultrafast optoelectronic devices and unprecedented control in the generation of attosecond electron and photon pulses. Here we utilize unsupported sub-wavelength dielectric nanospheres to generate near-fields with adjustable structure and study the resulting strong-field dynamics via photoelectron imaging. We demonstrate field propagation-induced tunability of the emission direction of fast recollision electrons up to a regime, where nonlinear charge interaction effects become dominant in the acceleration process. Our analysis supports that the timing of the recollision process remains controllable with attosecond resolution by the carrier-envelope phase, indicating the possibility to expand near-field-mediated control far into the realm of high-field phenomena.

The bond strength of chlorine peroxide (ClOOCl) is studied by photoionization mass spectrometry. The experimental results are obtained from the fragmentation threshold yielding ClO+, which is observed at 11.52 +/- 0.025 eV. The O-O bond strength D(o) is derived from this value in comparison to the first ionization energy of ClO, yielding D(o)298 = 72.39 +/- 2.8 kJ mol(-1). The present work provides a new and independent method to examine the equilibrium constant K(eq) for chlorine peroxide formation via dimerization of ClO in the stratosphere. This yields an approximation for the equilibrium constant in the stratospheric temperature regime between 190 and 230 K of the form K(eq) = 1.92 x 10(-27) cm3 molecules(-1) x exp(8430 K/T). This value of K(eq) is lower than current reference data and agrees well with high altitude aircraft measurements within their scattering range. Considering the error limits of the present experimental results and the resulting equilibrium constant, there is agreement with previous works, but the upper limit of current reference values appears to be too high. This result is discussed along with possible atmospheric implications.

Waveform-controlled light fields offer the possibility of manipulating ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is key to the design of electronic devices operating at up to petahertz frequencies.We have studied the directional control of the electron emission from 95 nm

High-speed, single-shot velocity-map imaging (VMI) is combined with carrier-envelope phase (CEP) tagging by a single-shot stereographic above-threshold ionization (ATI) phase-meter. The experimental setup provides a versatile tool for angle-resolved studies of the attosecond control of electrons in atoms, molecules, and nanostructures. Single-shot VMI at kHz repetition rate is realized with a highly sensitive megapixel complementary metal-oxide semiconductor camera omitting the need for additional image intensifiers. The developed camera software allows for efficient background suppression and the storage of up to 1024 events for each image in real time. The approach is demonstrated by measuring the CEP-dependence of the electron emission from ATI of Xe in strong (≈10(13) W/cm(2)) near single-cycle (4 fs) laser fields. Efficient background signal suppression with the system is illustrated for the electron emission from SiO(2) nanospheres.

Photodissociation of the ClO dimer (ClOOCl) is studied in the ultraviolet regime (250 and 308 nm) under collision-free conditions. The primary photolysis products are probed by photoionization mass spectrometry. At both photolysis wavelengths, exclusively the formation of 2Cl + O 2 is observed, corresponding to a primary quantum yield γ Cl near unity. Considering the error limit of the experimental results one obtains γ Cl g 0.98 at 250 nm and γ Cl g 0.90 at 308 nm, respectively. At both photolysis wavelengths the pathway yielding ClO is not observed, corresponding to γ ClO e 0.02 at 250 nm and γ ClO e 0.10 at 308 nm. Sensitivity studies of these results with respect to ozone depletion in the stratosphere regarding photochemically induced ozone loss are discussed using model simulations. These simulations suggest that a change of γ Cl from 1.0 to 0.9 leads to a reduction of polar ozone loss of ∼5%.

We show experimentally that spectral phase manipulation of ultrashort extreme-uv light pulses can induce and control coherent transient excitation of the He͑1s3p͒ excited state by the nonresonant components of the broadband extreme-ultraviolet light. The spectral phase manipulation of the 15th harmonic of an intense 805 nm, 80 fs pulse is achieved by propagation of the euv light through a variable optical density of He gas. The acquired spectral phase due to the dispersive interaction of the off-resonance components in the euv pulse with the He͑1s3p͒ resonance enhances and modifies the transient excitation. The temporal evolution of the coherently prepared transient He͑1s3p͒ amplitude is probed by ionization to the continuum with a 400 nm, 80 fs pulse.

Photoionization of the primary photofragments of chlorine dioxide (OClO) and dichlorine monoxide is (Cl 2 O) reported. The nascent photofragments are formed by UV photolysis, they are subsequently photoionized by time-correlated XUV laser radiation and Ðnally detected by time-of-Ñight mass spectrometry. Primary photolysis of OClO leads to the formation of ClO ] O at j \ 359.5 nm, whereas ClO ] Cl are formed by photolysis of at j \ 250 nm. The XUV photoionization of the photolysis products relies on single Cl 2 O photon ionization. This allows to derive partial photoionization cross sections of the parent cations and their photolysis products from mass spectral intensities by using the absolute photoionization cross sections of the atomic products for calibration. SpeciÐcally, we obtain for OClO at E \ 13.74 eV : Mb and p ClO \ 27 ^5 Mb. Consistent Ðndings are obtained from equivalent experiments on The present p OClO \ 18.5 ^3 C l 2 O. results are compared with previous photoionization work on ClO and OClO to demonstrate the reliability of UV-pump/XUV-probe spectroscopy.