Investigation of Interferences in Carbon Dioxide through Multidimensional Molecular-Frame High-Harmonic Spectroscopy.

We present molecular-frame high-harmonic spectroscopic measurements of the spectral intensity and group delay of carbon dioxide. Using four different driving wavelengths and a range of intensities at each wavelength for high-harmonic generation, we observe a well-characterized minimum in the harmonic emission that exhibits both a wavelength and intensity dependence. Using the intensity dependence at each driving wavelength, we classify the minimum as due to either a structural two-center interference or dynamic multichannel interference, consistent with previous literature.

High-harmonic spectroscopy of transient two-center interference calculated with time-dependent density-functional theory.

We demonstrate high-harmonic spectroscopy in many-electron molecules using time-dependent density-functional theory. We show that a weak attosecond-pulse-train ionization seed that is properly synchronized with the strong driving mid-infrared laser field can produce experimentally relevant high-harmonic generation (HHG) signals, from which we extract both the spectral amplitude and the target-specific phase (group delay). We also show that further processing of the HHG signal can be used to achieve molecular-frame resolution, i.

Comparison of ultrafast intense-field photodynamics in aniline and nitrobenzene: stability under amino and nitro substitution.

We report on the photoionization and photofragmentation of aniline (CHNH) and nitrobenzene (CHNO) under single-molecule conditions in the focus of 50 fs, 800 nm laser pulses. Ion mass spectra are recorded as a function of intensity ranging from 6 × 10 to 3 × 10 W cm. Ion yields are measured in the absence of the focal volume effect and without the need for additional deconvolution of data.

Imaging surface acoustic wave dynamics in semiconducting polymers by scanning ultrafast electron microscopy.

Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales.

Ultrafast dynamics. Four-dimensional imaging of carrier interface dynamics in p-n junctions.

The dynamics of charge transfer at interfaces are fundamental to the understanding of many processes, including light conversion to chemical energy. Here, we report imaging of charge carrier excitation, transport, and recombination in a silicon p-n junction, where the interface is well defined on the nanoscale. The recorded images elucidate the spatiotemporal behavior of carrier density after optical excitation.

Observation and identification of metastable excited states in ultrafast laser-ionized pyridine.

We report on the fragmentation of ionized pyridine (C(5)H(5)N) molecules by focused 50 fs, 800 nm laser pulses. Such ionization produces several metastable ionic states that fragment within the field-free drift region of a reflectron-type time of flight mass spectrometer, with one particular metastable dissociation being the leading fragmentation process. Because the time of flight is no longer dependent in a simple way on the mass of the ion, the metastable decay is manifested as an unfocused peak on the mass spectrum that appears at a time of flight not corresponding to an integer mass.

Ultrafast resonance-enhanced multiphoton ionization in the azabenzenes: pyridine, pyridazine, pyrimidine, and pyrazine.

We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C-H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions.

Ultrafast REMPI in benzene and the monohalobenzenes without the focal volume effect.

We report on the photoionization and photofragmentation of benzene (C(6)H(6)) and of the monohalobenzenes C(6)H(5)-X (X = F, Cl, Br, I) under intense-field, single-molecule conditions. We focus 50-fs, 804-nm pulses from a Ti:sapphire laser source, and record ion mass spectra as a function of intensity in the range ∼10(13) W/cm(2) to ∼10(15) W/cm(2). We count ions that were created in the central, most intense part of the focal area; ions from other regions are rejected.

Ultrashort intense-field optical vortices produced with laser-etched mirrors.

We introduce a simple and practical method to create ultrashort intense optical vortices for applications involving high-intensity lasers. Our method utilizes femtosecond laser pulses to laser etch grating lines into laser-quality gold mirrors. These grating lines holographically encode an optical vortex.