Ultrafast pulse duration measurement method of near-infrared pulses for a broad range of wavelengths using two-photon absorption in a liquid and fluorescent dye solution.

A novel characterization method to measure the pulse duration of ultrafast near-IR pulses is introduced, which uses simple tabletop optics, is relatively inexpensive, and is expected to work in a broad wavelength range. Our diagnostic tool quantitatively characterizes the laser pulse duration of any near-IR wavelength assuming a Gaussian pulse shape with a linear chirp. We negatively prechirp near-IR pulses with a home-built broadband pulse compressor (BPC) and send this prechirped beam through a cell filled with a low-molar solution of a fluorescent dye in a liquid.

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 of alignment and structural changes of carbon disulfide molecules using ultrafast electron diffraction.

Imaging the structure of molecules in transient-excited states remains a challenge due to the extreme requirements for spatial and temporal resolution. Ultrafast electron diffraction from aligned molecules provides atomic resolution and allows for the retrieval of structural information without the need to rely on theoretical models. Here we use ultrafast electron diffraction from aligned molecules and femtosecond laser mass spectrometry to investigate the dynamics in carbon disulfide following the interaction with an intense femtosecond laser pulse.

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.

Temporal lenses for attosecond and femtosecond electron pulses.

Here, we describe the "temporal lens" concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived.

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.

Creation of optical vortices in femtosecond pulses.

We experimentally created a femtosecond optical vortex using a pair of computer-synthesized holographic gratings arranged in a 2f - 2f optical setup. We present measurements showing that the resulting donut mode is free of spatial chirp, and support this finding with an analysis of the optical wave propagation through our system based on the Kirchhoff-Fresnel diffraction integral. An interferogram confirms that our ultrashort vortex has topological charge 1, and a conservative experimental estimation of its duration is 280 fs.