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Xe**2** plus ions can easily be formed by multiphoton absorption in Xe atoms at 0. 53 mu m. A kinetic model is developed which is based on the rate equations describing the evolution of populations of Xe atoms, Xe** plus and Xe**2** plus ions. The result is that the ratio of the number of Xe**2** plus to Xe** plus ions varies with the pulse duration tau as tau ** minus **3**/**2.
Multiphoton ionisation of He at 532 nm is investigated at about 1013 W cm-2 by measuring both electron energy distribution, and the laser intensity dependence of the production of He+ and He2+ ions. He2+ ions solely come from multiphoton ionisation of He+ ions.
A retarding-potential method has been used to analyse the energy of electrons produced in the process of generating singly and doubly charged ions in Xe and Ne at 532 and 1064 nm. Energetic electrons observed in Xe at 1064 nm imply that up to 30 photons have been absorbed in the ionisation process, while only 11 photons are necessary to release one electron. The laser intensity dependence of energ
We present results of experiments testing the influence of elliptical polarization on the production of high-order harmonics. Experiments were conducted both with a 600-nm, 1-psec dye laser and with an 825-nm, 140-fsec Cr:LiSAF6 (Cr:LiSAF) laser system, over a wide range of intensities and target gases (xenon, argon, and neon), using a detection system with a dynamical range of more than three ord
A new generation of sources of XUV harmonic radiation, delivering 'attosecond' pulses, makes feasible to investigate photoionization in the time domain, with unprecedented resolution. Here, we discuss theoretical aspects related to this new class of experiments.
We present a theory attempting an interpretation of existing data on three- and four-photon ionization of Sr in the wavelength range 557-575 nm and at 532 nm. Two-photon resonances with bound excited states and three-photon resonances with doubly excited autoionizing states are studied. ac Stark shifts and broadening of resonances, as well as singlet-triplet transitions, are shown to yield interes
We present a technique for characterizing ultrashort pulses in the spatiotemporal domain with high spatial resolution, based on a spatially-resolved Fourier-transform spectrometer. Spatiotemporal characterization of a pulse with pulse-front tilt is presented.
We present experimental measurements of vacuum ultraviolet light emission processes in a 15-Torr rare-gas medium exposed to a strong 1064-nm laser field. Apart from a small number of lines which correspond to discrete transitions, and a broad continuum emission, we essentially observe the odd harmonics of the laser field, up to very high order. At a 3×1013 W cm-2 laser intensity, the highest-order
We perform detailed calculations of harmonic conversion in a 15-Torr jet of xenon into which a 1064-nm-wavelength 36-ps-pulse-width laser has been tightly focused, so that the peak intensity ranges from 5×1012 to 5×1013 W cm-2. The single-atom emission rates are obtained by integrating the time-dependent Schrödinger equation. We employ an improved atomic model which includes excitation and ionizat
We present a simple, analytic, and fully quantum theory of high-harmonic generation by low-frequency laser fields. The theory recovers the classical interpretation of Kulander et al. in Proceedings of the SILAP III Works hop, edited by B. Piraux (Plenum, New York, 1993) and Corkum [Phys. Rev. Lett. 71, 1994 (1993)] and clearly explains why the single-atom harmonic-generation spectra fall off at an
A pulsed-gas jet with interesting properties has been developed. A typical pressure obtained at the output of this pulsed-gas jet is 25 Torr for a backing pressure of 150 Torr. At a repetition rate of 10 Hz, the background pressure stays below 1.5×10-4 Torr. Laser-induced fluoresence measurements permit one to determine the pressure and the divergence of the gas jet accurately.
We report the self-compression of linearly and circularly polarized light pulses down to the few-cycle regime by self-guided beam propagation of intense 38-fs pulses in different gases with uniform density and with a pressure gradient.
In this paper, we review the optimization and characterization of a high-order harmonic generation (HHG) source for application in coherence imaging, and the use of this light source in a digital in-line holography setup. The high-order harmonic beam is generated by focusing a powerful infrared beam into an Ar gas cell. The length of the cell and the focusing parameters are optimized to maximize t
The authors report the observation of very-high-order odd harmonics of Nd:YAG laser radiation in rare gases at an intensity of about 1013 W cm-2. Harmonic light as high as the 33rd harmonic in the XUV range (32.2 nm) is generated in argon. The key point is that the harmonic intensity falls slowly beyond the fifth harmonic as the order increases. Finally, a UV continuum, beginning at 350 nm and ext
We demonstrate that we can use the extreme ultraviolet radiation produced by high order harmonic generation to perform photoionization experiments. With harmonics from the 11th to the 69th of a 140 fs Cr:LiSAF laser operating at 825 nm, we measure the relative photoionization cross sections of xenon, krypton, argon and neon over the range 10 to 110 eV. With narrow bandwidth harmonics produced by a
In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E 1u, v = 0 and v = 1 states of CO are experimentally determined. For E 'D, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.6% result for 12C16O, 13C16O
High-content real-time imaging of hormone secretion in tissues or cell populations is a challenging task, which is unlikely to be resolved directly, despite immense translational value. We approach this problem indirectly, using compensatory endocytosis, a process that closely follows exocytosis in the cell, as a surrogate read-out for secretion. The tissue is immobilized in an open-air perifusion
We present temporal characterization of attosecond pulse trains generated during selfguided propagation of intense pulses in a long gas target. Spectral phase jumps are observed, affecting the temporal shape of the attosecond pulse train.
Huge dynamic Stark shifts of atomic energy levels in xenon induced by high-intensity laser light have been measured by a new method based upon multiphoton ionization by a tunable femtosecond laser source. Stark-induced multiphoton resonances appear as identifiable structures in the photoelectron energy spectra. The change in the structures positions, when the photon energy is tuned, is directly re
