Formation of Rydberg states in collisions of fast hydrogen atoms with H2, N2 and He

The cross sections for production of hydrogen Rydberg states (n=24-27) in collisions of fast (accelerated to 3.6 keV) hydrogen atoms with H2, N2 and He were measured. Field ionization was used to select states in terms of the principal quantum number n. The field ionizer was calibrated by the ionization of Rydberg states selectively excited by dye lasers. It has been found that the cross sections scale with n in the same way as the cross sections of hydrogen Rydberg state production, when the fast protons exchange their charge on potassium. © 1991 IOP Publishing Ltd.status: publishe

IONIZATION OF FAST RYDBERG ATOMS IN LONGITUDINAL AND TRANSVERSE ELECTRIC-FIELDS

The main properties of longitudinal and transverse electric field ionizers for fast Rydberg atoms n=21-40 have been investigated. The dispersion and the background due to collisional processes between fast atoms and residual gas molecules have been measured and calculated. The kinetic energy spread of ions formed by field ionization of Rydberg atoms and their trajectories have been calculated. The potassium beam energy was 3.9 keV. © 1993 Springer-Verlag.status: publishe

A METHOD OF DETECTING THE RARE ISOTOPES KR-85 AND KR-81 BY MEANS OF COLLINEAR LASER PHOTOIONIZATION OF ATOMS IN AN ACCELERATED BEAM

A method is suggested for detecting rare krypton isotopes, based on the collinear laser photoionization of atoms in an accelerated beam at the exit from a mass separator. The results of investigations into the two-step collinear laser photoionization of metastable krypton atoms in an accelerated beam are presented. © 1991 IOP Publishing Ltd.status: publishe

Laser collinear ionization of accelerated atoms in a beam as a method for detecting rare isotopes of krypton

In this study, the estimates presented showed that the proposed technique of collinear laser photoionization of fast atoms in conjunction with preliminary mass enrichment of the ionic beam in a rare isotope level of 10 5 should permit reliable detection of rare isotopes of krypton. At an ion current I=10 13 s -1, the time needed to count 10 photoions of a rare isotope at the input to a mass separator was 0.5 and 45 min. for 85Kr and 81Kr, respectively. Among the schemes of laser excitation of a krypton atom to a Rydberg state, the single-stage scheme was distinguished for its simplicity and high selectivity. It should be taken note of that a comparable scheme of single-stage excitation can be applied for detecting rare isotopes of other noble gases.status: publishe

DETECTION OF VERY RARE ISOTOPES BY COLLINEAR RESONANCE IONIZATION OF ACCELERATED ATOMS

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Attosecond electron wave packet interferometry

International audienceAcomplete quantum-mechanical description of matter and its interaction with the environment requires detailed knowledge of a number of complex parameters. In particular, information about the phase of wavefunctions is important for predicting the behaviour of atoms, molecules or larger systems. In optics, information about the evolution of the phase of light in time and space is obtained by interferometry. To obtain similar information for atoms and molecules, it is vital to develop analogous techniques. Here we present an interferometric method for determining the phase variation of electronic wave packets in momentum space, and demonstrate its applicability to the fundamental process of single-photon ionization. We use a sequence of extreme-ultraviolet attosecond pulses to ionize argon atoms and an infrared laser field, which induces a momentum shear between consecutive electron wave packets. The interferograms that result from the interaction of these wave packets provide useful information about their phase. This technique opens a promising new avenue for reconstructing the wavefunctions of atoms and molecules and for following the ultrafast dynamics of electronic wave packets

The Role of Backbone Hydration of Poly(N-isopropyl acrylamide) Across the Volume Phase Transition Compared to its Monomer

Abstract Thermo-responsive polymers undergo a reversible coil-to-globule transition in water after which the chains collapse and aggregate into bigger globules when passing to above its lower critical solution temperature (LCST). The hydrogen bonding with the amide groups in the side chains has to be contrasted with the hydration interaction of the hydrophobic main-chain hydrocarbons. In the present investigation we study molecular changes in the polymer poly(N-isopropyl acrylamide) (PNIPAM) and in its monomer N-isopropyl acrylamide (NIPAM) in solution across the LCST transition. Employing Fourier-transform infrared spectroscopy we probe changes in conformation and hydrogen bonding. We observe a nearly discontinuous shift of the peak frequencies and areas of vibrational bands across the LCST transition for PNIPAM whereas NIPAM exhibits a continuous linear change with temperature. This supports the crucial role of the polymer backbone with respect to hydration changes in the amide group in combination with cooperative interactions of bound water along the backbone chain

Nonlinear Optics

This chapter provides a brief introduction into the basic nonlinear-optical phenomena and discusses some of the most significant recent advances and breakthroughs in nonlinear optics, as well as novel applications of nonlinear-optical processes and devices. Nonlinear optics is the area of optics that studies the interaction of light with matter in the regime where the response of the material system to the applied electromagnetic field is nonlinear in the amplitude of this field. At low light intensities, typical of non-laser sources, the properties of materials remain independent of the intensity of illumination. The superposition principle holds true in this regime, and light waves can pass through materials or be reflected from boundaries and interfaces without interacting with each other. Laser sources, on the other hand, can provide sufficiently high light intensities to modify the optical properties of materials. Light waves can then interact with each other, exchanging momentum and energy, and the superposition principle is no longer valid. This interaction of light waves can result in the generation of optical fields at new frequencies, including optical harmonics of incident radiation or sum- or difference-frequency signals