Two-electron ionization in strong laser fields below intensity threshold: signatures of attosecond timing in correlated spectra

We develop an analytical model of correlated two-electron ionization in strong infrared laser fields. The model includes all relevant interactions between the electrons, the laser field, and the ionic core nonperturbatively. We focus on the deeply quantum regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. In this regime, the electron-electron and the electron-ion interactions leave distinct footprints in the correlated two-electron spectra, recording the mutual dynamics of the escaping electrons.Comment: 25 pages and 4 figure

Simultaneous Measurement for Strain and Temperature Using Fiber Bragg Gratings and Multimode Fibers

An all-fiber sensor capable of simultaneous measurement of temperature and strain is newly presented. The sensing head is formed by a fiber Bragg grating combined with a section of multimode fiber that acts as a Mach-Zehnder interferometer for temperature and strain discrimination. The strain and temperature coefficients of multimode fibers vary with the core sizes and materials. This feature can be used to improve the strain and temperature resolution by suitably choosing the multimode fiber. For a 10 pm wavelength resolution, a resolution of 9.21 μ∈ in strain and 0.26°C in temperature can be achieved

Photoelectron spectra in strong-field ionization by a high frequency field

We analyze atomic photoelectron momentum distributions induced by bichromatic and monochromatic laser fields within the strong field approximation (SFA), separable Coulomb-Volkov approximation (SCVA), and ab initio treatment. We focus on the high frequency regime -- the smallest frequency used is larger than the ionization potential of the atom. We observe a remarkable agreement between the ab initio and velocity gauge SFA results while the velocity gauge SCVA fails to agree. Reasons of such a failure are discussed.Comment: Completely rewritten paper. Ionization by a two-color field is adde

Core-Offset Small-Core-Diameter Dispersion Compensation Fiber Interferometer and its Applications in Fiber Sensors

We propose a core-offset small core diameter dispersion compensation fiber (DCF) interferometer and investigate its applications in fiber sensors. If the transverse force is applied to a short section of the DCF, there is almost no crosstalk on the transmission spectrum between the extinction ratio variation induced by the transverse force and the wavelength shift caused by the longitudinal strain or ambient temperature, which can be applied to measure both transverse and longitudinal strain, or both transverse strain and temperature, simultaneously. The proposed sensors have the advantages of low cost, simple and compact structure, and good reproducibility

Temperature- and Phase-Independent Lateral Force Sensor based on a Core-Offset Multi-Mode Fiber Interferometer

A novel lateral force sensor based on a core-offset multi-mode fiber (MMF) interferometer is reported. High extinction ratio can be obtained by misaligning a fused cross section between the single-mode fiber (SMF) and MMF. With the variation of the lateral force applied to a short section of the MMF, the extinction ratio changes while the interference phase remains almost constant. The change of the extinction ratio is independent of temperature variations. The proposed force sensor has the advantages of temperature- and phase-independency, high extinction ratio sensitivity, good repeatability, low cost, and simple structure. Moreover, the core-offset MMF interferometer is expected to have applications in fiber filters and tunable phase-independent attenuators

Semiclassical theory of the effects of collisions between rotors on molecular spectral lineshapes. II. Calculations for several systems

The T2 (microwave line broadening) and T1 (microwave transient experiments) collisional cross sections are obtained by Monte Carlo trajectory evaluations of semiclassical (WKB) expressions for those quantities derived in a previous paper in this series. The calculated values of the cross sections presented here yields the relation T1~T2 (within standard error) for the systems OCS–OCS, OCS–N2, OCS–H2, OCS–CO2, and HCN–HCN, a result which agrees with recent experimental findings. Reasonable agreement was also found between the calculated values of the T2 cross section and those observed spectroscopically

On the theory of the relaxation matrix and its application to microwave transient phenomena

The phenomenological relaxation times T1 and T2 measured in microwave transient experiments are expressed in terms of specific molecular relaxation matrix elements. Conditions for this simple T1, T2 description are also given. The system is described in terms of a kinetic equation for the density matrix, which provides a unified treatment of the microwave transient behavior, spectral line shapes, and double resonance phenomena. Spatial degeneracy of the states and m dependence of T1 and T2 are discussed in detail. The recently developed semiclassical theory of molecular collisions is then applied to obtain expressions for the relevant relaxation times

Theory of the relaxation matrix and its relation to microwave transient phenomena. II. Semiclassical calculations for systems of OCS and nonpolar collision partners

Cross sections corresponding to relaxation times T1 and T2 measured in microwave transient experiments are calculated for systems of OCS and nonpolar collision partners, employing the recently developed semiclassical theory of molecular collisions. Cases in the presence and absence of static Stark field are described. The over-all agreement with existing experimental results is encouraging. Similarities and differences between T1/T2 values in microwave transient experiments and in molecular beam maser experiments are discussed, together with a role of semiclassical collisional selection rules