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We describe early and recent advances in the fascinating field of combined magnetic and optical properties of inorganic coordination compounds and in particular of 3d–4f single molecule magnets. We cover various applied techniques which allow for the correlation of results obtained in the frequency and time domain in order to highlight the specific properties of these compounds and the future challenges towards multidimensional spectroscopic tools. An important point is to understand the details of the interplay of magnetic and optical properties through performing time‐resolved studies in the presence of external fields especially magnetic ones. This will enable further exploration of this fundamental interactions i. e. the two components of electromagnetic radiation influencing optical properties. [ABSTRACT FROM AUTHOR]

Active nanostructured optical components show promise as potential building blocks for novel light‐based computing and data processing architectures. However, nanoscale all‐optical switches that have low activation powers and high‐contrast ultrafast switching have been elusive so far. Here, pump–probe measurements performed on amorphous‐Ge‐based micro‐resonator metasurfaces that exhibit strong resonant modes in the mid‐infrared are reported. Relative change is observed in transmittance of ΔT/T ≈ 1 with picosecond (down to τ ≈ 0.5 ps) free carrier relaxation rates, obtained with very low pump fluences of 50 μJ cm−2. These observations are attributed to efficient free carrier promotion, affecting light transmittance via high quality‐factor optical resonances, followed by an increased electron–phonon scattering of free carriers due to the amorphous crystal structure of Ge. Full‐wave simulations based on a permittivity model that describes free‐carrier damping through crystal structure disorder find excellent agreement with the experimental data. These findings offer an efficient and robust platform for all‐optical switching at the nanoscale. [ABSTRACT FROM AUTHOR]

It is remarkable that time delay is an experimentally measurable quantity, but time itself is not. Time delay in quantum collisions and in photoionisation/photodetachment of atomic and molecular systems is reviewed in this paper. Wigner–Eisenbud formalism of time delay in quantum collision of a wavepacket with a target is discussed. Its equivalence with Smith's formalism of time delay, based on an independent basis for time delay in terms of excess particle density in the collision zone, is demonstrated. Similarity and difference between quantum collision of an electron with a positive atomic/molecular ion and photoionisation/photodetachment of a neutral atom/molecule are discussed, and the underlying quantum dynamics involving the time-reversal symmetry between solutions with outgoing and ingoing wave boundary conditions is pointed out to interpret photoionisation/photodetachment as half-scattering. This relationship is subsequently taken advantage to extend the formalism of Wigner–Eisenbud–Smith time delay in photoionisation/photodetachment. The measurability of time delay is accounted for in terms of a self-adjoint quantum operator that characterises it, even if there is no such operator for time itself. A few illustrative examples of theoretical and experimental studies of time delay are given to indicate outstanding advances made in this field in the last two decades. [ABSTRACT FROM AUTHOR]

This study investigates recent advances in photoelectron emission generated by irradiating ultrashort lasers on metallic nanostructures and low-dimensional carbon materials. Recently, primary focus has been on improving the efficiency of emitters, i.e. increasing the number of field-emitted electrons and their respective kinetic energies. An example of this is the modification of the conventional metal nanotip through adiabatic nanofocusing and various plasmonic metal structures, such as nanorods and bowtie antenna. The coherent emission control with two color irradiation enabled modulation in the emission yield. In addition, THz waves near the metallic nanostructure induced a highly accelerated, monochromatic energy. Alternative to metallic nanotips, carbon nanotubes are emerging as efficient photoelectron emitters, due to the large enhancement factor associated with their high aspect ratio and damage threshold. They particularly allowed the use of femtosecond light sources with a relatively short wavelength, resulting in the generation of photoelectrons with a narrow bandwidth. Additionally, electronic control over the single-walled nanotubes band structure added a degree of freedom for controlling the electron emission yield. Finally, we review the strong-field tunneling emission in graphene edge, with the emission yield showing an anomalous increase of nonlinear order, corresponding to the deep strong tunneling regime.

The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.

Filamentation of infrared femtosecond pulses in Tellurite glass is reported, leading to the generation of a supercontinuum generation spanning from the visible up to 4 μm. The angular distribution of the supercontinuum shows clear evidence of conical waves generation, in particular, in the visible region. Moreover, taking advantage of the spatio-temporal self-focusing effect occurring in the Tellurite glass, a twofold pulse shortening is demonstrated. Tellurite glass appears as a very convenient, versatile and promising medium for femtosecond nonlinear optics in the infrared region. [ABSTRACT FROM AUTHOR]

After UV excitation, gas phase thymine returns to a ground state in 5 to 7 ps, showing multiple time constants. There is no consensus on the assignment of these processes, with a dispute between models claiming that thymine is trapped either in the first (S1) or in the second (S2) excited states. In the present study, a nonadiabatic dynamics simulation of thymine is performed on the basis of ADC(2) surfaces, to understand the role of dynamic electron correlation on the deactivation pathways. The results show that trapping in S2 is strongly reduced in comparison to previous simulations considering only non-dynamic electron correlation on CASSCF surfaces. The reason for the difference is traced back to the energetic cost for formation of a CO π bond in S2. [ABSTRACT FROM AUTHOR]

We introduce a novel method for direct and accurate measurement of refractive index dispersion based on carrier-envelope phase detection of few-cycle laser pulses, exploiting the difference between phase and group velocity in a dispersive medium. In a layout similar to an interferometer, two carrier-envelope phasemeters are capable of measuring the dispersion of a transparent or reflective sample, where one phasemeter serves as the reference and the other records the influence of the sample. Here we report on proof-of-principle measurements that already reach relative uncertainties of a few 10 ^−4 . Further development is expected to allow for unprecedented precision.

The physical process of forming a modified region in soda-lime glass was investigated using 1 kHz intense femtosecond laser pulses from a Ti: sapphire laser at 775 nm. Through the modifications induced by the femtosecond laser radiation using selective chemical etching techniques, we fabricated reproducible and defined microstructures and further studied their morphologies and etching properties. Moreover, a possible physical mechanism for the femtosecond laser modification in soda-lime glass was proposed. [ABSTRACT FROM AUTHOR]

A response function theory and scattering theory applicable to the study of physical properties of systems driven arbitrarily far removed from equilibrium, specialized for dealing with ultrafast processes, and in conditions of space resolution (including the nanometric scale) are presented. The derivation is done in the framework of a Gibbs-style nonequilibrium statistical ensemble formalism. The observable properties are shown to be connected with time- and space-dependent correlation functions out of equilibrium. A generalized fluctuation-dissipation theorem, which relates these correlation functions with generalized susceptibilities, is derived. The method of nonequilibrium-thermodynamic Green functions, which proves useful for calculations, is also presented. Two illustrative applications of the formalism, which study optical responses in ultrafast laser spectroscopy and Raman scattering of electrons in III-N semiconductors (of 'blue diodes') driven away from equilibrium by electric fields of moderate to high intensities, are described. [ABSTRACT FROM AUTHOR]

Abstract: We present a phase-reconstruction algorithm for a self-referenced spectrographic pulse characterization technique called “very advanced method for phase and intensity retrieval of e-fields” (VAMPIRE). This technique permits a spectral phase reconstruction of pulses with separated frequency components. The algorithm uses the particular characteristics of VAMPIRE spectrograms. It is a locally structured algorithm which is fast, robust, and it allows us to master stagnation problems. The algorithm is tested by use of both simulated and measured data. [Copyright &y& Elsevier]

A combined electronic structure and quantum dynamical study is presented that addresses the nature of the low-lying excitonic states in thiophene oligomers, and the evolution of such states in the presence of a torsional defect. Electronic structure calculations for a thiophene hexamer are carried out using the Second-Order Approximate Coupled-Cluster (CC2) method in conjunction with a transition density analysis. The latter analysis connects to an electron-hole quasi-particle representation that is subsequently used in the quantum dynamical description. Quantum dynamical propagation using the Multi-Configuration Time-Dependent Hartree (MCTDH) method is carried out on a minimal six-site lattice, yielding a basis of 36 electron-hole states in accordance with a Merrifield exciton model. The analysis accounts for vibronic coupling to site-correlated inter-ring stretch modes and a central ring torsional mode that in turn interacts with a dissipative harmonic-oscillator bath, similarly to our recent study of oligo-(p-phenylene vinylene) systems (Binder et al., Faraday Discuss. 163, 205, 2013). The dynamical description illustrates how a partially delocalized initial exciton coherently expands across a torsional defect and converges to a local exciton ground state on a larger fragment within about 300 femtoseconds. Exciton relaxation is found to occur as an intrinsic property of the finite-dimensional lattice structure featuring vibronic couplings. [ABSTRACT FROM AUTHOR]

Using a femtosecond time-resolved optical polarigraphy (FTOP) imaging technique, we measured the ultrafast propagation dynamics of femtosecond laser pulses in transparent materials, CS2 and fused silica, respectively. The FTOP images showed different profiles in these two media due to their different nonlinear response time. Based on the FTOP technique, a femtosecond time-resolved single-shot optical Kerr effect measurement was demonstrated, which can be accomplished using a single-laser shot and has a time resolution of about 100 fs. The polarization dependence of the image intensity indicated that the FTOP images were mainly induced by the transient birefringence effect induced by the pump pulse. [ABSTRACT FROM AUTHOR]

A comparative study in terms of optimized output power and stability is made on cascaded second-order nonlinear optical mode-locking with KTP, BBO and LBO crystals for both 1064 nm and 532 nm. Large nonlinear optical phase shift achieved in a non-phase-matched second harmonic generating crystal, is transformed into amplitude modulation through soft aperturing the nonlinear cavity mode variation at the laser gain medium to mode-lock a Nd:YVO4 laser. The laser delivers stable dual wavelength cw mode-locked pulse train with pulse duration 10.3 ps and average power of 1.84 W and 255 mW at 1064 nm and 532 nm respectively for the optimum performance in type-II KTP crystal. The exceptional stability achieved with KTP is accounted by simulating the mode-size variation with phase mismatch. [ABSTRACT FROM AUTHOR]

The ultrafast reflectivity of silicon, excited and probed with femtosecond laser pulses, is studied for different wavelengths and energy densities. The confinement of carriers in a thin surface layer delimited by a nanoscale Si-layered system buried in a Si heavily-doped wafer reduces the critical density of carriers necessary to create the electron plasma by a factor of ten. We performed two types of reflectivity measurements, using either a single beam or two beams. The plasma strongly depends on the photon energy density because of the intervalley scattering of the electrons revealed by two different mechanisms assisted by the electron–phonon interaction. One mechanism leads to a negative differential reflectivity that can be attributed to an induced absorption in X valleys. The other mechanism occurs, when the carrier population is thermalizing and gives rise to a positive differential reflectivity corresponding to Pauli-blocked intervalley gamma to X scattering. These results are important for improving the efficiency of Si light-to-electricity converters, in which there is a possibility of multiplying carriers by nanostructurization of Si. [ABSTRACT FROM AUTHOR]

A type of glass modifications occurring after femto-second laser irradiation gives rise to strong (10−2) from birefringence. This form birefringence is thought to be related to index nanostructure (called nanogratings). Analyzing induced tracks in fused silica using scanning electron microscopy (SEM) with nm resolution shows that nanostructures are porous nanoplanes with an average index lower than typical silica (Δ n ∼ -0.20). Their origin is explained as arising from fast decomposition of the glass under localized, high-intensity femtosecond laser radiation where strong nonlinear, multiphoton-induced photoionization leads to plasma generation. Mechanistic details include Coulombic explosions characteristic of strong photoionization and the production of self-trapped exciton (STE). Rapid relaxation of these STE prevents recombination and dissociated atomic oxygen instead recombines with each other to form molecular oxygen pointed out using Raman microscopy. Some of it is dissolved in the condensed glass whilst the rest is trapped within nanovoids. A chemical recombination can only occur at 1200 °C for many hours. This explains the thermal stability of such a nanostructure. Precise laser translation and control of these birefringent nanoporous structures allo arbitrarily tuning and positioning within the glass, an important tool for controlling optical properties for photonic applications, catalysts, molecular sieves, composites and more. [ABSTRACT FROM AUTHOR]

Abstract: We report results of a systematic study of the morphology of laser-written structures within transparent media like fused silica, borosilicate glass (BK7), and polymethylmethylacrylate (PMMA) using a high-energy, 5.1MHz repetition rate, femtosecond laser oscillator. Depending on experimental conditions, both smooth channels as well as dot patterns can be laser-written. The periodicity of the written dots is readily controlled by the energy dose, a single parameter that encompasses laser energy, translation speed at fixed repetition rate, and focusing conditions. We discover the importance of the direction in which laser-writing is carried out: the periodicity of the dot patterns written at fixed energy dose but with opposite writing directions is significantly different. In PMMA, extremely large rod-like structures (∼200µm) are observed whose formation is also dependent on writing direction. We quantify guidance of 632nm and 830nm light in structures written in BK7. [Copyright &y& Elsevier]

Generation and evolution of plasma during femtosecond laser ablation of silicon are studied by steady-state and time-resolved spectroscopy in air, N2, SF6, and under vacuum. The plasma is generated faster than 200 ps (time resolution of our experiment) after excitation and mainly contains atoms and monovalent ions of silicon. Time-resolved spectra prove that silicon ions are faster than the silicon atoms which may be attributed to Coulomb repulsion and a local electric field when they are ejected from the silicon surface. During plasma evolution, ambient gas causes a confinement effect that enhances the dissociation of ambient gas molecules and the re-deposition of the removed material and leads to higher intensity and longer lifetime of the emission spectra. In SF6, a chemical reaction increases the plasma density and weakens the re-deposition effect. The different processes during plasma evolution strongly influence microstructure formation. [ABSTRACT FROM PUBLISHER]

Abstract: The harmonic generations of molecular ion H2 + and D2 + exposed to an intense laser field have been studied with the collinear reduced-dimensionality model. The numerical solution of the time-dependent Schrödinger equation for H2 + and its isotopic variant D2 + shows that high-order harmonic generation is sensitive to the initial vibrational states of the molecular ion. By comparing the spectra of H2 + with D2 +, it is shown more intense harmonics are generated in lighter isotopes. [Copyright &y& Elsevier]

We present an investigation of the critical frequency windows permitting modulation instability in negative index materials. The principal motivation for our analysis stems from the impact of the inevitable presence of the effective dispersive magnetic permeability in addition to the effective dielectric permittivity determining the propagation model for ultrashort pulses in negative index materials. We emphasize the influence of nonlinear dispersion terms, arising out of the combinatorial effect of the dispersive permeability with the nonlinear polarization, over the MI phenomena, the outcome of its development achieved by using linear stability analysis. Gain spectrum investigation has been carried out for both anomalous and normal dispersion regime in the focusing and defocusing cases of nonlinearity and near zero dispersion regime where higher order linear dispersive effects emerge. The results of linear stability analysis have been validated by direct numerical simulation of the governing equation using the split-step Fourier transform method. We show that second-order nonlinear dispersion opens up distinct MI windows with their appropriate conditions and unlike the first-order nonlinear dispersion term, the sign of it has got deep consequences in the modulation instability scenario. [ABSTRACT FROM AUTHOR]

Abstract: We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150μJ and durations 15–50fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. [Copyright &y& Elsevier]

Abstract: Ag nanoparticles embedded in soda-lime silicate glasses were fabricated by the ion-exchange technique. Effects of thermal treatment on the optical nonlinearity and ultrafast dynamics of Ag nanoparticles were investigated by applying time-resolved optical Kerr effect and pump-probe techniques. The results indicate that thermal treatment is an efficient method to improve the nonlinear optical performance of this kind of material. [Copyright &y& Elsevier]

Abstract: We describe a method of ultrashort-pulse and ultrafast-pulse-train generation through optical parametric amplification of a laser beat wave. Numerical simulation shows that 250-fs laser pulses at 1.55μm are generated from a beat-wave seeded optical parametric amplifier pumped by a 30-ps laser at 1064nm. The pulse compression is attributable to sideband generation and parametric amplification under group velocity mismatch. Our experimental result confirms efficient generation of comb-like sidebands for the mixing waves from such an optical parametric amplifier. [Copyright &y& Elsevier]

Abstract: Tunable line emission (LE) over a large wavelength region (340–980nm) is obtained by pumping thick crystals of β-barium borate (BBO) with picosecond pulses at 532nm. Phenomena of group velocity dispersion, diffraction and phase matching take place simultaneously such that the radiation shows specific features that are characteristic of (i) strongly coupled fundamental and harmonic fields, (ii) amplified phase matched superfluorescence, (iii) conical emission and (iv) four wave mixing. [Copyright &y& Elsevier]

We present an experimental study that provides insight into the charge carrier dynamics that lead to terahertz (THz) emission. We perform time-resolved THz experiments on semiinsulating GaAs structures with periodically poled surface electrodes. The individual charge carrier dynamics that contribute to the THz emission process are identified by their dependence on the applied field. Electron transport in inhomogeneous fields is found to dominate the emission of THz radiation. Other dynamics that become visible by their specific THz emission are the Dember effect, the intervalley transfer of electrons, and hole currents at high field strengths. [ABSTRACT FROM PUBLISHER]

We have carried out an experimental study of the nonlinear optical properties of multilayer heterostructures based on zinc chalcogenides when excited by ultrashort laser pulses. We have observed a strong change in the optical properties of the samples over a broad spectral region for two-photon and one-photon excitation of the ZnSe sublattice. The fast relaxation time of the nonlinearity is ∼2–5 psec in both cases. We propose a physical model qualitatively explaining the observed effects. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1×4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse. [Copyright &y& Elsevier]

In this paper we present a systematic study of the spatial and temporal effects of intense femtosecond laser pulses in BK-7 over a broad range of input powers, 1{1000 times the critical power for self-focusing (Pcr) by numerically solving the nonlinear Schrödinger equation (NLS). Most numerical studies have not been extended to such high powers. A clear-cut classification of spatio-temporal dynamics up to very high powers into three regimes -- the group-velocity dispersion (GVD) regime, the ionization regime and the dominant plasma regime -- as done here, is a significant step towards a better understanding. Further, we examine in detail the role of GVD in channel formation by comparing BK-7 to an 'artificial' medium. Our investigations bring forth the important observation that diffraction plays a minimal role in the formation of multiple cones and that plasma plays a diffraction-like role at very high powers. A detailed study of the spatio-temporal dynamics in any condensed medium over this range of powers has not been reported hitherto, to the best of our knowledge. We also suggest appropriate operational powers for various applications employing BK-7 on the basis of our results. [ABSTRACT FROM AUTHOR]

Abstract: Photonic-crystal fibers allow the creation of novel compact and convenient light sources for nonlinear spectroscopy. In experiments discussed in this paper, photonic-crystal fibers provide efficient nonlinear-optical transformations of femtosecond Cr:forsterite laser pulses, delivering linearly chirped frequency-shifted broadband light pulses with central wavelengths ranging from 400 to 900nm. These pulses were cross-correlated with the femtosecond second-harmonic output of the Cr:forsterite laser in toluene solution, used as a test object, in boxcars geometry to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene molecules (XFROG CARS). The blue-shifted chirped-pulse output of a photonic-crystal fiber with a spectrum stretching from 530 to 680nm is shown to be ideally suited for time-resolved nonlinear absorption spectroscopy of exciton bands in molecular aggregates excited by femtosecond laser pulses. [Copyright &y& Elsevier]

Abstract: Femtosecond and nanosecond laser flash photolysis was used to determine the photophysical and photochemical processes in aqueous solutions of Fe(III) ion and 5-sulfosalicylic acid (SSA) containing the FeSSA complex and the free ligand. Excitation of the FeSSA complex in the charge transfer band (λ max =505nm) is followed by an ultrafast relaxation to the ground electronic state with two characteristic times of 0.26 and 1.8ps. The shorter time constant is ascribed to internal conversion to the vibrationally hot electronic ground state of FeSSA and the 1.8ps time constant is assigned to the vibrational cooling of the ground state. The UV irradiation of the solution (308nm) leads to the excitation of both the free ligand and the FeSSA complex. The latter relaxes rapidly and the free ligand undergoes intersystem crossing to the triplet state. This system undergoes an irreversible photochemical reaction originating from an electron transfer (k =(9±2)×108 M−1 s−1) from the free ligand in the triplet state to the FeSSA complex. This electron transfer is accompanied by an energy transfer between these species (k =(1.3±0.2)×109 M−1 s−1). [Copyright &y& Elsevier]

Abstract: Intersystem crossing between zeroth-order states of different spin quantum numbers can be characterized as fast (≥1012 s−1) or slow. The bulk of the extant results on the fast unquenchable processes has been limited to the evaluation of efficiencies, the fraction of the initially excited molecules that undergo intersystem crossing. Cr(III) complexes have been the main systems studied. The increasing availability of sub-picosecond lasers has led to the determination of rates. Both prompt intersystem crossing which precedes thermalization and intersystem crossing from thermalized states contribute to the total efficiency, but the relative contributions of the two processes have not been determined. The magnitude of the efficiency reflects the relative rates of vibrational relaxation and prompt intersystem crossing in the Franck–Condon level, but both efficiencies and rates are available for few metal complexes. The published efficiency results are examined with a kinetic model. The relationship between the several different measures of intersystem crossing is considered. Identification of reactive states cannot be made from kinetic measurements alone. The reliability of the results is evaluated and the possible dependence on excitation wave length is judged. [Copyright &y& Elsevier]

Abstract: The Colquiriite crystals are attractive materials for directly diode-pumped femtosecond oscillators and amplifiers. Cr:LiSAF, Cr:LiSGAF and Cr:LiCAF are for the first time directly compared for their use in regenerative amplifiers both experimentally and theoretically. A maximum pulse energy of 10μJ was obtained at an absorbed pump power of 1.1W. A review of the work is given including a Cr:LiSAF seed oscillator, outlining specific needs for seeding. [Copyright &y& Elsevier]

Abstract: The recently proposed multi-layer extension of the multi-configuration time-dependent Hartree method is applied to study the quantum dynamics of ultrafast molecular processes in a condensed phase environment. In extension of our previous work, we consider reactions where anharmonicities of the intramolecular vibrational degrees of freedom or the nuclear degrees of freedom of the environment are important. As an example for the former we consider a model for a non-adiabatic photoisomerization reaction, the latter case is investigated for an electron transfer model coupled to an anharmonic bath. [Copyright &y& Elsevier]

Abstract: The nonlinear absorption properties of ‘axial-bonding’ type hybrid porphyrin arrays based on a tin(IV) tetratolylporphyrin (SnTTP) scaffold are studied with picosecond and nanosecond pulses. The effect of different central metal atoms substituted adjacent to the tin(IV) porphyrin in the oligomer structure is discussed. In the picosecond regime the lifetimes of the excited singlet states and two-photon absorption (TPA) processes dominate leading to interesting switching of nonlinear absorption behaviour. The TPA cross-section (σ TPA) is found to be as high as 396×10−46 cm4 sphoton−1 molecule−1, for an oligomer with Sn and Ni porphyrin macrocycles. However, in the nanosecond regime the optical limiting performance has increased considerably with increasing number of porphyrins in the array and excited state absorption is found to play a major role. [Copyright &y& Elsevier]

Type-II frequency doubling of short Gaussian laser pulses is studied theoretically. The situation is analysed when the group velocity mismatch and the walk-off angle of the interacting waves limit the frequency conversion efficiency. It is shown that with collinear ‘o’ and ‘e’ polarized fundamental waves a temporal and spatial separation of the fundamental beams is necessary to compensate for both effects. Results of the presented model are discussed for KDP crystals. [ABSTRACT FROM AUTHOR]

Photochromism describes the dye-based events of sensory photoreceptors initiating the signalling cascades in living organisms. Research on synthetic dye conjugates related to these primary processes are presented. Isoalloxazine(flavin)-borondipyrromethene 1a and its photoredox switching with 1,3-propanedithiol parallels in some aspects the flavin-based blue-light photoreceptors. Dihydroazulene/vinylheptafulvene (DHA/VHF) photochromism resembles the retinal-type photoreceptors. They both proceed by a photochemical “on” and a thermal “off” switching. Details on the electronically excited state properties of DHA/VHF photochromism are reported. [ABSTRACT FROM AUTHOR]

Abstract: Numerical solutions of the time-dependent Schroedinger equation, TDSE, for a non-Born Oppenheimer molecule exposed to the combination of a sub-femtosecond (attosecond) XUV pulse and a short (∼5fs) intense (I≥1013W/cm2) 800nm pulse allow for studying the nonlinear nonperturbative response of electrons and nuclei in molecules exposed to extreme laser conditions. New nonlinear phenomena, such as high order harmonic generation (HOHG), are considerably enhanced. This is a consequence of nonlinear photon processes and offers new routes for ‘attosecond’ pulse generation. Coupling the molecular TDSE to the photon Maxwell equations leads to the synthesis of even shorter attosecond and wavelength pulses, as new ultrashort sources for time-resolved XUV-Raman spectroscopy. [Copyright &y& Elsevier]

A class of X-ray optical elements for the sub-picosecond manipulation of X-rays is proposed. The design of these elements is based upon a time-dependent dynamical diffraction theory that synthesizes the eikonal theory with the Takagi–Taupin theory. A brief outline of the theory is given. [Copyright &y& Elsevier]

Nonadiabatic effects play an important role in many areas of physics and chemistry. The coupling between electrons and nuclei may, for example, lead to the formation of a conical intersection between potential energy surfaces, which provides an efficient pathway for radiationless decay between electronic states. At such intersections the Born-Oppenheimer approximation breaks down, and unexpected dynamical processes result, which can be observed spectroscopically. We review the basic theory required to understand and describe conical, and related, intersections. A simple model is presented, which can be used to classify the different types of intersections known. An example is also given using wavepacket dynamics simulations to demonstrate the prototypical features of how a molecular system passes through a conical intersection. [ABSTRACT FROM AUTHOR]

Tunable femtosecond pulse generation in the mid-IR between 6.6 and 11 μm is demonstrated by optical parametric amplification in Cd0.35Hg0.65Ga2S4 pumped at 820 nm by a 1 kHz repetition rate Ti:sapphire regenerative amplifier. Femtosecond pulses at the idler wave with energies as high as 2 μJ at 6.6 μm are produced for the first time by such a single conversion step from the Ti:sapphire spectral range. [Copyright &y& Elsevier]