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The concept of enhancing recollisions after laser-induced ionization via antisymmetric molecular or atomic orbitals is investigated. The underlying mechanism, first motivated by classical arguments, is based on partial compensation of the electron drift induced by antisymmetry and the drift induced by the laser magnetic field. The numerical solution of the time-dependent Schrödinger equation confirms our concept in terms of the increase of the harmonic signal for the first excited antisymmetric state of H2+, as an important example of a recollision-dependent process, but also reveals novel aspects of two-centre interference structures in high-harmonic spectra. Finally, density contour plots illustrate the recollisions from antisymmetric orbitals and the virtues of employing ions rather than molecules. [ABSTRACT FROM AUTHOR]

We address several questions related to the nonlinear ionization processes observed when atoms are in the simultaneous presence of intense and coherent infrared (IR) and extreme ultraviolet (XUV) laser pulses. This topic is of much interest in the context of the current development of new XUV and soft-X-ray coherent sources, either from high-order harmonics or from X-ray free-electron laser (XFEL) devices that can be synchronized with IR lasers. The theoretical description of this class of two- (more generally multi-) colour ionization processes is challenging for theory. Here, we discuss the advantages and limitations of the so-called "soft-photon approximation", which, we believe, provides most useful insights in the analysis of these processes. [ABSTRACT FROM AUTHOR]

The R-matrix-Floquet theory is a non-perturbative ab initio approach which can be used to analyse in a unified way the various multiphoton processes occurring in atomic or molecular systems interacting with intense laser fields. The method is applicable to an arbitrary atom or molecule, and allows the inclusion of electron correlation effects. After reviewing the basic concepts and recent developments of the theory, we discuss some illustrative results. These include multiphoton ionization rates obtained for a number of atoms and ions and for the hydrogen molecule, laser-induced degeneracies in complex atoms, harmonic generation rates and differential cross-sections for laser-assisted electron-atom collisions. Finally, possible future applications and extensions of the theory are considered. [ABSTRACT FROM AUTHOR]

To attempt to control the quantum state of a physical system with a femtosecond two-colour laser field, a model for the two-level system is analysed as a first step. We investigate the coherent control of the two-colour laser pulses propagating in a two-level medium. Based on calculating the influence of the laser field with various laser parameters on the electron dynamics, it is found the electronic state can be changed up and down by choosing the appropriate laser pulses and the coherent control of the two-colour laser pulses can substantially modify the behaviour of the electronic dynamics: a quicker change of two states can be produced even for small pulse duration. Moreover, the oscillatory structures around the resonant frequency and the propagation features of the laser pulses depend sensitively on the relative phase of the two-colour laser pulses. Finally, the influence of a finite lifetime of the upper level is discussed in brief. [ABSTRACT FROM AUTHOR]

We investigate QED field-dependent effects in radiative shifts of atomic levels driven by a strong laser field. Our focus is on indirect laser-induced corrections to the Lamb shift of an atomic reference state due to a strong laser field which near-resonantly couples two other states, but not the reference state. Our aim is to show how to generalize previous treatments of related scenarios to the case of an induced indirect coupling. We also derive an expression of self-energy corrections in the Floquet picture and analyse various coupling schemes with respect to the shift of Floquet quasi-energies. The semi-classical Floquet picture and the fully quantized dressed-state approach are contrasted. [ABSTRACT FROM AUTHOR]

High-order harmonic generation (HHG) from aligned CO2 is studied within the framework of the strong-field approximation (SFA). Our results are in qualitative agreements with recent pump-probe experiments. The experimentally observed inverted modulation in HHG signals as a function of pump-probe delay time has previously been attributed to the quantum interference from the two oxygen centres. Our results, however, indicate that this is not necessary for the inverted modulation. The angular dependence of the HHG and the evolution of the HHG yield as functions of delay time are influenced strongly by the depletion of the ground state and, therefore, are sensitive to the probe laser intensity. [ABSTRACT FROM AUTHOR]

A laser-diode-pumped passively Q-switched Nd:YVO4 green laser with periodically poled KTP (PPKTP) and GaAs saturable absorber has been realized. The dependences of pulse repetition rate, pulse energy, pulse width and peak power on incident pump power for the generated-green-light pulses are measured. At the maximum incident pump power of 4.1 W, the maximum average output power of 113 mW is obtained, corresponding to an optical conversion efficiency of 2.8%. At the same pump power, stable green laser pulses of duration of 44.6 ns and energy of 0.28 µJ are generated at a repetition rate of 403.4 kHz. The coupling wave rate equations for a passively Q-switched laser are also given and the numerical solutions agree with the experimental results. [ABSTRACT FROM AUTHOR]

A low cost, accurate and relatively simple technique based on the Lau effect coupled with Moiré readout for measuring the focal length of collimating lenses is demonstrated. The method is based on defocusing the collimating lens and measuring the corresponding variation in the inclination angle of the Moiré fringes. Details of theoretical background, experimental arrangement and error analysis are presented. Experimental results of the measurements are in close agreement with the true values. [ABSTRACT FROM AUTHOR]

We present a detailed calculation to analyse the threshold properties of individual localized modes in two-dimensional random media. Some long- and short-life localized modes are selected and indicated from the spectral intensity of a passive system. By pumping the system, the pumping rate dependence of the peak intensity of the indicated modes is obtained. Results identify that these modes have a typical threshold gain behaviour, and the pumping thresholds of long-life modes are lower than those of short-life modes. By calculating the energy decay rate, the lifetime is obtained for each mode, and the results show that there exists a certain correspondence between the mode threshold and lifetime and that, the longer the lifetime, the lower the threshold is. [ABSTRACT FROM AUTHOR]

The frequency stability of the laser transmitter is essential for wind measurement of the direct-detect wind lidar. Given that the external frequency actuator can only achieve green radiation stability and is technically complicated, here, a simple and robust method is presented – locking the laser to iodine absorption lines with an automated PID controller. The frequency stability is better than 200?kHz over 3 hours. Both the fundamental and second-harmonic frequencies are stabilized, essential for seed injection and frequency monitoring. The frequency stability performance of the laser using thermal tuning can be improved to a significant extent by the improved PID control. Two kinds of cw single-frequency lasers with different tuning actuators are applied in the frequency locking system. The root Allan variance is kept below 3.5?×?10 -11 around t?=?0.003?s, and long-term stability of 2?×?10 -10 for integration up to 3000?s was obtained. This locking technique is simpler and requires less laser power than locking to Doppler-free lines. [ABSTRACT FROM AUTHOR]

Beam profiles that consist of a sum of complex-Gaussian functions and a sum of polynomial-Gaussian functions offset by some fixed amount are proposed as two types of models for a hard aperture function. By expanding an aperture function into two types of models, the approximate analytical expression of a flattened Gaussian beam through a paraxial ABCD optical system with an annular aperture is derived. As special cases, the corresponding closed forms for the unaperture or circular aperture or circular black screen cases are also obtained. The results provide a more convenient way of studying propagation and transformation than the usual method using diffraction integral formula directly. Numerical examples are given to illustrate the propagation properties of flattened Gaussian beams. [ABSTRACT FROM AUTHOR]

Theoretical studies of filamentation of ultra-short near-IR laser pulses propagating in a noble gas predict near single-cycle pulses with the intensity being clamped to the field ionization threshold. Experimental results show that this method is carrier envelope offset phase preserving and provides a very simple source for generating few-cycle intense laser pulses. This suggests a very simple design for the generation of ultra-short, sub-femtosecond XUV optical pulses. [ABSTRACT FROM AUTHOR]

We demonstrate that the motion and recollision of an electron after tunnelling in the field of the laser can be fully determined by phase-locked, orthogonal two-colour laser fields. Design rules for the field to arbitrarily define the instants of ionization and return, the angle between ejection and recollision and the return energy are given and applications of this technique to attosecond physics are discussed. [ABSTRACT FROM AUTHOR]

We present a triple-wavelength design for a compact optical pickup head which uses two rhomboid prisms in parallel with three laser diodes. The design can be used for compact disk, digital versatile disk and high-density digital versatile disk devices. The specific prism lens used decreases the geometrical size and reduces the total number of optical components. The trade-off between tolerance and fabrication is also presented. [ABSTRACT FROM AUTHOR]

We describe a prototype instrument using a Peltier cooled quantum cascade laser for precise measurement of stable carbon ( 13 C/ 12 C) isotopologue ratios in atmospheric CO 2 . Using novel optics and signal processing techniques in a compact instrument, we are able to detect the difference between sample and reference with a precision of 0.1‰ (2σ standard error of mean of 11 samples) in 10min of analysis time. The standard deviation of 0.18‰ for individual 30  s measurements shows that this prototype instrument already approaches the best reported literature values using continuous wave lead alloy tunable diode lasers. The application of pulsed near room-temperature quantum cascade lasers to this demanding problem opens the possibility of field worthy rapid response isotopic instrumentation and attests to the maturity of these lasers as spectroscopic sources. [ABSTRACT FROM AUTHOR]

We suggest and fabricate butt-joint diode lasers for efficient non-linear wave mixing in semiconductors. The first experimental demonstration of sum-frequency and second harmonic continuous-wave generation in InGaAs/GaAs/InGaP butt-joint diode lasers in the edge-emitting geometry is reported. [ABSTRACT FROM AUTHOR]

We study experimentally the effect of diffusion of Rb atoms on electromagnetically induced transparency (EIT) in a buffer gas vapour cell. In particular, we find that diffusion of atomic coherence in and out of the laser beam plays a crucial role in determining the EIT resonance lineshape and the stored light lifetime. [ABSTRACT FROM AUTHOR]

A dual hybrid ion–neutral trap has been built to study collisions between a cloud of ultracold atoms and small numbers of co-trapped atomic or molecular ions, in a common volume. Ultracold Na atoms are trapped in a vapour-cell magneto-optical trap (MOT), via a single-mode frequency-stabilized ring-dye laser, with repumping. A linear rf quadrupole Paul ion trap, centred on the MOT, co-traps selected atomic or molecular ions, for example Ca + . Control of the initial ion temperature involves laser cooling Ca + ions via the resonant Fraunhofer K line at 397  nm. We showed the rf ion trap can operate simultaneously with the MOT without destroying the ultracold atom cloud. The goal is to investigate the physics of ion–neutral sympathetic cooling, the cooling by neutrals of translationally cold and vibrorotationally hot molecular ions (e.g. Na 2 + ( v *, J *)), and the observation of other ion–neutral processes near 0  K, of potential interest in astrophysics. [ABSTRACT FROM AUTHOR]

Super-lensing is an electromagnetic phenomenon, based on the amplification of evanescent waves, capable of increasing the resolution of an optical imaging device beyond the diffraction limit. A multi-layer planar super-lens can be constructed from two materials: one with a negative dielectric permittivity ε d = -ε > 0. We numerically modelled and experimentally implemented a super-lens in the mid-infrared spectral range (around 11 μm) by creating a three-layered structure of submicron thickness, SiO 2 /SiC/SiO 2 , in which the polaritonic material SiC has a negative dielectric permittivity in the restrahlen band between the frequencies of the transverse and longitudinal optical phonons. A far-field diagnostic of super-lensing based on measuring transmission and reflection coefficients through the metal-coated super-lens has been implemented using a tunable CO 2 laser. [ABSTRACT FROM AUTHOR]

A novel dual-slab laser with off-axis one-sided hybrid resonator is presented. The mode properties of the hybrid resonator are calculated using a fast Fourier transform method (FFT). The influence of wavefront distoration on the output beam quality is considered. Results indicate that the novel dual-slab laser is better than the normal dual-slab laser with off-axis one-sided hybrid resonator. [ABSTRACT FROM AUTHOR]

All compositions of a mixed-stale density operator are equivalent for the prediction of the probabilities of future outcomes of measurements. For retrodictive, however, this is not the case. The retrodictive formalism of quantum mechanics provides a criterion for deciding that some compositions are fictional. Fictional compositions do not contain preparation device operators, that is operators corresponding to states that could have been prepared. We apply this to Mølmer's controversial conjecture that optical coherences in laser light are a fiction and find agreement with his conjecture. We generalize Mølmer's derivation of the interference between two lasers to avoid the use of any fictional states. We also examine another possible method for discriminating between coherent states and photon number states in laser light and find that it does not work, with the equivalence for prediction saved by entanglement. [ABSTRACT FROM AUTHOR]

A model is presented of pulse evolution in broadband intra-cavity frequency-doubled lasers. The model utilizes normalized coupled rate equations for each mode, including terms that represent the loss due to nonlinear mixing between longitudinal modes. The pulse energy, shape, peak power and duration are calculated by numerical solution of these equations. The model shows that the pulse duration depends not only on the initial population inversion, photon lifetime and the effective nonlinear coupling coefficient, as is the case for narrowband lasers, but also on the fundamental bandwidth. A gain-switched Ti:sapphire laser, pumped by a Q-switched Nd-doped yttrium aluminium garnet laser at 532 nm, was frequency doubled using an intra-cavity β-barium borate crystal. The bandwidth was reduced from about 25 nm to about 1.5 nm in two steps using a series of prisms, and the resulting changes in experimental pulse durations and energies agree well with the model. [ABSTRACT FROM AUTHOR]

Discusses the history of quantum electronics research in the Soviet Union. Outstanding contributions of many scientists to the development of quantum electronics and related fields; Key ideas, formulation of basic principals, and first experiments; Development and applications of microwave EPR masers; Transition from maser to laser; Contribution of some Soviet institutions to laser fields.

We investigate how observation of upper state atomic populations localize atomic position distributions for three-level atoms within a classical standing wave light field. We consider a three-level atom, with the standing wave near-resonantly coupling one transition and a probe laser field near-resonantly coupling the second transition. Two different eases of localization are identified and we explore the dependence of localization on the parameters of the field atom interaction. [ABSTRACT FROM AUTHOR]

The earliest works that demonstrated quantum coherence of masers and lasers are described. Phase coherence of the maser was studied by heterodyning outputs of two independent masers in 1955, and that of lasers in 1963. We also studied coherent superposition of two eigenstates by observing the induced dipole moment of ammonia in the downstream of the maser, oscillating at the frequency of the maser. [ABSTRACT FROM AUTHOR]

In order to achieve a better understanding of the mechanisms of hologram formation and higher diffraction efficiencies in volume gratings stored in acrylamide based photopolymers, a crosslinker (N,N'methylene-bis-acrylamide) has been incorporated in the photopolymer to record holograms by pulsed laser exposure. The presence of this component increases the polymerization rate and refractive index modulation. The recording was performed using a holographic copying process. The original was a grating of 1000?lines/mm processed using silver halide sensitized gelatin. First, the effect of the pulse fluence was investigated. When the pulse fluence was optimized, the results obtained using the new composition of material were compared with those using the composition without a crosslinker. Using a pulsed laser at 532?nm the photopolymer without crosslinker presented diffraction efficiencies slightly less than 60%. On the other hand, when the crosslinker was introduced in the photopolymer composition, the diffraction efficiencies achieved were higher than 85%. The non-linearity of the material's response was also studied comparing the energetic sensitivity, diffraction efficiencies and index modulation of gratings recorded with pulsed and continuous laser exposure. This study was performed fitting the angular scan of each grating using Kogelnik's theory. [ABSTRACT FROM AUTHOR]

We present a formalism describing the dynamics of a semiconductor diode and apply it to the study of the dynamics of external cavity lasers within the strong regime. The formalism is based upon the usual travelling wave phenomenological model for the field and carriers within the semiconductor gain medium. Since the non-radiative recombination time of the carriers is typically much longer than the diode round trip time, we use a multiple scales analysis to obtain a model much simpler in form than the travelling wave model, but as accurate, without assuming that the gain within the diode is uniform. We apply this model to the external cavity laser. Rather than including multiple external cavity reflections explicitly, we include all external cavity reflections through the introduction of a single additional feedback parameter and one extra term in the field equation. In the limit of a single external cavity reflection, our field equation reduces to a form of the well-known Lang-Kobayashi equation that describes very weak external feedback. For strong feedback, we examine both the steady state and dynamical laser properties such as small signal response and large signal current modulation. [ABSTRACT FROM AUTHOR]

This article details a new design for a laser-reflecting mirror utilizing phase-change-cooling technology, which is innovative in using spiral cooling ducts filled with solid-liquid phase-change material to maintain a constant temperature inside the reflecting mirror in a positive-branch telescopic, virtually confocal unstable resonator. The structure no longer needs the 45° scraper plate that is always utilized in a positive-branch telescopic, virtually confocal unstable resonator for coupling the output and provides a high-quality coaxial laser output. The numerical calculation results show, that when phase-change cooling is utilized, the localized maximum temperature dropped from 44 to 33°C. Experiments show that the total surface deformation of a copper mirror dropped from 1.4?µm to 0.27?µm when using phase-change cooling, after continued laser exposure for 10?s and, under the same conditions, that of a silicon mirror dropped from 1.1?µm to 0.4?µm. [ABSTRACT FROM AUTHOR]

Self-mode-locking in single-clad Tm-doped silica fibre lasers operating at 1.92?µm is reported with 100% modulated mode-locked pulses observed for longer fibre lengths up to 6?m. The self-mode-locking was accompanied by self Q-switching. A mode-locked pulse duration of 191?ps has been measured using an autocorrelator based on a two-photon absorption detector for operation at 2?µm assembled for the purpose of this experiment. The experimental pulse train characteristics are found to be consistent with mode-locking theoretical analysis. The origin and properties of self-mode-locking in heavily Tm-doped fibre lasers are discussed. [ABSTRACT FROM AUTHOR]

Observations of self-induced pulsations, Q-switching and mode-locking in Tm–silica fibre lasers are described. Continuous-wave (CW) self-mode-locking in single-clad and double-clad Tm–silica fibre lasers operating at 2?µm is demonstrated when pumped at 1.3?µm and 803?nm, respectively. An ideal CW mode-locked pulse train is obtained for output powers greater than 100?mW while, at lower powers, self-pulsations were dominant in both types of fibre. The experimental mode-locked pulse train periods are found to be consistent with theoretical analysis. Self-induced mode-locking for a single-clad fibre laser with an external cavity has also been observed for short fibre lengths when pumped at 1064?nm and Q-switched using an external cavity or pulse pumped. The mechanisms of self-pulsations and mode-locking in heavily doped Tm fibre lasers are discussed. [ABSTRACT FROM AUTHOR]

We propose a novel mechanism of energy absorption in dielectric materials with ultrashort infrared laser pulses of intensities below the damage threshold. Analytical theory, generalized to hole-assisted processes in arbitrarily polarized laser fields, is validated using one-dimensional numerical simulations of the time-dependent Schrödinger equation. Large enhancements in the multiphoton transition rates are found both numerically and analytically. The one-dimensional calculations are extended to two dimensions via a forest fire percolation model, in which nanoplasma-like structures have been identified. [ABSTRACT FROM AUTHOR]

A new theoretical model based on the standard-model equations but ensuring conservation of energy by accounting for the optical powers stored in the laser cavity is presented. This model succeeds in grouping two sorts of previous models: those based on standard equations and those based on conservation of number of photons. Furthermore, it provides a more complete quantitative description of EDSFLs (erbium-doped silica fibre lasers) and also improves the qualitative description of these devices by including the spontaneous emission terms and by determining the optical powers involved as well as the oscillation wavelength. The possibility of solving the EDSFL system including the power modal distribution within the fibre is also considered. Finally, a detailed comparison between this model and the models proposed by other authors is shown, where it is proved that the new model describes much better the behaviour of EDSFLs. [ABSTRACT FROM AUTHOR]

A number of variations on adiabatic passage for the realization of efficient and selective population transfer in both the gas and liquid phases are presented. The advantageous use of decaying quantum states and/or the influence of continuous measurements during the population transfer are stressed and an intriguing adiabatic passage scheme, which is sensitive to the relative phases of the control laser fields, is introduced. [ABSTRACT FROM AUTHOR]

Diffractive beam-splitting elements with a large fan angle of about 45° were realized as binary phase elements for application in a commercial laser device operating at the wavelength of 635 nm. The fan-out elements designated to split a laser beam into a line of 43 equal power spots were fabricated in silica by means of microstructuring techniques and replicated in acrylate by ultraviolet curing. Two different gratings have been designed using scalar unidirectional iterative methods, based on the iterative discrete on-axis and on the direct binary search algorithms. The optical properties of both gratings obtained by these scalar methods were compared with simulations based on rigorous electromagnetic calculations in order to verify and control the application-relevant specifications. The experimentally measured optical performance of the replicated fan-out elements is in good agreement with the theoretical predictions. The complete procedure for realizing the linear beam splitters, that is the design method, the fabrication of the master, and the replication process, will be presented. The optical properties and characteristic data of the replicas will be compared with scalar simulations as well as rigorous calculations; the results will be discussed. [ABSTRACT FROM AUTHOR]

We report laser-induced spatial self-phase modulation in C 60 -toluene solution using a low-power continuous-wave He-Ne laser. An experiment is performed to measure the thermal diffusivity of a nonlinear medium using thermal self-defocusing phenomenon. We have measured several parameters in this study, for example the local change in refractive index Δ n ( r ), the ratio (∂ n /∂ T )/ k of the temperature coefficient of the refractive index to the thermal conductivity, the time constant τ c and the thermal diffusivity D of the thermal blooming. The self-focusing effect of the liquid medium is also observed. [ABSTRACT FROM AUTHOR]

We present the results of an experiment on superradiant Rayleigh scattering from a moving Bose-Einstein condensate, where a superposition of two atomic wavepackets is created by the interaction of a far-detuned laser beam with the condensate. The system is described by the CARL-BEC model which is a generalization of the Gross-Pitaevskii model to include the self-consistent evolution of the scattered field. The experiment gives evidence of a damping of the matter-wave grating which depends on the initial velocity of the condensate. We describe this damping in terms of a phase-diffusion decoherence process, in good agreement with the experimental results. In a second experiment we add a seeding beam counterpropagating with respect to the pump beam. Varying intensity and frequency of the seed, we investigate the transition from the superradiant regime to the Rabi oscillations regime, evidencing fundamental differences between these two processes. [ABSTRACT FROM AUTHOR]

The interaction between a Bose-Einstein condensate and a single-mode quantized radiation field in the presence of a strong far-off-resonant pump laser generates, in proper regimes, atom-atom and atom-field entanglement. The effects of cavity losses are taken into account and an analytic solution of the corresponding master equation is given in terms of the Wigner function of the system. [ABSTRACT FROM AUTHOR]

In many biomedical applications of laser radiation to estimate optical parameters in tissue, it is desirable, if not crucial, to describe the region being probed. We suggest a parameter for this purpose, based on a lattice random walk on a simple cubic lattice. It is the expected number of distinct sites visited by a random walker. This is relatively easy to compute, although higher moments are not. Detailed computations are given for a continuous-wave measurement on a semi-infinite medium bounded by an absorbing plane and for a slab geometry required to analyse transillumination experiments. [ABSTRACT FROM AUTHOR]

We report the dynamic regimes obtained in a bipolarized neodymium-doped fibre laser self Q switched by a thin slice of a polymer-based saturable absorber. We demonstrate the influence of the total losses and of the anisotropic losses induced by defocusing the saturable absorber and by tilting the cavity mirror, respectively. Starting from a global chaotic behaviour for low-loss configuration, the system evolves toward an n -periodic ( n = 4, 2 and 1) regime for increasing losses. Stabilization of these regimes depends on the anisotropic losses. Conversely, when cavity mirrors are tilted alone, an additional regime such as intermittence is obtained. All these regimes have been identified as due to nonlinear coupling through the saturable absorber between two distinct polarized modes. These modes have been experimentally resolved. [ABSTRACT FROM AUTHOR]

We consider a gaseous atomic Bose-Einstein condensate with dipole-dipole interactions induced by a far off-resonance laser. The long-range dipolar interactions introduce atom-atom correlations on the new scale of the laser wavelength, giving a controllable method of squeezing low energy modes. At high enough laser intensities the correlations lead to a roton minimum in the excitation spectrum. [ABSTRACT FROM AUTHOR]

We show that the gas-phase HXeI molecules can be strongly oriented via a pseudo-first-order Stark effect. This occurs owing to combined electrostatic and non-resonant laser fields acting synergically on the induced and permanent dipole moments of the molecule. The orientation effect aids in identifying the HXeI molecule, by virtue of the pronounced asymmetry of the detected H-atom fragments generated by the photodissociation of oriented HXeI. [ABSTRACT FROM AUTHOR]

Dipicolinic acid (DPA) is an important component of bacterial spores. The Raman spectrum of DPA in the form of compacted powder was measured in reflection at room temperature with excitation by a nanosecond laser at 532 nm. The spectrum presents a set of characteristic frequency bands in the region 700-3090 cm -1 that were identified with characteristic vibrational modes of the DPA molecule. [ABSTRACT FROM AUTHOR]

Practical implementations of quantum cryptography use attenuated laser pulses as the signal source rather than single photons. The channels used to transmit are also lossy. Here we give a simple derivation of two beam-splitting attacks on quantum cryptographic systems using laser pulses, either coherent or mixed states with any mean photon number. We also give a simple derivation of a photon-number splitting attack, the most advanced, both in terms of performance and technology required. We find bounds on the maximum disturbance for a given mean photon number and observed channel transmission efficiency for which a secret key can be distilled. We start by reviewing two incoherent attacks that can be used on single photon quantum cryptographic systems. These results are then adapted to systems that use laser pulses and lossy channels. [ABSTRACT FROM AUTHOR]

We present a first experimental test of the existence of spontaneus parametric up conversion predicted in Marshall and co-workers [2000, J. mod. Optics, 47, 1273]. The measurement has been made using a ccd camera on the emission of a LiIO[SUB3] crystal pumped by a 351 nm and/or a 789 nm laser. We obtain an upper limit of 160 times on the ratio between the intensity of spontaneous parametric up conversion and spontaneous parametric down conversion. [ABSTRACT FROM AUTHOR]

It has been argued that continuous-variable quantum teleportation at optical frequencies has not been achieved because the source used (a laser) was not 'truly coherent'. Here it is shown that 'true coherence' is always illusory, as the concept of absolute time on a scale beyond direct human experience is meaningless. A laser is as good a clock as any other, even in principle, and this objection to teleportation experiments is baseless. [ABSTRACT FROM AUTHOR]

We present a method for the controlled alignment or rotation of birefringent particles trapped in multiple optical trap sites of an interference pattern between two Laguerre-Gaussian laser modes. Controlled spin or alignment of the particles within each individual trap site is achieved independently of the lateral or rotational motion of the interference pattern as a whole. This technique may lead to driving arrays of micro-machines and micro-fluidic studies and can be used in combination with dynamically generated trapping arrays for uniformly distributed stirring throughout microscopic volumes of fluid. [ABSTRACT FROM AUTHOR]

The spinning of asymmetric objects trapped within optical tweezers that have a rotating rectangular aperture inserted into the trapping laser beam is characterized. The measured maximum rotation rates of various asymmetric micron-sized objects are in agreement with a linear dependence on laser power. Maximum rotation rates of up to 0.2 Hz per mW of laser power suggest that rotation rates in the region of 10-20 Hz should be readily achievable in commercially available tweezers that have been modified by the inclusion of a rotating rectangular aperture. In addition, the possibility to alter the orientation of the aperture allows convenient control over the orientation of tweezed objects. [ABSTRACT FROM AUTHOR]

We investigate the space-time dynamics of a homogeneously broadened single-mode laser when local field correction (LFC) is taken into account. We demonstrate that the Maxwell-Bloch equations modified by LFC admit travelling-wave solutions, as when LFC is not taken into account. Their stability is discussed and compared to the case without LFC. [ABSTRACT FROM AUTHOR]

A systematic study of the temporal and spectral properties of high-harmonic generation was explored using a low-binding energy atom (caesium) excited by an intense mid-infrared (3-4 µm) laser pulse. The long-wavelength fundamental field produces odd-order high harmonic radiation, which is experimentally accessible with standard temporal and spectral metrology. We present measurements of the pulse width and coherence times of the 5th through 9th harmonic orders with their corresponding bandwidths. Our study demonstrates that the strategy of using a scaled laser-atom interaction can offer not only a practical solution for direct probing of the properties of high harmonic radiation but also a means for exploring the physics in novel conditions. We present results showing the enhanced harmonic emission from an 'incoherent' target of ground and excited state atoms. [ABSTRACT FROM AUTHOR]

Exact (non-Born-Oppenheimer) numerical solutions of the time-dependent Schrödinger equation for a 1-D model of the one-electron systems $ \rm H^+ _2 $ , HD + and HT + have been obtained in a two-colour laser control scheme, ω + 2 ω, of dissociation and dissociative ionization. Calculations have been performed at wavelengths λCO 2 = 10.3 µm and λ YAG = 1.064 µm. It is found that the phase sensitivity of the asymmetric nuclear dissociation is completely different in the two wavelength regimes. Quasistatic models of the dissociation process are used to interpret the results and the effect of ionization is investigated at high intensities ( I ≥ 10 14 W cm -2 ). [ABSTRACT FROM AUTHOR]