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This paper proposes an optical amplification method of measuring the minute displacement of a laser beam. The relationship between the displacement of the incident laser beam and the reflective beam is calculated by geometric optical analysis. The equation of displacement is derived to calculate its magnification. We demonstrate that by employing the reflection characteristics of a cylindrical mirror, the minute-displacement of a laser beam can be enlarged to the millimetre level. Experimental results confirm that the magnification can be hundreds of times. Such an enlarged displacement measuring system of laser beam could be suitable for the study of Goos–Hänchen shift. [ABSTRACT FROM AUTHOR]

In free space optical (FSO) communication links, atmospheric effects including absorption, scattering and turbulence have significant impacts on the quality of the laser beam propagating through the free space channel. Absorption and/or scattering due to the atmospheric particles result in optical losses, whereas turbulence contributes to the intensity scintillation which can severely impair the operation of FSO links. In this paper, using a modified model we analyze the atmospheric effects on the signal-to-noise ratio (SNR) and the bit error rate (BER) performance of an FSO system. We show that for multiple detectors with the same surface area as a single detector there is a critical link range less than which the SNR decreases for larger values of M. [ABSTRACT FROM AUTHOR]

This paper reports nonlinear optical response studies of thin layers using graphene oxide (GO) and their performance for detecting water content in transformer oil using three sets of approaches. The sensor performance is evaluated based on bare optical fibre, D-shape optical fibre integrated with GO and the effects of the covering device with polydimethylsiloxane (PDMS). The improvement of this study is to ensure the stability of the recorded signal. The nonlinear optical response of the prepared dispersion was explored using the Z-scan technique with an 800 nm continuous wave laser beam. Taking advantage of the graphene-induced evanescent field using D-shape optical fibre with PDMS covers on the device can give high sensitivity and good stability for water dissolved in the oil at 1550 nm. We measured fluctuations in transmitted light associated with varying water contents ranging from 16 to 38 ppm. [ABSTRACT FROM AUTHOR]

In this paper, coherent Rydberg excitation of a single four-level atom in tightly confining trap so-called 'far-off-resonance optical dipole-quadrupole trap' (FORDQT) by considering Laguerre Gaussian (LG) beams spatial features is demonstrated. The self-trapping potential results from the position dependent differential AC Stark shift of the ground state and Rydberg state in the effective quadrupole Rydberg excitation. By introducing the effective stiffness of the FORDQT potential in terms of the key parameters of the first and Rydberg excitation laser beams, a technique to obtain sub-micron localization of Rydberg excitation is explored. The complete matched trapping potential of the ground state and Rydberg state near the center of the trap maintains the coherence of the Rydberg excitation. Transfer of optical orbital angular momentum from the LG-beam to the Rydberg-state via localized effective quadrupole excitation process paves the way for implementation of high fidelity qudit gates in high dimensional quantum information process. [ABSTRACT FROM AUTHOR]

Thermal effects are a result of the temperature field and temperature fluctuation. They are an important factor in the design and operation of end-pumped lasers. In this paper, we investigate both the thermal effect and thermally induced diffraction losses. A thermal model is established that can explain the thermal effect in an anisotropic cubic laser crystal that is end-pumped by a laser diode during repeated pulsed operation. By solving the thermal flow equation numerically, the dynamics of the thermal build-up as well as the temperature distribution in the laser crystal were obtained. When the laser crystal reached a quasi-steady state, the thermally induced diffraction losses show oscillatory behaviour, which is inversely proportional to the frequency of the pump pulses and pump power. [ABSTRACT FROM AUTHOR]

The concept of a partially coherent anomalous hollow vortex beam generated by a Schell-model source was introduced in this paper. Next, the analytical expressions of a partially coherent anomalous hollow vortex beam propagating in a uniaxial crystal orthogonal to the optical axis were derived, and the evolution properties of a partially coherent anomalous hollow vortex beam propagating in a uniaxial crystal were illustrated using numerical examples. Finally, the influences of the uniaxial crystal and the beam parameters on the spreading properties of partially coherent anomalous hollow vortex beam were analysed in detail. [ABSTRACT FROM AUTHOR]

The Winter Colloquium on the Physics of Quantum Electronics (PQE) has been a seminal force in quantum optics and related areas since 1971. It is rather mind-boggling to recognize how the concepts presented at these conferences have transformed scientific understanding and human society. In January 2017, the participants of PQE were asked to consider the equally important prospects for the future, and to formulate a set of questions representing some of the greatest aspirations in this broad field. The result is this multi-authored paper, in which many of the world’s leading experts address the following fundamental questions: (1) What is the future of gravitational wave astronomy? (2) Are there new quantum phases of matter away from equilibrium that can be found and exploited - such as the time crystal? (3) Quantum theory in uncharted territory: What can we learn? (4) What are the ultimate limits for laser photon energies? (5) What are the ultimate limits to temporal, spatial and optical resolution? (6) What novel roles will atoms play in technology? (7) What applications lie ahead for nitrogen-vacancy centres in diamond? (8) What is the future of quantum coherence, squeezing and entanglement for enhanced super-resolution and sensing? (9) How can we solve (some of) humanity’s biggest problems through new quantum technologies? (10) What new understanding of materials and biological molecules will result from their dynamical characterization with free-electron lasers? (11) What new technologies and fundamental discoveries might quantum optics achieve by the end of this century? (12) What novel topological structures can be created and employed in quantum optics? [ABSTRACT FROM AUTHOR]

Cooperative scattering in cold atoms has gained renewed interest, in particular in the context of single-photon superradiance, with the recent experimental observation of super- and subradiance in dilute atomic clouds. Numerical simulations to support experimental signatures of cooperative scattering are often limited by the number of dipoles which can be treated, well below the number of atoms in the experiments. In this paper, we provide systematic numerical studies aimed at matching the regime of dilute atomic clouds. We use a scalar coupled-dipole model in the low excitation limit and an exclusion volume to avoid density-related effects. Scaling laws for super- and subradiance are obtained and the limits of numerical studies are pointed out. We also illustrate the cooperative nature of light scattering by considering an incident laser field, where half of the beam has a phase shift. The enhanced subradiance obtained under such condition provides an additional signature of the role of coherence in the detected signal. [ABSTRACT FROM AUTHOR]

The recent development of ultra-high intensity laser facilities is finally opening up the possibility of studying high-field quantum electrodynamics in the laboratory. Arguably, one of the central phenomena in this area is that of quantum radiation reaction experienced by an ultra-relativistic electron beam as it propagates through the tight focus of a laser beam. In this paper, we discuss the major experimental challenges that are to be faced in order to extract meaningful and quantitative information from this class of experiments using existing and near-term laser facilities. [ABSTRACT FROM AUTHOR]

A single mode laser based on novel deep etched V-notch reflectors is presented in this paper. The reported device has a stable single mode operation and a side mode suppression ratio of 37 dB. The laser is widely tunable and it can be fine-tuned. Moreover, the laser cavity is monolithically integrated with an active multimode interference reflector, and has a total length of. [ABSTRACT FROM AUTHOR]

Reshaping of a Gaussian laser beam into a uniform or other intensity distribution is required for various applications. The laser beam shaping system with a radial birefringent filter is presented in this paper. With such a system the Gaussian beams can be transformed into uniform or annular beams. The theory and simulation of the proposed systems are described in detail. The primary advantage of such a system is that the out beam profile can be tunable with the rotation of the radial birefringent element. [ABSTRACT FROM AUTHOR]

In the paper, the modulation instability (MI) of the pulses with different powers is studied based on the modified coupled nonlinear Schrödinger equations in nonlinear fiber. By analyzing MI gain spectrum with different power ratios, it shows that the increase of power ratio leads to the diminution in the range of strongly unstable frequency and the decrease in the gain of MI spectra. With a fixed power ratio, the increased relaxation time is equally suppressing overall MI. [ABSTRACT FROM AUTHOR]

Lasing eigenvalue problems (LEPs) are non-conventional eigenvalue problems involving the frequency and gain threshold at the onset of lasing directly. Efficient numerical methods are needed to solve LEPs for the analysis, design and optimization of microcavity lasers. Existing computational methods for two-dimensional LEPs include the multipole method and the boundary integral equation method. In particular, the multipole method has been applied to LEPs of periodic structures, but it requires sophisticated mathematical techniques for evaluating slowly converging infinite sums that appear due to the periodicity. In this paper, a new method is developed for periodic LEPs based on the so-called Dirichlet-to-Neumann maps. The method is efficient since it avoids the slowly converging sums and can easily handle periodic structures with many arrays. [ABSTRACT FROM PUBLISHER]

In this paper the authors present the idea for reconstructing one-photon states. Reconstructing a quantum state means measuring the probability distribution P that allows one to write the density operator for the analysed state. The most commonly known approach for the quantum reconstruction is the quantum tomography. Our alternative method assumes that the analysed field is coupled with the reference field which is described by the parameters settled during a measurement. In the proposed gedankenexperiment the degree of linear polarisation (DOLP) of this combined beam is measured using a rotating linear polariser. We state that it is possible to obtain the P-function by changing the parameters of reference beams and by preparing the series of DOLP measurements. This series of data leads to the system of equations. The values of the P-function at chosen points are the unknowns of this system. This article focuses on the numerical algorithm for solving these equations. [ABSTRACT FROM AUTHOR]

A type of mode-locked fiber laser, which can generate the bound solitons in the anomalous group-velocity dispersion regime, is suggested in this paper via symbolic computation. A transformation is given to convert the coupled nonlinear Schrödinger equations to a simpler form. Analytic two-, three- and N-soliton solutions for the coupled nonlinear Schrödinger equations are obtained. Based on those solutions, formation of the bound solitons is analyzed, and methods for the soliton control are presented. The soliton intensity and collision period can be controlled with the changes in the nonlinearity and group-velocity dispersion of optical fibers. The slight phase shift has a great influence on the bound states of solitons after the soliton collision. To support the results, numerical simulations of three-soliton propagation are performed. Finally, the modulational instability of bound solitons is analyzed. [ABSTRACT FROM AUTHOR]

This paper presents an analytical and numerical investigation of a circularly polarized beam propagating along the static magnetic field parallel to oscillating magnetic field in plasma at relativistic intensities. In the high intensity regime, such a magnetic field is created by the pulse itself. The authors have identified three regimes of propagation taking into account the relativistic mass correction. Based on WKB and paraxial ray theory, an appropriate expression for a dielectric tensor has been evaluated in the presence of an externally applied magnetic field. The natural electromagnetic modes are circularly polarized. Consequently, extraordinary and ordinary modes propagate, which are significantly affected due to the relativistic mechanism. The regimes are characterized by dimensionless power and beamwidth, characterizing the nature of propagation as steady divergence, oscillatory divergence and self-focusing. Numerical computations are presented and discussed for typical parameters of laser plasma interaction; defined through critical parameters, namely cyclotron-to-beam frequency (Ωc), plasma-to-beam frequency (Ωp) and beam power for arbitrary large intensities. [ABSTRACT FROM AUTHOR]

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>1018 W cm-2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes. [ABSTRACT FROM AUTHOR]

A subwavelength aperture surrounded by periodic grooves can give rise to enhanced transmission and directional beaming and the groove depths can be tuned to control the focusing length, but the one-dimensional structure is still restricted to certain applications where a symmetric focus spot is needed. In this paper, we study the nano-beaming effect using a central circular hole surrounded by annular grooves with different depth tuning or depth. We found two plasmonic modes at wavelengths 440 and 560 nm and there is no mode shift due to a different amount of depth tuning. Of the modes, the former is suitable for collimation and the other for focusing. Particularly good subwavelength collimation is obtained, e.g. FWHM = 0.85λ along the lateral direction and FWHM = 1.1λ along the transverse direction at λ = 440 nm, over the propagation distance z = 1.75 μm (= 4λ). Hence, we propose a new plasmonic lens using depth-tuned annular structures. [ABSTRACT FROM AUTHOR]

In this paper, we analytically investigate Hermite-cosh-Gaussian (HChG) laser beam propagation in non-degenerate germanium having space charge neutrality for the first three mode indices. The field distribution in the medium is expressed in terms of beam-width parameter f and decentred parameter b. The differential equations for the f parameter are established by a parabolic wave equation approach under paraxial approximation. Analytical solutions are obtained under the condition Rn < Rd, where Rn is the self-focusing length and Rd is the diffraction length. The behaviour of the f parameter with the dimensionless distance of propagation η for various b values is examined by numerical estimates. The results are presented graphically. [ABSTRACT FROM AUTHOR]

Recent developments in laser physics have called renewed attention to Laguerre-Gaussian (LG) beams of paraxial light. In this paper we consider the corresponding LG modes for the two-dimensional harmonic oscillator, which appear in the transversal plane at the laser beam's waist. We see how they arise as Wigner transforms of Hermite-Gaussian modes, and we proceed to find a closed form for their own Wigner transforms, providing an alternative to the methods of Simon and Agarwal. Our main observation is that the Wigner transform intertwines the creation and annihilation operators for the two classes of modes. [ABSTRACT FROM AUTHOR]

The large third-order nonlinearities of metal nanocluster doped oxide matrix composite films have been investigated widely, but there is very little literature reporting third-order nonlinearity of metal nanoparticle doped azobenzene molecule thin films induced by picosecond laser pulses. This paper has investigated the third-order nonlinearity of colloidal Ag and methyl orange composite films using the Z-scan technique with 38 ps pulses at 532 nm apart from the surface plasma resonance frequency of composite film. Large and negative third-order nonlinearity was observed. The mechanism responsible for the process of nonlinear refraction was discussed in terms of the enhancement of the local field effect, which was confirmed by using the SERS technique. At the end, the figures of merit were evaluated and the results showed that this material would be valuable in the application of all-optical devices. [ABSTRACT FROM AUTHOR]

Following excitation by a strong ultra-short laser pulse, molecules develop coordinated rotational motion, exhibiting transient alignment along the direction of the laser electric field, followed by periodic full and fractional revivals that depend on the molecular rotational constants. In mixtures, the different species undergo similar rotational dynamics, all starting together but evolving differently with each demonstrating its own periodic revival cycles. For a bimolecular mixture of linear molecules, at predetermined times, one species may attain a maximally aligned state while the other is anti-aligned (i.e. molecular axes are confined in a plane perpendicular to the laser electric field direction). By a properly timed second laser pulse, the rotational excitation of the undesired species may be almost completely removed leaving only the desired species to rotate and periodically realign, thus facilitating further selective manipulations by polarized light. In this paper, such double excitation schemes are demonstrated for mixtures of molecular isotopes (isotopologues) and for nuclear spin isomers. [ABSTRACT FROM AUTHOR]

A new kind of laser beam called the decentred elliptical flat-topped light beam (DEFTB) is introduced in this paper by using a tensor method. Based on the generalized Collins integral, the propagation formula for a DEFTB passing through an axially nonsymmetrical paraxial optical system is derived through vector integration. The derived formula can be reduced to the formulae for the generalized decentred elliptical Gaussian beam and elliptical flat-topped light beam under certain conditions. As a typical application example of the derived formula, the propagation characteristics of a DEFTB in a thin lens system are calculated and discussed. Furthermore, the generalized laser beam arrays with rectangular symmetry and radial symmetry by using DEFTBs as fundamental modes are constructed and the propagation properties of both a coherent and an incoherent combination of DEFTBs in the thin lens system with numerical examples are investigated. [ABSTRACT FROM AUTHOR]

We demonstrate a long-term continuous readout of a two-dimensional image in a photorefractive holographic memory with a BaTiO3 crystal. A considerable extension of reading time is achieved by use of a hologram sustainment technique with an optical feedback circuit. Hologram rewritings by the simultaneous illumination of the reading beam and the feedback beam, which is incident on a crystal from the opposite direction to the reading beam, contribute to all-optical hologram sustainment without any fixing technique. In this paper, the effectiveness of the hologram sustainment technique is explained by the analysis of the temporal property of the amplitude of the index grating in a crystal. By calculating the temporal properties of the reconstructed beam intensity, we reveal the feedback rate and the coupling strength for high output efficiency. We perform an experiment on two-dimensional image reading and writing with a 45° cut BaTiO3 crystal and show that a recorded image can be reconstructed over 20?min without critical image degradation whereas a reconstructed image fades away within 20?s in the conventional readout technique. [ABSTRACT FROM AUTHOR]

The paper describes the design, performance and illustrative spectroscopic applications of a high power, pulsed, injection seeded, narrow bandwidth and continuously tuneable optical parametric oscillator (OPO) based on two β-barium borate (BBO) nonlinear crystals. A ring cavity OPO was injection seeded with an external cavity diode laser in the spectral range 755- 855nm. The OPO generated high power transform limited nanosecond light pulses in this range and, simultaneously, at 606-667nm. Spectral parameters of the OPO were investigated as a function of pump power for two different cavity lengths. A bandwidth of ~120MHz (0.004cm[sup -1]) in the visible has been achieved with a 40-cm-long cavity. The potential of the OPO system is demonstrated by recording high resolution sub-Doppler spectra in the UV of PF and C[sub 3] radicals in a pulsed supersonic jet expansion. [ABSTRACT FROM AUTHOR]

It has been widely accepted that spatial beam smoothing is essential in coupling laser energy to inertial confinement fusion targets. In this paper, kinoform phase plate arrays have been proposed to produce spatially homogenized far fields for a broad range of phase and irradiance non-uniformities in the incident beam. A global-local united search algorithm has been presented to design a phase plate element to concentrate more than 95% energy of laser beams on a flat-top super-Gaussian (SG) envelope. A spatial-fining technique has been proposed to control the intermediate-spatial-frequency overlapping intensity modulation generated by various phase plate elements. For a flat incident aperture size of 40 cm, a laser wavelength of 351 nm, and a lens focal length of 1000 mm, 10 × 10 phase plate arrays have been designed to produce sixteenth-order SG profiles with the intensity modulation interval less than 5 μ. More than 96% of the incident energy is homogeneously constrained in the desired region. [ABSTRACT FROM AUTHOR]

In underwater turbulent medium, field correlations are found when the incidence is a laser beam array. Variations of the field correlations against the variations in the ring radius of laser array beam, number of beamlets composing the laser array, source size, underwater turbulence parameters, i.e. the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature and rate of dissipation of kinetic energy per unit mass of fluid, are investigated. Field correlations of laser arrays are found to be larger than the field correlations of the single beams. The effect of underwater turbulence is to reduce the field correlation of laser arrays. [ABSTRACT FROM AUTHOR]

The propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically. The analytical expressions for a CiChGB propagating through apertured and unapertured FRFT systems are derived based on the Collins formula and the expansion of the hard-aperture function into a finite sum of Gaussian functions. From the obtained expressions, the evolution of the intensity distribution at the output plane is analysed with illustrative numerical examples. It is shown that the intensity distribution of the CiChGB propagating in FRFT is closely dependent on the decentred beam parameter and the aperture size besides the fractional order of the FRFT system. The results obtained may be beneficial to applications in laser beam shaping, optical trapping, and micro-particle manipulation. [ABSTRACT FROM AUTHOR]

A method that combines Lucy-Richardson deconvolution algorithm (LRA) with a multiview projection setup to improve imaging reconstruction of objects embedded in scattering media is presented. In the first step, the medium was illuminated with a laser beam and single-shot multiple images of the object were obtained from different viewpoints. Next, the above procedure was performed under the same conditions but only the medium, without the object, was illuminated by a light point source to obtain the system PSF. Third, each sub-image of the object was digitally cropped, extracted from the array, and deconvolved with the average PSF image following the LRA. Finally, all the sub-deconvolved images were shifted to a common point and superimposed to reveal the shape of the hidden object. Various setup conditions including medium turbidity, thickness, target shape, and illumination state were tested and compared. Results indicate an effective performance of the proposed method. [ABSTRACT FROM AUTHOR]

For total reflection, the Goos–Hänchen (GH) shift is proportional to the wavelength of the laser beam. At critical angles, such a shift is instead proportional to the square root of the product of the beam waist and wavelength. By using the stationary phase method (SPM) and, when necessary, numerical calculations, we present a detailed analysis of the frequency crossover for the GH shift. The study, done in different incidence regions, sheds new light on the validity of the analytic formulas found in literature. [ABSTRACT FROM PUBLISHER]

TheM2factor matrix of a paraxial Laguerre–Gaussian beam has been derived based on the combination of theM2factor definition and introduced quantities such as the coupled beam’s half width square, the coupledM2factor and 2×2 rotational matrix, when the beam is rotated around the propagationz-axis by an arbitrary azimuth angleα. The beam’s half widths at different distances from the beam waist along thez-axis, theM2factors of the beam with different orders, and the track ofM2factor matrix elements versusαhave been obtained by numerical simulation and analytical derivation. Results illustrate that by using the invariability of theM2factor matrix, the beam quality of the mode with an arbitrary rotational angle can be easily evaluated. Like theM2factor matrix of the Hermite–Gaussian mode, thisM2factor matrix is meaningful in the evaluation of the beam quality of a two-dimensional astigmatic or asymmetric laser beam. [ABSTRACT FROM PUBLISHER]

A numerical study is reported of the transparent propagation of few-cycle laser pulses with arbitrary intensity. The phenomenon is based on the preparation of steady maximum coherent superposition state of the lower two levels in double-lambda atomic systems. The transparency of the few-cycle pulse is sensitive to its parameters such as the arriving time and relative phase. The advantages of the method are discussed. [ABSTRACT FROM AUTHOR]

We investigate the possibility of cooling an atomic gas enclosed in an optical cavity using blue-detuned laser light of sufficient intensity that excitation of the atoms cannot be neglected. We consider an ensemble of two-level atoms confined inside a simple Fabry–Perot cavity in two different geometric configurations: in one (‘cavity-pump’ configuration) the pump field is directed along the cavity axis and in the other (‘atom-pump’ configuration) the pump field is directed perpendicular to the cavity axis. Numerical simulations of the semi-classical models for each configuration are compared. Both configurations demonstrate cooling using a blue-detuned pump field. It is shown that in the cavity-pump configuration there is no collective enhancement of the cooling rate over that of free space blue-cooling. In contrast, the atom-pump configuration demonstrates collective enhancement of the cooling rate and intracavity field intensity. [ABSTRACT FROM PUBLISHER]

The dynamics of a one-dimensional atom driven by three-laser fields is investigated. The total electric field is made up of a fundamental laser field of intensity [image omitted] W cm-2 and wavelength λ = 820 nm and two weak lasers with larger wavelengths. The intensity of the two weak fields is [image omitted] with k = 0.25. The frequencies of the weak fields are [image omitted] and [image omitted], with [image omitted] and [image omitted]. The three lasers have a Gaussian envelope of 72 fs FWHM. It is shown, by numerical computation and using the semiclassical theory of high-harmonic generation, that the atom interacting with this combined field is able to emit an isolated attosecond burst of radiation. [ABSTRACT FROM AUTHOR]

The propagation factors of phased locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens-Fresnel integral and the Wigner distribution function. Analytical propagation formulae for the propagation factors are derived and numerical examples are illustrated. We find that unlike their propagation invariant properties in free space, the propagation factors of laser array beams increase when propagating in turbulent atmosphere, and are closely related to the parameters of initial beams and the atmosphere. [ABSTRACT FROM AUTHOR]

We propose a new scheme for the generation of single zeptosecond pulses by using a one-dimensional muonic hydrogen atom model. Owing to the large mass of the muon, the muonic atoms can survive much stronger fields, which causes a very broad plateau in the high-order harmonic spectrum. By solving a one-dimensional time-dependent Schrodinger equation, the high-order harmonic spectrum of the muonic atom in super-intense nonlinear chirped laser pulses is obtained. It is found that the harmonic spectrum is greatly affected by the chirp rate parameters of the laser field. By adjusting the chirp rate parameters, an ultra-broad super-continuum spectrum could be obtained, from which a single zeptosecond pulse could be generated without phase compensation. [ABSTRACT FROM AUTHOR]

In this article we present a theoretical model for the light-matter interaction of a two-level atom and a femtosecond laser pulse, spectrally cut in the vicinity of the atomic resonance. The model utilizes a transformation into an interaction picture from a bare atomic state basis and is applicable to two-level systems. This transformation simplifies some of the dynamics of the interaction. A complementary intuitive picture is also presented and describes the interaction of the induced dipole with the pulse's transients. The calculations are in excellent agreement with experimental measurements performed on an ultracold rubidium gas. [ABSTRACT FROM AUTHOR]

The dynamics of a homonuclear diatomic molecule driven by a laser pulse is obtained beyond the fixed nuclei approximation. Laser parameters can be adjusted to confine the electron over one of the two nuclei for a relatively long time or not. A time-resolved analysis of the electromagnetic spectrum emitted by the molecule presents the usual odd harmonics far from confinement and even harmonics during the confinement periods. A physical interpretation of the results is given. [ABSTRACT FROM AUTHOR]

The effects of the relative phase between two laser beams on the propagation of a weak electromagnetic pulse are investigated in a V-type system with spontaneously generated coherence (SGC). Due to the relative phase, the subluminal and superluminal group velocity can be unified. Meanwhile, SGC can be regarded as a knob to manipulate light propagation between subluminal and superluminal. [ABSTRACT FROM AUTHOR]

We study nuclear elastic forward scattering of synchrotron radiation. In a simple model, we show that suppression of nuclear excitation by synchrotron radiation as well as nuclear elastic forward scattering are possible due to the formation of nuclear coherent population trapping. We consider a nucleus with ground- and excited-state nuclear momenta , , respectively. We demonstrate that nuclear coherent population trapping can be achieved for random phases of pulses in synchrotron radiation. [ABSTRACT FROM AUTHOR]

A symmetrical iterative Fourier-transform algorithm (IFTA) using a combination of phase and amplitude freedom for the design of diffractive optical elements for highly precise laser beam shaping is presented. We compare this method with the basic IFTA and the symmetrical IFTA exclusively using phase freedom, and the basic IFTA using both phase and amplitude freedom, by employing these methods for super-Gaussian beam shaping. While the latter three methods fail to produce satisfactory solutions, the first method results in a beam non-uniformity error of 0.44% and a theoretical efficiency of 97.2%. Moreover, the new approach avoids the use of the trial-and-error method for finding the appropriate modified Fourier-domain constraints during the iteration, which can be difficult for some beam-shaping problems. [ABSTRACT FROM AUTHOR]

The propagation characteristics of the kurtosis parameters of a standard Hermite—Gaussian (SHG) beam and of an elegant Hermite—Gaussian (EHG) beam, each passing through a fractional Fourier transformation (FRFT) system with a spherically aberrated lens, are studied in detail. Some numerical calculations are made by introducing an efficient algorithm, based on the Collins diffraction integral formula. The resulting graphs illustrate the striking difference between ideal FRFT systems and those with a spherically aberrated lens. The kurtosis parameters of both SHG and EHG beams passing through a type I Lohmann system with a spherically aberrated lens are seen to change with the fractional order periodically and the fundamental period is 4, but for type II the fundamental period is 2. Different values of spherical aberration coefficients affect the kurtosis parameters in greatly different ways. The values of the kurtosis parameters of a SHG beam passing through either type of Lohmann system with a spherically aberrated lens are no longer equal to those of an EHG beam, even when they have the same fractional orders and the same spherical aberration coefficients. [ABSTRACT FROM AUTHOR]

The oblique incidence of a He-Ne laser beam onto a phase-only diffractive optical element (DOE) that simultaneously produces several unimode different-order Bessel beams propagating at various angles with respect to the optical axis is studied theoretically and experimentally. It is shown that, under obliquely incident illumination of a DOE that forms Bessel beams, the resulting astigmatic diffraction pattern can be used to unambiguously identify the direction of the Bessel beam's phase rotation and the order of the Bessel mode. [ABSTRACT FROM AUTHOR]

Based on the treatment that the rectangular function can be expanded into an approximate sum of complex Gaussian functions with finite numbers, the analytical expressions for the propagation of partially nonuniform laser beams through apertured ABCD optical systems were derived. The typical numerical examples were given and were compared with those obtained from numerically integral calculations. It can be shown from the results of our study that our method can significantly improve the numerical calculation efficiency. [ABSTRACT FROM AUTHOR]

With the Hermite-Gaussian mode used to describe radial laser arrays and the M²-factor and power in the bucket (PIB) chosen as criteria for characterizing beam quality, a detailed study of beam quality of coherent and incoherent radial laser arrays is made. The closed-form expression for the M²- factor of incoherent radial arrays, which depends upon the Hermite-Gaussian order m , inverse radial fill factor r' and aspect ratio w[sub 0x]/w[sub 0y], is derived. Numerical examples are given to illustrate and compare beam quality of coherent and incoherent radial arrays. [ABSTRACT FROM AUTHOR]

Intensity correlations in turbulent biological tissues are evaluated when collimated Gaussian laser beam is used. Variations of the intensity correlations in biological tissues are investigated versus the diagonal distance from the origin of the observation plane for various tissue distances, biological tissue types, strength coefficients of the refractive-index fluctuations, starting points at the observation plane. Also, intensity correlations in biological tissues for various biological tissue types versus the strength coefficient of the refractive-index fluctuations, small length-scale factor, fractal dimension. It is found that intensity correlations become smaller at larger diagonal distance, tissue distance, strength coefficients of the refractive-index fluctuations, and at smaller source size, small length-scale factor and fractal dimensions. Behaviour of the intensity correlations is found to depend on the type of the biological tissue. Our results can be used in tissue identification and to find the disorders in biological tissues. [ABSTRACT FROM AUTHOR]

The power-in-the bucket and the intensity distribution generated by the coherent combination of a definite number of similar laser beams with Gaussian profiles are numerically studied at different observation planes in the far-field. A precise method is introduced for optimal engineering of the array aperture size and the observation plane location in the far-field. A relation between the array aperture size and the observation plane distance is proposed using the Fresnel zone concept for coherent beam combining to achieve the maximum power-in-the bucket (PIB). The results reveal that the maximum PIB in a small bucket radius of 5 or 10 cm in the observation plane (radii in directed-energy applications) can be obtained either when the observation plane is located at the primary region of the far-field for a specified array aperture size or when the array aperture size is equal to or less than the size of the first Fresnel zone (0.4 ≤ N F ≤ 1). Also, the proposed approach is independent of array geometry so that it will be practical for different array geometries, namely square, circular, and hexagonal. Furthermore, it is also independent of other parameters such as numbers and divergence of beams. The maximum amount of PIB in a specified observation plane location can be obtained for array aperture sizes lower than the first Fresnel zone, regardless of the number of beams or their waist radius. [ABSTRACT FROM AUTHOR]

The transformation of (l,n)th mode Laguerre-Gaussian (LG) laser beam, in the process of its diffraction by a curved fork-shaped grating with topological charge p, is theoretically studied. The analytical solutions for the diffracted wave field amplitudes are derived in the Fresnel regime and in the back focal plane of a convergent lens. The zeroth-diffraction order is found as (l,n)th mode LG beam. The higher, (± m) th diffraction-order beam is described in the radial direction through a product of the Gauss-doughnut function by the double sum of hypergeometric Kummer functions. Its topological charge can be increased or reduced compared to that of the incident beam, or it can be equal to zero. The radial intensity distributions are plotted and compared to the corresponding ones valid when a fork-shaped grating is used. The results are specialized for the cases of incident LG beams of modes (l, n = 0), (l = 0,n) and (l = 0,n = 0) i.e. Gaussian mode. [ABSTRACT FROM AUTHOR]

Based on computer simulation, we demonstrate the nonlinear localization of a femtosecond laser pulse energy in 1D- and 2D photonic structures at the inclined incidence of a beam (or several beams) on a face of the photonic structure consisting of layers or rectangular elements. We show that, in 1D photonic crystal (PC), the energy localization is due to the formation of the moving soliton with the aberrated wave front – the aberrated soliton, which moves inside the photonic structure, being reflected many times from the PC faces, and its appearance depends on the photonic structure elements, ambient medium and the incident laser pulse shape. The dependence of the light energy localization on the sizes of the rectangular elements is investigated. We demonstrate controlling the light energy localization due to the incidence of several beams on the photonic structure and discuss the possibility of observing the described phenomena in a physical experiment. [ABSTRACT FROM AUTHOR]

The free-space evolution of a conically refracted Gaussian beam after being imaged by a lens is studied both theoretically and experimentally. It is shown that, in contrast to the longitudinal symmetry of a regular conically refracted beam with respect to its focal plane, the imaged beam acquires a strong longitudinal asymmetry, similarly to other known coherent beams with complex internal structure evolving upon propagation. Paraxial amplitude expressions for the two conical refraction components of the imaged beam are derived as functions of the imaging lens focal length and of the magnification value. A very good agreement between theoretical and experimental results is demonstrated. [ABSTRACT FROM AUTHOR]