Pulse-periodic Laser Research Articles

Powerful solid-state transversely diode-pumped YAG: Nd lasers with improved radiation quality

YAG: Nd lasers with transverse diode pumping of a cylindrical active (lasing) element are developed and studied. Pumping is carried out with continuous-wave (cw) laser diode array modules. At pump powers of 500, 820, and 1400 W, the output powers of the lasers operating in the multimodal regime are, respectively, 150, 350, and 500 W. The optical efficiency exceeds 30%. In the case of an unstable resonator operating in the negative branch of the stability diagram, the laser power equals 320 W with a beam divergence only twice as large as the diffraction limit. The design of a YAG: Nd laser pumped with pulsed-periodic laser diode array modules is presented. The total pump energy is 5 J, and the width and repetition rate of pulses are, respectively, 250 μs and 100 Hz.

Optical recording system for a flow-through optical method of analyzing bioaerosols

An optical system has been developed for a device for recording biological aerosols, based on a low-power pulsed-periodic UV laser. The possibility of differentiating aerosols of dust, protein, and bacterial spores by means of the given device has been experimentally checked. It has been investigated how the design parameters of the optical system thus developed affect the solution of the problem of classifying aerosols of various substances. Data are presented on the anisotropy of the fluorescence radiation of aerosol particles.

Photon creation in a resonant cavity with a nonstationary plasma mirror and its detection with Rydberg atoms

We investigate the dynamical Casimir effect and its detection with Rydberg atoms. The photons are created in a resonant cavity with a plasma mirror of a semiconductor slab which is irradiated by periodic laser pulses. The canonical Hamiltonian is derived for the creation and annihilation operators, showing the explicit time variation in the couplings, which originates from the external configuration such as a nonstationary plasma mirror. The number of created photons is evaluated as squeezing from the Heisenberg equations with the Hamiltonian. Then the detection of the photons as the atomic excitations is examined through the atom-field interaction. Some consideration is made for a feasible experimental realization with a semiconductor plasma mirror.

空间能量传导通道模型的实验和理论成果

The results of experimental and theoretical studies on creation of a super-long conductive canal technology for energy delivery from the space are presented.A high repetition rate pulse-periodic laser system and the most important components for the project realization are analyzed.The optical system and dust plasma based the conductive canal idea for long range energy delivery is discussed in details,then,some experimental approaches to dust plasma conductivity tests and new data of measurements are investigated.Finally,new applications of Impulsator program suggested are highlighted.

Unified single-photon and single-electron counting statistics: From cavity QED to electron transport

A key ingredient of cavity quantum-electrodynamics (QED) is the coupling between the discrete energy levels of an atom and photons in a single-mode cavity. The addition of periodic ultra-short laser pulses allows one to use such a system as a source of single photons; a vital ingredient in quantum information and optical computing schemes. Here, we analyze and ``time-adjust'' the photon-counting statistics of such a single-photon source, and show that the photon statistics can be described by a simple `transport-like' non-equilibrium model. We then show that there is a one-to-one correspondence of this model to that of non-equilibrium transport of electrons through a double quantum dot nanostructure. Then we prove that the statistics of the tunnelling electrons is equivalent to the statistics of the emitted photons. This represents a unification of the fields of photon counting statistics and electron transport statistics. This correspondence empowers us to adapt several tools previously used for detecting quantum behavior in electron transport systems (e.g., super-Poissonian shot noise, and an extension of the Leggett-Garg inequality) to single-photon-source experiments.

Effect of phase formation in the Mo-Ni system on the rate of change of the thermal conductivity of the interface

The formation and growth of new phases in a film (coating)-substrate system is shown to be diagnosed from a change in the shape of the oscillating component of the temperature field on the sample surface that is induced by the radiation of a periodic pulsed laser. For the Mo(10 μm)-Ni(5 mm) system, a change in the coefficient of correlation of the shape of a pyrometric signal and the relative change in the thermal conductivity of the interface are studied experimentally and theoretically during thermal annealing and 9-MeV electron irradiation.

Spectral characteristics of the thermal properties of multilayer metallic materials

The possibility of using periodic pulsed laser radiation for spectral analysis of the thermal properties of multilayer metallic materials is studied. Pulse and frequency characteristics of samples are found. An expression for the transfer constant of a thermal signal in multilayer materials is obtained. A parametric model is used to determine the thermal conductivity of the interface in a three-layer Mo(1 μm)-W(48 μm)-Mo(1 μm) sample from the amplitude-frequency characteristic measured before and after irradiation by 9-MeV electrons.

Some Features of Pulse-Periodic Energy Supply in Supersonic Flow

In the present work, the results of numerical and experimental investigations of supersonic flows with a localized energy supply are considered. The energy supply region (the heat source) was formed by the plasma created by a focused pulsed-periodic laser emission either by combustion in the separation zone upstream of the blunted body. The main attention is paid to the unsteady effects the role of which is determining at the integral flow structure formation. A physical model of energy source is formulated. The numerical and experimental data on the structure of the flow around the source and the characteristics of a thermal wake arising behind the source are compared. The energy pulses frequency and capacity are shown to determine the wake properties: the formation and development of subsonic regions, vortex structures, and reverse flow regions. It follows from an analysis of the aerodynamic drag variation at a flow with a thermal wake of the energy supply source around blunt bodies that the energy and pulse as well as its duration are the main parameters determining the efficiency of the frequency effect. A high sensitivity of the results to the physical model accepted in numerical investigation is shown. The pressure variation dynamics on a conical surface is presented versus the frequency of pulses. Comparison with experiment has shown a good quantitative agreement.

Resolving range ambiguity in a photon counting depth imager operating at kilometer distances

Time-correlated single-photon counting techniques have recently been used in ranging and depth imaging systems that are based on time-of-flight measurements. These systems transmit low average power pulsed laser signals and measure the scattered return photons. The use of periodic laser pulses means that absolute ranges can only be measured unambiguously at low repetition rates (typically <100 kHz for > 1 km) to ensure that only one pulse is in transit at any instant. We demonstrate the application of a pseudo-random pattern matching technique to a scanning rangefinder system using GHz base clock rates, permitting the acquisition of unambiguous, three-dimensional images at average pulse rates equivalent to >10 MHz. Depth images with centimeter distance uncertainty at ranges between 50 m and 4.4 km are presented.

Effect of pulse-periodic CO2 laser radiation on the laminar flame of a propane-air mixture

To date, an acute ecological problem is toxic gas exhausts into the atmosphere. One approach to solving it is to control the process of combustion by various electromagnetic fields, in particular laser irradiation of the combustion zone. The present work reports the results of an experimental study of the effect of pulse-periodic CO2 laser radiation on the combustion of a propane-air mixture outflowing into the atmosphere.

Electron-beam sustained CO2 laser operating on CO2 : N2 : H2O mix

Users of high power CO2 lasers may be interested in finding a substitute for expensive He which would provide sufficient efficiency and specific power of laser radiation. In the present work, operating modes of the electron-beam sustained discharge CO2 pulse-periodic laser operating on CO2:N2:H2O mixes were investigated. The research has revealed that at equal energies of radiations the efficiency for CO2:N2:H2O mixes are approximately 25% lower than those for CO2:N2:He mixes. The decrease in efficiency is compensated for by an increase in electric strength of the mixes containing H2O, both in pulse and in pulse-periodic modes.

High-power pulse-periodic Nd3+-YAG laser with combined pumping by diode arrays

Output characteristics of the pulse-periodic solid-state laser pumped by diode arrays at a pump pulse repetition rate of 8...512 Hz were studied. Three pump types are used: longitudinal raster-lightguide, transverse, and combined ones. Diode arrays with a pulse power of ∼800 W, emitting area sizes of 5 × 25 mm2, and radiation divergence along two mutually perpendicular axes equal to 4° and 15°, respectively, were used as a pump source. The pump current pulse duration was varied within 100–350 µs. Three operating modes were studied: (i) free generation, (ii) passive Q-switch, and (iii) acousto-optic Q-switch ones. The lasing peak pulse power was (i) ∼2 kW(free generation mode), (ii) ∼1.5 MW (passive Q-switch mode), and (iii) ∼100 kW (acousto-optic Q-switch mode). The highest average lasing power was 150 W at a pump pulse repetition rate of 512 Hz. The highest pulsed lasing energy was 0.65 J.

Coupled electron-nuclear spin dynamics in quantum dots: A graded box model approach

The dynamics of electron and nuclear spin polarization in an ensemble of singly negatively charged quantum dots subject to optical excitation is theoretically studied using a graded box model, in which the electron density is approximated by a sequence of steps. The model is numerically implemented for a limited number of nuclei (up to $N=192$) with spins $I=1/2$ or $I=3/2$. The polarization dynamics is found to depend strongly on the polarized excitation protocol. For excitation by periodic laser pulses, the electron-nuclear spin dynamics evolves coherently and gives rise to a recurrence effect in the electron spin dynamics as well as to a decelerated nuclear polarization. The validity of the model is justified by comparison with experimental data on the electron spin polarization in (In,Ga)As/GaAs quantum dots.

Use of picosecond infrared laser for micromanipulation of early mammalian embryos

A high repetition rate (80 MHz) picosecond pulse (approximately 2 psec) infrared laser was used for the inactivation (functional enucleation) of oocytes and two-cell mouse embryos and also for the fusion of blastomeres of two-cell mouse embryos. The laser inactivation of both blastomeres of two-cell mouse embryos by irradiation of nucleoli completely blocked further development of the embryo. The inactivation of one blastomere, however, did not affect the ability of the second intact blastomere to develop into a blastocyst after treatment. Laser inactivation of oocytes at Metaphase II (MII) stage and parthenogenetically activated pronuclear oocytes also completely blocked their ability for further development. Suitable doses of irradiation in cytoplasm region did not affect the ability of embryos and activated oocytes to development. The efficiency of laser induced fusion for blastomeres of two-cell embryos was 66.7% and all the tetraploid embryos developed successfully into blastocysts in culture. Our results demonstrate unique opportunities of the applications of a suitable infrared periodic pulse laser as a universal microsurgery tool for individual living cells.

Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248 nm KrF eximer laser at room temperature and 10 −3 mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332 cm −1, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp 3-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20 mJ per impulse) is possible.

A way to a single frequency precession of an inhomogeneous ensemble of electron spins in InGaAs quantum dots

AbstractWe show a possible way to the realization of a robust macroscopical quantum bit on the basis of an inhomogeneous ensemble of electron spins. In our case, electrons are confined in a self‐assembled (In,Ga)As/GaAs quantum dots which are excited by a periodical laser pulses. The precession of electron spins in a transversemagnetic field is monitored by the time‐resolved Faraday rotation technique. Due to mode‐locking effect and a focusing of the electron spins precession on a discrete number of modes by the nuclei it should be possible to drive all the electron spins into a single precession mode. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The impact of relaxation on the damping of high-frequency temperature fluctuations arising in tungsten under periodic pulsed laser heating

The possibility is considered of employing periodic pulsed lasers for the investigation of relaxation processes in solids. Results are given of measurements of temperature dependence of the coefficient of damping of high-frequency temperature oscillation in thin tungsten samples.

Source of radiation for diagnostics of the divertor plasma on the ITER facility

An optical scheme of a diode-pumped, two-channel, solid-state laser is considered. The scheme is destined for diagnostics of the physical processes occurring in the divertor area of the tokamak-type fusion facilities by the method of Thomson scattering and has been developed on the basis of modern engineering and technological advancements made in powerful pulse-periodic laser systems. The schemes for the laser diode pumping of the active elements are considered, and the results of thermal and hydraulic calculations of a pumping module are presented. The results of the energy calculation confirm the feasibility of a laser system with technical parameters meeting the requirements of a task assigned.

Formation of surface periodic microstructure at laser irradiation of the multilayer Ni/Cu/Cr system

The effect of periodic pulsed laser irradiation ( λ = 1.06 μm and power density of 0.6–0.8 × 10 4 W/cm 2) on the solid-phase reaction in thin-film Ni/Cu/Cr structure (each layer of 100 nm thick) is studied by means of Auger electron spectroscopy and scanning electron microscopy. Thin-film structure is found to transform under irradiation into eutectic Cr–Ni structure with the particles of the leading Cr(Ni) phase having the radii equal to the total thickness of the film (300 nm). Eutectic colonies of these particles form the surface microstructure which consists of periodic arc-shaped bands with bars between them. The laser-induced diffusion is shown to occur under the sign-variable temperature gradient (∼10 5 K/s), high deformation rate (∼20 s −1), and large dislocation flow ( ρ v ∼ 10 11 c m − 1 s − 1 ) at low deformation degree (∼0.01).

Mechanism of the formation and evolution of periodic surface relief nanostructures under the scanning laser-induced inelastic photodeformation of semiconductors

A defect-deformational (DD) mechanism is proposed for the self-organization of laser-induced point defects (vacancies and interstitials) under low-threshold (far from the melting point) local (10–100 μm) light-induced heating with the scanning periodic pulsed laser irradiation of a semiconductor resulting in an inelastic deformation of micron-sized regions of Ge. A linear theory of DD instability is developed within the model of a biaxially stressed defective film. This model describes the main experimental data on the formation of two-and one-dimensional periodic nanostructures on a semiconductor surface relief.