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Specific manifestations of the effect of self-saturation in unidirectional-wave spectroscopy compared with spectroscopy of counterpropagating waves have been identified. The possibility of direct measurement of the rates of the stimulated transfer caused by its own spontaneous emission is shown for spectroscopy of unidirectional waves. [ABSTRACT FROM AUTHOR]

Nonlinear laser spectroscopy is considered in the scheme of two collinear waves with arbitrary elliptical polarizations. Emphasis is placed on investigating the nonlinear corrections in the absorption spectrum of one of the waves. The spontaneous transfer of low-frequency Zeeman coherence is shown to affect the sign of the subnatural-width resonance. For a closed transition, the direction of the resonance profile has been found to depend only on the angular momenta F and F. On this basis, a classification has been developed for various transitions by the direction of the subnatural-width resonance profile. [ABSTRACT FROM AUTHOR]

Mechanisms of multiple-wavelength oscillation at the lines of He I, Ne I, Sr I, and Sr II ions in the active medium of a high-voltage pulse-periodic laser based on a He + Ne + Sr mixture at a total pressure of ∼200 Torr and duration of the current pulse of about 150-300 ns are analyzed. An important role played by collisional thermal mixing of the laser levels of Ne I and Sr I in multiplets, as well as by collisions of the second kind between metastable and unexcited atoms, in populating and depopulating atomic levels is demonstrated. Absolute populations of the upper and lower levels of the laser transitions in Ne I are found. It is discovered that the degree of ionization nonequilibrium of plasma, both during and after the pulse of current, determines the mechanism of population inversion in laser transitions. [ABSTRACT FROM AUTHOR]

Hyperbolic metamaterial (HMM), a sub-wavelength periodic artificial structure with hyperbolic dispersion, can enhance the spontaneous emission of quantum emitters. Here, we demonstrate the large spontaneous emission rate enhancement of an organic dye placed in a grating coupled hyperbolic metamaterial (GCHMM). A two-dimensional (2D) silver diffraction grating coupled with an Ag/Al2O3 HMM shows 18-fold spontaneous emission decay rate enhancement of dye molecules with respect to the same HMM without grating. The experimental results are compared with analytical models and numerical simulations, which confirm that the observed enhancement of GCHMM is due to the outcoupling of non-radiative plasmonic modes as well as strong plasmon-exciton coupling in HMM via diffracting grating. [ABSTRACT FROM AUTHOR]

It is shown that high-contrast resonance of electromagnetically induced transparency (EIT) in a ladder Ξ-system of 5 S-5 P-5 D levels can be formed in optical cells containing a column of rubidium vapor with thickness L in an interval of 100 nm ≤ L ≤ 780 nm. Using bichromatic laser radiation with certain parameters, an 83% contrast of the EIT resonance (or dark resonance, DR) has been achieved for a vapor column thickness of L = 780 nm. An important condition for the formation of high-contrast DR is that the frequency of the coupling laser radiation must be resonant with the frequency of the corresponding 5 P-5 D transition (for the probe radiation frequency scanned over the 5 S-5 P transition). It is also shown that a DR can be formed at a record small vapor column thickness of L ≈ 100 nm. Expressions that can be used to estimate the expected DR width at small L values are presented. [ABSTRACT FROM AUTHOR]

Parametrical investigations of pulsed-periodic strontium vapor laser are carried out. Conditions of simultaneous generation on strontium atom and ion transitions (λ = 1.03 and 1.09 μm; 2.69, 2.6, 2.92, 3.01 and 3.06 μm; and 6.45 μm) formed during the period of ionization plasma inhomogeneity on the leading front of the excitation pulse and on strontium ion transitions (λ = 416.2 and 430.5 nm) formed during the period of recombination plasma inhomogeneity in the near afterglow of the discharge are determined. Simultaneous generation is understood as the presence of all generation lines per excitation period of high-voltage pulsed-periodic discharge in one resonator whose nontransmitting mirror has the reflection coefficient ≥90% and a CaF plane-parallel plate without deposited coating is used as an output mirror. [ABSTRACT FROM AUTHOR]

The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (α-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the α-factor is examined. The temperature dependence of the spectra of the α-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the α-factor with increasing temperature. [ABSTRACT FROM AUTHOR]

We have performed numerical simulation of a laser generating few-cycle pulses in the regime of coherent mode locking. It is shown that such a laser can support generation of pulses with a duration close to the reciprocal of the main laser transition frequency of the gain medium in a wide range of laser parameters. [ABSTRACT FROM AUTHOR]

The spontaneous emission yield from the 5 d[3/2] → 6 p[3/2] transition in atomic xenon with a wavelength of 2.03 μm upon excitation of a He-Ar-Xe medium by an electron beam of short duration (∼3 ns) was measured as a function of time for a wide range of partial composition of the gas mixture. The obtained data are analyzed. The experimental data agree with the calculated total lifetime of the level 5 d[3/2] of XeI in He-Ar-Xe mixtures with different partial composition. It is shown that the lifetime of this level determined by quenching induced by heavy particles is not established immediately following beam injection, but rather with a certain time delay determined by recombination processes in plasma. [ABSTRACT FROM AUTHOR]

The correlation of inhomogeneous broadening at various frequency transitions in three-level systems is investigated, as is its effect on the intensity of a stimulated photon echo. It is shown that the correlation coefficient of inhomogeneous broadening at two different transitions and the response intensity of the stimulated photon echo depend on the parameter of the random interaction of an optical electron with a local field, as well as on the distribution width of additional frequency shifts owing to a partial fixation of transition energies. In this case, an insignificant variation of the correlation coefficient results in a considerable decrease in the response intensity. [ABSTRACT FROM AUTHOR]

An explicitly gauge invariant strong field theory is introduced and tested using a model laser-atom interaction. The theory relies on a power series in the target potential. Transitions amplitudes are obtained by using a corresponding series in the momentum space wave function. We demonstrate that this approach is explicitly gauge invariant to all orders. A well know 1D delta function potential model is used to test the convergence of the series in the evaluation of total ionization probabilities and ionization spectra. Actually, the convergence is verified when both, the perturbation as well as the order of the expansion, are increased. [ABSTRACT FROM AUTHOR]

We study theoretically the absorption and dispersion of a probe field in the presence of a near-resonant pump field and the four-wave mixing in intersubband transitions of a semiconductor quantum-well structure. We take into account the effects of electron-electron interactions and consider the interaction of the two-subband system with rectangular electromagnetic fields. For the description of the system dynamics we use the effective nonlinear Bloch equations, which due to the effects of electron-electron interactions contain renormalized terms for the transition energy and the applied field. We combine these equations and write the proper differential equations of the density matrix elements for the several nonlinear optical processes, under the rotating wave approximation. These equations are solved analytically, in the steady state, for a GaAs/AlGaAs quantum-well structure. We show that the probe absorption and dispersion and the four-wave mixing spectra of a strongly driven two-subband system can be significantly dependent on the frequency and the intensity of the pump field and on electron sheet density. Specifically, we have found that the absorption, dispersion and the four-wave mixing spectra are practically independent of the electron sheet density in the case that the pump field is on resonance, and in the case for a rather strong pump field independently of its detuning. In the case of moderate intensity and off-resonant pump fields the influence of the electron-electron interactions on the reported spectra is more eminent for positive detuning of the pump field. [ABSTRACT FROM AUTHOR]

Taking advantage of the pump beam confinement and the excellent thermal management offered by Nd:YAG single crystal fibers, we demonstrated a maximum output power of 34 W at 946 nm for an incident pump power of 86 W. A high slope efficiency of 53% was obtained. There was no rollover observed in the efficiency curves and the maximum output power was only limited by the available pump power. [ABSTRACT FROM AUTHOR]

We investigated the CDI isotopomer of methyl iodide as a source of TeraHertz laser radiation using the optical pumping technique. We used a pulsed waveguide CO laser as the pump laser and an open Fabry-Pérot cavity for new laser line generation. We discovered 18 new laser lines with wavelengths ranging from 308.4 to 1132.7 μm, plus two lines previously assigned to CDI. All of the lines were characterized in wavelength, pump frequency offset, optimum pressure of operation, and relative polarization and intensity. [ABSTRACT FROM AUTHOR]

The optical torque wrench is a laser trapping technique capable of applying and directly measuring torque on microscopic birefringent particles using spin momentum transfer, and has found application in the measurement of static torsional properties of biological molecules such as single DNAs. Motivated by the potential of the optical torque wrench to access the fast rotational dynamics of biological systems, a result of its all-optical manipulation and detection, we focus on the angular dynamics of the trapped birefringent particle, demonstrating its excitability in the vicinity of a critical point. This links the optical torque wrench to nonlinear dynamical systems such as neuronal and cardiovascular tissues, nonlinear optics and chemical reactions, all of which display an excitable binary ('all-or-none') response to input perturbations. On the basis of this dynamical feature, we devise and implement a conceptually new sensing technique capable of detecting single perturbation events with high signal-to-noise ratio and continuously adjustable sensitivity. [ABSTRACT FROM AUTHOR]

We measured the absorption and luminescence spectra of Nd ions in an inorganic solvent POCl-BCl. The spectra were analyzed in terms of the Judd-Ofelt theory. We calculated the Judd-Ofelt parameters, oscillator strengths, spontaneous emission probabilities, luminescence quantum yield, and the stimulated emission cross section for the laser transition F → I of the neodymium ion in a POCl-BCl-Nd solution. [ABSTRACT FROM AUTHOR]

time-resolved shadowgraphic technique was used to investigate local transfer of diamond nanopowder from a thin titanium film on a silica support under irradiation by 450-fs or 50-ps laser pulses. Clean powder ejection driven by blistering of the metal film remaining on the target surface was found possible in a limited fluence range, but the metal film was removed from the target together with the powder when higher laser fluences were applied. The velocity of the powder ejection demonstrates an approximately linear rise in a wide range of the incident fluences, while the slope of the velocity curve decreases for thicker metal layers. The maximum ejection velocity achievable in the blistering regime was evaluated as ∼100 m/s independently of the metal thickness and pulse width. [ABSTRACT FROM AUTHOR]

nalysis of the main factors of the temperature dependence of inverse population on shallow-impurity transitions in semiconductors is carried out in the context of the four-level inversion scheme: the population of the lower state of the laser transition by heating from the ground state and a decrease in the population of the long-lived impurity state due to thermal ionization and an increase in the rate if direct recombination to the ground state with optical-phonon emission occurs. The temperatures at which these factors become substantial are determined. It is shown that thermal ionization from the long-lived state is the major factor determining the temperature quenching of stimulated emission upon shallow-donor transitions in silicon. [ABSTRACT FROM AUTHOR]

We report on an injection-seeded Ti:sapphire laser pumped by the second harmonic of a Nd:YAG laser. Due to an excellent spatial beam profile and narrow linewidth near the Fourier transform limit we are able to achieve high conversion efficiencies and stable output power in harmonic generation as well as in sum and difference frequency mixing with the pump pulse. The laser system can potentially cover a spectral range from 190 to over 6000 nm. [ABSTRACT FROM AUTHOR]

It is shown that the dip in the power output spectrum of a single-mode laser is caused by the nonlinear interaction of waves with the laser medium and is independent of the type of the laser transition broadening. When the cavity mode frequency is tuned to the center of the gain curve, the laser pumping rate exceeds the threshold value, causing increased gain saturation. Moreover, the rate of gain saturation is higher than that of the gain increase, which results in a decrease of the output intensity. Maximum saturation and the corresponding minimum of the output intensity occur at the center of the gain curve. [ABSTRACT FROM AUTHOR]

We have performed a parametric analysis of the influence of the percentage fraction of atomic oxygen in the O2:O2(1Δ):O flow on the formation of population inversion for a laser transition in iodine atoms and the temperature regime at an elevated pressure of P = 5 Torr in a system with axisymmetric injection of a I2: He mixture to the flow of oxygen excited by an electric-discharge singlet oxygen generator. [ABSTRACT FROM AUTHOR]

A method of periodic short-term inversion for intersubband laser transitions in a quantum well with a repetition frequency of ∼1 GHz and inversion retention time ∼1 ps is suggested. The method is based on fast population of the upper transition level as a result of resonance tunneling of charge carriers from neighboring quantum wells as the electric field applied to the heterostructure is varied. As a consequence, the peak value of the population inversion can be as large, for example, as 8 × 1010 cm−2 for the transition corresponding to the wavelength λ ≈ 10 μm and 2 × 1010 cm−2 in the case of λ ≈ 25 μm. This method can be implemented at room temperature, which makes it attractive for fabrication of amplifiers of picosecond pulses for the middle and far infrared optical regions and the terahertz band. [ABSTRACT FROM AUTHOR]

The photolysis of AgBr nanocrystals irradiated by picosecond light pulses with quantum energies of 3.51 and 1.17 eV is theoretically analyzed. The observed dependences of the photometric density on the long-wavelength radiation intensity are shown to be determined by the photogeneration of nonequilibrium electron-hole pairs as a result of indirect interband phototransitions involving free electrons. For such electrons to be involved in this process, they should possess a high kinetic energy, which is acquired due to intraband non-linear absorption of the intense long-wavelength radiation. [ABSTRACT FROM AUTHOR]

A method of classification of many-electron states that involves symmetry groups of four-dimensional space is developed. Taking into account the spatial and temporal symmetry, the selection rules for electric and magnetic dipole transitions are investigated. The reduction relations for the irreducible representations of the orthogonal group O 4 and the group R 4 of pure rotations of the four-dimensional space on the groups and O and O 4 of the four-dimensional cube and of the octahedron on the three-dimensional groups O h and D 6 h of the cubic and hexagonal systems, respectively, are obtained. The four-dimensional classification of the levels of the spin-orbit interaction of rare earth ions for the intermediate reduction on the group of the four-dimensional cube is performed. With the help of the irreducible representations of the O 4 group, the selection rules of magnetic and forbidden electric dipole transitions, as well as of intercombination transitions, are investigated. [ABSTRACT FROM AUTHOR]

The absorption and luminescence spectra of neodymium in a binary inorganic solvent—phosphorus oxychloride-antimony pentachloride—are measured. The spectra are analyzed in terms of the Judd-Ofelt theory. The Judd-Ofelt parameters Ωλ, the oscillator strengths of the main absorption bands, the spontaneous emission probabilities, the radiative lifetime, the luminescence quantum yields, and the stimulated emission cross sections for the 4 F 3/2 → 4 I 11/2 laser transition are calculated. [ABSTRACT FROM AUTHOR]

The absorption and luminescence spectra of neodymium in a binary inorganic solvent—phosphorus oxychloride-antimony pentachloride—are measured. The spectra are analyzed in terms of the Judd-Ofelt theory. The Judd-Ofelt parameters Ωλ, the oscillator strengths of the main absorption bands, the spontaneous emission probabilities, the radiative lifetime, the luminescence quantum yields, and the stimulated emission cross sections for the 4 F 3/2 → 4 I 11/2 laser transition are calculated. [ABSTRACT FROM AUTHOR]

High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of 2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method to construct a reliable compact red laser. [ABSTRACT FROM AUTHOR]

High power red light was generated from a periodically-poled stoichiometric LiTaO3 (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of 2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method to construct a reliable compact red laser. [ABSTRACT FROM AUTHOR]

A continuous-wave, diode-pumped Nd:GdVO4 thin disk laser with simultaneous dual-wavelength emission at the 912 nm 4 F 3/2→4 I 9/2 quasi-three-level transition and the 1063 nm 4 F 3/2→4 I 11/2 four-level transition is demonstrated and analyzed. Output powers of 1.7 W at 912 nm and of 1.6 W at 1063 nm were achieved simultaneously from a 0.3-at.%, 300-μm thick Nd:GdVO4 crystal that was multi-pass excited with 26.8 W of available diode pump power. Second harmonic generation to 456 nm with LiB3O5 yielded 0.96 W in 912 nm single-wavelength operation and 0.73 W in 912 nm/1063 nm dual-wavelength operation. [ABSTRACT FROM AUTHOR]

A continuous-wave, diode-pumped Nd:GdVO4 thin disk laser with simultaneous dual-wavelength emission at the 912 nm 4 F 3/2→4 I 9/2 quasi-three-level transition and the 1063 nm 4 F 3/2→4 I 11/2 four-level transition is demonstrated and analyzed. Output powers of 1.7 W at 912 nm and of 1.6 W at 1063 nm were achieved simultaneously from a 0.3-at.%, 300-μm thick Nd:GdVO4 crystal that was multi-pass excited with 26.8 W of available diode pump power. Second harmonic generation to 456 nm with LiB3O5 yielded 0.96 W in 912 nm single-wavelength operation and 0.73 W in 912 nm/1063 nm dual-wavelength operation. [ABSTRACT FROM AUTHOR]

An intracavity laser spectrometer has been used to study the laser-spark absorption spectrum of C2 radicals near 1.06 μm. The spectra recorded have been assigned, and the rotational lines of the transitions 3-0, 4-1, and 5-2 b 3Σ- a 3Π u and 2-1 and 1-0 A 1Π u - X 1Σ have been identified. The vibrational and rotational temperatures have been determined. [ABSTRACT FROM AUTHOR]

For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate and spontaneous emission factor. [ABSTRACT FROM AUTHOR]

The effect of the dimension of the 3D homogeneous and isotropic Euclidean space, and the electron spin on the self-organization of the electron systems of atoms of chemical elements is considered. It is shown that the finite dimension of space creates the possibility of periodicity in the structure of an electron cloud, while the value of the dimension determines the number of stable systems of electrons at different levels of the periodic table of chemical elements and some characteristics of the systems. The conditions for the stability of systems of electrons and the electron system of an atom as a whole are considered. On the basis of the results obtained, comparison with other hierarchical systems (nanostructures and biological structures) is performed. [ABSTRACT FROM AUTHOR]

Tm3+-Eu3+ energy transfer processes and relaxation dynamics of the 3 H 4 and 3 F 4 excited states of Tm3+ ions in 1 at. % Tm3+, 5 at. % Eu3+:YVO4 single crystal were studied. Contribution of Tm3+-Eu3+ energy transfer reduces effectively the lifetime of terminal level in a potential 3 H 4–3 F 4 laser transition at around 1.48 μm. Adverse quenching of the 3 H 4 emission by Eu3+ ions is found to be less efficient than that reported for Tm3+ + Tb3+ system in YVO4. The classical Inokuti–Hirayama model accounts well for an experimental decay curve of the 3 H 4 emission recorded for co-doped crystal. Stimulated emission cross section for 3 H 4–3 F 4 transition of Tm3+ at around 1.48 μm was analyzed taking into account the anisotropy of YVO4 crystal. [ABSTRACT FROM AUTHOR]

Single crystals of disordered double sodium-gadolinium tungstate NaGd(WO4)2 doped with Tm ions were grown by the Czochralski method. The polarized absorption and emission spectra of these crystals with different activator concentrations and the decay kinetics of the 3 H 4 and 3 F 4 excited states of Tm3+ ions at 300 K were investigated. The absorption and emission cross sections of the expected laser transition 3 F 4 ↔ 3 H 6 in the Tm3+ ion were determined and the amplification spectra of the active laser medium NaGd(WO4)2:Tm at different levels of inverse population of the upper laser level 3 F 4 of the Tm3+ ion were constructed. The prospects for using these crystals as active media in 2-μm solid-state lasers are discussed. [ABSTRACT FROM AUTHOR]

A laser scheme implementing a combination of negatively and positively chirped pulse amplification (NPCPA) is demonstrated. This method of amplification suppresses spectral narrowing typically appearing in chirped pulse amplification (CPA) lasers thus supporting pulse spectrum much broader than a conventional CPA. With a NPCPA Ti:Sapphire laser we have achieved laser pulses of 50 nm spectral width and 150 mJ energy without any additional spectral correction. The scheme appears as an easy and reliable solution to preserve spectral bandwidth in Ti:Sapphire lasers, especially at high power levels up to the Petawatt regime. [ABSTRACT FROM AUTHOR]

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to Doppler-free transitions of the ν1 + ν3 and ν1 + ν2 + ν4 + ν5 combination bands of 13C2H2. The Allan deviation σ/f for a laser locked to line P(10) of the former band follows a slope of 1.6 × 10−12τ−1/2, reaching a minimum of 5.7 × 10−14 at τ = 4000 s. The absolute frequencies of 61 lines of the ν1 + ν3 band and 43 lines of the ν1 + ν2 + ν4 + ν5 band, covering the spectral region 1520 nm to 1552 nm, have been measured by use of a combined frequency chain and femtosecond comb, together with a passive optical frequency comb generator. The mean uncertainties for the line frequencies within each band are 1.4 kHz for the ν1 + ν3 band and 1.9 kHz for the ν1 + ν2 + ν4 + ν5 band, representing improvements on the precision of previously published data by factors of 100 and 104, respectively. Improved values of the rotational constant B″ and centrifugal distortion coefficients D″, H″ and L″ of the vibrational ground state are presented. [ABSTRACT FROM AUTHOR]

We report on the application of polarization spectroscopy in the mid-infrared spectral region for the detection of methane by probing its asymmetric ro-vibrational transitions. Tunable infrared laser radiation, near 3.4 μm, was obtained from difference-frequency generation in a LiNbO3 crystal. Infrared polarization spectroscopy (IRPS) spectra of the P, Q and R branches of the ν3 band, recorded with both linearly and circularly polarized pump beams, are presented. The experiments were performed in an atmospheric pressure gas jet with methane diluted with Ar. An IRPS spectrum with signal-to-noise ratio better than 104 was observed. The dependence of the IRPS signal intensity on the methane mole fraction and on the pumping laser power density was investigated. [ABSTRACT FROM AUTHOR]

A partial polarization of luminescence in laser phosphate and silicate erbium-doped glasses was found to take place for the fundamental laser transition [sup 4]I[sub 13/2]→[sup 4]I[sub 15/2](λ=1.55μm) under excitation by linearly polarized laser radiation (532 and 790–990 nm). The shape of the luminescence spectrum depends on the wavelength of the exciting light and on the composition of the glass matrix. The degree of polarization of the luminescence depends on the spectral range of both the excitation and the detection, attaining a maximum of ∼1%. The concentration dependence of the degree of polarization is studied. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A theoretical model for the F[sub 2](D[sup ′]–A[sup ′]) laser transitions is built. The model includes a scheme of the main laser transitions proposed. A value of the radiative lifetime of the upper laser level in the conventional kinetic models of the F[sub 2] laser is proved to be underestimated by one order of magnitude. A general theory of steady-state light amplification in a molecular laser with non-equilibrium vibrational distribution is developed. Relations of the small-signal gain and the saturating energy flux with parameters of molecular electronic–vibrational kinetics are established. The theory is applied to explain properties of F[sub 2] laser amplifiers. [ABSTRACT FROM AUTHOR]

Terahertz stimulated emission of phosphorus donors in silicon optically excited by radiation from the free-electron laser FELIX has been studied. It is found that a spectral line of the Si:P laser emission depends on pump frequency. Stimulated emission arises on the 2p[SUB0] → 1s(T[SUB2]) intra-centre transition (21.2 meV) under resonant pumping of the 2p[SUB0] state and on the 2p[SUB0] → 1s(T[SUB2]) transition (22.3 meV) under pumping of the 2p± or higher odd-parity donor states. The line shift is attributed to the Auger redistribution of the 1s(E)-and 1s(T[SUB2])-state populations. [ABSTRACT FROM AUTHOR]

Multi-line laser transitions from one metastable triplet state to another at wavelengths of 2.92, 3.01, 2.69 and 2.60 μm have been obtained through high pulse repetition frequency longitudinal discharge in a mixed gas of strontium vapor and helium buffer gas. The intensity ratio of these laser lines was 5:4:4:1. As far as we know, these laser lines have never been reported except for 3.01 μm. Some mechanisms for forming a population inversion are initially discussed on the basis of analyzing features of corresponding energy-level structure and experimental phenomena. It is reasonable to name this kind of laser as an M–M transition laser according to the feature of the lasing process. [ABSTRACT FROM AUTHOR]

Laser cooling and trapping of radioactive atoms represent the new frontier in atomic physics and a new powerful tool in nuclear physics. We are setting up at the INFN-Legnaro National Laboratories a laser cooling facility that has as a first goal the realization of a 210Fr magneto-optical trap. The general outline of the experiment and the improvements of the final trap efficiency are discussed. Some preliminary results are presented. [ABSTRACT FROM AUTHOR]

Fibroin is the main component of silk and is expected to be used as a novel functional material in medicine and bioelectronics. The main secondary structures of this protein are of the random-coil and the β-sheet types. In this study, we carried out laser-induced transformation of the secondary structure, from the random-coil type to the β-sheettype, in solid fibroin films. We prepared two types of fibroin films with the random-coil structure. One is a fibroin film doped with a dye as a photosensitizer with a small amount (1 wt %), and the other is a neat fibroin film. The former was excited at 532 nm and the latter was excited at 266 nm. Irradiations were carried out with fluences much lower than each ablation threshold. The excitation of the dye at 532 nm did not affect the secondary structure of the random-coil type. By contrast, 266-nm laser irradiation, which excites tryptophan (an amino-acid residue) involved in fibroin, created the β-sheetdomain in the film. The structural transformation was revealed by infrared absorption spectroscopy and atomic force microscopy. [ABSTRACT FROM AUTHOR]

Abstract. Ca[sub 3]Sc[sub 2]Ge[sub 3]O[sub 12] (CaSGG) single crystals with the garnet structure have been grown by means of the flux growth technique. The doping with Nd[sup 3+] and Mg[sup 2+] (as charge compensator) yields samples suitable for optical spectroscopy experiments. The absorption and emission properties have been measured at temperatures ranging from 10 to 298 K. The emission spectra give evidence of the presence of nonequivalent Nd[sup 3+] sites. The decay time of the 1.06-micro m emission band has been measured as a function of temperature and incident power. The intensities of the 298 K absorption transitions have been analyzed by means of the Judd-Ofelt theory. The radiative lifetimes, the branching ratios (beta), and the spontaneous emission probabilities have been evaluated for the 4F[sub 3/2] excited state using the calculated intensity parameters. The stimulated-emission cross sections and the branching ratios have been estimated from the experimental data for the most important laser transitions indicating that this crystal can be considered an interesting material for solid-state laser applications. [ABSTRACT FROM AUTHOR]

Abstract. Absorption, excitation, and emission spectra of trivalent thulium in SrGdGa[sub 3]O[sub 7] crystal have been recorded at room temperature and at approximately 8 K. Room-temperature luminescence lifetimes of [sup 1]D[sub 2], [sup 1]G[sub 4], [sup 3]H[sub 4], and [sup 3]F[sub 4] states have been measured for Tm concentration ranging from 0.5 at. % to 9 at. %. Based upon these data the crystal field splitting of luminescent states has been derived and radiative transitions rates have been evaluated. Strong self-quenching of luminescence originating in the [sup 1]G[sub 4] and [sup 3]H[sub 4] states has been found in this activator-host combination. Peak emission cross section of the potential laser transition at 1800nm was determined to be 3.9 x 10[sup -21] cm[sup 2] and the gain coefficient versus wavelength was estimated and discussed. [ABSTRACT FROM AUTHOR]

Presents research which realized a single artificial semiconductor material with distinct optical transitions. Simultaneous laser action at several wavelengths in systems; Nature of most semiconductor lasers; Achievement of an allowance of simultaneous multiwavelength laser action at mid-infrared wavelengths; Use of a superlattice layered structure; Potential applications.

We present a very high resolution spectrometer for the spectral region around 60 THz (5 μm). It is based on a CO laser which is frequency-offset locked to combination frequencies of two CO[sub 2] laser standards. Using this technique, we can tune the CO laser frequency with absolute frequency control within the gain profile of each laser transition. The frequency uncertainty is smaller than 15 kHz, corresponding to Δν/ν=2.5×10[sup -10] . Moreover, we obtain a reduction of the CO laser linewidth by a factor of 2 down to 65 kHz, corresponding to a spectral resolution of δν/ν=1×10[sup -9] . With this outstanding accuracy and resolution we studied the shape of saturation dips in rovibrational lines of CO and carbonyl sulfide (OCS) at low pressure (<5 Pa). The self-pressure-broadening rate of CO was found to be γ[sub c] =+83(7) kHz/Pa in this pressure region. This value is about four times higher than values resulting from previous measurements at much higher pressures. To our knowledge the measurements described here are the first line-shape studies with sub-Doppler resolution in the 5 μm spectral region. [ABSTRACT FROM AUTHOR]

We report the efficient compact green laser at 515 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a diode-pumped Yb:YAG laser on the transition at 1030 nm. An LBO crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation (SHG) of the laser. With the incident pump power of 10 W, 270 mW of CW output power at 515 nm is achieved with 15-mm-long LBO. The optical-to-optical conversion efficiency is 2.7%, and the power stability in 8 h is better than 2.36% with low noise. [ABSTRACT FROM AUTHOR]

The energy dependence of the effective cross sections for the electron-impact excitation of 4d[sup 9]5s² ²D[sub 5/2, 3/2] - 4d[sup 10]5p²P[sup 0, sub 1/2, 3/2] laser transitions in cadmium ions was studied by a high-precision spectroscopic technique using crossed electron and ion beams. The absolute effective cross sections for the laser line excitation at λ = 441.6 and 325.0 nm have the peak values 2.5 × 10[sup -16] and 1.3 × 10[sup -16] cm², respectively. It is shown that population of the 4d[sup 9]5s² ²D[sub 5/2, 3/2] upper laser levels by the electron impact on cadmium ions in the 4d[sup 10]5s ²S[sub ½] ground state takes place predominantly due to the resonance processes; that is, it proceeds via atomic and ionic autoionization states. [ABSTRACT FROM AUTHOR]