Interference-filter-stabilized external-cavity diode lasers

We have developed external cavity diode lasers, where the wavelength selection is assured by a low loss interference filter instead of the common diffraction grating. The filter allows a linear cavity design reducing the sensitivity of the wavelength and the external cavity feedback against misalignment. By separating the feedback and wavelength selection functions, both can be optimized independently leading to an increased tunability of the laser. The design is employed for the generation of laser light at 698, 780 and 852 nm. Its characteristics make it a well suited candidate for space-born lasers.     

钙、锶、钡和汞离子激光中的共振辐射俘获效应

根据Holstein的共振辐射俘获理论，讨论了气体温度和辐射俘获下能级粒子数密度对辐射俘获上能级有效辐射寿命的影响，显示辐射俘获下能级粒子数密度是辐射俘获效应中的主导因素.计算了钙，锶，钡和汞四种离子七条共振-亚稳能级跃迁激光在不同电离率下产生共振辐射俘获效应的阈值条件，发现当电离率为5%时这类激光的出光温度与共振辐射俘获的阈值温度相一致，这与实验得出的电离率为3%—5%相符合.表明达到共振辐射俘获阈值条件是该类激光实现粒子数反转的重要因素.     

Electron-vibrational interaction in 4f-5d optical transitions in Ba, Ca, Sr thiogallates doped with Eu ions

This study is devoted to the problem of the electron-vibrational interaction in 4f-5d optical transitions. We analyze the room temperature experimental data on the vibronically assisted broad bands arising from the 4f-5d transitions in Ba, Ca, and Sr thiogallates doped with Eu²⁺ ions. An approximate simple expression is given for the shape function of the broad vibronic bands with allowance for the terms corresponding to the emission (absorption) from both ground and first excited vibrational levels. We estimate the vibronic coupling parameters and the Stokes shifts for these systems. The theoretical results are in a good agreement with the experimental data.     

A kinetic model for alternate oscillation of self-terminating and recombination lasers in strontium ions

A self-consistent model has been developed to simulate the kinetics of alternate oscillation of self-terminating and recombination lasers in univalent ions of strontium excited by the high-repetition-rate (HRR) pulsed discharge. Photoelectric pulse waveforms predicted by the model are in good agreement with the experimental measurement. The model also gives temporal behaviors of long-life particles, the population densities of upper and lower laser levels and the electron temperature (Te) in He-Sr discharge plasma. The emission process of the two laser alternate oscillations, the characteristic of the laser pulse width and the population inversion mechanics are also analyzed.     

Electronic structures and ferroelectric properties of ABi2Ta2O9 (A=Ca, Sr, and Ba)

The electronic structures of ABi₂Ta₂O₉ (A=Ca, Sr, and Ba) were calculated by using first-principles under optimized structure. As the size of A-site cation decreases from that of Ba²⁺ to Ca²⁺, the band-gap between O 2p and Ta 5d increases from 2.0 to 2.9 eV, which responses to the stronger orbital hybridizations between Ta 5d and O 2p orbits favoring improvement of the ferroelectric property, decrease in leakage current, and increase in both spontaneous polarization and Curie temperature by the structural distortion. In contrast to CaBi₂Ta₂O₉ and SrBi₂Ta₂O₉, the hybridization between Ba 5p orbits and O 2p orbits in BaBi₂Ta₂O₉ has better structural stability.     

Physical properties of double perovskite compounds ALaVMoO6 (A=Ca, Sr, Ba)—a possible half-metallic antiferromagnetic system

Double perovskite compounds ALaVMoO₆ (A=Ca, Sr, Ba) have been synthesized and their electrical and magnetic properties have been investigated. Magnetization measurements have indicated the possible antiferromagnetic transitions at 120 and 130 K for A=Ca and Sr samples, respectively. Electrical resistivity ρ for this system shows metallic temperature dependence from 300 to 20 K, though the sample with A=Ca shows weak semiconducting behavior in the low temperature region (<70 K). Considering the magnetic and electrical properties and assuming the V³⁺S=1 and Mo⁴⁺S=1 valence and spin states, the samples with A=Ca and Sr can be promising candidates for half-metallic antiferromagnets.     

Studies on widely tunable ultra-short laser pulses using energy transfer distributed feedback dye laser

This paper presents both theoretical and experimental study of the characteristics of Nd: YAG laser pumped energy transfer distributed feedback dye laser (ETDFDL). Using theoretical model proposed, the behavior of ETDFDL such as the characteristics of donor DFDL, the acceptor DFDL, the dependence of their pulse width and output power on donor-acceptor concentrations and pump power are studied for dye mixture Rhodamine 6G and Cresyl Violet in detail. Experimentally using prism-dye cell configuration, the ETDFDL output is obtained and the output energy of DFDL is measured at the emission peaks of donor and acceptor dyes for different pump powers and donor-acceptor concentrations. In addition, the DFDL linewidth measurement has been carried out at the lasing wavelengths of the donor and acceptor dyes using Fabry-Perot etalon and the tunability of DFDL is measured to be in the wavelength range of 545-.     

Relaxor behavior of (Ba,Sr)(Zr,Ti)O3 ferroelectric ceramics

We examine the ferroelectric-relaxor behavior of (Ba_0.65Sr_0.35)(Zr_0.35Ti_0.65)O₃ (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with T_VF=107 K, E_a=0.121 eV, and ν₀=6.83×10¹⁴ Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>T_m (T_m, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications.     

Oscillations conditions in a gain grating in the Bragg diffraction regime

Coupled-wave analysis is applied to the determination of an oscillation threshold in thick periodic grating with gain (distributed-feedback oscillator). Pure phase (refractive index modulation), amplitude (gain modulation) and mixed-type gratings are considered. The origin of oscillation modes and their position on the diffraction efficiency contour is analyzed. The threshold conditions are determined on a basis of analytical expressions.     

Influence of B2O3 to the inhomogeneous broadening and spectroscopic properties of Er/Yb codoped fluorophosphate glasses

In a three-components fluorophosphate glass system, the introduction of H₃BO₃ brings some valuable influence to the spectroscopic and thermal properties of the glasses. With H₃BO₃ increases from 2 to 20 mol%, Ω₆, S_ed4I13/2, FWHM, T_g and fluorescence lifetime change from 3.21×10⁻²⁰ cm², 1.77×10⁻²⁰ cm², 45 nm, 480 °C and 8.8 ms to 4.66×10⁻²⁰ cm², 2.11×10⁻²⁰ cm², 50 nm, 541 °C and 7.4 ms, respectively. σ_abs, σ_emi, FWHM×τ_f×σ_emi has a maximum when H₃BO₃ is 11 mol%. T_g and T_x−T_g increases with H₃BO₃ introduction. Results showed that in fluorophosphate glasses, proper amount of B₂O₃ can be used as a modifier to suppress upconversion and improve spectroscopic properties, broadband property and crystallization stability of the glasses while keeps the fluorescence lifetime relatively high.     

Laser-assisted decontamination—A wavelength dependent study

We present here the experimental results on cleaning of radioactive dielectric particulates, loosely deposited on stainless steel, by coherent light of 1064 nm wavelength and its three harmonics occurring at 532 nm, 355 nm and 266 nm, derived from an Nd-YAG laser. For the initial few exposures, the decontamination factor has been found to be highest when exposed to 1064 nm radiation. With increasing number of exposures, however, the radiation with reducing wavelength assumes a more important role as a cleaning agent. The observation of almost no cleaning with 1064 nm and much reduced cleaning with its harmonics when the contamination is deposited on a transparent substrate confirms the dominant role played by metal substrate towards expelling the loose particulates from its surface.     

NIR luminescence from Er/Yb, Tm/Yb, Er/Tm and Nd ions-doped zincborotellurite glasses for optical amplification

In this paper, we report the near-infrared luminescence from the Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺, Er³⁺/Tm³⁺ and Nd³⁺ ions-doped TeO₂-ZnO-B₂O₃-Li₂O-Na₂O glasses for optical amplification. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) profiles of the host glass matrix have been carried out. From the DSC thermogram, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The near-infrared spectra of Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺, Er³⁺/Tm³⁺ and Nd³⁺ ions-doped glasses have shown full-width at half-maxima (FWHM) around 58, 127, 87 and 35 nm, respectively. These glasses with better thermal stability and broad near-infrared emissions should have potential applications in broadly tunable laser sources and broadband optical amplification at low-loss telecommunication windows.     

1 W tunable near diffraction limited light from a broad area laser diode in an external cavity with a line width of 1.7 MHz

A novel unstable external cavity for a broad area laser diode is presented. The cavity is based on a V-shaped setup that improves the slow axis beam quality by coupling the internal modes of a gain guided laser diode. The novelty here is the compact unstable resonator design without lenses in direction of the slow axis. For frequency stabilisation and to narrow the line width of the laser diode emission a diffraction grating in a Littrow configuration is used. With this setup up to 1 W of near diffraction limited light with a beam quality of M² ? 1.3 and a line width of 1.7 MHz could be achieved. The external cavity laser was tunable over a range of 35 nm (FWHM) around the center wavelength of 976 nm.     

Numerical study on gain and optical properties of AlGaInAs, InGaNAs, and InGaAsP material systems for 1.3-μm semiconductor lasers

In reference to real devices fabricated in laboratories, the optical properties of AlGaInAs, InGaNAs, and InGaAsP semiconductor material systems for 1.3-μm semiconductor lasers are systematically studied. Simulation results show that both the AlGaInAs/InP and InGaNAs/GaAs material systems have better gain performance and smaller transparency carrier density than the InGaAsP/InP material system. For the AlGaInAs/InP material system, the characteristic temperature is improved by using compensating tensile strain in barrier. Specifically, for a 250-μm-long short-cavity AlGaInAs/InP laser, when the barrier is with a compensating tensile strain of 0.39%, the characteristic temperatures in 290-330 K and 330-350 K can be enhanced to 121.7 K and 58.9 K, respectively. For the InGaNAs/GaAs material system, simulation results suggest that the laser performance can be significantly improved when the laser is with strain-compensated GaNAs barriers.     

Metallo-organic decomposition derived (Ca, Sr)ZrO3 dielectric thin films on Pt coated Si substrate

Metallo-organic decomposition derived dielectric thin films of calcium zirconate doped with various concentrations of strontium ((Ca, Sr)ZrO₃) were prepared on Pt coated silicon substrate. Mainly in this paper, we present the investigations of their structural developments and present their electric and dielectric properties as well. The structural developments show that the CaZrO₃ film has amorphous structure with carbonate existing when annealed at 600 °C, while annealed at 650 °C and above, the carbonate is decomposed and those films crystallize into perovskite phase without preferred orientation. In addition, the prepared (Ca, Sr)ZrO₃ films with their Zr-O bonds affected by strontium doping are homogenous and stable as solid solutions in any concentration of strontium and all Bragg diffraction characteristics for the films shift downward with the increase in the concentration of strontium. Moreover, the electric properties show that the (Ca, Sr)ZrO₃ films have very low leakage current density and high breakdown strength; typically, the CaZrO₃ film annealed at 650 °C has the leakage current density approximately 9.5 × 10⁻⁸ A cm⁻² in the field strength of 2.6 MV cm⁻¹. Furthermore, the dielectric properties show that their dielectric constants are higher than 12.8 with very little dispersion in the frequency range from 100 Hz to 1 MHz and are independent of applied dc bias as well. The dielectric properties, in combination with the electric properties, make the materials promising candidates for high-voltage and high-reliability capacitor applications.     

Anisotropy in the nonlinear absorption of elongated silver nanoparticles in silica, probed by femtosecond pulses

We present measurements of the anisotropy of the nonlinear absorption of a silica matrix doped with aligned spheroidal silver nanoparticles, produced by a double ion-implantation process of silver nanoparticles followed by an irradiation with Si ions. The nonlinear response was studied using the z-scan technique with fs pulses at 530 nm, which lies very close to the surface-plasmon absorption peak of the sample. The observed saturable absorption is studied for different angles of the input linear polarization of the pulses, showing a strong anisotropy, which is consistent with the fact that the nanorods are aligned.     

High accuracy ranging with Yb-doped fiber-ring frequency-shifted feedback laser with phase-modulated seed

This paper demonstrates that a frequency-shifted feedback laser, when seeded by a phase-modulated narrow-band radiation field, is a powerful tool for distance measurements to accuracy better than 10 μm and resolution better than 100 μm, for distances of a few meters. In such measurements the unknown distance forms one arm of a Michelson interferometer, in which the intensity of the output signal is modulated at the phase-modulation frequency of the seed. The amplitude of the output-signal modulation exhibits a resonance for every distinct signal delay, i.e. for each distinct distance within the laser spot on the target. The use of a phase-modulated input seed allows one to use a very narrow-bandwidth filter when measuring the return signal. The results reported in this paper are in excellent agreement with previous theoretical predictions [L. Yatsenko et al., Opt. Commun. 242 (2004) 581] for the resolution limit and high signal-to-noise ratio for this new technique.     

New fast-decaying green and red phosphors for 3D application of plasma display panels

Fast-decaying phosphors are essential for a 3D plasma display panel (PDP) with high image quality. However, conventional green and red PDP phosphors have slow-decaying characteristics. We present the luminescence properties of new phosphors for 3D PDP application. Decay times of Y₃Al₅O₁₂:Ce³⁺, (Y,Gd)Al₃(BO₃)₄:Tb³⁺, and (Y,Gd)₂O₃:Eu³⁺ were significantly shorter than those of conventional PDP phosphors. CIE chromaticity coordinates and luminescence efficiencies of the phosphors were also suitable for PDP application. The development of fast-decaying PDP phosphors has enabled commercialization of 3D/2D switchable PDP television for the first time in PDP industry.     

Experimental characterization of an Yb-doped fiber ring laser with frequency-shifted feedback

We present experimental characteristics of an Yb³⁺-doped fiber ring laser operating with frequency-shifted feedback (FSF) through an acousto-optic modulator (AOM) and seeded by both a stationary continuous-wave (CW) laser and spontaneous emission. We show the spectrum and output characteristics for operations with several effective gain bandwidths, as established by Fabry-Perot etalons inside the cavity. Observation using a high finesse Fabry-Perot interferometer shows that, as expected from earlier work, although the spectrum of the FSF laser without seeding is continuous, when seeded by a CW-laser the spectrum consists of a comb of discrete modes, each offset from the seed by an integer number of AOM frequency shifts. The experimental results are in excellent quantitative agreement with the theory developed earlier [L. Yatsenko, B.W. Shore, K. Bergmann, Opt. Commun. 236 (2004) 183].