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• A novel solid-state gain medium structure is used to achieve high-power, high beam quality laser output. • Thermal control of bulk gain media is more conducive to high-quality laser output. • Simple stacking can achieve the utilization of pump light and the extraction of laser power. • Limited control reduction of pump light absorption by gain media and efficient extraction to achieve cooling requirements of gain media. Obtaining high power, high beam quality, and high efficiency laser sources has always been one of the important development goals in solid-state laser technology. However, up to now, hundred-watt TEM 00 mode (large-volume) beams directly from simple solid-state lasers without liquid cooling are not available. To overcome these challenges, here we propose a new approach based on the principle of low thermal effect and the power superposition method. By doing so, at room temperature, a 131 W TEM 00 mode is obtained from the simplest Nd:YAG laser. Importantly, the laser can work stably for a long time (root mean square: 0.307 % over 3 h), and the gain medium is cooled by a fan. This demonstration promises to upgrade high-power and high beam quality applications for solid-state laser sources. [ABSTRACT FROM AUTHOR]

Presents information photoconductive semiconductor devices (PCDs) while focusing on the chemical vapor deposited (CVD) diamond films. How are the diamond films deposited; Limitation of the grain sizes of the measured diamond films.

Presents a study that developed a three-dimensional computer code of amplified spontaneous emission for a high power krypton fluoride laser amplifier having a cylindrical symmetry and small aspect ratio. Indication of the analysis using the code; Requirement for the achievement of a high extraction efficiency; High efficiency extraction being guaranteed by the code.

The article presents a study on laser-diode pumped self-Q-switched microchip lasers. It involves the investigation of the optical properties of Cr, Yb: YAG, Cr, Nd: YAG crystals and composite Yb:YAG/Cr:YAG ceramics self-Q-swtiched solid state laser materials. It was found out that the performance of monolithic microchip Cr, Yb:YAG laser is limited by the absorption of Cr4+ ions at a pump wavelength of 940 nm and powerful flourescence quenching at high concentration of Cr.

We design a novel interferometer for the real-time wavefront measurement, which is based on the diffraction grating holography technique, where the diffraction gratings act as a beam splitter and a phase retarder, thus four interference patterns can be simultaneously obtained. Computer simulations show the validity of the approach and experimental setup is also presented. [Copyright &y& Elsevier]

We have developed and adequately characterized a new generation of solid-state laser and optical materials on the basis of highly transparent nanocrystalline yttrium aluminium garnet Y3Al5O12 (YAG) ceramics. We consider this new type of inorganic laser media as an illustration of selected results of the latest investigations of laser and spectroscopic parameters of nanocrystalline Nd3+:YAG ceramics. In particular, absorption, luminescence, stimulated Raman scattering properties, as well as highly efficient CW laser oscillation at wavelength of 1064 nm under laser-diode pumping were investigated. The results show that this new laser material is a very good alternative to Nd3+:YAG single crystals. In particular, in preliminary comparison laser experiments with both Nd3+:YAG ceramic and single-crystal rods, output powers of 88 W and 99 W were obtained corresponding to optical-to-optical efficiencies of 30% and 34% for ceramic and single crystal rods, respectively. A CW 1.46 kW high power Nd:YAG ceramic laser was developed. Quite recently, laser oscillation at ≈1.32 μm was also demonstrated. [Copyright &y& Elsevier]

Focuses on a study which investigated the spectral and laser properties of an Yttrium gallium garnet structure oxide crystals. Methodology of the study; Results; Conclusions.

Examines the characteristics of K[sub 2] yellow and Rb[sub 2] orange diffuse bands excimer emissions by electron-beam excitation. Importance of the diffuse bands of alkali dimers in the development of excimer-type laser sources; Observation of the continuum spectra; Discussion of the dissociative recombination as an efficient formation process of upper states.

Examines the vacuum ultraviolet transitions from rare-gas alkali ionic excimers (XeRb)[sup +] and (KrRb)[sub +]. Use of electron beam excitation; Range of the gas mixture diffuse emission bands; Assignment of the bands to the ultraviolet fluorescence of the mixtures.

Investigates the photoconductive properties of diamond optical switch mode by chemical vapor deposition (CVD) method. Improvement of static electrical properties by CVD diamond switch; Effects of grain boundary on CVD diamond; Measurement of output amplitude for CVD diamond switch.

A method of measuring photoacoustic (PA) waves in situ is proposed and experimentally demonstrated. A focused probe ultrasonic beam passes through a sample and tags the position of the interested PA signal. The probe beam interacts with PA wave. The PA signal modulated probe beam is recorded outside the sample. Reconstruction of the original in situ PA signal is accomplished by demodulating the probe beam. The method, thus, provides a measurement system with a high signal-to-noise ratio and reduced background noise for PA wave form recording. [ABSTRACT FROM AUTHOR]

Abstract: We report three new laser materials. Nd3+-doped Ba(Zr, Mg, Ta)O3 ceramic indicates a broadband luminescence spectrum due to its disordered structure. By optimizing the manufacturing process and laser configuration, high output power and high slope efficiency operation was obtained. Nd3+(Na+):Ca2MgSi2O7 shows another type of spectral broadening caused by its structural modulation. In the input–output property, an anomalous behavior due to phase transition was observed. Yb3+:Lu3Al5O12 is one of the important laser materials for thin-disk laser because it indicates mild reduction of the thermal conductivity as an increase of concentration. The highly efficient CW laser operation is reported. [Copyright &y& Elsevier]

Angularly selective mirrors (ASMs) are proposed as a means to expand the mode area and modal discrimination of microchip lasers. ASMs used as output couplers selectively reflect incoming k vectors over a narrow angular range, while they transmit more inclined components. The eigenvalue problem of a microchip resonator equipped with a Gaussian ASM is solved analytically, in the paraxial optics approximation using the ABCD matrix formalism. The narrow angular distribution of the reflected beam produces, through the laws of diffraction, a significant increase of the mode size and improved transverse mode discrimination, at the expense of higher oscillation threshold due to larger output coupling losses. Simulations performed using the parameters of Yb3+ -doped YAG material show that one order of magnitude increase of the mode area can reasonably be achieved without causing overheating and thermal fracture. ASMs can be directly deposited on the active material in the form of a resonant grating mirror. This technology involves only planar batch processes that retain the mass production advantage of microchip lasers. The significant increase of brightness of microchips expected from this innovation will give rise to more effective and more compact devices and new applications. [ABSTRACT FROM AUTHOR]

Laser-diode pumped nearly diffraction-limited beam quality (M2<1.05), high peak power, subnanosecond passively Q-switched Yb:Y3Al5O12 ceramic miniature laser with Cr4+:Y3Al5O12 ceramic as saturable absorber has been achieved. The slope efficiency is as high as 36% for 80% initial transmission of Cr4+:Y3Al5O12 ceramic. The pulse width of 335 ps and peak power of over 150 kW at repetition rate of 5 kHz were obtained. Laser oscillates at single-longitudinal-mode oscillation and wide-separated multilongitudinal-mode oscillation due to the combined etalon effect of the Cr4+:YAG thin plate and thin glass plate as output coupler. [ABSTRACT FROM AUTHOR]

Abstract: Transparent chromium-doped Y3Al5O12 ceramics were fabricated. The absorption and emission spectra of these ceramics were measured at room temperature. The absorption and emission spectra of Cr:Y3Al5O12 ceramics varied with annealing conditions. By high-temperature annealing, the absorption intensity increased, and its peak wavelengths changed from 430nm and 600nm to approximately 465 nm and 612nm, respectively, because the valence changed from Cr3+ to Cr4+. For the samples, emissions from both Cr3+ and Cr4+ ions were detected. However, emission from only the Cr3+ ions was observed in samples that annealed at low temperature or unannealed. [Copyright &y& Elsevier]

Abstract: A Nd3+:Y3Al5O12 ceramic laser under the hard-UV cutting condition of Xe flashlamp pumping was demonstrated for the first time. By using a 16.4kW Xe flashlamp and a samarium-doped flow tube, an average laser output power of 386W was obtained at 1064nm with a 1.1at.% Nd3+:Y3Al5O12 ceramic rod of Ø10mm×152mm. The slope efficiency was measured to be 2.3%, which was the same as for a Nd3+:Y3Al5O12 single crystal rod of similar size. The degradation of output power by the solarization effect was found to be negligible when the UV radiation below 350nm wavelength was cut by a Sm:glass flow tube. [Copyright &y& Elsevier]

Abstract: We describe experiments on warm dense plasmas created with an ultra-short pulse UV laser, and probed with short pulses of various frequencies. The reflected probe pulse is analyzed to give the three Stokes’ parameters which describe its elliptic polarization. From this data,—we infer the dielectric function of the warm dense plasma, taking account of its non-uniform density–temperature structure. In the experiments, we can identify an early time period when the plasma has not yet expanded significantly. In this first phase, the Fresnel formulas uniquely determine the dielectric function of hot solid-density matter from any two of the measured signals. Comparing reconstructed signals to the observed Stokes’ parameters we can determine the time (usually a few 100fsec) after which surface expansion becomes important. In the second phase , the plasma expansion is appreciable and must be modeled with analytical or numerical hydrodynamics. Comparing to experiment, we can approximately determine the plasma dielectric function. We find the free electron contribution to the dielectric function is often much less than expected from the usual Spitzer-Drude theory. Studies of dependence of probe reflection on probe laser frequency may enable us to extract the DC electrical conductivity from measured AC optical constants. New scattered-light measurements identify the onset of condensation of the expanding plasma and the formation of droplets of liquid metal. [Copyright &y& Elsevier]

he dynamic and laser characteristics of the self-Q-switched Crk,Yb:YAG laser were studied by solving the coupled rate equations; the effects of the pump rate, reflectivity of the output couplers and the concentrations of the saturable absorbers on the laser performance were investigated in detail and the numerical simulation of the Cr,Yb:YAG lasers was in good agreement with the experimental data. Better laser performance of the Cr,Yb:YAG self-Q-switched laser can be obtained by using high pump rate, higher concentration of the saturable absorber and suitable reflectivity of the output coupler according to our numerical calculations. A typical self-Q-switched laser pulse of 269.5 µJ pulse energy with 319 ps pulse width (FWHM) at a repetition rate of 3.1 kHz can be obtained with a monolithic laser cavity, which results in 843.5 kW peak power. [ABSTRACT FROM AUTHOR]

Explores the properties of double-color high-power continuous wave Raman fiber laser. Interaction of fiber lasers with phosphosilicate and fiber Bragg grating (FBG) mirrors; Simulation of Raman scattering; Assessment of the mirror reflexivity of FBG.

Provides information on a study which realized a high-power singlemode Raman fiber laser (RFL) using continuous wave fiber laser as a pump. Power conversion efficiency of RFL; Output characteristics of the RFL; Fiber length and output coupler reflectivity.

Crystalline-orientation and pump dependent polarization states of Yb:Y3Al5O12 microchip lasers were observed experimentally. Linear polarization was observed at six crystalline orientations in the (111) plane relative to the beam propagation direction along the [111] crystalline axis of Yb:Y3Al5O12 crystal. The extinction ratio of the linear polarization decreases and the laser tends to oscillate at random polarization state at high pump power levels. Linear polarization states of Yb:Y3Al5O12 microchip laser was selected by the anisotropic spectroscopic properties of the Yb3+-ion in cubic Y3Al5O12 crystal. The random polarization oscillation at high pump power was caused by the strong thermal-induced birefringence and depolarization. [ABSTRACT FROM AUTHOR]

Reversible jump of thermal emission accompanied with jump of photocurrent is observed in highly doped Yb3+:Y2O3 and Lu2O3 bulk ceramics pumped at 940 nm wavelength. In contrast, when these materials are heated with a CO2 laser at 10.6 μm wavelength, only a gradual increase of thermal emission and photoconductivity are observed up to the melting point. These results are interpreted as a ytterbium mediated, photoassisted avalanche of thermal emission. [ABSTRACT FROM AUTHOR]

Composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramics were fabricated by using vacuum sintering technique and nanocrystalline technology. Self-Q-switched composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic lasers with pulse energy of 125 μJ and peak power of over 105 kW at repetition rate of 3.8 kHz have been demonstrated. Nearly diffraction-limited beam quality with M2 less than 1.35 was achieved in this composite Yb:Y3Al5O12/Cr:Y3Al5O12 ceramic self-Q-switched lasers. [ABSTRACT FROM AUTHOR]

Low-threshold and highly efficient continuous-wave (cw) Yb3+:Y3Al5O12 (Yb:YAG) ceramic laser with near-diffraction-limited beam quality was demonstrated at room temperature. Dual-wavelength operation at 1030 and 1049 nm with 5% transmission of the output coupler was achieved by varying pump power intensity. Slope efficiencies of 79% at 1030 nm and 67% at 1049 nm were achieved for 1-mm-thick Yb:YAG ceramic plate (CYb=9.8 at. %) under cw laser-diode pumping. The effect of pump power on the laser emission spectra of both wavelengths is addressed. Excellent laser performance indicates that Yb:YAG ceramic laser materials could be potentially used in high-power solid-state lasers. [ABSTRACT FROM AUTHOR]

Low-threshold and highly efficient continuous-wave laser performance of Yb:Y3Al5O12 (Yb:YAG) single crystal grown by a temperature gradient technique (TGT) was achieved at room temperature. The laser can be operated at 1030 and 1049 nm by varying the transmission of the output coupler. Slope efficiencies of 57% and 68% at 1049 and 1030 nm, respectively, were achieved for 10 at. % Yb:YAG sample in continuous-wave laser-diode pumping. The effect of pump power on the laser emission spectrum of both wavelengths is addressed. The near-diffraction-limited beam quality for different laser cavities was achieved. The excellent laser performance indicates that TGT-grown Yb:YAG crystals have very good optical quality and can be potentially used in high-power solid-state lasers. [ABSTRACT FROM AUTHOR]

The dependences of the observed maximum proton energy on laser fluence, and the type and thickness of the target material were studied. The maximum proton energy depended on the laser fluence rather than on the laser intensity for laser pulses with energies between 40 and 430 mJ and pulse durations between 55 and 400 fs. The maximum proton energy increased as the product of target thickness and target mass density decreased. When a polyimide tape target of 7.5 μm thickness was irradiated, the observed maximum proton energy and flux, counted as the number of etched tracks with a solid angle of 0.25 sr, were 3.3±0.1 MeV and 4×106/MeV/shot, respectively. For efficient proton acceleration when a wide ion emission angle is acceptable, polyimide was suitable for the tape target because it contains much hydrogen, and furthermore, it has a low mass density and a high tensile strength. [ABSTRACT FROM AUTHOR]

We demonstrated an LG 01 -mode vortex Ti:Sapphire laser by utilizing an intracavity spot defect for spatial filtering. At the 140-μm diameter of spot defect, the power of vortex laser output reached 135 mW, and the slope efficiency of laser was 17.7%. The effects of the sizes of spot defects on the transverse laser modes and laser powers were also discussed. [ABSTRACT FROM AUTHOR]

A pulsed relativistic electron beam with a 3 ns duration was produced using Febetron 706 and electron beam tube with velvet cathode. Cathode current density of 7 kA/cm² and lifetime of longer than 1000 shots were obtained. [ABSTRACT FROM AUTHOR]

Lead carbonate chloride, Pb2CO3Cl2, known as mineral phosgenite, is introduced as a novel SRS-active carbonate crystal with tetragonal symmetry. Under picosecond one-micron laser pumping Raman-induced χ(3)-nonlinear generation in the near-IR is observed. All recorded high-order Stokes and anti-Stokes sidebands are identified and attributed to two SRS-promoting vibration modes with ωSRS1 ≈ 1062 cm-1 and ωSRS2 ≈ 86 cm-1. [ABSTRACT FROM AUTHOR]

Abstract: The excitation of vector modes in a few-mode fiber by varying the polarization states of Gaussian incident beam at different off-axis conditions was investigated. As a result, the linearly polarized incidence orientated at four different off-axis conditions excited radially polarized TM01 mode, azimuthally polarized TE01 mode, hybrid polarized HE21 mode, or linearly polarized two-lobe mode separately. Further, the left/right circularly polarized incidence excited linearly polarized two-lobe mode and the excited mode was interpreted as the combination of HE21 and TM01 (/TE01) modes with equal amplitude. The left/right elliptically polarized incidence excited the two-lobe mode with the crescent conglutination between each pair of lobes and the excited mode was interpreted as the combination of HE21 mode and TM01 (or TE01) mode with unequal amplitude. [Copyright &y& Elsevier]

Efficient high-gain many-phonon steady-state stimulated Raman scattering (SRS) was excited in the novel χ(3)-active organic crystal of di-glycine nitrate (DGN), (NH2CH2COOH)2 · HNO3, at room temperature under picosecond laser pumping in the visible and near-IR regions. Besides high-order Stokes and anti-Stokes (comb) generation in this centrosymmetric crystal, several cascaded and cross-cascaded χ(3) ↔ χ(3) nonlinear photon-phonon interactions were observed. The recorded Raman-induced lasing wavelengths were identified and attributed to the SRS-promoting optical vibration modes ωSRS1 ≈ 1058 cm−1, ωSRS2 ≈ 2985 cm−1, ωSRS3 ≈ 895 cm−1, and ωSRS4 ≈ 3000 cm−1. The measured large Raman frequency shifts (≈3000 cm−1) and estimated moderately high steady-state Raman gain coefficients ( $g_{{\rm ssR}}^{{\rm St}_{1} } $ ≥ 6.5 cm · GW−1) make this DGN crystal attractive for a number of new applications in modern laser physics and nonlinear optics. [ABSTRACT FROM AUTHOR]

Abstract: Participatory adaptive management is widely promoted as the new paradigm in public lands management. It is grounded in two underlying principles – that management experiments and diverse sources of information should be used to continually refine management in complex ecological systems, and that the public must be included throughout the adaptive management process. Access to scientific results and exchange of information is at the core of both of these principles. The recent proliferation of Internet communities and web-based participation tools raises the question of how the Internet might help facilitate information exchange in participatory adaptive management. Using a case study approach, the role of web technologies in facilitating the flow of transparent and useful information was examined in a participatory adaptive management project focused on Forest Service vegetation management treatments in California''s Sierra Nevada. Three evaluation methods were used: analysis of web usage and content, a survey of active participants, and a review of comments posted to the project website. Results suggest that the web played an important role throughout the adaptive management cycle by supporting communication through disseminating information to the public and increasing the transparency of the scientific process. The web played a small, but important role in public consultation, by providing a forum for targeted questions and feedback from the public. Internet technology did not actively support the two-way flow of information necessary for mutual learning. Web technology complements face-to-face interactions and public meetings, rather than replacing them. [Copyright &y& Elsevier]

Over the last twenty years, diode pumping of solid-state lasers has opened new prospects for the mode control and formation of Laguerre-Gaussian (LG) beams, enabling a large variety of applications. Experiments on scalar and vector LG modes selection in Nd- and Yb-doped ceramics and crystal lasers carried out at the Institute for Laser Science, Tokyo are reviewed. Selection of LG modes from low to high orders using intra-cavity elements, polarization-selective mirrors, or shaping the pump beam profile, is considered. Illustrations of record-high-order LG hollow modes, multiring modes with highly directional propagation properties, characteristics of cw and pulsed lasers with radially or azimuthally polarized beams of high polarization purity are presented. General solutions of the wave equation for the axi-symmetric electric field, which describe LG beams of various profiles, are proposed for data analysis. In parallel, a short review on LG modes selection studies carried out at other laboratories is given. [ABSTRACT FROM AUTHOR]

Abstract: Continuous-wave and passively Q-switched microchip laser performance of Yb:YAG ceramics and single-crystals was investigated. Highly efficient continuous-wave Yb:YAG laser performance was observed at 1030nm and 1049nm for both Yb:YAG ceramics and crystals with different transmissions of output couplers. The laser performance of Yb:YAG ceramic is comparable to that of Yb:YAG single crystal. Meanwhile, the laser performance of laser-diode pumped Yb:YAG/Cr4+:YAG all-ceramics- and all-crystals-combination passively Q-switched microchip lasers were investigated. Sub-nanosecond laser pulses with peak power over 150kW were obtained with different Yb:YAG/Cr4+:YAG combinations. Linearly polarized laser was observed in Yb:YAG/Cr4+:YAG all-crystals combination and circular polarized laser was obtained in Yb:YAG/Cr4+:YAG all-ceramics combination. The best laser performance was obtained with Yb:YAG/Cr4+:YAG all-crystals combination. [Copyright &y& Elsevier]

Abstract: A short-focus glass lens with strong spherical aberration was used for mode selection in the cw LD-end-pumped Yb:YAG ceramic laser. Sequence of low to very high order Laguerre–Gaussian (LGpl) modes with different combinations of radial, p and azimuthal, l indices (p ⩽10, l ⩽28), with output beam diameters 2–13mm and power up to 30mW was obtained. Peaked and hollow multi-ring beams with near-diffraction free propagation of the central minimum or maximum over 40m distance from the laser resonator were observed. Mechanisms of mode selection and possible applications of the proposed laser scheme are considered. [Copyright &y& Elsevier]

Abstract: Yb-doped fiber laser operating at the long-wavelength edge (1150–1200nm) of the broad gain spectrum has been investigated for yellow-orange sources. Power scaling in this region has been recently achieved by Yb-doped solid-core photonic bandgap fibers, in which the Yb gain profile is engineered by the sharp-cut, bandpass distributed filtering and therefore amplified spontaneous emission in the high-gain region (1030–1100nm) is strictly inhibited. We have recently demonstrated amplification with as high as 167W output power and 61% slope efficiency at 1178nm. The novel gain profiling technique by photonic bandgap fibers can be extended to other rare-earth doped fibers. [ABSTRACT FROM AUTHOR]

Abstract: Transparent laser quality cerium codoped Nd: YAG ceramics were prepared using nanotechnology assisted ceramic preparation technique. The sample shows a very good transparency with a strong absorption peaks corresponding to Ce and Nd ions. Lasing oscillation was observed at IR laser wavelength of Nd emission with a maximum slope efficiency of 17.6%. Cross-energy transfer mechanism between these two ions was analyzed using 407nm laser diode. Quantum yield of both the ions was calculated with an integrating sphere and UV-laser diode and the results were compared with Nd: YAG ceramics. The results show the efficient energy transfer between Ce3+ and Nd3+ and the transfer mechanism has been explained with the energy level diagrams. [ABSTRACT FROM AUTHOR]

Abstract: The recent development of ceramic laser materials is probably the most important innovation in the field of laser material fabrication technology. Recently, we have been able to fabricate highly transparent neodymium doped Y3Al5O12 ceramics as solid-state laser materials by the vacuum sintering technique and nanocrystalline technology. The optical properties and microstructure of those ceramics were investigated. Flashlamp-pumped laser operation with the ceramic rod was demonstrated. Laser diode (LD) pumped composite ceramic laser was also demonstrated. [Copyright &y& Elsevier]

Abstract: We have developed a practical and precise frequency measurement system at 1.5μm telecommunication band. An electro-optic-modulator based optical frequency comb is phase-locked to a dither-free acetylene-stabilized laser to realize an optical frequency comb with frequency uncertainty of 10kHz (5×10−11) and the linewidth of 15kHz. The present frequency comb can be also used as an optical frequency reference grid defined by ITU-T (International Telecommunication Union, Telecommunication Standardization Sector). Using the present frequency measurement system, we have demonstrated the first optical frequency measurement of 12C16O overtone absorption lines around 1.56μm with the uncertainty of lower than 900kHz. [Copyright &y& Elsevier]

Abstract: The transient temperature profile in CW- and end-pumped passively Q-switched (PQS) microchip laser is investigated qualitatively by treating the population inversion (thereby the thermal load) as the sawtooth function of the time. The numerical results reveal not only the dynamics of thermal buildup, but also the dependence of the quasi-steady-state temperature rise and the repetitively oscillatory amplitude on the incident pump power and the pulse repetition rate of PQS laser. The abruptly ascending branch of the repetitive temperature oscillation is synchronized with the pulsing stage of PQS laser. As the result, the abrupt temperature transition during the pulsing stage would introduce the fluctuation into the PQS pulse parameters (pulse energy, pulse width, and peak power) via temperature-dependent stimulated emission and thermal lensing effect. [Copyright &y& Elsevier]

The article examines the results of heat transfer measurements in polycrystalline Y3Al5O12 garnets as well as Y2O3 and Lu2O3 sesquioxide materials obtained via self-energy-driven sintering of nanoparticles. It was observed that the average phonon mean free path in Y3Al5O12 is much bigger than the average grain size and to scale with temperature as T-2 at low temperature.

Abstract: Stable longitudinal multi-mode chromium and ytterbium co-doped Cr,Yb:YAG self-Q-switched laser formed by a plano-concave resonator has been demonstrated at room temperature without cooling system. An average output power of as much as 70mW at 1.03μm with a pulse width (FWHM) as short as 12.3ns was obtained with 5% transmission output coupler. High beam quality (M 2 <2.4) output with transverse gaussian profile was obtained. The non-linear mode coupling effects of this longitudinal multi-mode laser was investigated and stable pulse sequence was attributed to the non-linear mode coupling effects between main mode oscillation and the side-mode oscillation. [Copyright &y& Elsevier]

The production of energetic protons using a polyimide tape of 7.5 μm thickness was carried out with laser pulses of 30 mJ energy and 80 fs duration. A deformable mirror system with a genetic algorithm (GA) was developed to optimize the laser-focusing spot. The fitness values used in the GA were measured from the focusing intensities under the low-gain condition of the power amplifier, or from x-ray in situ signals emitted from the target. Although we obtained a diffraction-limited size of 2 μm (full width at half maximum) using the former value, a precise compensation using the latter value was essential to accelerate protons whose flux was 106/MeV/shot to a maximum energy of 1.1±0.3 MeV with laser pulses of only 30 mJ energy since a laser spot that is too tight may be sensitive to wave-front distortion caused by residual thermal lenses of the power amplifier. [ABSTRACT FROM AUTHOR]

A Nd:YAG rod active element placed inside a resonator was pumped by the second harmonic radiation (the wavelength A = 0.532 μm) of a Q-switched Nd:YAG laser diffracted at a circular aperture. Various distributions of pumping intensity in the Fresnel (near-field) region along the direction of the pump beam diffraction were produced. Inversion profiles with maxima or minima at the resonator axis were formed in the active element, depending on its distance from the circular aperture. Gain-switched operation of the Nd:YAG rod laser at λ = 1.064 μm is reported at the fundamental mode and also at the TEM01 TEM01, and other higher-order modes for different positions of the active element in the near-field region. Applications of such diffractive optical pumping for the concentration of the pumping radiation into the active media and for laser beam profiling are discussed. [ABSTRACT FROM AUTHOR]

Transparent Er3+ doped YAG ceramic was prepared by the vacuum sintering technique. Scanning electron microscope and transmission electron microscope measurements reveal that the pore volume in our sample is approximately 1ppm, the average grain size is about 10μm and the grain boundary width is about 1nm. With the excitation of a 960nm laser diode, intense green and red upconversion emissions were observed in our sample. Based on the intensity dependence of the upconversion emissions on the pump power, the upconversion mechanisms were discussed. [Copyright &y& Elsevier]

Millimeter signal generation with high spectral purity and low phase fluctuations up to 100 GHz were demonstrated with an optical method in which two external-cavity laser diodes were phase-locked to an electro-optic modulator (EOM)-based optical frequency comb generator (OFCG). The additional phase noise caused from the cavity fluctuation in OFCG was completely canceled, and the phase noise of the heterodyne beat note of two LDs was determined only by that of the signal generator below offset frequency of 10 kHz. The detailed investigation of such a high frequency signal had never been done before, and the measured frequency of 100 GHz was limited only by the bandwidth of the phase noise detection system, and can be expanded up to more than 1 THz. [Copyright &y& Elsevier]

We propose a new concept for wavefront curvature sensing, which is based on diffraction grating and fractional Fourier transforms systems. An explicit formula is derived expressing the wavefront curvature, and the wavefront shape can also be retrieved rapidly. The experimental setup is presented and numerical simulations show the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Nd: YAG ceramic materials have been synthesize( using vacuum sintering technique with the raw materials prepared by the nano-crystalline methods. The spectroscopic studies suggest overall improvement in absorption and emission and reduction in scattering loss. Judd-Ofelt analysis has been employed to compute the relevant spectroscopic and radiative parameter of the material. The SEM and TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. fluorescence and Raman measurements reveal that the Nd3+ -doped YAG ceramic is almost equivalent to its single-crystal counterpart in its radiative and nonradiatjve properties. Individual Stark levels for 2s+ 1Lj manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd: YAG ceramic. Laser performance studies favor the use of high-concentration Nd: YAG ceramics in the design of an efficient microchip laser. With 4 at% Nd: YAG ceramic acting as a microchip laser, we obtained a slope efficiency of 40%. High-power laser experiments yield an optical-to-optical conversion efficiency of 30% for Nd (0.6 at % ):YAG ceramic as compared to 34% for an Nd (0.6 at%):YAG single crystal. The oscillation experiments at 1.3 pm gives a slope efficiency of 35%. Optical gain measurements conducted in these materials also show values comparable to single crystal, supporting that these materials could be suitable substitutes to single crystals in solid-state laser applications. [ABSTRACT FROM AUTHOR]