10 J operation of a conductive-cooled Yb:YAG active-mirror amplifier and prospects for 100 Hz operation.

We report, to the best of our knowledge, the highest power conductive-cooled active-mirror amplifier (CcAMA) using Yb:YAG with a pulse energy of 10 J. By using four liquid-nitrogen circulating cooled laser heads, we achieved a repetition rate, pulse energy, and average power of 33.3 Hz, 9.3 J, and 310 W, respectively. The problem of wavefront distortion, which is difficult to solve with a large-aperture active-mirror laser, is suppressed by using reinforcing materials with the same thermal expansion coefficient. We have confirmed that the wavefront distortion is small (0.15λ P-V per head) at 100 Hz operation, which paves the way for 100 Hz operation with the CcAMA concept.

Fast pulse train control using filled-aperture coherent beam combining for high-average-power laser systems.

This study demonstrates fast pulse train switching using a coherent polarization beam combiner with a phase difference detection (PDD) algorithm. Based on the highly stable feedback control obtained with the PDD algorithm, stable burst-mode extraction with an arbitrary duty cycle was achieved with a contrast ratio of 800:1 for a third-harmonic light (347 nm) of a 5 MHz pulsed Yb-doped fiber laser. The proposed method can be effectively used for high-speed switching in high-average-power pulsed laser systems.

Development of Ultra-Performance Liquid Chromatography with Post-Column Fluorescent Derivatization for the Rapid Detection of Saxitoxin Analogues and Analysis of Bivalve Monitoring Samples.

Saxitoxin (STX) and its analogues produced by toxic dinoflagellates accumulate in bivalves, and routine monitoring of bivalves is important to prevent cases of human poisoning. In this study, we describe a rapid detection method for the analysis of STXs using ultra-performance liquid chromatography with post-column fluorescent detection and to investigate water depths and sampling points optimal for shellfish toxin monitoring. Cultured scallops (Mizuhopecten yessoensis) and mussels (Mytilus galloprovincialis) were collected from various water depths and sampling points were used in this study. Irrespective of bivalve species, toxin concentrations in bivalves were lower at deeper water depths. The toxin concentrations of bivalves did not differ greatly when bivalves were collected from the same bay. Although the levels of contamination of bivalves with STXs can depend on various environmental and geographical factors, our findings are useful for formulating a sampling protocol for the prevention of harvesting contaminated shellfish.

600 W green and 300 W UV light generated from an eight-beam, sub-nanosecond fiber laser system.

We describe a sub-nanosecond pulse laser system that delivers high-average-power green and ultraviolet (UV) light. This system includes a front end, two modules each of which has four photonic crystal fiber main amplifiers, two sets of coherent beam combiners with efficiencies of 83 and 90%, and two sets of harmonic converters. A single beam was ultimately produced through polarization-beam combining. The maximum average output power was 955 W at the fundamental wavelength (1040 nm) with a 10 MHz repetition rate and 285 ps pulse duration. The M-square of the UV was 1.3. The average power of each of its harmonics is 600 W in green (520 nm) and 300 W in UV (347 nm). The nonlinear crystals were longitudinally cooled by Peltier devices for efficient harmonic conversion.

Spatial asymmetry of optical parametric fluorescence with a divergent pump beam and potential applications.

The spatial distribution of the optical parametric fluorescence generated in a negative uniaxial nonlinear crystal is asymmetric with respect to the pump when the pump beam has a slight divergence angle. The formation mechanism of this phenomenon and the influence of parameters were analyzed and discussed from a theoretical standpoint. Moreover, two potential applications of this phenomenon were experimentally demonstrated, showing the temporal contrast improvement of ultra-intense lasers and the intensity enhancement of special light sources induced by the optical parametric generation.

High-average-power green laser using Nd:YAG amplifier with stimulated Brillouin scattering phase-conjugate pulse-cleaning mirror.

We present a high-average-power green laser based on second harmonic conversion of a laser diode-pumped master oscillator Nd:YAG power amplifier system. The power amplifier chain includes a stimulated Brillouin scattering (SBS) cell that was used a phase-conjugate mirror to double-pass scheme. That suppresses the thermal phase distortion and compresses the pulse duration. The fundamental beam output power was 670 W with a pulse width of 7.9 ns. A second harmonic power of 335 W with a 4.8-ns pulse width and 80-mJ pulse energy was produced using a LiB3O5 (LBO) crystal.

Generation of sub-7-cycle optical pulses from a mode-locked ytterbium-doped single-mode fiber oscillator pumped by polarization-combined 915 nm laser diodes.

We report on a passively mode-locked ytterbium-doped fiber oscillator pumped by polarization-combined diodes emitting at a wavelength of 915 nm instead of 976 nm. Stable mode-locked operation based on nonlinear polarization evolution generated a broad spectrum of 140 nm, spanning from 950 to 1090 nm. The output power was 16.3 mW at a repetition rate of 93.1 MHz. External compression using a pair of transmission gratings resulted in pulse durations as short as 21.6 fs, which is equivalent to 6.6 cycle optical pulses at a wavelength of around 1000 nm.

Optical properties and Faraday effect of ceramic terbium gallium garnet for a room temperature Faraday rotator.

The optical properties, Faraday effect and Verdet constant of ceramic terbium gallium garnet (TGG) have been measured at 1064 nm, and were found to be similar to those of single crystal TGG at room temperature. Observed optical characteristics, laser induced bulk-damage threshold and optical scattering properties of ceramic TGG were compared with those of single crystal TGG. Ceramic TGG is a promising Faraday material for high-average-power YAG lasers, Yb fiber lasers and high-peak power glass lasers for inertial fusion energy drivers.

Dispersion compensation in an Yb-doped fiber oscillator for generating transform-limited, wing-free pulses.

We investigate the effect of dispersion compensation on temporal characteristics in mode-locking by nonlinear polarization rotation in an ytterbium-doped fiber (YDF) oscillator with intracavity and external grating pairs. A short fixed length YDF was spliced with a longer single-mode fiber (SMF). Using experimentally measured dispersion characteristics of the YDF, SMF and cavity optics, we control the group velocity dispersion (GVD) and spectral broadening in a cavity by changing the SMF length. As a result, the oscillator generated 29.4-fs transform-limited wing-free pulses, which are to our knowledge the shortest and cleanest pulses achieved without the use of additional optics like a prism pair for high-order dispersion compensation. The results show that a precise balance of higher order terms of the GVD and self-phase modulation is essential for shortening pulse duration.

A high-energy 160-ps pulse generation by stimulated Brillouin scattering from heavy fluorocarbon liquid at 1064 nm wavelength.

We have achieved a high compression ratio by stimulated Brillouin scattering (SBS) consisting of two long cells. A 13-ns Nd:YAG laser pulse was temporally compressed to about 160-ps phase-conjugated pulse in heavy fluorocarbon FC-40 liquid at a 1064 nm wavelength. The maximum reflectivity of SBS process was over 80 % without an optical damage. The compressed pulse brightness was about 65-fold higher than that of the incident pulse.

213 W average power of 2.4 GW pulsed thermally controlled Nd:glass zigzag slab laser with a stimulated Brillouin scattering mirror.

We report a high-average-power and high-pulse-energy diode-pumped Nd:glass laser amplifier system consisting of two thermally-edge-controlled zigzag slab amplifiers and a stimulated Brillouin scattering mirror. This phase-conjugated system produces an average power of 213 W at 10 Hz in a 8.9 ns pulse (2.4 GW peak power) with an optical-to-optical conversion efficiency of 11.7% and a near-diffraction-limited beam. To the best of our knowledge, this is the highest performance from a Nd:glass-based laser amplifier system ever built.

Cryogenic temperature characteristics of Verdet constant on terbium gallium garnet ceramics.

As the first demonstration of Faraday effect in a TGG ceramics, its Verdet constant at 1053 nm is evaluated to be 36.4 rad/Tm at room temperature which is same as that of the single crystal. In addition, the temperature dependence of Verdet constant is obtained experimentally. At liquid helium temperature, it is 87 times greater than that at room temperature.

Electron acceleration in an ultraintense-laser-illuminated capillary.

An ultraintense laser injected a 10 J of power at 1.053 microm in 0.5 ps into a glass capillary of 1 cm long and 60 microm in diameter and accelerated plasma electrons to 100 MeV. One- and two-dimensional particle codes describe wakefields with 10 GV/m gradient excited behind the laser pulse, which are guided by a plasma density channel far beyond the Rayleigh range. The blueshift of the laser spectrum supports that a plasma of 10(16) cm(-3) is inside the capillary. A bump at the high energy tail suggests the electron trapping in the wakefield.

360-W average power operation with a single-stage diode-pumped Nd:YAG amplifier at a 1-kHz repetition rate.

We report a high-average-power laser-diode-pumped Nd:YAG master oscillator power amplifier system that has a minimum number of elements in the single multipass zigzag-slab amplifier stage and is used to pump a high-peak-power and high-average-power Ti:sapphire laser system. This phase-conjugated system produces an average power of 362 W at 1 kHz in a 30-ns pulse with an optical-to-optical conversion efficiency of 14%. With an external KTP doubler this system generates 132 W of green average output power at 1 kHz with a conversion efficiency of 60% when pumped at a power level of 222 W. To the best of our knowledge these results represent the highest average output power at both infrared and green wavelengths achieved in a single amplifier stage.