Kathleen I. Schaffers

Cr/sup 2+/-doped zinc chalcogenides as efficient, widely tunable mid-infrared lasers

Transition-metal-doped zinc chalcogenide crystals have recently been investigated as potential mid-infrared lasers. Tetrahedrally coordinated Cr/sup 2+/ ions are especially attractive as lasants on account of high luminescence quantum yields for emission in the 2000-3000-nm range. Radiative lifetimes and emission cross sections of the upper /sup 5/E state are respectively /spl sim/10 /spl mu/s and /spl sim/10/sup -18/ cm/sup 2/. The associated absorption band peaked at /spl sim/1800 mm enables laser-diode pumping of the Cr/sup 2+/ systems. Laser demonstrations with ZnS:Cr and ZnSe:Cr (using a MgF/sub 2/:Co/sup 2+/ laser pump source) gave slope efficiencies up to 30%. Excited-state-absorption losses appear small, and passive losses dominate at present. Tuning experiments with a diffraction grating produce a tuning range covering at least 2150-2800 nm. Laser crystals can be produced by Bridgman growth, seeded physical vapor transport, or diffusion doping. Zinc chalcogenide thermomechanical properties of interest for medium-to-high-power operation compare favorably with those of other host materials, except for the larger refractive-index derivative dn/dT.

Continuous-wave broadly tunable Cr2+:ZnSe laser.

We report room-temperature operation of an all-solid-state broadly tunable continuous-wave Cr(2+):ZnSe laser. Output power of 250 mW, an absorbed power slope efficiency of 63%, and continuous tunability from 2138 to 2760 nm are demonstrated.

Broadly tunable compact continuous-wave Cr 2+ :ZnS laser

We report the development of a continuous-wave, room-temperature Cr(2+) ZnS laser that is compact and tunable over 700 nm. The laser is pumped by a diode-pumped Er-fiber laser and generates 0.7 W of linearly polarized radiation at 2.35microm , at up to 40% slope efficiency. Cr(2+) ZnS directly diode-pumped at 1.6microm yields polarized radiation that is tunable over 400 nm at up to 25 mW of output power. A comparison of Cr(2+) ZnS with Cr ZnSe (70 mW, 350 nm) in a similar setup is given. As opposed to Cr ZnSe, the Cr ZnS laser is intrinsically polarized. Finally, we observe sensitization of the output radiation by a few milliwatts of the visible (470-500-nm) and near-infrared (740-770-nm) radiation.

The mercury project : A high average power, gas-cooled laser for inertial fusion energy development

Abstract Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 109 shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 × 6 cm2 ytterbium doped strontium fluoroapatite amplifier slabs pumped by eight 100 kW diode arrays. A portion of the output 1047 nm was converted to 523 nm at 160 W average power with 73 % conversion efficiency using yttrium calcium oxy-borate (YCOB).

Efficient broadly tunable continuous-wave Cr 2+ :ZnSe laser

An efficient continuous-wave Cr2+-doped ZnSe laser pumped by a Co:MgF2 laser is experimentally demonstrated. In a single-pass pump scheme we observed up to 520 mW at ∼2500 nm in 0.4-nm narrow-band operation, with 52% incident-power slope efficiency, and a tuning range between 2180 and 2800 nm. In the multipass pump scheme we also observed and analyzed the effect of dual Q-switching laser action at 1.75 and 2.5 µm in the Co:MgF2–Cr:ZnSe coupled-cavity oscillator. Finally, we report the measurement of the passive losses and of the ground-state absorption at the lasing wavelength.

Crystal growth, frequency doubling, and infrared laser performance of Yb/sup 3+/:BaCaBO/sub 3/F

Yb:BaCaBO/sub 3/F(Yb:BCBF) has been investigated as a new laser crystal with potential for self-frequency doubling, Yb/sup 3+/ in BCBF exhibits a maximum absorption cross section at 912 nm of 1.1/spl times/10/sup -20/ cm/sup 2/ with a bandwidth (FWHM) of 19 nm. The maximum emission cross section at 1034 nm is 1.3/spl times/10/sup -20/ cm/sup 2/ with a transition bandwidth of 24 nm. The measured emission lifetime of Yb/sup 3+/ is 1.17 ms. An Yb:BCBF laser has been demonstrated with a Ti:sapphire pump source, and a measured slope efficiency of 38% has been obtained for the fundamental laser output. Single crystal powders of BCBF have been compared with KD/sup +/P for a relative measure of the second-harmonic generating potential, yielding d/sub eff/(BCBF)/spl sim/0.26 pm/V. The phasematching angle has been estimated from the refractive index data for type I second-harmonic generation of 0.517 /spl mu/m light; the predicted angle is 37/spl deg/ from the c-axis. The growth, spectroscopy, laser performance, and linear and nonlinear optical properties of Yb:BCBF are reported.

High-average-power femto-petawatt laser pumped by the Mercury laser facility

The Mercury laser system is a diode-pumped solid-state laser that has demonstrated over 60 J at a repetition rate of 10 Hz (600 W) of near-infrared light (1047 nm). Using a yttrium calcium oxyborate frequency converter, we have demonstrated 31.7 J/pulse at 10 Hz of second harmonic generation. The frequency converted Mercury laser system will pump a high-average-power Ti:sapphire chirped pulse amplifier system that will produce a compressed peak power > 1 PW and peak irradiance > 1023W/cm2.

Compact, Efficient Laser Systems Required for Laser Inertial Fusion Energy

Abstract This paper presents our conceptual design for laser drivers used in Laser Inertial Fusion Energy (LIFE) power plants. Although we have used only modest extensions of existing laser technology to ensure near-term feasibility, predicted performance meets or exceeds plant requirements: 2.2 MJ pulse energy produced by 384 beamlines at 16 Hz, with 18% wall-plug efficiency. High reliability and maintainability are achieved by mounting components in compact line-replaceable units that can be removed and replaced rapidly while other beamlines continue to operate, at up to ˜13% above normal energy, to compensate for neighboring beamlines that have failed. Statistical modeling predicts that laser-system availability can be greater than 99% provided that components meet reasonable mean-time-between-failure specifications.

Dy-doped chlorides as gain media for 1.3 /spl mu/m telecommunications amplifiers

We propose that Dy/sup 3+/-doped chloride crystals be considered as candidates for amplification of the 1.3 /spl mu/m signal used by the telecommunications network. While several of these types of crystals can provide gain at the specified operating wavelength of 1.31 /spl mu/m, and furthermore offer adequate bandwidth, we have focused our attention on LaCl/sub 3/:Dy as an illustrative case to explore in greater depth. Spectroscopic measurements were made on un-oriented samples of this material; excited-state lifetimes and LaCl/sub 3/:Dy/sup 3+/ Judd-Ofelt parameters are reported. Wavelength-resolved absorption and emission cross sections are presented for the 1.3 /spl mu/m W/spl rlhar2/Z band. Pump-probe measurements (using 0.92 /spl mu/m and 1.32 /spl mu/m, respectively) prove that the observed gain properties of LaCl/sub 3/:Dy are consistent with those predicted on the basis of the spectroscopic cross sections. The Dy:chloride gain media appear to have fundamental optical characteristics amenable to superior 1.3 /spl mu/m telecom amplifier performance, although many fabrication issues would have to be addressed to produce a practical amplifier.

Comparison of Nd:phosphate glass, Yb:YAG and Yb:S-FAP laser beamlines for laser inertial fusion energy (LIFE) [Invited]

We present the results of performance modeling of diode-pumped solid state laser beamlines designed for use in Laser Inertial Fusion Energy (LIFE) power plants. Our modeling quantifies the efficiency increases that can be obtained by increasing peak diode power and reducing pump-pulse duration, to reduce decay losses. At the same efficiency, beamlines that use laser slabs of Yb:YAG or Yb:S-FAP require lower diode power than beamlines that use laser slabs of Nd:phosphate glass, since Yb:YAG and Yb:S-FAP have longer storage lifetimes. Beamlines using Yb:YAG attain their highest efficiency at a temperature of about 200K. Beamlines using Nd:phosphate glass or Yb:S-FAP attain high efficiency at or near room temperature.