John A. Caird

Spectroscopic, optical, and thermomechanical properties of neodymium- and chromium-doped gadolinium scandium gallium garnet

Spectroscopic, optical, and thermomechanical properties of gadolinium scandium gallium garnet doped with trivalent neodymium and/or chromium are reported for use in the design of high-power solid-state lasers.

Quantum electronic properties of the Na/sub 3/Ga/sub 2/Li/sub 3/F/sub 12/:Cr/sup 3+/ laser

Few of the existing Cr/sup 3+/ vibronic lasers have achieved the slope efficiency and tuning range expected based on their known spectroscopic properties. To discover the cause of this behavior, the performance of chromium-doped gallium fluoride garnet, Na/sub 3/Ga/sub 2/Li/sub 3/F/sub 12/:Cr/sup 3+/, as a laser material has been investigated experimentally. The data reported include absorption and emission spectra, emission rates, quantum efficiency, laser wavelength tuning range, laser output slope efficiencies, and excited-state absorption spectra. Similar properties of the alexandrite laser material were studied for comparison. The results indicate that the performance of the gallium fluoride garnet laser is severely limited by Cr/sup 3+/ excited-state absorption (ESA). A model is presented to account for the unexpected nature of the ESA, which appears to be a common problem for all Cr/sup 3+/ vibronic lasers. Criteria are suggested for choosing Cr/sup 3+/ hosts for which the effects of ESA will be minimized. >

Demonstration of a 1.1 petawatt laser based on a hybrid optical parametric chirped pulse amplification/mixed Nd:glass amplifier

We present the design and performance of the Texas Petawatt Laser, which produces a 186 J 167 fs pulse based on the combination of optical parametric chirped pulse amplification (OPCPA) and mixed Nd:glass amplification. OPCPA provides the majority of the gain and is used to broaden and shape the seed spectrum, while amplification in Nd:glass accounts for >99% of the final pulse energy. Compression is achieved with highly efficient multilayer dielectric gratings.

An overview of LLNL high-energy short-pulse technology for advanced radiography of laser fusion experiments

The technical challenges and motivations for high-energy, short-pulse generation with the National Ignition Facility (NIF) and possibly other large-scale Nd : glass lasers are reviewed. High-energy short-pulse generation (multi-kilojoule, picosecond pulses) will be possible via the adaptation of chirped pulse amplification laser techniques on NIF. Development of metre-scale, high-efficiency, high-damage-threshold final optics is a key technical challenge. In addition, deployment of high energy petawatt (HEPW) pulses on NIF is constrained by existing laser infrastructure and requires new, compact compressor designs and short-pulse, fibre-based, seed-laser systems. The key motivations for HEPW pulses on NIF is briefly outlined and includes high-energy, x-ray radiography, proton beam radiography, proton isochoric heating and tests of the fast ignitor concept for inertial confinement fusion.

Spectroscopy and gain measurements of Nd 3+ in SrF 2 and other fluorite-structure hosts

We investigate the optical properties of Nd3+ in CaF2, SrF2, and BaF2 with the intent of determining whether any of these materials might usefully serve as a laser-pumped-amplifier medium. The Nd3+ impurities tend to cluster at low levels of doping in CaF2, leading to the formation of nonluminescent centers. The addition of La or Y buffer ions to CaF2:Nd serves to increase the luminescent yield, but it also renders the system spectrally inhomogeneous. Although single-ion centers predominate in BaF2, the interstitial fluoride compensator occurs at the next-nearest-neighbor position relative to Nd3+, leading to unsuitably low transition strengths. The interstitial fluoride occurs at the nearest-neighbor site of Nd3+ in SrF2 and thereby induces significant oscillator strength into the 4f–4f transitions by breaking the inversion symmetry. The radiative lifetime of SrF2:Nd is found to be 1470 μsec by measuring the emission lifetime and quantum efficiency; this value was confirmed by Judd–Ofelt analysis of the absorption features. The peak-emission cross section at room temperature was determined to be 1.7 × 10−20 cm at 1036.5 nm. A maximum of 0.20 at. % Nd3+ may be doped into SrF2 without the occurrence of significant Nd clustering. Direct measurements of the gain spectrum in SrF2:Nd reveal the presence of the 4F3/2 → 2G9/2 excited-state absorption, although its effect on the emission cross section is only minor.

Z-Beamlet: a multikilojoule, terawatt-class laser system

A large-aperture (30-cm) kilojoule-class Nd:glass laser system known as Z-Beamlet has been constructed to perform x-ray radiography of high-energy-density science experiments conducted on the Z facility at Sandia National Laboratories, Albuquerque, New Mexico. The laser, operating with typical pulse durations from 0.3 to 1.5 ns, employs a sequence of successively larger multipass amplifiers to achieve up to 3-kJ energy at 1054 nm. Large-aperture frequency conversion and long-distance beam transport can provide on-target energies of up to 1.5 kJ at 527 nm.

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).

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.

Measurements of losses and lasing efficiency in GSGG:Cr, Nd and YAG:Nd laser rods

Laser rods procured from four different vendors were examined to assess the state of the art in GSGG: Cr,Nd crystal growth. Measurement techniques included spectrophotometry (for absorption loss), interferometry (for distortion), polarimetry (for birefringence), and laser resonator insertion. Free running laser efficiency measurements were also performed. The level of losses characteristic of currently available GSGG:Cr,Nd laser rods was generally found to be much higher than that of commercially grown YAG:Nd. The intrinsic lasing efficiency of the co-doped GSGG rods, however, was typically found to exceed that of the YAG:Nd rods by more than a factor of 2.

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.