John B. Tassano

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.

YTTERBIUM-DOPED APATITE-STRUCTURE CRYSTALS : A NEW CLASS OF LASER MATERIALS

A new class of Yb‐lasers is summarized in this article. The apatite family of crystals, based on the hexagonal structure of the mineral fluorapatite, has been found to impose favorable spectroscopic and laser properties on the Yb3+ activator ion. Crystals of Yb‐doped Ca5(PO4)3F, Sr5(PO4)3F, CaxSr5−x(PO4)3F, and Sr5(VO4)3F have been grown and investigated. Several useful laser crystals have been identified which offer a variety of fundamental laser parameters for designing diode‐pumped systems. In general, this class of materials is characterized by high emission cross sections (3.6–13.1×10−20 cm2), useful emission lifetimes (0.59–1.26 ms), a strong pump band (σabs=2.0–10.0×10−20 cm2), and pump and extraction wavelengths near 900 and 1045 nm, respectively. Efficient lasing has been demonstrated for several of the members of this class of materials, and high optical quality crystals have been grown by the Czochralski method. A summary of the laser parameters and a discussion of the Yb:apatite class of laser...

Laser, optical, and thermomechanical properties of Yb-doped fluorapatite

The laser performance of Yb-doped fluorapatite (Ca/sub 5/(PO/sub 4/)/sub 3/F or FAP), is assessed by employing a Ti:sapphire laser operating at 905 nm as the pump source. We have measured slope efficiencies to be as high as 79%; the residual decrement from the quantum defect-limited efficiency of 87% is accounted for by the presence of passive loss at the 1043-nm laser wavelength. The important spectral properties of Yb:FAP were evaluated, including the absorption and emission cross sections, excited-state lifetime, and ground-state energy-level splitting. The emission and absorption cross sections of Yb/sup +3/ in FAP are found to be substantially larger than those of other Yb-doped media. The thermal, physical, and optical properties of the FAP host are reported as well. >

Vibrational structure in the emission spectra of Yb3+-doped apatite crystals

Abstract We have determined the ground state energy levels of Yb 3+ in crystals with the apatite structure from the low temperature emission spectra of Yb-doped crystals of calcium, strontium and barium fluorophosphates, calcium chlorophosphate and strontium fluorovanadate. Analyses of the data reveal that the previously reported laser transition arises from an electronic level of Yb interacting with the local vibrational modes of the Yb-O bond.

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.

752 nm wing-pumped Cr:LiSrAlF/sub 6/ laser

The authors have demonstrated a LiSrAlF/sub 6/:Cr/sup 3+/ (Cr:LiSrAlF/sub 6/) laser pumped at 752 nm in the longwave wing of the /sup 4/A/sub 2/ to /sup 4/T/sub 2/ pump band. Measured optical, laser, and thermal properties of LiSrAlF/sub 6/-LiSrCrF/sub 6/ solid solutions indicate that efficient laser pumping can be achieved in the 750-780 nm region, and that AlGaAs laser diode arrays may be used to make efficient high-power diode-pumped tunable solid-state lasers. >

The mechanism of Tm to Ho energy transfer in LiYF4

The energy transfer properties of the Tm, Ho:LiYF4 are examined, and special attention is given to the Tm(3F4) to Ho(5I7) transfer dynamics and equilibration. The measured transfer times are compared with the values calculated on the basis of the static Forster-Dexter and the migration-assisted Burshtein energy transfer models (which require only spectral information and rare-earth concentrations as input data). The detection of anomalously fast measured transfer rates at high Tm doping levels is interpreted within the context of percolation theory, since migration pathways from the excited Tm ion to a Ho ion must necessarily exist above a particular threshold concentration. Lastly, it is suggested that the use of low Tm concentrations below the percolation threshold may serve to minimize the Auger upconversion losses, and also will shift the excited-state equilibrium to the Ho population; this type of scenario requires that the Tm ions be pumped directly into the 3F4 state with 1.68 mu m InGaAs diode sources.

First selective mode excitation and amplification in a ribbon core optical fiber

We propose and demonstrate amplification of a single high-order mode in an optical fiber having an elongated, ribbon-like core having an effective mode area of area of 600 µm(2) and an aspect ratio of 13:1. When operated as an amplifier, the double-clad, ytterbium doped, photonic crystal fiber produced 50% slope efficiency and a seed-limited power of 10.5 W, corresponding to a gain of 24 dB. The high order mode remained pure through 20 dB of gain without intervention or realignment.

Diode-pumped Nd:YVO 4 /Yb:S-FAP laser emitting at 985 and 492.5 nm

For the first time, to the best of our knowledge, Yb:S-FAP crystals have been intracavity pumped by a Nd:YVO(4) laser at 914 nm. This original pumping scheme allows efficient laser action on the three-level transition at 985 nm with 1.4 W output power. Second-harmonic generation is also presented with a total output power of 120 mW at 492.5 nm.