LLE Review 106

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Highlights

This volume of the LLE Review, covering January–March 2006, features a description of the characteristics and performance of a high-gain, polarization-preserving, Yb-doped fiber amplifier for low-duty-cycle pulse amplification. The authors report on a high-gain, low-noise, double-pass ytterbium-doped amplifier for which amplified spontaneous emission (ASE) suppression techniques were utilized to fabricate a double-pass amplifier with the noise properties of a single-pass amplifier. A double-pass configuration allows for significantly higher gains to be obtained in a fiber amplifier than can be achieved in a single-pass configuration. Simulations based on a rate equation model were used to analyze the ASE and the impact of the suppression techniques. These techniques were implemented in an alignment-free, double-pass fiber amplifier with 26-dB gain at a wavelength 23 nm off the gain peak and a –48-dB noise floor, while amplifying linearly polarized optical pulses with a low duty cycle.

Additional highlights of research presented in this issue include the following:

• Development of methods and techniques for the decontamination of metals and alloys from tritium is reported. The efficacy of tritium removal from stainless steel using four different approaches has been studied: thermal desorption in a dry inert gas purge, thermal desorption in a wet inert gas purge, thermal desorption in an inert gas purge containing hydrogen peroxide, and radio-frequency-driven argon plasma irradiation. This study indicates that reducing the activity in metals below 0.5 µCi/g is feasible without generating secondary active waste byproducts other than water.
• A review of the basic concept of laser-driven ICF ignition is presented with emphasis on the direct-drive ignition target designing, requirements for the temporal shape of the laser pulse, and consideration of the stability issues.
• The results on direct-drive implosions of targets filled with different mixtures of D₂ and ³He gas on the OMEGA Laser System are reported. At temperatures above a few electron volts, D₂ and ³He gasses are fully ionized and hydrodynamically equivalent fuels with different ratios of D₂ and ³He can be chosen to have the same mass density, total particle density, and equation of state. Implosions with a 50/50 mixture of D:³He by atom consistently result in measured nuclear yields half of that anticipated by scaling from measured yields of implosions with pure D₂ and nearly pure ³He. This observation is seen over a wide range of experimental configurations, including targets with a variety of shell thicknesses and fill pressures, simultaneously for two different nuclear yields (D-D and D-³He), as well as for shock and compression yields. A number of possible mechanisms to cause the scaling are considered, but no dominant mechanism has been identified.
• Deterministically polarized fluorescence from single emitters (dye molecules) is demonstrated for the first time. In this experiment a planar-aligned, nematic liquid-crystal host provides uniaxial alignment of single-dye molecules in a preferred direction. As a result, fluorescence of these single emitters is deterministically polarized (single-photon source) which allows one to consider such systems for applications in photonic quantum information.
• The performance of the fiber-coupled single-photon detectors based on NbN superconducting nanostructures for practical quantum cryptography and photon-correlation studies is described. Several two-channel, single-photon detector systems based on two fiber-coupled superconducting single-photon detectors were built and characterized. The best device reached the system quantum efficiency of 0.3% in the 1540-nm telecommunication wavelength with a fiber-to-detector coupling factor of about 30%.
• The results on design and synthesis of transition metal dithiolene near-IR dyes are presented. Transition metal complexes based on nickel, palladium, or platinum dithiolene cores show substantial promise for guest–host liquid crystal devices operating in the near- to mid-IR region. The authors show some specific application examples for these materials in LC electro-optical devices and discuss the most recent results in the computational modeling of physical and optical properties of this interesting class of organometallic optical materials.