Diode-Pumped Solid-State Lasers for Inertial Fusion Energy

We have begun building the Mercury laser system as the first in a series of new generation diode-pumped solid-state lasers for inertial fusion research. Mercury will integrate three key technologies: diodes, crystals, and gas cooling, within a unique laser architecture that is scalable to kilojoule and megajoule energy levels for fusion energy applications. The primary near-term performance goals include 10% electrical efficiencies at 10 Hz and 100J with a 2–10 ns pulse length at 1.047 m wavelength. When completed, Mercury will allow rep-rated target experiments with multiple chambers for high energy density physics research.     

Diode-pumped ytterbium-doped Sr5(PO4)3F laser performance

The performance of the first diode-pumped Yb³⁺-doped Sr ₅(PO₄)₃F (Yb:S-FAP) solid-state laser is discussed. An InGaAs diode array has been fabricated that has suitable specifications for pumping a 3×3×30 mm Yb:S-FAP rod. The saturation fluence for diode pumping was deduced to be 5.5 J/cm ² for the particular 2.8 kW peak power diode array utilized in our studies. This is 2.5× higher than the intrinsic 2.2 J/cm ² saturation fluence as is attributed to the 6.5 nm bandwidth of our diode pump array. The small signal gain is consistent with the previously measured emission cross section of 6.0×10^-20 cm², obtained from a narrowband-laser pumped gain experiment. Up to 1.7 J/cm³ of stored energy density was achieved in a 6×6×44 mm Yb:S-FAP amplifier rod. In a free running configuration, diode-pumped slope efficiencies up to 43% (laser output energy/absorbed pump energy) were observed with output energies up to ~0.5 J per 1 ms pulse. When the rod was mounted in a copper block for cooling, 13 W of average power was produced with power supply limited operation at 70 Hz with 500 μs pulses     

Cr2+-doped zinc chalcogenides as efficient, widelytunable mid-infrared lasers

Transition-metal-doped zinc chalcogenide crystals have recently been investigated as potential mid-infrared lasers. Tetrahedrally coordinated Cr²⁺ 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 ⁵E state are respectively ~10 μs and ~10^-18 cm². The associated absorption band peaked at ~1800 mm enables laser-diode pumping of the Cr²⁺ systems. Laser demonstrations with ZnS:Cr and ZnSe:Cr (using a MgF₂:Co²⁺ 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     

Preventing phage lysis of Lactococcus lactis in cheese production using a neutralizing heavy-chain antibody fragment from llama

Bacteriophage infection is still a persistent problem in large dairy processes despite extensive studies over the last decades. Consequently, new methods are constantly sought to prevent phage infection. In this paper, we show that phage neutralizing heavy-chain antibody fragments, obtained from Camelidae and produced at a large scale in the generally regarded as safe microorganism Saccharomyces cerevisiae, can effectively be used to impede phage induced lysis during a cheese process. The growth inhibition of the cheese starter culture by 10(5) pfu/ml cheese-milk of the small isometric-headed 936-type phage p2 was prevented by the addition of only 0.1 microg/ml (7 nM) of the neutralizing antibody fragment. The use of such antibody fragments in cheese manufacturing are a realistic and interesting option because of the small amount of antibody fragments that are needed. Moreover the antibodies are produced in a food grade microorganism and can easily be isolated from the fermentation liquid in a pure and DNA free form.     

Efficient laser operation of an Yb:S-FAP crystal at 985 nm

We have obtained three-level cw laser operation at 985 nm with a Yb-doped S-FAP bulk crystal pumped by a Ti:sapphire laser. An output power of 250 mW for an incident pump power of 1.45 W has been achieved, which is the highest cw output power ever obtained, to our knowledge, at this wavelength with a Yb-doped crystal. The experimental results are in good agreement with the numerical model that we have developed.     

Innovation and systems change: the example of mobile, collaborative workplaces

Forces such as increasing globalisation, demographic change, European enlargement, and the emergence of networked organisations stimulate the emergence of new forms of organisation and collaborative working. Mobility, sharing of information and knowledge, and collaboration across organisational networks are key aspects of workplace innovations. New information and communication technologies enable a diversity of future workplace scenarios. However, coping with the human and organisational aspects involved will determine their success or failure. In order to exploit the potential of workplace innovations we, therefore, must better understand their systemic nature. This article, based on the MOSAIC project, explores the potential of mobile and multi-location collaborative workplaces, investigates some future scenarios and roadmaps, and discusses the strategies and research approaches for systemic innovation.

Yb:S-FAP lasers

It has recently been reported that several high power, diode-pumped laser systems have been developed based on crystals of Yb:S-FAP [Yb³⁺:Sr₅(PO₄)₃F]. The mercury laser, at Lawrence Livermore National Laboratory, is the most prominent system using Yb:S-FAP and is currently producing 23 J at 5 Hz in a 15 nsec pulse, based on partial activation of the system. In addition, a regenerative amplifier is being developed at Waseda University in Japan and has produced greater than 12 mJ with high beam quality at 50 Hz repetition rate. Q-Peak has demonstrated 16 mJ of maximum energy/output pulse in a multi-pass, diode side-pumped amplifier and ELSA in France is implementing Yb:S-FAP in a 985 nm pump for an EDFA, producing 250 mW. Growth of high optical quality crystals of Yb:S-FAP is a challenge due to multiple crystalline defects. However, at this time, a growth process has been developed to produce high quality 3.5 cm diameter Yb:S-FAP crystals and a process is under development for producing 6.5 cm diameter crystals.     

Dy-doped chlorides as gain media for 1.3 μm telecommunicationsamplifiers

We propose that Dy³⁺-doped chloride crystals be considered as candidates for amplification of the 1.3 μm signal used by the telecommunications network. While several of these types of crystals can provide gain at the specified operating wavelength of 1.31 μm, and furthermore offer adequate bandwidth, we have focused our attention on LaCl₃: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 LaCl₃:Dy³⁺ Judd-Ofelt parameters are reported. Wavelength-resolved absorption and emission cross sections are presented for the 1.3 μm W&rlhar2;Z band. Pump-probe measurements (using 0.92 μm and 1.32 μm, respectively) prove that the observed gain properties of LaCl₃: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 μm telecom amplifier performance, although many fabrication issues would have to be addressed to produce a practical amplifier     

Crystal growth, frequency doubling, and infrared laser performanceof Yb3+:BaCaBO3F

Yb:BaCaBO₃F(Yb:BCBF) has been investigated as a new laser crystal with potential for self-frequency doubling, Yb³⁺ in BCBF exhibits a maximum absorption cross section at 912 nm of 1.1×10^-20 cm² with a bandwidth (FWHM) of 19 nm. The maximum emission cross section at 1034 nm is 1.3×10^-20 cm² with a transition bandwidth of 24 nm. The measured emission lifetime of Yb³⁺ 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 ⁺P for a relative measure of the second-harmonic generating potential, yielding d_eff(BCBF)~0.26 pm/V. The phasematching angle has been estimated from the refractive index data for type I second-harmonic generation of 0.517 μm light; the predicted angle is 37° from the c-axis. The growth, spectroscopy, laser performance, and linear and nonlinear optical properties of Yb:BCBF are reported     

Diode arrays, crystals, and thermal management for solid-statelasers

We summarize our efforts in the development of solid-state lasers, including the laser diode arrays, pump light delivery, approaches to thermal management, and novel gain media. Our interests are in developing unique solid-state lasers, including those operating at higher powers, offering less common wavelengths, and having other specialized features. In this paper, we discuss high-power Tm:YAG and Yb:YAG lasers. The gas cooled slab laser concept using Yb:S-FAP, and side-pumped Er:YAG and Cr:ZnSe lasers. We address the optical and thermal physics of these systems and also mention several additional gain media that have the potential of offering unique performance characteristics: Ce:LiSAF, APG-2 laser glass, Dy:LaCl₃, and Yb:BCBF