High power diode-pumped Nd³⁺ fibre laser

In the medical field high power fibre-coupled AlGaAs diode lasers operating around 800nm are already making an impact in surgery but for more specialised applications high powers at other wavelengths are required. It is an attractive idea to develop active fibres as add-ons to such fibre coupled diode systems increasing the range of applications of such devices at little extra cost and minimal additional complexity. Rare-earth-doped optical fibres exhibit the traditional advantages of a glass laser host of broad emission and absorption spectra but without the usual associated thermal problems. With fibre lasers wavelength selection and temperature stabilisation of the pump diode is unnecessary, and the emission spectra allows for broad tuning. Double-clad fibres comprising a doped core, usually single-moded located within a large multimode waveguide enable efficient pumping of fibre lasers with diode ways or diode bars. Fibre lasers can thus be considered as simple wavelength convertors and brightness enhancers for the high power but poorly specified output of diode sources. In the this paper we describe a multiwatt Nd3+ fibre laser pumped via a second cladding by the DIOMED 25 laser diode unit. This multi diode array source is designed for coupling up to 25 Watts of diode power into a plastic-clad silica fibre of 400µm diameter. The laser fibre which is a double-clad structure fabricated from lead-silicate glasses is interchangeable with the normal PCS delivery fibre. The device operates at 1.058µm with a slope efficiency >50% and a 150 times brightness enhancement. This laser though useful in itself is also a key intermediate laser for generation of high powers at other wavelengths. Tandem pumping of Tm3+ and Er3+/Yb3+ fibre lasers at 1.058µm enables efficient generation of 2.0µm and 1.55µm radiation respectively. In addition the Nd3+ laser can be operated close to 1.3µm and there are prospects for in-fibre frequency doubling of the 1.06µm line to generate a high power source in the green

Comment on 'arsenite and arsenate adsorption on ferrihydrite: Surface charge reduction and net OH- release stoichiometry' (multiple letters)

10.1021/es990573fEnvironmental Science and Technology33203695-3696ESTH

Distribution of cadmium in a cultivated soil in Britanny, France Distribuição de cádmio em solo cultivado na Bretanha, França

Cadmium (Cd) can be potentially toxic to the environment, and its bioavailability is related to the chemical forms it occurs in the soils. The distribution of Cd into the solid phase and its availability was investigated in a cultivated soil in Britanny, France. Cd sequential extraction was performed using a modified Tessier's sequential extraction protocol. Total content of Cd (n = 22 samples) ranged from 0.13 to 0.37 mg kg¹. Long term history of organic and mineral fertilizers application increased Cd concentration in the surface horizon. The fate of Cd was correlated with soil available P2O5 concentration and pH. The regression analysis (linear and non-linear) and Principal Component Analysis revealed the synergistic effect of P2O5 in the retention of Cd in cultivated soils. The following fractions' sequence was observed: bounded to Fe and Al oxides + phosphates > exchangeable > bound to organic matter » residual fraction.<br>O cádmio (Cd) pode ser tóxico no ambiente e sua biodisponibilidade está relacionada às formas químicas em que os metais se encontram no solo. Apresenta-se a distribuição deste metal na fase sólida de um solo cultivado na Bretanha, França, assim como fatores que influenciam sua disponibilidade. Foi realizada a extração sequencial do Cd utilizando o método Tessier, modificado. A concentração total de Cd, avaliada em 22 amostras, variou de 0,13 a 0,37 mg kg¹. O uso contínuo de fertilizantes orgânicos e minerais aumentou a concentração de Cd no horizonte superficial do solo. A distribuição do Cd foi relacionada à concentração de P2O5 disponível e ao pH. Análises de regressão (linear e não linear) e a Análise de Componentes Principais mostraram efeito sinérgico do P2O5 na retenção de Cd nos solos cultivados. O fracionamento apresentou a seguinte sequência: ligado a óxidos de Fe e de Al + fosfatos > trocável > ligado à matéria orgânica » residual