Experimentally verified modeling of erbium-ytterbium co-doped DFB lasers

For the first time, the simulation results of fiber distributed feedback (DFB) lasers are compared against experimental data in this paper. The pump source, active medium, and grating are all modeled and simulated to predict actual laser characteristics. Simple characterization methods are illustrated for the measurement of model parameters. Large loss at the pump wavelength is observed, attributed to the lifetime quenching of Yb ions, and included in the model as a critical parameter. DFB lasers with two different apodization profiles successfully simulated with the same set of model parameters

A multilevel analysis of three randomised controlled trials of the Australian Medical Sheepskin in the prevention of sacral pressure ulcers.

Objective: To assess the effectiveness of the Australian Medical Sheepskin in preventing sacral pressure ulcers (PUs), based on combined data from existing published trials. Design and setting: Data from two randomised controlled trials (RCTs) among Australian hospital patients and one RCT among Dutch nursing home patients were pooled, comprising a total population of 1281 patients from 45 nursing wards in 11 institutions. These data were analysed in two ways: with conventional meta-analysis based on the published effect sizes; and with multilevel binary logistic regression based on the combined individual patient data. In the multilevel analysis, patient, nursing ward and institution were used as levels and we controlled for sex, age, PU risk and number of days of observation. Main outcome measure: Incidence of sacral PUs. Results: Overall, the incidence of sacral PUs was 12.2% in the control group versus 5.4% in the intervention group with an Australian Medical Sheepskin. Conventional meta-analysis showed significantly reduced odds of developing a PU while using the sheepskin (odds ratio [OR], 0.37 [95% CI, 0.17–0.77]). Multilevel analysis gave an OR of 0.35 and narrowed the confidence interval by almost 50% (95% CI, 0.23–0.55). Conclusions: These analyses of pooled data confirm that the Australian Medical Sheepskin is effective in preventing sacral PUs. Multilevel analysis of individual patient data gives a more precise effect estimate than conventional meta-analysis. (aut. ref.

'Australische medische schapenvacht' ter preventie van decubitus: meta-analyse met individuele patiëntendata toont effectiviteit

OBJECTIVE: To assess the effectiveness of the Australian Medical Sheepskin (AMS) on the prevention of sacral pressure ulcers based on combined data from 3 previously published trials. DESIGN: Meta-analysis of randomised clinical trials (RCTs). METHOD: The effectiveness of these specially treated sheepskins from the Merino sheep was studied in three RCT's (2 involving Australian hospital patients and 1 involving Dutch nursing-home patients). In all 3 trials patients were randomized to 1 of 2 groups: a control group, who received standard care, and an intervention group, who, in addition to standard care, had at least one AMS placed under the sacral area when in bed. The total research population consisted of 1,281 patients from 11 institutions with 45 nursing wards. Data from the 3 RCT's were pooled and analysed: (a) with conventional meta-analysis based on the published effect sizes and (b) with multilevel logistic regression analysis based on the combined individual patient data for each trial separately and for the combined dataset. The primary outcome measure was the incidence of sacral pressure ulcers. RESULTS: The incidence of sacral pressure ulcers was 12.2% in the control group versus 5.4% in the intervention group. The odds-ratio was 0.37 (95% CI: 0.17-0.77) with conventional meta-analysis, and 0.35 (95% CI: 0.23-0.55) with multilevel logistic regression analysis on the combined individual patient data. CONCLUSION: Both analysis methods confirm that the AMS is effective in preventing sacral pressure ulcers. The confidence interval in the multilevel logistic regression analysis on individual patient data was almost 50% smaller than in the conventional meta-analysis, and gave a more reliable picture of the actual effect.(aut. ref.

Burning of forest materials under late Paleozoic high atmospheric oxygen levels

Theoretical models suggest that atmospheric oxygen reached concentrations as high as 35% O2 during the past 550 m.y. Previous burning experiments using strips of paper have challenged this idea, concluding that ancient wildfires would have decimated plant life if O2 significantly exceeded its present level of 21 %. New thermochemistry and flame-spread experiments using natural fuels contradict these results and indicate that sustained burning of forest fuels at moisture contents common to living plants does not occur between 21% and 35% O2. Therefore, the fires under atmospheres with high oxygen concentrations would not have prevented the persistence of plant communities. Times of high O2 also agree with observations of concurrent fire-resistant plant morphology, large insects, and high concentrations of fossil charcoal

400mW 1060nm ytterbium doped fiber DFB laser

We report for the first time, more than 400mW of output power at 1056.1nm from a distributed feedback (DFB) fiber laser. The DFB fiber laser comprises a simple pi-phase-shifted Bragg grating written into a photosensitive ytterbium-doped fiber. The laser operates with a single longitudinal mode at a wavelength defined by the phase shift and the grating period. Without any internal polarisation selection mechanism, the cavity supports orthogonal polarisation modes, which operate simultaneously. The DFB fiber laser was pumped by a 976nm amplified spontaneous emission (ASE) source based on a ytterbium doped jacketed air clad (JAC) fiber pumped by a 915nm multimode laser diode source. An output of 400mW at 1056.1nm was obtained from the output port while 70mW was obtained from the other port, when pumped with 1.5W of 976nm radiation. The total output from the DFB fiber laser was approximately linear with increasing pump power and the overall performance was limited by the available pump power. The spectral characteristics and signal to noise ratio remained similar over the pump power range. The output of the DFB was in single-mode fiber (ie. M2~1)

Planar waveguide lasers of Ti:sapphire and Nd:YAG (YAP) grown by PLD

Introduction:Passive and active planar waveguides belong to perspective components of integrated optics and optoelectronics for generation and processing of visible and near infrared signals and for the development of new generation of integrated optics technology in which sources. non-linear structures, detectors and electronics waveguides will be produced on a single substrate. Because of this reason planar and channel waveguide lasers are of great interest during the last several years.Waveguide lasers have excellent properties as compared with conventional bulk lasers, such as low threshold operation due to the high pumping efficiency (particularly for transitions with large population in lower laser level [1]), output power and mode pattern stability. and easy coupling with other waveguide structure devices. The future of waveguide technology is placed in the construction of widely tunable laser operating at threshold low enough to allow the pumping by laser diodes.Planar and channel waveguide lasers were successfully created by ion implantation, liquid phase epitaxy (LPE), diffusion, thermal bonding, proton exchange and recently also by pulsed laser deposition PLD). The layers exhibiting at present the lowest losses were created by LPE method.One of the novel thin film technology, the PLD, has some advantages as stoichiometric deposition of even very complex materials, a high deposition rate. enhanced film crystallinity due to the presence of high energy particles in incoming plasma plume (light oriented or epitaxially films are grown) and the higher density in thin films than that of bulk material can be achieved. Basic experimental apparatus for laser thin film deposition consists of interaction chamber, a substrate holder with precise temperature control. and source material-target. Laser is usually located outside of the chamber.Till now, the lasing in the following planar waveguide lasers, created by various techniques, was reached: Er:Ti:LiNbO3 [2,3], Nd:YAG [4,5,6.7,8,9,10,11,12,13], Yb:YAG [14,15,9], LiNdP4O12 [16], Tm:YAG [17], Ti:sapphire [18], Nd:MgO:LiNbO3 [19,20,21], Nd:YAP [22], Nd:GGG [23], Tm:germanate glass [24], Nd:LiTaO3 ;[25], Yb:Tl:LiNbO3 [1], Yb:Er:YAG [26]. TmY2SiO5 (27].Recently the laser generation was obtained also in films created by meihod of PLD, as Nd:GGG grown on YAG substrate [28], and Ti:sapphire grown on sapphire [29]