Articles you may be interested inInitial growth, refractive index, and crystallinity of thermal and plasma-enhanced atomic layer deposition AlN films J. Vac. Sci. Technol. A 33, 01A111 (2015); 10.1116/1.4898434Effects of rapid thermal anneal on refractive index and hydrogen content of plasmaenhanced chemical vapor deposited silicon nitride films Etch mechanism in the low refractive index silicon nitride plasmaenhanced chemical vapor deposition process Appl.Secondary ion mass spectrometry and refractive index measurements have been carried out on silicon oxy-nitride produced by plasma-enhanced chemical vapor deposition (PECVD). Nitrous oxide and ammonia were added to a constant flow of 2% silane in nitrogen, to produce oxy-nitride films with atomic nitrogen concentrations between 2 and 10 at. %. A simple atomic valence model is found to describe both the measured atomic concentrations and published material compositions for silicon oxy-nitride produced by PECVD. A relation between the SGN bond concentration and the refractive index is found. This relation suggest that the refractive index of oxy-nitride with a low nitrogen concentration is determined by the maferial density. It is suggested that the relative oxygen concentration in the gas flow is the major deposition characterization parameter, and that water vapor is the predominant reaction by-product. A model, that combine the chemicaf net reaction and the stoichiometric rules, is found to agree with measured deposition rates for given material compositions. Effects of annealing in a nitrogen atmosphere has been investigated for the 4UO "C-1100 "C temperature range. It is observed that PECVD oxy-nitrides release nitrogen and hydrogen in the form of NH for annealing temperatures in the 500 "C-700 "C range, The relaxation process during annealing is found to be governed by a viscoelastic relaxation process similar to the relaxation process observed for thermally grown SiO, . Upon nitrogen release. the PECVD material is in a state of internal tension. The viscoelastic relaxation process for temperatures above 700 "C is dominated by the relaxation of this internal tension. A linear relation between the refractive index and material density is determined for silicon oxy-nitride with a nitrogen concentration be.low 30 at. 70. 0 1995 American Institute qf Physics. 6616

The photo darkening (PD) absorption spectra from unseeded amplifier operation (by 915 nm pumping) of ytterbium / aluminum and co-doped silica fibers is after prolonged operation observed to develop a characteristic line at 2.6 eV (477 nm). This line is proposed to be due to inter center excitation transfer from type II oxygen deficiency centers ODC(II) to Tm3+ trace impurities. The ODC(II) is proposed to be the result of a displacive transition of a 4-fold silica ring hosting two 3-fold silicon units that presents two non-bridging oxygen to Yb3+ (as part of its 6-fold coordination by oxygen). The displacive transition is initiated by a charge disproportionation process which leads to NBO transfer in forming dioxasilirane (2-fold coordinated silicon with two NBO attached) next to silylene (2-fold coordinated silicon with a lone electron pair). In collaboration with a valence electron of Yb3+ a new ½ / 1½ chemical bond is formed on dioxasilirane which comprises the PD color center for the visible and near-infrared. Difference in solid acidity of the silica material co-doped with Yb/Al and Yb/P may explain the observed difference in spectral shapes by change of bond order to the formed chemical bond.

Abstract:We demonstrate supercontinuum generation in a PCF pumped by a gain-switched high-power continuous wave (CW) fiber laser. The pulses generated by gain-switching have a peak power of more than 700 W, a duration around 200 ns, and a repetition rate of 200 kHz giving a high average power of almost 30 W. By coupling such a pulse train into a commercial nonlinear photonic crystal fiber, a supercontinuum is generated with a spectrum spanning from 500 to 2250 nm, a total output power of 12 W, and an infrared flatness of 6 dB over a bandwidth of more than 1000 nm with a power density above 5 dBm/nm (3 mW/nm). This is considerably broader than when operating the same system under CW conditions. The presented approach is attractive due to the high power, power scalability, and reduced system complexity compared to picosecond-pumped supercontinuum sources.

Abstract:Gain-switching is an alternative pulsing technique of fiber lasers, which is power scalable and has a low complexity. From a linear stability analysis of rate equations the relaxation oscillation period is derived and from it, the pulse duration is defined. Good agreement between the measured pulse duration and the theoretical prediction is found over a wide range of parameters. In particular we investigate the influence of an often present length of passive fiber in the cavity and show that it introduces a finite minimum in the achievable pulse duration. This minimum pulse duration is shown to occur at longer active fibers length with increased passive length of fiber in the cavity. The peak power is observed to depend linearly on the absorbed pump power and be independent of the passive fiber length. Given these conclusions, the pulse energy, duration, and peak power can be estimated with good precision.

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