Optimum design of NOLM-driven mode-locked fiber lasers.

Most of the saturable absorbers commonly used to perform mode locking in laser cavities affect the trigger conditions of laser oscillation, which requires manually forcing the laser start-up by various means such as polarization controllers. We present a procedure for designing a laser cavity driven by a nonlinear optical loop mirror, which allows the laser to operate optimally without interfering with the oscillation triggering conditions, thus opening up possibilities for integration of this type of laser.

Highly efficient few-mode spatial beam self-cleaning at 1.5µm.

We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers. By using 160 ps long, highly chirped (6 nm bandwidth at -3dB) optical pulses at 1562 nm, we demonstrate a one-decade reduction of the power threshold for spatial beam self-cleaning, with respect to previous experiments using pulses with laser wavelengths at 1030-1064 nm. Self-cleaned beams remain spatio-temporally stable for more than a decade of their peak power variation. The impact of input pulse temporal duration is also studied.

Spectral broadening of picosecond pulses forming dispersive shock waves in optical fibers.

We investigate analytically, numerically, and experimentally the spectral broadening of pulses that undergo the formation of dispersive shocks, addressing in particular pulses in the range of tens of ps generated via electro-optic modulation of a continuous-wave laser. We give an analytical estimate of the maximal spectral extension and show that super-Gaussian waveforms favor the generation of flat-topped spectra. We also show that the weak residual background of the modulator produces undesired spectral ripples. Spectral measurements confirm our estimates and agree well with numerical integration of the nonlinear Schrödinger equation.

Stream temperature response to three riparian vegetation scenarios by use of a distributed temperature validated model.

Elevated in-stream temperature has led to a surge in the occurrence of parasitic intrusion proliferative kidney disease and has resulted in fish kills throughout Switzerland's waterways. Data from distributed temperature sensing (DTS) in-stream measurements for three cloud-free days in August 2007 over a 1260 m stretch of the Boiron de Merges River in southwest Switzerland were used to calibrate and validate a physically based one-dimensional stream temperature model. Stream temperature response to three distinct riparian conditions were then modeled: open, in-stream reeds, and forest cover. Simulation predicted a mean peak stream temperature increase of 0.7 °C if current vegetation was removed, an increase of 0.1 °C if dense reeds covered the entire stream reach, and a decrease of 1.2 °C if a mature riparian forest covered the entire reach. Understanding that full vegetation canopy cover is the optimal riparian management option for limiting stream temperature, in-stream reeds, which require no riparian set-aside and grow very quickly, appear to provide substantial thermal control, potentially useful for land-use management.

Road runoff management using over-the-shoulder infiltration: real-scale experimentation.

A new management policy regarding road runoff was proposed in 2002 by the Swiss Federal Office for the Environment (FOEN). This new concept is based on the diffuse infiltration of road runoff into embankment slopes, where soils will filter particles and contaminants. The shoulder lying between road surface and infiltration slopes must be impervious in order to maximise the amount of water reaching the slope and avoid losses in the road structure. The implementation of this new concept should lower the impact of roads on the environment, improve aquifer recharge and reduce construction costs. The Swiss Federal Road Office (FedRO) decided to carry out real-scale investigations regarding this new policy and thus commissioned the GEOLEP to design, build, and test 5 different shoulder structures. This paper presents the results of a 2-years survey of infiltration processes in these shoulders to establish the best performing structure. The first three shoulders were overlaid with 5 cm of gravel mixed with humus, gravel mixed with clay, and seeded with lawn, respectively. The latter two had impervious layers located 26 cm deep: the road bituminous basement (road base) was prolonged and coated with bitumen in the first case, and a sodic-bentonite geotextile was used in the second. Both were covered with gravel. All shoulders were equipped with basal collecting devices that measured hydraulic fluxes seeping through the shoulders. In total, 112 natural precipitations and 3 artificial events were monitored. Artificial events mimicked known transitory regimes (thunderstorms) or were performed with constant regime. The goal was to effectively assess infiltration processes in shoulders. Results showed that shoulders made of gravel and humus or lawn were highly ineffective (only 30 to 40% of runoff is conducted to the infiltration slope). Gravel and clay was more efficient with a proportion of approximately 60%. The shoulder with prolonged road base showed similar results since the bituminous coating was in fact rather permeable. The best results were exhibited by the shoulder waterproofed with bentonitic geotextile, which allowed no water to penetrate. This material already proved to be very powerful in groundwater catchments. The authors thus proposed a combination of sodic-bentonite geotextile covered by a gravel and clay mixture. This would be the most efficient shoulder: it will convey all the runoff to infiltration slopes, thereby optimising its filtration, which in turn will enhance environmental conditions in the vicinity of roads.

On the hydro-dispersive equivalence between multi-layered mineral barriers.

In the context of municipal solid waste and hazardous waste disposal, the notion of "equivalence" between different barrier designs appears in regulatory documents from several industrialized countries. While in the past, equivalence has been thought of mainly in terms of contaminant travel times, in recent years it has been defined more in terms of the magnitude of a disposal site's potential impact on groundwater resources. This paper presents some original analytical solutions to the problem of contaminant migration through a multi-layered mineral barrier. The solutions account for the two major mechanisms of subsurface contaminant migration, namely, advection and diffusion-dispersion. An example application using the proposed solutions and a numerical model illustrates how one multi-layered mineral barrier can be considered superior to another from a strictly hydro-dispersive viewpoint. The influence of partial saturation of the mineral barrier is investigated using a numerical solution to the Richards equation for unsaturated flow. It is emphasized that conclusions relative to the superiority of one multi-layered barrier, with respect to another, should not only consider hydro-dispersive aspects, but also other processes such as the mechanical and chemical evolutions of the different barrier components. Although such phenomena are poorly addressed by existing models, failure to take them into account, at least in a qualitative fashion, may lead to unconservative conclusions with respect to barrier equivalence.