Improved Intrapulse Raman Scattering Control via Asymmetric Airy Pulses

We study the soliton self-frequency shift (SSFS) initiated by Airy pulses in a fiber, and demonstrate the versatility of these asymmetric pulses in controlling the frequency tuning of laser light. The time asymmetric features of input Airy pulses, with either leading or trailing oscillatory tails (relative to the main lobe), are revealed in the output primary and secondary Raman SSFS as a result of different soliton fission processes. Control of the Raman frequency shifts can be achieved by input pulse time reversal, or more simply offsetting the spectral phase (equivalently introducing linear chirps) of both tail-leading and –trailing Airy pulses. Such a flexible method has key feasibility and smoothness advantages for frequency tuning in contrast with using a pre-chirped Gaussian-like pulse. Furthermore, we demonstrate that linear chirping the input Airy pulses can be employed to control multi-color Raman solitons, with enhanced tunability for the tail-leading case. Our theoretical studies are well confirmed by experimental observations

Sending femtosecond pulses in circles: highly non-paraxial accelerating beams

We use caustic beam shaping on 100 fs pulses to experimentally generate non-paraxial accelerating beams along a 60 degree circular arc, moving laterally by 14 \mum over a 28 \mum propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of non-paraxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic

Non-Paraxial Wave Analysis of 3D Airy Beams

The 3D Airy beam (AiB) is thoroughly explored from a wave-theory point of view. We utilize the exact spectral integral for the AiB to derive local ray-based solutions that do not suffer from the limitations of the conventional parabolic equation (PE) solution, and are valid far beyond the paraxial zone and for longer ranges. The ray topology near the main lobe of the AiB delineates a hyperbolic umilic diffraction catastrophe, consisting of a cusped double-layered caustic, but this caustic is deformed in the far range where the field loses its beam shape. The field in the vicinity of this caustic is described uniformly by a hyperbolic umilic canonical integral which is structured explicitly on the local geometry of the caustic as obtained from the initial field distribution. In order to accommodate the finite-energy AiB we also modify the canonical integral by adding a complex loss parameter. The canonical integral is calculated using a series expansion and the results are used to identify the validity zone of the conventional PE solution. The analysis is performed within the framework of the non-dispersive AiB where the aperture field is scaled with frequency such that the ray skeleton is frequency-independent. This scaling enables an extension of the theory to the ultra wide band (UWB) regime and ensures that the pulsed field propagates along the curved beam trajectory without dispersion, as will be demonstrated in a subsequent publication

NIR-red reflectance-based algorithms for chlorophyll-a estimation in mesotrophic inland and coastal waters: Lake Kinneret case study

A variety of models have been developed for estimating chlorophyll-a (Chl-a) concentration in turbid and productive waters. All are based on optical information in a few spectral bands in the red and near-infra-red regions of the electromagnetic spectrum. The wavelength locations in the models used were meticulously tuned to provide the highest sensitivity to the presence of Chl-a and minimal sensitivity to other constituents in water. But the caveat in these models is the need for recurrent parameterization and calibration due to changes in the biophysical characteristics of water based on the location and/or time of the year. In this study we tested the performance of NIR-red models in estimating Chl-a concentrations in an environment with a range of Chl-a concentrations that is typical for coastal and mesotrophic inland waters. The models with the same spectral bands as MERIS, calibrated for small lakes in the Midwest U.S., were used to estimate Chla concentration in the subtropical Lake Kinneret (Israel), where Chl-a concentrations ranged from 4 to 21 mgm-3 during four field campaigns. A two-band model without reparameterization was able to estimate Chl-a concentration with a root mean square error less than 1.5 mgm-3. Our work thus indicates the potential of the model to be reliably applied without further need of parameterization and calibration based on geographical and/or seasonal regimes

Doing Gender Online : Digital Spaces for Identity Politics

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