Gain through losses in nonlinear optics

Instabilities of uniform states are ubiquitous processes occurring in a variety of spatially extended nonlinear systems. These instabilities are at the heart of symmetry breaking, condensate dynamics, self-organization, pattern formation and noise amplification across diverse disciplines, including physics, chemistry, engineering and biology. In nonlinear optics, modulation instabilities are generally linked to the so-called parametric amplification process, which occurs when certain phase-matching or quasi-phase-matching conditions are satisfied. In the present review article, we summarize the principle results on modulation instabilities and parametric amplification in nonlinear optics, with special emphasis on optical fibres. We then review state-of-the-art research about a peculiar class of modulation instabilities and signal amplification processes induced by dissipation in nonlinear optical systems. Losses applied to certain parts of the spectrum counterintuitively lead to the exponential growth of the damped mode themselves, causing gain through losses. We discuss the concept of imaging of losses into gain, showing how to map a given spectral loss profile into a gain spectrum. We demonstrate with concrete examples that dissipation-induced modulation instability, apart from being of fundamental theoretical interest, may pave the way towards the design of a new class of tuneable fibre-based optical amplifiers, optical parametric oscillators, frequency comb sources and pulsed lasers

Fall Exposure of Beech Saplings (Fagus sylvatica L.) to Ozone and Simulated Acidic Mist: Effects on Gas Exchange and Leachability.

Two yr old beech saplings (Fagus sylvatica L.) were exposed under an early autumn climate to four levels of O3 (10, 40, 75, and 110 nL L-1 O3) with or without preceding simulated acidic mist (pH 3.5). As a first response in gas exchange to O3, stomatal conductance was transiently increased followed by a decline in net photosynthesis. Thus, regarding exposure effects on stomatal behavior, both O3 and acidic mist increased the pollutant flux into the leaf interior. The subsequent impairment of cell permeability consisted of dose-dependent increases in efflux rates of dichlorofluorescein, indicating greater membrane permeabilities. While the efflux rates of Mg and Ca correlated with those of the fluorescent dye, the leachability of K was increased only at the highest O3 levels. Changes in compartmentation of K, Ca, Mg, and S was derived from selective cell wall extraction; thereafter, the exposure to O3 and acidic mist resulted in increased extracellular fractions of these elements