Towards a global sustainable development agenda built on social-ecological resilience.

Non-technical Summary: The United Nations' sustainable development goals (SDGs) articulate societal aspirations for people and our planet. Many scientists have criticised the SDGs and some have suggested that a better understanding of the complex interactions between society and the environment should underpin the next global development agenda. We further this discussion through the theory of social-ecological resilience, which emphasises the ability of systems to absorb, adapt, and transform in the face of change.

Governing complexity: Integrating science, governance, and law to manage accelerating change in the globalized commons.

The speed and uncertainty of environmental change in the Anthropocene challenge the capacity of coevolving social-ecological-technological systems (SETs) to adapt or transform to these changes. Formal government and legal structures further constrain the adaptive capacity of our SETs. However, new, self-organized forms of adaptive governance are emerging at multiple scales in natural resource-based SETs.

Untapped capacity for resilience in environmental law.

Over the past several decades, environmental governance has made substantial progress in addressing environmental change, but emerging environmental problems require new innovations in law, policy, and governance. While expansive legal reform is unlikely to occur soon, there is untapped potential in existing laws to address environmental change, both by leveraging adaptive and transformative capacities within the law itself to enhance social-ecological resilience and by using those laws to allow social-ecological systems to adapt and transform. Legal and policy research to date has largely overlooked this potential, even though it offers a more expedient approach to addressing environmental change than waiting for full-scale environmental law reform.

Balancing stability and flexibility in adaptive governance: an analysis of tools available in U.S. environmental law.

Adaptive governance must work "on the ground," that is, it must operate through structures and procedures that the people it governs perceive to be legitimate and fair, as well as incorporating processes and substantive goals that are effective in allowing social-ecological systems (SESs) to adapt to climate change and other impacts. To address the continuing and accelerating alterations that climate change is bringing to SESs, adaptive governance generally will require more flexibility than prior governance institutions have often allowed. However, to function as good governance, adaptive governance must pay real attention to the problem of how to balance this increased need for flexibility with continuing governance stability so that it can foster adaptation to change without being perceived or experienced as perpetually destabilizing, disruptive, and unfair.

Regime shifts and panarchies in regional scale social-ecological water systems.

In this article we summarize histories of nonlinear, complex interactions among societal, legal, and ecosystem dynamics in six North American water basins, as they respond to changing climate. These case studies were chosen to explore the conditions for emergence of adaptive governance in heavily regulated and developed social-ecological systems nested within a hierarchical governmental system. We summarize resilience assessments conducted in each system to provide a synthesis and reference by the other articles in this special feature.

The role of law in adaptive governance.

The term "governance" encompasses both governmental and nongovernmental participation in collective choice and action. Law dictates the structure, boundaries, rules, and processes within which governmental action takes place, and in doing so becomes one of the focal points for analysis of barriers to adaptation as the effects of climate change are felt. Adaptive governance must therefore contemplate a level of flexibility and evolution in governmental action beyond that currently found in the heavily administrative governments of many democracies.

Pseudo-random binary sequence phase modulation for narrow linewidth, kilowatt, monolithic fiber amplifiers.

We report on pseudo random binary sequence (PRBS) phase modulation for narrow-linewidth, kilowatt-class, monolithic (all-fiber) amplifiers. Stimulated Brillouin scattering (SBS) threshold enhancement factors for different patterns of PRBS modulated fiber amplifiers were experimentally analyzed and agreed well with the theoretical predictions. We also examined seeding of the SBS process by phase modulated signals when the effective linewidth is on the same order as the Brillouin shift frequency.

Modal instability-suppressing, single-frequency photonic crystal fiber amplifier with 811 W output power.

An acoustic- and gain-tailored Yb-doped polarization-maintaining photonic crystal fiber is used to demonstrate 811 W single-frequency output power with near diffraction-limited beam quality. The fiber core is composed of 7 individually doped segments arranged to create three distinct transverse acoustic regions; including one region that is Yb-free. The utility of the Yb-free region is to reduce coupling between the LP01 and LP11 modes to mitigate the modal instability.

Investigations of modal instabilities in fiber amplifiers through detailed numerical simulations.

We present detailed numerical simulations of modal instabilities in high-power Yb-doped fiber amplifiers using a time-dependent temperature solver coupled to the optical fields and population inversion equations. The temperature is computed by solving the heat equation in polar coordinates using a 2D second-order alternating direction implicit method. We show that the higher-order modal content rises dramatically in the vicinity of the threshold and we recover the three power-dependent regions that are characteristic of the transfer of energy.

Investigations of single-frequency Raman fiber amplifiers operating at 1178 nm.

We report on core-pumped single-stage and two-stage polarization-maintaining single-frequency Raman fiber amplifiers (RFAs). For a counter-pumped single-stage RFA, commercial-off-the shelf (COTS) single-mode fiber was utilized to generate 10 W of output power at 1178 nm through the application of a two-step thermal gradient in order to suppress SBS. The relatively high output can be explained by the Brillouin gain spectrum (BGS) of the COTS fiber.

Hyperthermia: from diagnostic and treatments to new discoveries.

Hyperthermia is an important approach for the treatment of several diseases. Hyperthermia is also thought to induce hypertrophy of skeletal muscles in vitro and in vivo, and has been used as a therapeutic tool for millennia. In the first part of our work, we revise several relevant patents related to the utilization of hyperthermia for the treatment and diagnostic of human diseases.

Two-dimensional diffractive coherent combining of 15 fiber amplifiers into a 600 W beam.

We demonstrate coherent beam combining using a two-dimensionally patterned diffractive optic combining element. Fifteen Yb-doped fiber amplifier beams arranged in a 3×5 array were combined into a single 600 W, M²=1.1 output beam with 68% combining efficiency.

A theoretical study of transient stimulated Brillouin scattering in optical fibers seeded with phase-modulated light.

Beam combining of phase-modulated kilowatt fiber amplifiers has generated considerable interest recently. We describe in the time domain how stimulated Brillouin scattering (SBS) is generated in an optical fiber under phase-modulated laser conditions, and we analyze different phase modulation techniques. The temporal and spatial evolutions of the acoustic phonon, laser, and Stokes fields are determined by solving the coupled three-wave interaction system.

18 W single-stage single-frequency acoustically tailored Raman fiber amplifier.

A single-mode polarization-maintaining fiber doped to increase the Raman gain while suppressing stimulated Brillouin scattering (SBS) was utilized in a single-stage counter-pumped Raman fiber amplifier. The SBS suppression was achieved through the acoustic tailoring of the core. A pump probe experiment was conducted to characterize the Brillouin gain and indicated the existence of multiple Brillouin peaks.

Acoustically segmented photonic crystal fiber for single-frequency high-power laser applications.

The Brillouin gain characteristics of a Yb-doped polarization-maintaining photonic crystal fiber possessing a segmented acoustic profile are investigated using a pump-probe technique. The concentrations of fluorine, aluminum, and germanium in two regions of the core were selected, such that the corresponding Brillouin shifts were sufficiently separated to allow for the introduction of a temperature profile along the fiber for further stimulated Brillouin scattering suppression. By using a cutback technique to measure loss, we estimated the Brillouin gain coefficient to be 1.

Stimulated Brillouin scattering suppression through laser gain competition: scalability to high power.

We demonstrate stimulated Brillouin scattering (SBS) suppression in a Yb-doped fiber amplifier by seeding with a combination of broad- and single-frequency laser beams that are separated sufficiently to suppress four-wave mixing and to allow for efficient laser gain competition between the two signals. In the experiment, a monolithic fiber configuration was used. With appropriate selection of seed power ratio, we were able to generate single-frequency 1064 nm light with a slope efficiency of 78% while simultaneously suppressing the backscattered Stokes light.

Experimental and theoretical investigations of photonic crystal fiber amplifier with 260 W output.

We report on a polarization-maintaining narrow-linewidth high power ytterbium-doped photonic crystal fiber amplifier with an output as high as 260 W and a slope efficiency of approximately 74%. Measurements of the beam quality yielded M2 values in the range of 1.2-1.

A theoretical treatment of two approaches to SBS mitigation with two-tone amplification.

A technique that employs two seed signals for the purpose of mitigating stimulated Brillouin scattering (SBS) effects in narrow-linewidth Yb-doped fiber amplifiers is investigated theoretically by constructing a self-consistent model that incorporates the laser gain, SBS, and four-wave mixing (FWM). The model reduces to solving a two-point boundary problem consisting of an 8x8 system of coupled nonlinear differential equations. Optimal operating conditions are determined by examining the interplay between the wavelength separation and power ratio of the two seeds.