Pattern formation in the transverse section of a laser with a large Fresnel number

We experimentally investigate pattern formation in a single-wavelength long laser cavity with a large Fresnel number. Near the laser threshold, we observe a single frequency spatially periodic structure corresponding to titled waves theoretically predicted by the Maxwell-Bloch equations. We also show the presence of secondary instabilities at other wavelengths and polarization instabilities at the same wavelength for different parameter values. (S0031-9007(99)08512-9)

Two-photon absorption properties of commercial fused silica and germanosilicate glass at 264 nm

Using high-intensity femtosecond pulses at lambda=264 nm, we have measured the two-photon absorption (TPA) coefficient in three fused silica samples Suprasil, Herasil, Infrasil (Heraeus) and in 3.5 mol % Ge-doped fused silica. While in fused silica samples the TPA coefficient value is about 2x10(-11) cm/W, in germanosilicate glass it equals (42+/-3)x10(-11) cm/W. (C) 2002 American Institute of Physics. (DOI: 10.1063/1.1448387

Simple model for tuberculosis in cattle and badgers

As an aid to the study of bovine tuberculosis (TB), a simple model has been developed of an epidemic involving two species, cattle and badgers. Each species may infect the other. The proportion of animals affected is assumed relatively small so that the usual nonlinear aspects of epidemic theory are avoided. The model is used to study the long-run and transient effect on cattle of culling badgers and the effect of a period without routine testing for TB, such as occurred during the 2001 epidemic of foot-and-mouth disease in Great Britain. Finally, by examining the changes in cattle TB over the last 15 years, and with some other working assumptions, it is estimated that the net reproduction number of the epidemic is 1.1. The implications for controlling the disease are discussed

Dynamics of a semiconductor laser with optical feedback

We investigate both experimentally and theoretically the dynamics of a semiconductor laser with optical feedback in the low-frequency fluctuation regime. First we demonstrate that low-frequency fluctuations can be observed for both single and multimode operation of a semiconductor laser with optical feedback. The analysis of the fast dynamics associated with this low-frequency instability is well described by single-mode rate equations. In the multimode regime, fast pulsation is observed in every laser mode. In this case the fluctuations in total intensity are much smaller than those in the intensity of each individual mode, This indicates the presence of anticorrelations dynamics at high frequency between the different laser modes. (S1050-2947(99)08307-9)

MERRA Analytic Services: Meeting the Big Data Challenges of Climate Science Through Cloud-enabled Climate Analytics-as-a-service

Climate science is a Big Data domain that is experiencing unprecedented growth. In our efforts to address the Big Data challenges of climate science, we are moving toward a notion of Climate Analytics-as-a-Service (CAaaS). We focus on analytics, because it is the knowledge gained from our interactions with Big Data that ultimately produce societal benefits. We focus on CAaaS because we believe it provides a useful way of thinking about the problem: a specialization of the concept of business process-as-a-service, which is an evolving extension of IaaS, PaaS, and SaaS enabled by Cloud Computing. Within this framework, Cloud Computing plays an important role; however, we it see it as only one element in a constellation of capabilities that are essential to delivering climate analytics as a service. These elements are essential because in the aggregate they lead to generativity, a capacity for self-assembly that we feel is the key to solving many of the Big Data challenges in this domain. MERRA Analytic Services (MERRAAS) is an example of cloud-enabled CAaaS built on this principle. MERRAAS enables MapReduce analytics over NASAs Modern-Era Retrospective Analysis for Research and Applications (MERRA) data collection. The MERRA reanalysis integrates observational data with numerical models to produce a global temporally and spatially consistent synthesis of 26 key climate variables. It represents a type of data product that is of growing importance to scientists doing climate change research and a wide range of decision support applications. MERRAAS brings together the following generative elements in a full, end-to-end demonstration of CAaaS capabilities: (1) high-performance, data proximal analytics, (2) scalable data management, (3) software appliance virtualization, (4) adaptive analytics, and (5) a domain-harmonized API. The effectiveness of MERRAAS has been demonstrated in several applications. In our experience, Cloud Computing lowers the barriers and risk to organizational change, fosters innovation and experimentation, facilitates technology transfer, and provides the agility required to meet our customers' increasing and changing needs. Cloud Computing is providing a new tier in the data services stack that helps connect earthbound, enterprise-level data and computational resources to new customers and new mobility-driven applications and modes of work. For climate science, Cloud Computing's capacity to engage communities in the construction of new capabilies is perhaps the most important link between Cloud Computing and Big Data

Excitability in a quantum dot semiconductor laser with optical injection

We experimentally analyze the dynamics of a quantum dot semiconductor laser operating under optical injection. We observe the appearance of single- and double-pulse excitability at one boundary of the locking region. Theoretical considerations show that these pulses are related to a saddle-node bifurcation on a limit cycle as in the Adler equation. The double pulses are related to a period-doubling bifurcation and occur on the same homoclinic curve as the single pulses

Phase synchronization of a two-channel phase-sensitive amplifier based on optical injection-locking of InP quantum-dash mode-locked lasers

A synchronization scheme for a two-channel phase sensitive amplifier is implemented based on the injection-locking of single InP quantum-dash mode-locked laser. Error free performance with penalty <1 dB is demonstrated for both channels

Microthermography of diode lasers: The impact of light propagation on image formation

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 mu m, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale