Enhancing and inhibiting stimulated Brillouin scattering in photonic integrated circuits.

On-chip nonlinear optics is a thriving research field, which creates transformative opportunities for manipulating classical or quantum signals in small-footprint integrated devices. Since the length scales are short, nonlinear interactions need to be enhanced by exploiting materials with large nonlinearity in combination with high-Q resonators or slow-light structures. This, however, often results in simultaneous enhancement of competing nonlinear processes, which limit the efficiency and can cause signal distortion. Here, we exploit the frequency dependence of the optical density-of-states near the edge of a photonic bandgap to selectively enhance or inhibit nonlinear interactions on a chip. We demonstrate this concept for one of the strongest nonlinear effects, stimulated Brillouin scattering using a narrow-band one-dimensional photonic bandgap structure: a Bragg grating. The stimulated Brillouin scattering enhancement enables the generation of a 15-line Brillouin frequency comb. In the inhibition case, we achieve stimulated Brillouin scattering free operation at a power level twice the threshold.

Low-threshold Brillouin laser at 2 µm based on suspended-core chalcogenide fiber.

We present, to the best of our knowledge, the first demonstration of a 2 µm Brillouin laser based on a thulium-doped fiber pump and a chalcogenide fiber. A short 1.5 m piece of suspended-core chalcogenide As38Se62 fiber is employed as a gain medium, taking advantage of its small effective mode area and high Brillouin gain coefficient. A record-low lasing threshold of 52 mW is achieved, which is about 10 times lower than previously demonstrated in silica fiber cavities.

Phase-locking and pulse generation in multi-frequency brillouin oscillator via four wave mixing.

There is an increasing demand for pulsed all-fibre lasers with gigahertz repetition rates for applications in telecommunications and metrology. The repetition rate of conventional passively mode-locked fibre lasers is fundamentally linked to the laser cavity length and is therefore typically ~10-100 MHz, which is orders of magnitude lower than required. Cascading stimulated Brillouin scattering (SBS) in nonlinear resonators, however, enables the formation of Brillouin frequency combs (BFCs) with GHz line spacing, which is determined by the acoustic properties of the medium and is independent of the resonator length. Phase-locking of such combs therefore holds a promise to achieve gigahertz repetition rate lasers. The interplay of SBS and Kerr-nonlinear four-wave mixing (FWM) in nonlinear resonators has been previously investigated, yet the phase relationship of the waves has not been considered. Here, we present for the first time experimental and numerical results that demonstrate phase-locking of BFCs generated in a nonlinear waveguide cavity. Using real-time measurements we demonstrate stable 40 ps pulse trains with 8 GHz repetition rate based on a chalcogenide fibre cavity, without the aid of any additional phase-locking element. Detailed numerical modelling, which is in agreement with the experimental results, highlight the essential role of FWM in phase-locking of the BFC.

Multi-wavelength gratings formed via cascaded stimulated Brillouin scattering.

We present the experimental observation of multi-wavelength fiber Bragg gratings in As2Se3 fiber. The gratings are internally written via two-photon absorption of 1550 nm pump light and its first and second order Stokes waves generated by cascaded stimulated Brillouin scattering (SBS). We demonstrate a parameter regime that allows for 4 dB grating enhancement by suppression of SBS.

Multicore, tapered optical fiber for nonlinear pulse reshaping and saturable absorption.

We present a new method to create a coupled waveguide array via tapering a seven-core telecommunications fiber. The fiber based waveguide array is demonstrated to exhibit the novel physics associated with coupled waveguide arrays, such as discrete diffraction and discrete self-focusing. The saturable absorber characteristics of the device are characterized and an autocorrelation measurement reveals significant single-pass pulse reshaping.

Capillary gas chromatography/mass spectrometry with chemical ionization and negative ion detection for confirmation of identity of patulin in apple juice.

Gas chromatography/mass spectrometry (GC/MS) with negative ion chemical ionization permits detection of underivatized patulin in apple juice extracts while minimizing co-extractive responses. The technique has been used with a variety of capillary columns in quadrupole, ion trap, and magnetic sector GC/MS instruments to confirm presumptive findings of patulin in apple juice at concentrations ranging from 68 to 3700 micrograms/L. The demonstrated ability to use any of these 3 mass spectrometers and several capillary columns to confirm the identity of patulin are significant strengths of the technique.

Determination of patulin in apple juice by liquid chromatography: collaborative study.

An AOAC International-International Union of Pure and Applied Chemistry-International Fruit Juice Union (AOAC-IUPAC-IFJU) collaborative study was conducted to evaluate a liquid chromatographic (LC) procedure for determination of patulin in apple juice. Patulin is a mold metabolite found naturally in rotting apples. Patulin is extracted with ethyl acetate, treated with sodium carbonate solution, and determined by reversed-phase LC with UV detection at 254 or 276 nm. Water, water-tetrahydrofuran, or water-acetonitrile was used as mobile phase. Levels determined in spiked test samples were 20, 50, 100, and 200 micrograms/L. A test sample naturally contaminated at 31 micrograms/L was also included. Twenty-two collaborators in 10 countries analyzed 12 test samples of apple juice. Recoveries averaged 96%, with a range of 91-108%. Repeatability relative standard deviations (RSDr) ranged from 10.9 to 53.8%. The reproducibility relative standard deviation (RSDR) ranged from 15.1 to 68.8%. The LC method for determination of patulin in apple juice has been adopted first action by AOAC INTERNATIONAL.

High-performance liquid chromatographic determination of 1,1'-ethylidenebis(L-tryptophan) in L-tryptophan preparations.

In studies to determine the cause or causes of the eosinophilia myalgic syndrome (EMS) and to monitor the purity of L-tryptophan preparations, an HPLC method has been developed for determining 1,1'-ethylidenebis(L-tryptophan) (EBT) in L-tryptophan (W) preparations. The W preparations are extracted with 0.1% trifluoroacetic acid (TFA) and filtered, and the EBT is purified by passage through a Sep-Pak C18 cartridge. The cartridge is washed with water and 6% acetonitrile in water, and EBT is eluted with methanol. The water-diluted eluate is then chromatographed on a silica-based, reversed-phase HPLC column with a gradient of water and 80% acetonitrile, both solvents containing 0.1% TFA. EBT absorbance is measured at 280 nm. The average recovery of EBT from L-tryptophan powder, spiked over the range 1.2-4.8 micrograms/g, was 91%. The limit of determination was approximately 0.6 micrograms/g. Sixteen test samples of W products manufactured by the company to which most of the cases of EMS have been traced contained > 70 micrograms of EBT/g. Three nonpatient-related test samples either did not contain EBT or contained < 2 micrograms of EBT/g.

1,1'-Ethylidenebis[L-tryptophan], a contaminant implicated in L-tryptophan eosinophilia myalgia syndrome, suppresses mRNA expression of hypothalamic corticotropin-releasing hormone in Lewis (LEW/N) rat brain.

The L-tryptophan eosinophilia myalgia syndrome (L-Trp-EMS), related to ingestion of impure L-Trp, occurred in epidemic proportions in the United States in 1989. Epidemiologic studies implicated 1,1'-ethylidenebis[L-tryptophan] (EBT) as the impurity most highly associated with development of human L-Trp-EMS. We have previously shown that Lewis (LEW/N) rats fed L-Trp implicated in the L-Trp-EMS epidemic (case-associated L-Trp) develop fasciitis and perimyositis which is associated with a reduction in corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus (PVN). In this study, we report the effects of EBT- and case-associated L-Trp on CRH mRNA expression in the hypothalamic PVN and secretion of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) into the plasma over a time course of 1-6 weeks in the same rats in which we have found fascial thickening and immune cell activation induced by these compounds. Both control L-Trp and EBT stimulated the secretion of ACTH and CORT at 1-2 weeks, whereas case-associated L-Trp did not. EBT and case-associated L-Trp decreased CRH mRNA expression in the PVN at 2-6 weeks, while control L-Trp had no effect. The striking contrast in the effects of case-associated L-Trp and EBT on the HPA axis suggests that the reduction in CRH mRNA levels in the PVN seen in each case may be related to different mechanisms. It is possible that EBT suppresses CRH mRNA expression directly, in the absence of inflammation, while case-associated L-Trp may act through multiple mechanisms, including that associated with inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)

A decomposition product of a contaminant implicated in L-tryptophan eosinophilia myalgia syndrome affects spinal cord neuronal cell death and survival through stereospecific, maturation and partly interleukin-1-dependent mechanisms.

The L-tryptophan eosinophilia myalgia syndrome (L-TRP-EMS), an inflammatory syndrome characterized by eosinophilia, myalgias, perimyositis, fasciitis and neuropathies, occurred in epidemic proportions in the United States in the summer and fall of 1989. The neuropathic clinical features in L-TRP EMS are complex and mixed. In the present study, one of the impurities most highly associated with development of L-TRP EMS, 1,1'-ethylidenebis[L-tryptophan] (EBT), and two of its diastereoisomeric breakdown products, were compared for evidence of neurotoxicity in vitro. In 1-month-old spinal cord cultures derived from fetal mice, synthetic (-)-(1S,3S)-1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1S-beta-C) produced a 30 to 35% loss in numbers of neurons. Toxicity was not apparent after treatment with the R-isomer of the same compound or with the parent compound, EBT. Cotreatment of cultures with 1S-beta-C and neutralizing antiserum to interleukin-1 alpha (IL-1 alpha), or with 1S-beta-C and neutralizing antiserum against the murine IL-1 receptor, prevented neuronal cell death associated with 1S-beta-C. Recombinant IL-1 alpha also produced neuronal killing that was not additive to that observed with the 1S-beta-C treatment. In contrast, in immature spinal cord neuronal cultures, the 1S-beta-C, but not the 1R-beta-C or EBT, prevented the 30% cell death which normally occurs in these cultures. Neither neutralizing anti-IL-1 antibody, nor anti-IL-1 receptor antibody blocked the neuronal survival effect, suggesting that 1S-beta-C induces neuronal survival through a receptor-mediated mechanism independent of IL-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast neutron radiotherapy for locally advanced prostate cancer. Update of a past trial and future research directions.

Between June, 1977, and April, 1983, the Radiation Therapy Oncology Group (RTOG) sponsored a phase III study comparing fast neutron radiotherapy as part of a mixed beam (neutron/photon) regimen with conventional photon (x-ray) radiotherapy for patients with locally advanced (Stages C and D1) adenocarcinoma of the prostate. A total of 91 analyzable patients were entered into the study with the two treatment groups balanced in regard to all major prognostic variables. The current analysis is for a median follow-up of 6.7 years (range 3.4-9.0 yrs.). The results are statistically significant in favor of the mixed-beam group of all parameters mentioned. At five years the freedom from local/regional relapse rate is 81 percent on the mixed-beam arm compared with 60 percent on the photon arm. The actuarial overall survival rate at five years is 70 percent on the mixed beam compared with 56 percent on the conventional photon arm. The determinantal survival at five years (which excluded death due to intercurrent disease in patients clinically free of cancer) was 82 percent on the mixed-beam arm compared with 61 percent on the photon arm. The type of therapy appeared to be the most important predictor of both local tumor control and patient survival in a step-wise Cox analysis. There was no difference in the treatment-related morbidity for the two patient groups. Mixed-beam therapy may be superior to standard photon radiotherapy for treatment of locally advanced prostate cancer.