High-frequency bone conduction audiometry using a piezoelectric transducer

NRC publication: Ye

Wavelength scaling of high harmonic generation efficiency

Using longer wavelength laser drivers for high harmonic generation is desirable because the highest extreme ultraviolet frequency scales as the square of the wavelength. Recent numerical studies predict that high harmonic efficiency falls dramatically with increasing wavelength, with a very unfavorable \u3bb-(5-6) scaling. We performed an experimental study of the high harmonic yield over a wavelength range of 800\u20131850 nm. A thin gas jet was employed to minimize phase matching effects, and the laser intensity and focal spot size were kept constant as the wavelength was changed. Ion yield was simultaneously measured so that the total number of emitting atoms was known. We found that the scaling at constant laser intensity is \u3bb-6.3\ub11.1 in Xe and \u3bb-6.5\ub11.1 in Kr over the wavelength range of 800\u20131850 nm, somewhat worse than the theoretical predictions.Peer reviewed: YesNRC publication: Ye

High harmonic generation with long-wavelength few-cycle laser pulses

We report the extension of hollow-core fibre pulse compression to longer wavelengths. High-energy multi-cycle infrared pulses are generated via optical parametric amplification and subsequently broadened in the fibre. 2.5-cycle pulses at the Signal wavelength (1.4 \ub5m) and 1.6-cycle pulses at the Idler wavelength (1.8 \ub5m) in the sub-millijoule regime have been generated. New compression schemes can be applied at 1.8 \ub5m and beyond. In this manner, 1.6-cycle carrier envelope phase stable pulses were generated by linear propagation in the anomalous dispersion regime of bulk glass which surprisingly enables compression below its third-order dispersion limit. Furthermore, a dispersion-free way of controlling the carrier envelope phase is demonstrated. Moreover, we experimentally confirm the increase in high-harmonic cut-off energy with driving laser wavelength and demonstrate the beneficial effect of few-cycle pulses which enable higher saturation intensities on target compared to multi-cycle pulses. It will be an ideal tool for future synthesis of isolated attosecond pulses in the sub-keV regime. With this laser source, we revealed for the first time multi-electron effects in high harmonic generation in xenon.Peer reviewed: YesNRC publication: Ye

Pulse compression of submillijoule few-optical-cycle infrared laser pulses using chirped mirrors

We report generation of 400 \u3bcJ, 13.1 fs, 1425 nm optical parametric amplifier laser pulses. Spectral broadening of a 100 Hz optical parametric amplifier laser source is achieved by self-phase modulation in an argon-filled hollow-core fiber, and dispersion compensation is performed using chirped mirrors. This laser source will be useful for ultrafast time-resolved molecular orbital tomography.Peer reviewed: YesNRC publication: Ye

Intense few-cycle infrared laser pulses at the advanced laser light source

To push the generation of isolated attosecond pulses towards shorter XUV wavelengths (0.3 to 1 keV), intense few-cycle driving pulses are required whose center frequency is significantly red shifted compared to established Ti-Sa technology. A simple route for generating these pulses is demonstrated using an optical parametric amplifier (OPA). Its infrared (IR) multi-cycle laser pulses with millijoule of energy are spectrally broadened by nonlinear propagation in a hollow-core fiber (HCF) filled with Argon. For the OPA Signal wavelength (\u3bb = 1.4 micron), chirped mirrors were used for dispersion compensation with a resulting pulse duration of 13.1 fs. For the OPA Idler wavelength at 1.8 micron, a new compression scheme has been developed with which 11.2 fs laser pulses have been characterized (1 cycle= 6 fs). Here, pulse compression is achieved through the combined effects of self-steepening during nonlinear propagation in the HCF followed by anomalous dispersion during linear propagation in fused silica.Peer reviewed: YesNRC publication: Ye

Helicobacter pylori eradication with a capsule containing bismuth subcitrate potassium, metronidazole, and tetracycline given with omeprazole versus clarithromycin-based triple therapy: a randomised, open-label, non-inferiority, phase 3 trial

BACKGROUND: Helicobacter pylori is associated with benign and malignant diseases of the upper gastrointestinal tract, and increasing antibiotic resistance has made alternative treatments necessary. Our aim was to assess the efficacy and safety of a new, single-capsule treatment versus the gold standard for H pylori eradication. METHODS: We did a randomised, open-label, non-inferiority, phase 3 trial in 39 sites in Europe, comparing the efficacy and safety of 10 days of quadruple therapy with omeprazole plus a single three-in-one capsule containing bismuth subcitrate potassium, metronidazole, and tetracycline (quadruple therapy) versus 7 days of omeprazole, amoxicillin, and clarithromycin (standard therapy) in adults with recorded H pylori infection. Patients were randomly assigned treatment according to a predetermined list independently generated by Quintiles Canada (Ville St-Laurent, QC, Canada). Our study was designed as a non-inferiority trial but was powered to detect superiority. Our primary outcome was H pylori eradication, established by two negative (13)C urea breath tests at a minimum of 28 and 56 days after the end of treatment. Our assessment for non-inferiority was in the per-protocol population, with subsequent assessment for superiority in the intention-to-treat population (ie, all participants randomly assigned treatment). This study is registered with ClinicalTrials.gov, number NCT00669955. FINDINGS: 12 participants were lost to follow-up and 101 were excluded from the per-protocol analysis. In the per-protocol population (n=339), the lower bound of the CI for treatment with quadruple therapy was greater than the pre-established non-inferiority margin of -10% (95% CI 15\ub71-32\ub73; p<0\ub70001). In the intention-to-treat population (n=440), eradication rates were 80% (174 of 218 participants) in the quadruple therapy group versus 55% (123 of 222) in the standard therapy group (p<0\ub70001). Safety profiles for both treatments were similar; main adverse events were gastrointestinal and CNS disorders. INTERPRETATION: Quadruple therapy should be considered for first-line treatment in view of the rising prevalence of clarithromycin-resistant H pylori, especially since quadruple therapy provides superior eradication with similar safety and tolerability to standard therapy.Background: Helicobacter pylori is associated with benign and malignant diseases of the upper gastrointestinal tract, and increasing antibiotic resistance has made alternative treatments necessary. Our aim was to assess the efficacy and safety of a new, single-capsule treatment versus the gold standard for H pylori eradication. Methods: We did a randomised, open-label, non-inferiority, phase 3 trial in 39 sites in Europe, comparing the efficacy and safety of 10 days of quadruple therapy with omeprazole plus a single three-in-one capsule containing bismuth subcitrate potassium, metronidazole, and tetracycline (quadruple therapy) versus 7 days of omeprazole, amoxicillin, and clarithromycin (standard therapy) in adults with recorded H pylori infection. Patients were randomly assigned treatment according to a predetermined list independently generated by Quintiles Canada (Ville St-Laurent, QC, Canada). Our study was designed as a non-inferiority trial but was powered to detect superiority. Our primary outcome was H pylori eradication, established by two negative 13C urea breath tests at a minimum of 28 and 56 days after the end of treatment. Our assessment for non-inferiority was in the per-protocol population, with subsequent assessment for superiority in the intention-to-treat population (ie, all participants randomly assigned treatment). This study is registered with ClinicalTrials.gov, number NCT00669955. Findings: 12 participants were lost to follow-up and 101 were excluded from the per-protocol analysis. In the per-protocol population (n=339), the lower bound of the CI for treatment with quadruple therapy was greater than the pre-established non-inferiority margin of -10% (95% CI 15.1-32.3; p<0.0001). In the intention-to-treat population (n=440), eradication rates were 80% (174 of 218 participants) in the quadruple therapy group versus 55% (123 of 222) in the standard therapy group (p<0.0001). Safety profiles for both treatments were similar; main adverse events were gastrointestinal and CNS disorders. Interpretation: Quadruple therapy should be considered for first-line treatment in view of the rising prevalence of clarithromycin-resistant H pylori, especially since quadruple therapy provides superior eradication with similar safety and tolerability to standard therapy. Funding: Axcan Pharma Inc. \ua9 2011 Elsevier Ltd