Improved limits on the mass of the tau neutrino

Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τν_τ/B(D→μν_μ,B(F→τν_τ/B(D→μν_μ can be sensitive to tau-neutrino masses of 30 MeV or greater.     

Dual-color operation of a femtosecond optical parametric oscillator exhibiting stable relative carrier-envelope phase-slip frequencies

A femtosecond optical parametric oscillator is demonstrated that can operate in a regime where two signal pulses with well-separated center wavelengths are simultaneously resonant. Measurements show that the oscillator output contains a stable modulation at a frequency corresponding to the difference in the carrier-envelope phase-slip frequencies of the co-resonant pulses. The physical origin of this internal beat signal is attributed to second-order mixing effects, and its frequency is shown to be consistent with theory.     

Effective mass anisotropy of hot electrons in nonparabolic conduction bands of n-doped InGaAs films using ultrafast terahertz pump-probe techniques

The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response.     

Gain dynamics of the 4.3 μm CO2 laser

A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 m CO₂ laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 m amplifier using low-power pulses from a 4.3 m probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 m amplifier. Optimization of the gain is discussed.     

Measurement of the transition strength of the 00o2 9.4 μm sequence band in CO2 using a tunable diode laser

We report the first accurate measurements of the transition strengths and linewidths of the 00^o2 9.4 μm sequence lines of CO₂. This sequence band is found to be very similar to the regular 00^o1 laser band, except for an experimentally determined factor of 1.89±0.12 increase in transition strength (if the CO₂ molecule is treated as a simple harmonic oscillator the theoretical increase in transition strength is 2.0). The laser absorption spectrometer used for these measurements can detect absorption coefficients in CO₂ of ≈10⁻⁷ m⁻¹, and we discuss the feasibility of using this sensitivity to monitor rare isotopic forms of CO₂. Work supported by the Department of National Health and Welfare, Environment Canada, Ontario Ministry of the Environment, and Atmospheric Environment Service, Environment Canada.     

Muonium in silicon tetrachloride

Muonium in liquid SiCl has been observed for the first time at low temperature (−65°C) The observed polarization of muonium is as much as 25% of the total spin polarization and shows a fast relaxation rate.     

The μSR facilities at PSI

TheSR Facility Instruments presently available at PSI and the envisaged medium- and long-term developments are presented. The plans focus on further upgrades of the existing instruments and the development of new techniques using the very high fluxes becoming available at PSI, in particular the setup of a beamline with a fast kicker for muons on request (MORE) and the development of very low energy muon beams.