Generation of amplitude-squeezed light from a room-temperature Fabry-Perot semiconductor laser

Amplitude-squeezed light with intensity fluctuations 29% below the standard quantum limit (SQL) is produced from a pump-suppressed room-temperature semiconductor laser, corresponding to 41% below the SQL after correction for detection efficiency. Excess noise, which degrades the observed squeezing, appears to be associated with the presence of weak longitudinal side modes

Linewidth reduction and frequency stabilization of a semiconductor laser with a combination of FM sideband locking and optical feedback

We describe a novel method for semiconductor laser noise reduction that uses a combination of optical and electronic feedback. A Doppler-free Faraday resonance in Cs vapor provided both optical feedback and discrimination for an electronic feedback scheme incorporating FM sideband spectroscopy. The introduction of electronic feedback further reduced the low-frequency fluctuation noise power by more than 2 orders of magnitude, resulting in a linewidth of 1.4 kHz

Self-quenching of the semiconductor laser linewidth below the Schawlow-Townes limit by using optical feedback

We demonstrate theoretically and experimentally self-quenching of the fundamental semiconductor laser frequency fluctuations to a level that is orders of magnitude below the Schawlow-Townes limit for a solitary laser. It is shown that the main operative mechanism is the combined action of a frequency-dependent internal loss and amplitude-to-phase coupling. The internal frequency-dependent loss is introduced by means of spectrally narrow external optical feedback, which provides a strong frequency-dependent dispersion. Linewidth reduction by a factor of 2 X 10^3 is demonstrated by using a narrow Doppler-free Faraday resonance in Cs vapor

Amplitude noise reduction in semiconductor lasers with weak, dispersive optical feedback

We present the theory and measurements of the amplitude noise spectrum from a semiconductor laser with weak optical feedback (Pfb/Pout ~10^-6) from an external cavity containing an element of dispersive loss. The laser noise is found to be reduced over most of the low-frequency spectrum, although an increase in the noise is observed at frequencies corresponding to multiples of the external-cavity free spectral range. The low-frequency noise reduction closely follows theoretical predictions, and a reduction of as much as 7 dB is measured at an injection current of 1.5 times the threshold current. The potential of this method for contributing to the production of amplitude-squeezed light is discussed

Failure of vaccination to prevent outbreaks of foot-and-mouth disease

Outbreaks of foot-and-mouth disease persist in dairy cattle herds in Saudi Arabia despite revaccination at intervals of 4-6 months. Vaccine trials provide data on antibody responses following vaccination. Using this information we developed a mathematical model of the decay of protective antibodies with which we estimated the fraction of susceptible animals at a given time after vaccination. The model describes the data well, suggesting over 95% take with an antibody half-life of 43 days. Farm records provided data on the time course of five outbreaks. We applied a 'SLIR' epidemiological model to these data, fitting a single parameter representing disease transmission rate. The analysis provides estimates of the basic reproduction number R(0), which may exceed 70 in some cases. We conclude that the critical intervaccination interval which would provide herd immunity against FMDV is unrealistically short, especially for heterologous challenge. We suggest that it may not be possible to prevent foot-and-mouth disease outbreaks on these farms using currently available vaccines

Semiconductor laser quantum noise limits

The quantum mechanical limits to the fundamental noise performance of semiconductor lasers are reviewed. Recent advances in pushing the laser noise below theses limits are then discussed with emphasis on pump suppression, electronic feedback, and correlation techniques such as optical feedback. It is found that narrow-linewidth semiconductor lasers with sub-shot- noise photon statistics are within the reach of current technology

Generation of amplitude-squeezed light from a pump-suppressed semiconductor laser with dispersive optical feedback

Amplitude-squeezed states are generated from a room-temperature semiconductor laser using a combination of pump suppression and dispersive optical feedback. The laser amplitude noise is found to be sensitive to extremely weak feedback levels, of the order of 10^(-8) of the output power. a reduction of the noise from 2% below the standard quantum limit (SQL) under free-running conditions to 19% below the SQL under optimal feedback conditions is obtained. A single mode theory is presented but is found to be inadequate in explaining the measured dependence of the noise reduction on the feedback power. A multimode theory including asymmetrical cross-mode nonlinear gain is proposed to explain this discrepancy

Theory of dark resonances for alkali vapors in a buffer-gas cell

We develop an analytical theory of dark resonances that accounts for the full atomic-level structure, as well as all field-induced effects such as coherence preparation, optical pumping, ac Stark shifts, and power broadening. The analysis uses a model based on relaxation constants that assumes the total collisional depolarization of the excited state. A good qualitative agreement with experiments for Cs in Ne is obtained.Comment: 16 pages; 7 figures; revtex4. Accepted for publication in PR