-70 dB optical carrier suppression by two-beam coupling in photorefractive media

Suppression of an optical carrier from an RF modulated laser beam of wavelength 532 nm is performed using two-beam coupling in photorefractive barium titanate. A theoretical analysis reveals that perfect suppression can be achieved at a specific modulation strength, which depends on the gain and intensity ratio between the two beams. The experiments achieve a maximum of -72.9±2.4 dB carrier suppression at the theoretically ideal modulation strength, and -61.0±2.4 dB for small modulation strengths. Received: 29 November 2000 / Revised version: 2 February 2001 / Published online: 27 April 2001     

Über die Chromosphärentheorie von A. Unsöld

Zeitschrift für Physik A Hadrons and nuclei - Vor kurzem hat A. Unsöld eine neue Theorie der Chromosphäre entwickelt. Gegen diese Theorie werden einige Einwände erhoben. Im...     

The electrostatic potentials in an electron-cyclotron-resonance processing plasma

The axial distribution of the electrostatic potentials ofan electron-cyclotron resonance (ECR) processing plasma confined in a do magnetic mirror geometry was characterized. The potential profiles far argon and helium at 8.0x 10^–4 and 4.0 × 10^–4 Torr were measured using electron emissive probes. The experimental measurements were then compared with the predictions of a one-dimensional, electrostatic, particle-in-cell computer code which runs on a personal computer. The potential profiles as predicted by the code showed good agreement with the experimental measurements.     

Multiple vibrational excitations of H2O and D2O on Si(100)(2 × 1): A HREELS study

The HREELS (high-resolution electron energy-loss spectroscopy) spectra from H₂O and D₂O chemisorbed on the clean Si(100)(2 × 1) surface have been investigated in the energy region between about 500 and 1400 meV. For the first time, second overtones have been observed for a chemisorbed species. This observation is believed to be due to the enhancement of the O-H stretching fundamental and overtone modes because of the temporary formation of a negative ion that occurs when the incident electron is briefly trapped in a shape resonance. Additional multiple and combination modes are observed involving the resonance enhanced overtones as well as the fundamental modes. Furthermore, the dissociation energy of the hydroxyl group has been determined and found to be much larger than the actual energy needed to dissociate hydroxyl groups on the surface, indicating that the driving force for the observed atomic rearrangements is probably Si-O bond formation rather than O-H dissociation.     

A Note on “Trial by Computer”—A Case Study of the Use of Simple Statistical Techniques in the Detection of a Fraud

We look at a statistical aspect of a recent case study. Although our discussion does not invalidate the general conclusions obtained there, it does suggest that the time series modelling may have been sub-optimal, and indicates how an alternative model specification could more probably have generated the sample statistics that were actually observed. The implication of our remarks is that discrimination between deterministic and stochastic non-stationarity, even if overlooked on preliminary inspection of the original data, will also be apparent from the raw sample autocorrelation plots.     

The microwave and millimeter-wave spectra of hypochlorous acid

To permit atmospheric monitoring of the molecule, the microwave spectra of two isotopic species of hypochlorous acid, HOCl, have been measured in the frequency range 8–650 GHz. Three b-type branches and an a-type Q branch have all been measured for the first time; improved measurements have been made for the a-type R branches. The analysis has included combination differences of earlier high-resolution infrared spectra to give accurate values for all rotational constants, five quartic and five higher degree centrifugal distortion constants, as well as the chlorine nuclear quadrupole and spin-rotation coupling constants. From the Stark effect, accurate values have also been obtained for both components of the molecular dipole moment. A table of transition frequencies of potential use in atmospheric monitoring is presented.