Monitoring of Paint Drying Process by Digital Speckle Correlation

The state of drying paint is monitored from the dynamic behaviors of the speckle pattern arising from laser illumination of the region inspected. Temporal variation of the peak height of the cross-correlation function between successive frames taken with a fixed interval is plotted until the peak maintains a stationary maximum value. We used a speckle pattern in the diffraction field for monitoring of a single region and that in the image field for simultaneous monitoring of various regions. Both the normal and the phase-only algorithms were compared for cross-correlation computation. The former showed more distinct variation of peak height.     

Doppler-free resonant two-photon transition for isotope separation

The Doppler-free two-photon transition by the use of two opposing laser beams makes the highly selective excitation of isotopic molecules possible. Saturation and pressure dependence of Doppler-free two-photon excitation with arbitrary amplitudes of the optical fields have been calculated and compared with those of the two-step transition and the single-photon transition. The result at the Doppler limit for low pressure gas reveals that the probability of the selective two-photon excitation with a moderate laser power can be larger than that of the single-photon excitation as well as that of the two-step excitation.     

Infrared-microwave double resonance of propynal by using the 3.51 μm HeXe laser

The 3.51 μm HeXe laser is magnetically tuned over a wavenumber of 0.2 cm^?1 and used for infrared absorption and double resonance spectroscopy. Eight rotation-vibration lines of propynal in the ν₂ band are assigned by the Stark effect. Eleven microwave transitions in the v₂ = 1 vibrational state are observed by the method of infrared-microwave double resonance. The rotational constants of the excited state and the band origin of the vibration ν₂ are determined from the observed spectra.     

Normal coordinate calculations of benzenoid hydrocarbons: Classification and characterization of Aromatic planar vibrations in polyacenes

Classification methods for aromatic planar vibrations are presented. These methods involve the potential energy distribution analysis and a ring motion analysis, which makes it possible to classify collective motions of CC bonds in these systems into certain typical patterns. The planar vibrations of benzene and polyacenes up to pentacene are classified in this way, and the characteristic vibrations of these molecules are so described and analyzed. Normal coordinate calculations of naphthacene and pentacene have been carried out to illustrate the classification, and results were found to be very satisfactory.     

Proton acceleration to 40 MeV using a high intensity, high contrast optical parametric chirped-pulse amplification/Ti:sapphire hybrid laser system

Using a high-contrast (10(10):1) and high-intensity (10(21) W/cm(2)) laser pulse with the duration of 40 fs from an optical parametric chirped-pulse amplification/Ti:sapphire laser, a 40 MeV proton bunch is obtained, which is a record for laser pulse with energy less than 10 J. The efficiency for generation of protons with kinetic energy above 15 MeV is 0.1%.     

Index-of-refraction sensors: virtually unlimited sensing power at the critical angle

In an effort to improve and simplify refractive index sensors, we identified a basic operation mode at the critical angle. Sensitivity to the refractive index is higher than in standard surface plasmon resonance sensors, and we have been able to demonstrate analytically that it is virtually an unbounded value. We describe this approach and submit a complete analytical study demonstrating its unlimited sensing power. To test the approach, we constructed an economical and basic sensor. Despite its simplicity, we demonstrated the discrimination capability to be of the order of 10(-6), as far as we know close to the best sensitivity ever recorded. This detection method is generally applicable to any optical system and may pave the way for the next generation of optical sensing devices.     

Determining the structure of phosphorus in phase IV

We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate.