Infrared laser-emission study in a resonantly excited sodium vapor

We report on a study of time dependence of ir laser emission at 3.41 μm in a dense Na vapor that is resonantly excited to the 3² P levels by a flashlamp, pumped dye laser. Energy-pooling collisions (excitation transfer) between excited atoms create a large population inversion among the 5² S _1/2 and 4² P _3/2 states which is destroyed by electron collisions as a result of subsequent plasma formation. The ir laser emission may serve as a new diagnostic tool to follow the time evolution of such media.     

Electroabsorption of excitons in f.c.c. TlBr and TlCl

The exciton binding energy, band gap, and static dialectric constant were obtained from electromodulation measurements on the face-centered cubic (NaCl structure) phase of TlBr. An unusual electroabsorption structure has been observed in TlBr and TlCl for features which have no established assignment.     

Central collisions with a projectile of 1.8 GeV/nucleon 40Ar

Single particle inclusive spectra and the associated multiplicity were obtained with a magnetic spectrometer and an azimuthal array of 30 ?erenkov counters from collisions of 1.8 GeV/nucleon ⁴⁰Ar on Be and Cu targets. No change is seen in the shape of the spectra obtained by the spectrometer for various multiplicity requirements.     

Categorization and discrimination of nonspeech sounds: differences between steady-state and rapidly-changing acoustic cues

Different patterns of performance across vowels and consonants in tests of categorization and discrimination indicate that vowels tend to be perceived more continuously, or less categorically, than consonants. The present experiments examined whether analogous differences in perception would arise in nonspeech sounds that share critical transient acoustic cues of consonants and steady-state spectral cues of simplified synthetic vowels. Listeners were trained to categorize novel nonspeech sounds varying along a continuum defined by a steady-state cue, a rapidly-changing cue, or both cues. Listeners' categorization of stimuli varying on the rapidly changing cue showed a sharp category boundary and posttraining discrimination was well predicted from the assumption of categorical perception. Listeners more accurately discriminated but less accurately categorized steady-state nonspeech stimuli. When listeners categorized stimuli defined by both rapidly-changing and steady-state cues, discrimination performance was accurate and the categorization function exhibited a sharp boundary. These data are similar to those found in experiments with dynamic vowels, which are defined by both steady-state and rapidly-changing acoustic cues. A general account for the speech and nonspeech patterns is proposed based on the supposition that the perceptual trace of rapidly-changing sounds decays faster than the trace of steady-state sounds.     

Squeezing in the audio gravitational-wave detection band

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.     

Measurement of gouy phase evolution by use of spatial mode interference

An experimental technique to observe and accurately measure the Gouy phase evolution of Hermite-Gaussian modes is presented. Because of the unique features of spatial mode interference frequency-locking error signals, we are able to readily perform explicit measurement of the Gouy phase in a simple and highly accurate manner. We present these data and discuss the technique and its implications.     

Advanced interferometry,quantum optics and optomechanics in gravitational wave detectors

Currently operating laser interferometric gravitational wave detectors are limited by quantum noise above a few hundred Hertz. Detectors that will come on line in the next decade are predicted to be limited by quantum noise over their entire useful frequency band (from 10 Hz to 10 kHz). Further sensitivity improvements will, therefore, rely on using quantum optical techniques such as squeezed state injection and quantum non‐demolition, which will, in turn, drive these massive mechanical systems into quantum states. This article reviews the principles behind these optical and quantum optical techniques and progress toward there realization.     

Stereochemically versatile synthesis of the C1-C12 fragment of tedanolide C

A flexible synthesis of the C1-C12 fragment of Tedanolide C has been accomplished in eight steps from 2-methyl-2,4-pentadienal. Asymmetric hydroformylation of a 1,3-diene allows for the late-stage generation of either C10 epimer with complete catalyst control. Diastereoselective addition of an isobutyryl β-ketoester dianion to an α,β-disubstituted chiral aldehyde sets the C5 stereochemistry while installing the geminal dimethyl unit. Differential protection of a syn-1,3-diol is performed as a highly efficient single-pot operation.     

Lasers and optics: looking towards third generation gravitational wave detectors

Third generation terrestrial interferometric gravitational wave detectors will likely require significant advances in laser and optical technologies to reduce two of the main limiting noise sources: thermal noise due to mirror coatings and quantum noise arising from a combination of shot noise and radiation pressure noise. Increases in laser power and possible changes of the operational wavelength require new high power laser sources and new electro-optic modulators and Faraday isolators. Squeezed light can be used to further reduce the quantum noise while nano-structured optical components can be used to reduce or eliminate mirror coating thermal noise as well as to implement all-reflective interferometer configurations to avoid thermal effects in mirror substrates. This paper is intended to give an overview on the current state-of-the-art and future trends in these areas of ongoing research and development.     

Molecular orientation of asphaltenes and PAH model compounds in Langmuir-Blodgett films using sum frequency generation spectroscopy

Asphaltenes are an important class of compounds in crude oil whose surface activity is important for establishing reservoir rock wettability which impacts reservoir drainage. While many phenomenological interfacial studies with crude oils and asphaltenes have been reported, there is very little known about the molecular level interactions between asphaltenes and mineral surfaces. In this study, we analyze Langmuir-Blodgett films of asphaltenes and related model compounds with sum frequency generation (SFG) vibrational spectroscopy. In SFG, the polarization of the input (vis, IR) and output (SFG) beams can be varied, which allows the orientation of different functional groups at the interface to be determined. SFG clearly indicates that asphaltene polycyclic aromatic hydrocarbons (PAHs) are highly oriented in the plane of the interface and that the peripheral alkanes are transverse to the interface. In contrast, model compounds with oxygen functionality have PAHs oriented transverse to the interface. Computational quantum chemistry is used to support corresponding band assignments, enabling robust determination of functional group orientations.