Visible Near Region Research Articles

Experimental microwave radiometry of a sonoluminescing bubble

In spite of substantial research in single-bubble sonoluminescence this decade, the electromagnetic emission mechanism is still not sufficiently understood. Current models of the mechanism are based on experimentally measured spectra in the visible and near-visible region. An experimental arrangement used to measure the microwave emission is described. For a xenon-doped bubble, which emits the greatest amount of light, no microwave radiation is observed at or above the minimum detectable power of the apparatus, which corresponds to a bubble radiating approximately 1 nW in a 1-GHz bandwidth at 2 GHz. Any theory of single-bubble sonoluminescence when extended to the microwave region must be consistent with this upper limit for the radiation.

Photoacoustic and filter measurements related to aerosol light absorption during the Northern Front Range Air Quality Study (Colorado 1996/1997)

A new photoacoustic instrument for the measurement of aerosol light absorption was collocated with conventional aerosol instrumentation during the 1996–1997 winter intensive monitoring period of the Northern Front Range Air Quality Study. Measurements of the light absorption efficiency for black carbon were 5 m2/g at 685 nm and 10 m2/g at 532 nm, and for elemental carbon, they were 3.6 m2/g at 685 nm. We show that these values together with previous photoacoustic measurements of aerosol light absorption shed some light on the wavelength dependence of absorption efficiency for carbonaceous aerosol in the visible and near‐visible region. Integrating plate type filter measurements of aerosol light absorption result in far larger values than those measured with the photoacoustic instrument. We demonstrate that a recently published correction technique [Horvath, 1997] can yield improved agreement.

Application of 2,6-Diphenylpyridine as a Tridentate [C∧N∧C] Dianionic Ligand in Organogold(III) Chemistry. Structural and Spectroscopic Properties of Mono- and Binuclear Transmetalated Gold(III) Complexes

The synthesis of a series of mono- and binuclear cyclometalated gold(III) complexes containing the tridentate C∧N∧C ligand (HC∧N∧CH = 2,6-diphenylpyridine) was developed using K[AuCl4] and the organomercury(II) compound Hg(C∧N∧CH)Cl as precursors. The molecular structures of [Au(C∧N∧C)(Spy-2)] (Spy-2 = 2-mercaptopyridine), [Au(C∧N∧C)PPh3]ClO4, [Au2(C∧N∧C)2(μ-dppm)](ClO4)2, and [Au2(C∧N∧C)2(μ-dppe)](ClO4)2 have been determined by X-ray crystallography. In the crystal lattice of [Au2(C∧N∧C)2(μ-dppm)](ClO4)2 and [Au2(C∧N∧C)2(μ-dppe)](ClO4)2, interplanar separations of 3.4 A are observed between the intramolecular [Au(C∧N∧C)] moieties, which imply the presence of weak π−π interactions. The torsion angle between the two [Au(C∧N∧C)] units in the former is 8.7°, while a larger angle (34.2°) is observed in the latter. In the absorption spectra, the binuclear complexes show a red shift for the absorption band in the near-visible region compared to the mononuclear analogues. This is attributed to π−π interactions b...

Epioptics: progress and opportunity

Progress is reviewed in the use of optical techniques operating in the visible and near-visible region of the spectrum to probe surfaces and interfaces. Epioptic techniques, such as spectroscopic ellipsometry, reflection anisotropy spectroscopy, Raman scattering, laser light scattering, second-harmonic generation and sum-frequency generation are discussed and their complementary nature emphasised. Opportunities for exploiting these techniques are outlined.

Trapped-hole centers in alkaline-earth oxides

Alkaline-earth oxides frequently exhibit a visible coloration when stimulated with photons or ionizing radiation. The defects responsible for this coloration are often due to paramagnetic hole centers, which absorb over a broad spectrum in the visible and near-visible region. As a result, the defects can be detrimental to the use of these materials as hosts for tunable lasers. In this article, we present our current understanding of trapped-hole (or V-type) centers in the alkaline-earth oxides with emphasis on experimental research using optical and magnetic resonance techniques. Discussions are focused on the production mechanisms, the structure of both intrinsic and impurity-compensated defects, and their thermal stability.

Linear one-step assay for the determination of orthophosphate

A rapid one-step spectrophotometric assay for orthophosphate that requires a single stable reagent solution is presented. The reagent solution, an aqueous mixture of ammonium molybdate and zinc acetate at pH 5.0, produces a stable complex with orthophosphate that absorbs strongly in the near-visible region of the light spectrum. Response to concentration of phosphate was linear up to 300 μ m phosphate with a molar absorptivity of 7200 m −1 cm −1 at 350 nm. The mild conditions for phosphate determination employed in this method are unique, making it particularly suitable for the assay of orthophosphate in the presence of labile organophosphates.

Atomic spectral lines when a quark is embedded in the nucleus

There has been a recent claim for the observation of fractionally charged particles. If this evidence is to be interpreted as due to a quark embedded in a heavy nucleus, a natural follow-up is to look for ''quark atoms'' through their spectral lines. The recent technique of single-atom detection may be one way of doing this. Such searches will require as inputs knowledge of the spectroscopic transitions in the quark atom. The presence of the quark causes large shifts in spectral lines which fall in the visible and near-visible regions and a simple technique is presented based on interpolations in isoelectronic series for estimating these shifts quickly and accurately for any atom. Results are also presented for the x-ray transitions in heavy atoms and very accurate results for the various series in quark hydrogen. The techniques and results of this paper may also be relevant for searches in laboratory and astrophysical spectra.