Robert B. Green

Galvanic detection of optical absorptions in a gas discharge

An electrical signal, resulting from discrete optical absorptions, has been observed for a variety of elements, including several for which such an effect had not been previously reported. In the present case, the effect is observed as a change in the voltage across a gas discharge tube produced by irradiation with a laser tuned to the wavelength of a transition of a species in the discharge. This signal may be used—without optical detection apparatus—for spectroscopic investigations or analytical determinations of materials in the discharge. Signals were obtained for transitions of lithium, sodium, calcium, barium, uranium, neon, and helium, in commercial hollow cathode lamps, and neon and helium in conventional discharge tubes.

Use of an opto-galvanic effect to frequency-lock a continuous wave dye laser

An electrical signal, derived from a gas discharge irradiated by a CW dye laser, is used to lock the laser to characteristic transition frequencies of species in the discharge. The technique may be used with commercial hollow cathode lamps to lock to both resonance and excited state transitions in a wide variety of elements.

Detection of sodium trace contamination in furnace atmospheres at 1000 °C

Free sodium atoms were detected by resonance fluorescence in an open contaminated quartz tube heated to 1000 °C. The quartz tube and furnace were similar to those used in semiconductor device processing. Fluorescence was excited by a cw dye laser tuned to the sodium D1 or D2 transition and directed along the axis of the furnace. Fluorescence from the sodium D2 line emitted in the axial direction was collected by a telescopic system and focused onto a photomultiplier tube. The estimated minimum detectable sodium density in the furnace is 5×105 atoms/cm3. No free sodium was detectable in a processing tube that had not been intentionally contaminated.

Laser-Enhanced Ionization of Refractory Elements in a Nitrous Oxide-Acetylene Flame:

Laser-enhanced ionization (LEI) spectrometry using a water-cooled electrode immersed directly in a nitrous oxide-acetylene flame has been examined for the determination of refractory elements. LEI detection limits for refractory elements in aqueous solution are comparable to or better than detection limits obtained by flame atomic absorption, plasma emission, and atomic fluorescence techniques. Only graphite furnace atomic absorption spectrometry exhibits superior detectability for certain refractory elements in aqueous solution over LEI spectrometry using a nitrous oxide-acetylene flame. The successful application of the nitrous oxide-acetylene flame now extends the applicability of LEI spectrometry to include most of the elements in the periodic table which can be determined by other common atomic spectrochemical techniques.

An Active Nitrogen Plasma Atom Reservoir for Laser-Induced Ionization Spectrometry

Abstract A microwave-induced, atmospheric pressure active nitrogen plasma has been investigated as an atom reservoir for laser-induced ionlzation spectrometry. Discrete analyte samples were introduced into the active nitrogen plasma by a microarc atomizer. Both laser-enhanced ionizatlon (LEI) and dual laser ionlzation (DLI) were carried out in the plasma plume that extended from the Beenakker cavity.

Laser-Induced Ionization in on Atmospheric-Pressure Microarc-Induced Plasma

Abstract A microarc discharge operated at atmospheric pressure in flowing helium is investigated as an atom reservoir for laserinduced ionization spectrometry. The operational characteristics of the microarc discharge as a primary atom source for atomic spectrometry are briefly examined. Preliminary observations of atomic emission and laser-induced ionization of sputtered analyte atoms in the microarc discharge and plasma are presented. A detection limit of 3 ng has been estimated for sodium by direct laser ionization in the helium microarc-induced plasma.

Electrical characteristics of microwave-induced plasmas for laser-induced ionization spectrometry

Abstract The electrical properties of microwave-induced plasmas (MIPs), relevant to signal detection of laser-induced ionization, have been investigated. Direct current vs. applied voltage relationships have been characterized for both argon and argon-active nitrogen plasmas. Suppression of signal detection for laser-induced ionization in the active nitrogen plasma is similar to that encountered in flames in the presence of thermally-ionized Group IA elements.