S. D. Kramer

Method for counting noble gas atoms with isotopic selectivity

A method has been developed for direct counting of noble gas atoms and has been demonstrated for selected isotopes of krypton. In principle, a few atoms of the noble gases argon, krypton, xenon and radon can now be counted with isotopic selectivity whether stable or radioactive. A concept was originated in which a laser method would be used to count noble gas atoms of a particular isotope that are moving freely in an enclosure. As the concept developed, a parallel with Maxwells sorting demon became quite obvious since the plan was to sort out only atoms of a given type (Z selection), e.g. krypton atoms, from any other atom in the enclosure and then to sort the atom by isotope (A selection) before removing the atoms from the gas compartment. The plan was to count each atom as it was stored in a target until all atoms were counted.

A sensitive, absolute, and time-resolved method for the study of reactive atoms

Abstract Laser techniques for the production of free atoms at time t = 0 and their detection at r > 0 have been developed to measure the diffusion of Cs atoms in Ar and the reaction of Cs with O 2 in Ar gas.

Studies of lifetimes of rotationally cooled NO2 using time-resolved fluorescence excitation spectra

Abstract A taunble, pulsed dye laser with output in the region of 5750 to 6000 A was used to excite rotationally cooled NO 2 which was produced by expansion in conjunction with argon carrier gas through a supersonic nozzle. The resulting time-resolved fluorescence excitation spectra were used the lifetimes of various vibronic bands of NO 2 ( 2 B 2 ). The lifetimes measured were in the region of 15 to 40 μs which were shorter than those obtained from cell experiments. For each individual excitation wavelength, only a single exponential decay was observed from very early times through 250 μs.

One-atom detection in individual ionization tracks.

A major advance in one-atom detection using laser photoionization makes it possible to detect with microsecond time resolution single neutral atoms resulting from the stopping of energetic heavy ions in a buffer gas. This detection at the one-atom level, which gives the first direct evidence of nearly complete charge neutralization of stopped energetic ions, is shown to be possible even under the extremely adverse conditions associated with a densely ionized particle track.

Tunable VUV light generation for the low-level resonant ionization detection of krypton

High-power tunable VUV light pulses with energies up to 0.7 μJ were generated in the 115.7–116.9-nm region by use of a two-photon resonant four-wave mixing scheme in a Xe–Ar gas mixture. This is the highest reported pulse energy that has been produced in this wavelength region using a four-wave mixing process. Efficient detection of krypton isotopes at densities as low as 10 atoms/cm3 was demonstrated by resonantly ionizing the atom through its one-photon allowed state at the vacuum wavelength of 116.49 nm.

Determination of dissociative limit of NO2 and characteristics of a molecular beam by fluorescence excitation spectra

Abstract Fluorescence excitation spectra are used to determine the onset of predissociation of rotationally cooled NO 2 with an accuracy of 0.2 meV. The divergence and velocity distribution of the molecular beam are measured using only time-resolved and time-integrated fluorescence spectra. This eliminates the need for a separate velocity selector and mass spectrometer.

Resonance ionization spectroscopy of lithium

Abstract Saturated three-step resonance ionization of ground state lithium was demonstrated and the first measurement of the photoionization cross section from the excited n = 3 manifold of lithium was made. This demonstration of saturation shows the feasibility of detecting single atoms of lithium using sensitive charge detection methods.

Resonance ionization spectroscopy schemes for Ar, Kr and Xe

Abstract Laser schemes are suggested for the efficient ionization of Ar, Kr and Xe and the related two-photon transition rates are given. Ionization yields are calculated for each gas with reasonable laser parameters.

The reaction of Li with O2 in the presence of He or Ar

The reaction of Li with O2 in the presence of He or Ar was studied at a temperature near 150 °C for inert gas pressures between 29 and 1500 Torr. In both cases, the rate of loss of free Li atoms was linear with O2 partial pressure between approximately 0.003 and 1.3 Torr, but had a more complex dependence on inert gas pressure. In He, the reaction probably proceeded by means of the energy transfer mechanism where the dominant intermediate was LiO2*. The results in Ar are consistent with a reaction occurring through both the energy transfer mechanism in which LiO2* plays an important role and the bound intermediate complex mechanism where LiAr is the primary intermediate.

Resonance ionization spectroscopy with amplification

Abstract Resonance ionization spectroscopy (RIS) can be used to ionize selectively nearly all of the atoms in the periodic table. Here we propose RIS with amplification (RISA) which incorporates collisional processes occurring during a laser pulse in order to complete a photoionization cycle and thereby amplify the number of ion pairs produced from one atom. With RISA the ability to distinguisha “two-atom” sample from a “one-atom” sample is greatly enhanced.