W. R. MacGillivray

Stepwise electron and laser excitation of atoms

Abstract A review is presented of the application of stepwise electron/laser excitation techniques to the study of electron-atom collision processes. The theory associated with such techniques is reviewed and includes a number of typical case studies. A full discussion of laser excitation processes is included. A detailed review of stepwise electron/laser excitation experiments is also presented.

Lithographic pattern formation via metastable state rare gas atomic beams

Atomic beams of argon and neon in excited electronic metastable states have been used to pattern bare and dodecanethiol (DDT) resist coated Au/Si substrates. Positive and negative contrast patterning has been observed for DDT-Au/Si, and negative patterning has been observed for bare Au/Si. Our results provide evidence for the formation of these negative patterns resulting from significant background pump oil contamination, and at significantly lower metastable dosages than previously observed. X-ray photoelectron spectroscopy (XPS) results indicate the growth of a carbonaceous layer as the origin of the negative resists in DDT-Au/Si and bare Au/Si substrates. For DDT-Au/Si, results indicate that the transition from positive to negative resist formation relies both on the metastable dosages and level of background pump oil contamination.

The current status of superelastic scattering studies for e--Na atom collisions

New data from a superelastic scattering experiment on e--Na atom collisions at 10, 15, 20, 25 and 30 eV incident energy are presented and compared with existing experimental data and theories based respectively on the distorted wave second-order Born approximation, 15 state close-coupling and coupled channel optical potential calculations. Overall, fair to good agreement is found between theory and experiments for individual atomic scattering parameters. The loss of coherence previously observed by some workers at small scattering angles (5-20 degrees ), is confirmed at 20 eV and also observed at 25 eV. This loss of coherence is poorly modelled by existing theories.

Superelastic electron scattering from laser excited rubidium at 20 eV incident energy

Superelastic electron scattering measurements are presented from rubidium atoms excited by laser radiation to the 52P states at around 780 nm. The incident energy of the electrons was 18.4 eV corresponding to 20 eV incident electrons for the excitation process 52S-52P. The measurements were conducted over a range of scattering angles from 5° through to 125°. A complete set of atomic collision parameters for the interaction process is presented together with the associated pseudo-Stokes parameters obtained from the measurements. A comparison with three sophisticated theoretical models indicates that none of the models completely describes the interaction process at this energy, and that further experimental and theoretical work is needed.

Electron-impact excitation of the 3D state of sodium from the optically prepared 3P state

An experimental investigation of electron-impact excitation of the 3 2D-state from the laser-excited 3 2P state of atomic sodium is reported for 30 eV incident electron energy. A detailed consideration of the measurement technique is presented, based on the density matrix description of electron-impact-induced atomic transitions for target atoms in which the spin of the target electron is unchanged. It is shown that some inference about excitation probabilities between individual magnetic substates of the P- to D-state transition can be made from measurements of the four pseudo-Stokes parameters. A description of the inelastic scattering experiment and an analysis of the experimental measurements in terms of both the standard atomic collision parameters and magnetic substate excitation probabilities are presented. Convergent close-coupling theoretical calculations are compared with the experimental results and show good agreement.

Effect of Laser Intensity Variation and Coherence on the Resonant Excitation of the 61P1–61D2 Transition of Atomic Mercury

Abstract The effects of resonant laser excitation of an atomic transition whose lower state is not a ground state are reported. The system studied is the optical excitation to the 61D2 state from the electron-excited 61P1 state of Hg. Both the total fluorescence intensity and the time-resolved electron-photon coincidence fluorescence signal from the 61D2–63P1 relaxation channel are observed as the laser intensity is varied. In the coincidence signals, a manifestation of Rabi cycling in the optically excited transition is evident. The experimental data are in generally good agreement with predictions from a quantum-electrodynamic model.

The theory of stepwise electron and laser excitation of atoms. I. Weak optical excitation case

For pt.I see ibid., vol.17, p.1675 (1984). A theory of stepwise excitation of atoms is presented in which electron excitation is followed by strong single-mode laser excitation. A model of the strong laser excitation processes is considered and theoretical expressions are obtained for line polarizations and electron-photon coincidence signals applicable to both axial and planar symmetry stepwise excitation experiments.

Long term laser frequency control for applications in atomic physics

An improvement to the saturated absorption technique of long term stabilization of lasers is reported. This new method enables stabilization to the centre of saturated absorption features regardless of whether the peaks are symmetric or asymmetric. Another feature of the locking system is its ability to stabilize the laser at precisely known small detunings from the centre of the absorption line. The locking system has been applied to both dye laser and titanium sapphire laser systems. The long term drift for each was measured to be smaller than the laser jitter bandwidth of about 1 MHz for periods of hours, and no mode hops were recorded over several weeks of operation.

Experimental determination of atomic state-dependent optical forces

An experimental demonstration of the state-dependent nature of the forces exerted on an atom by resonant radiation is reported. Sodium atoms, which are contained in a highly collimated beam, are initially prepared in a particular ground hyperfine substate by optical pumping. They are then deflected by resonant laser radiation of known polarization. Measurements of the magnitude of the deflection show a dependence on the way the atoms were initially prepared, confirming the predictions of a recently developed theoretical model. The experimental data show good agreement with calculations of the theory using a full quantum electrodynamic description of the sodium transition involved.

Observation of optical nutations in atomic sodium using a fast light switch

Abstract Optical nutations in the D 2 line of sodium have been observed when a rectangular light pulse is incident on the vapour. The pulse, with a rise time of approximately 1 ns, is derived from an extracavity electro-optic device. The resulting transient emanates from only one velocity class of atoms.