Adam James Palmer

Quantitative comparison of rare-gas cold cathode discharge metastable atomic beam sources

Two commonly used cold cathode discharge sources to create rare gas metastable atomic beams are experimentally compared with respect to the output flux and the most probable velocity of the resulting beams. The systems are characterized with the same detection system thereby enabling an unambiguous performance comparison. The results of the experiments show that there is a clear distinction between the output beam characteristics of the beam sources.

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.

A high flux metastable atomic discharge source with three-dimensional translation

We present a new apparatus for the generation of a high flux metastable atomic beam. This source has provided a high flux of metastable helium and argon atoms via a cold cathode discharge with fluxes for metastable helium of up to 9 × 1014 sr−1 s−1. This new source can be translated in three dimensions whilst under vacuum and cooled to 77 K. Experimental results demonstrate that the distance of the source nozzle from the skimmer is important in obtaining the optimum flux. Under typical operating conditions, this optimal distance is 9–10 mm using He. Time-of-flight spectra show that for Ar the average thermal velocity of the beam is 540 m s−1 and can be reduced to 330 m s−1 by cooling the source with liquid nitrogen.

A hexapole magnetic guide for neutral atomic beams

In this paper we present a multiple element magnetic device to guide atoms using a spatially inhomogeneous magnetic field formed by a series of permanent hexapole magnets. The operation of the device is demonstrated using an enhanced beam of neon atoms in the 3P2 metastable state. These atoms are guided around a bend of 30 degrees from their original path. A flux of 4.35 x 10(9) +/- 2 x 10(7) atoms s(-1) was measured after the device yielding a transmission efficiency of approximately 9% of the input flux. Simulations of the center of mass motion of the atoms through the magnetic guide have been performed giving reasonable agreement with the experimental results.

Transverse electron momentum distribution in tunneling and over the barrier ionization by laser pulses with varying ellipticity

We study transverse electron momentum distribution in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, both experimentally and theoretically, that the transverse electron momentum distribution in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases.

Experimental ionization of atomic hydrogen with few-cycle pulses

We present experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an ab initio simulation over a wide range of laser intensities and electron energies.

Carrier-envelope phase effects in above-threshold ionization of atomic hydrogen

Recent experiments in ultrafast physics have established the importance of above-threshold ionization (ATI) experiments in measuring and controlling the carrier-envelope phase (CEP) of few-cycle laser pulses. We have performed an investigation of atomic hydrogen subjected to intense CEP- stable few-cycle laser pulses. The experimental ATI spectra have been compared to predictions from an ab initio numerical solution of the time-dependent Schr¨ odinger equation in three dimensions. Good agreement between experiment

The interaction of excited atoms and few-cycle laser pulses

This work describes the first observations of the ionisation of neon in a metastable atomic state utilising a strong-field, few-cycle light pulse. We compare the observations to theoretical predictions based on the Ammosov-Delone-Krainov (ADK) theory and a solution to the time-dependent Schrödinger equation (TDSE). The TDSE provides better agreement with the experimental data than the ADK theory. We optically pump the target atomic species and measure the ionisation rate as the a function of different steady-state populations in the fine structure of the target state which shows significant ionisation rate dependence on populations of spin-polarised states. The physical mechanism for this effect is unknown.

Transverse electron momentum distribution in tunneling and over the barrier ionization by strong-field laser pulses

We present the results of an investigation of the measurement of the transverse electron momentum (TEMD) distribution of atoms ionized though the interaction of strong-field light pulses of varying ellipticity. We show though experiment and theory that the TEMD for the tunneling regime and the over-the-barrier regime (OB) evolves in a qualitatively different way when polarization state of the ionizing laser changes ellipticity.

The interaction of ultrashort laser pulses and exotic atoms

In this work we present results for the ionization of metastable neon with ultrashort laser pulses. In addition to improving on the accuracy of previous measurements of ion yield, we show comparisons to advanced TDSE based theory. This work presents preliminary experimental evidence of the effects of preparing the target atoms into particular angular momentum projection (mj) states on the total ionization yield.