Thomas Morrow

Properties of ZnS thin films prepared by 248‐nm pulsed laser deposition

Pulsed laser deposition (PLD) from a hot pressed manganese doped ZnS target using a KrF laser, has produced a high rate deposition method for growing luminescent thin films. Good stoichiometric quality and typical luminescent crystal structures have been observed with a predominant hexagonal phase and little evidence of the cubic phase. The luminescent characteristics were determined by cathodoluminescence and photoluminescence excitation and stable electroluminescence was observed under pulsed dc conditions with a minimum brightness of 150 cd/m2. PLD film characteristics are compared with those observed in radio‐frequency sputtered samples.

Electron number density measurements in magnesium laser produced plumes

Abstract Interferometry has been used to investigate the spatio-temporal evolution of electron number density following 248 nm laser ablation of a magnesium target. Fringe shifts were measured as a function of laser power density for a circular spot obtained using a random phase plate. Line averaged electron number densities were obtained at delay times up to ∼100 ns after the laser pulse. Density profiles normal to the target surface were recorded for power densities on target in the range 125–300 MW cm −2 .

Spatially and temporally resolved emission intensities and number densities in low temperature laser-induced plasmas in vacuum and in ambient gases

Abstract Spectroscopic measurements on plasmas produced by laser ablation of YBa2Cu3O7 show that the presence of ambient oxygen leads to enhanced local number densities and temperatures at the expanding front of the plasma plume. Enhanced local temperatures (and local excitation rates) are attributed to the increased collisional redistribution of high initial {ce:inline-formula}z-directed{/ce:inline-formula} plume velocities observed via increased spectral line widths in ambient gases.

Use of a random phase plate as a KrF laser beam homogenizer for thin film deposition applications

Fabrication of devices based on thin film structures deposited using the pulsed laser deposition technique relies on reproducibility and control of deposition rates over substrate areas as large as possible. Here we present an application of the random phase plate technique to smooth and homogenize the intensity distribution of a KrF laser footprint on the surface of a target which is to be ablated. It is demonstrated that intensity distributions over millimeter-sized spots on the target can be made insensitive to the typical changes that occur in the near-field intensity distribution of the ultraviolet output from a KrF laser.

A technique for mapping three-dimensional number densities of species in laser produced plumes

The potential of a diagnostic technique to provide quantitative three‐dimensional (3D) density distributions of species in a low temperature laser‐produced plume is shown. An expanded, short pulse, tunable dye laser is used to probe the plume at a set time during the expansion. Simultaneous recording of two‐dimensional in‐line absorbance maps and orthogonal recording of laser induced fluorescence permits the 3D density mapping by scanning the dye laser frequency. Preliminary data, supported by a simple model, is presented for the case of Bau2009II ions in a YBCO plume heated by a KrF laser.

Spectral simulation of laser ablated magnesium plasmas

We describe a collisional-radiative equilibrium model for predicting the optical emission spectrum of low-temperature magnesium plasmas, specifically those created by laser ablation. In the model, levels are populated by a balance of collisional and radiative rates. We include Stark widths of lines and trapping of radiation in the calculations. By use of this model we discuss various issues of importance in spectral analysis of laser ablated plasma plumes, such as the partial local thermodynamic equilibrium approximation, line trapping and time dependence.

Three-dimensional electron number densities in a titanium PLD plasma using interferometry

Interferometry has been used to investigate the spatio-temporal evolution of the electron number density in the initial stages of expansion following 248 nm ablation of a titanium target. Three-dimensional electron number densities are obtained from an interferogram of the plasma plume using the Abel inversion technique.

Study of ground-state titanium ion velocity distributions in laser-produced plasma plumes

The velocity distribution of ground-state titanium ions within a low-temperature plasma resulting from the laser ablation of a titanium target has been investigated. A KrF excimer laser was focused onto the target at moderate fluences (<10 Ju200acm−2) in vacuum (∼2×10−5u200aTorr). Time-of-flight distributions were determined as functions of distance from target and laser fluence using absorption spectroscopy. The results were found to be described consistently by a Maxwell–Boltzmann distribution with zero flow velocity. The most probable velocity was found to scale with the square root of the incident laser fluence.

Line shape study of Ba ions in laser produced plasmas

Detailed measurements of spatio-temporal variations in the line strengths and line shapes for Ba ion absorption lines, observed in laser-ablated YBCO plasma plumes, show that the presence of ambient oxygen leads to enhanced local number densities and temperatures at the expanding front of the plasma plume. Enhanced local temperatures (and local excitation rates) are attributed to the increased collisional redistribution of high initial z-directed plume velocities in the presence of ambient oxygen.

Two-dimensional imaging of low temperature laser produced plasmas

Laser induced fluorescence images of a low temperature laser-produced plasma expanding into vacuum are presented and compared to a computer simulation. The complex nature of a plume expanding into background gas is highlighted, along with a potential means of simplifying the study of such systems.