Barry K. Ward

High-pressure (>1 bar) dielectric barrier discharge lamps generating short pulses of high-peak power vacuum ultraviolet radiation

We have investigated the scaling of peak vacuum ultraviolet output power from homogeneous Xe dielectric barrier discharges excited by short voltage pulses. Increasing the Xe fill pressure above 1 bar provides an increased output pulse energy, a shortened pulse duration and increases in the peak output power of two to three orders of magnitude. High peak power pulses of up to 6 W cm−2 are generated with a high efficiency for pulse rates up to 50 kHz. We show that the temporal pulse characteristics are in good agreement with results from detailed computer modelling of the discharge kinetics.

Enhanced performance of an EUV light source (λ = 84 nm) using short-pulse excitation of a windowless dielectric barrier discharge in neon

The electrical and optical characteristics of a dielectric barrier discharge (DBD) based neon excimer lamp generating output in the extreme ultraviolet (EUV) spectral range (? = 84?nm) have been investigated experimentally. We report a detailed comparison of lamp performance for both pulsed and sinusoidal voltage excitation waveforms, using otherwise identical operating conditions. The results show that pulsed voltage excitation yields a ~50% increase in the overall electrical to EUV conversion efficiency compared with sinusoidal waveforms, when operating in the pressure range 500?900?mbar. Pulsed operation allows greater control of parameters associated with the temporal evolution of the EUV pulse shapes (risetime, instantaneous peak power). The Ne DBD based source is also found to be highly monochromatic with respect to its spectral output from the second continuum band at ? ~ 84?nm (5?nm FWHM). This continuum band dominates the spectral emission over the wavelength range 30?550?nm. Lamp performance; as measured by the overall EUV output energy, electrical to EUV conversion efficiency and spectral purity at ? ~ 84?nm; improves with increasing gas pressure up to p = 900?mbar.

Pulsed VUV sources and their application to surface cleaning of optical materials

Development of pulsed excitation techniques for high-pressure dielectric barrier discharges (DBD) has led to a short-pulsed, high-peak-power, spatially uniform source of UV7VUV radiation -- a preferred type of output for materials processing and many other applications. Results of such a Xe2* DBD source at 172 nm for removing mountants from optical surfaces and for removing hydrocarbon contamination from optical and polymer surfaces are presented.

Is There a Link Between Quantum Mechanics and Consciousness

This essay examines the link (if any) between quantum mechanics and consciousness and the problem of interpretation. The ‘measurement problem’ that arises from the ‘Copenhagen Interpretation’ is discussed and alternative interpretations such as Everett’s ‘Parallel Worlds’, Bohm’s ‘Hidden Variables’ and the ‘Heisenberg-Dirac Propensity’ interpretations are examined. The role of consciousness in the ‘Parallel Worlds’ theory is examined in greater detail together with quantum theories of mind due to Stapp, Eccles, Hodgson and Penrose. The affect of ‘Interactive Decoherence’ on proposed theories of quantum dependant brain function is also discussed.

Development of incoherent EUV/VUV light sources: Tailoring the output pulse characteristics for materials processing applications

The temporal characteristics of the output pulses generated by an excimer-based incoherent light source operating in the deep ultraviolet between 80nm<λ<160nm have been investigated in detail. Generation of output pulses with the highest peak powers, shortest durations (FWHM) and fastest leading-edge risetimes, occurred at the highest operating pressure studied (900mbar).

Measurements of the electrical to VUV conversion efficiency in a xenon dielectric barrier discharge lamp by oxygen actinometry

Within the plasma of high-pressure Xe2* excimer lamps, measurements of the intrinsic efficiency for the conversion of electrical input power into lambda~172nm output are notoriously difficult to undertake experimentally. In particular, the spatially integrated VUV output is difficult to determine with reasonable accuracy. Direct measurements of the far-field VUV irradiance from the lamp require either evacuated or inert-gas filled photon propagation paths to prevent photo- absorption by O2 that occurs for lambda< 190nm1. However, by using controlled flows of pure oxygen through an external cell surrounding the lamp, the total VUV output power may be measured by means of O2 actinometry. In this paper, a medium-scale Xenon excimer lamp was fabricated using Suprasil 310 fused-silica tubing fitted with VUV transmitting fine metal mesh electrodes to allow the VUV photons to exit the plasma region with minimal attenuation. The performance of the Xenon excimer lamp was investigated using electrical excitation from custom-built high-voltage pulsed power supplies with fast pulse slew rates (<1mus) and at elevated pulse repetition frequencies (3-30kHz). The results obtained for a range of operating conditions (Xe pressure, pulse voltage amplitude, pulse frequency) clearly demonstrate that even in pulsed operation, the lamp can operate in two distinct modes of efficiency with well-defined transition or switching points. Analysis of the measured Ozone production rates from VUV photolysis indicate the highest intrinsic efficiency for VUV production within the plasma was 38% (Xe = 225 mb, pulse rate = 2.77kHz for input power loadings 5-10 W). This compares with ~60% reported by Hitzschke and 56% - 62% from detailed modelling of the discharge kinetics in Xe2* excimer lamps3.