P. F. Barker

Temperature measurements by coherent Rayleigh scattering

We demonstrate, for the first time to our knowledge, the utility of coherent Rayleigh scattering (CRS) for temperature measurements in low-density gases and weakly ionized plasmas by measuring the translational temperature of neutral argon in a glow discharge. By analysis of the near-Gaussian spectral profile of the CRS signal, we determine temperatures with an uncertainty of </=3%. We also investigate the intensity range over which this simple Gaussian analysis can be used for temperature measurements and discuss its potential for gas diagnostics.

Optical Stark deceleration of nitric oxide and benzene molecules using optical lattices

We describe the deceleration of nitric oxide, benzene and xenon atoms in a molecular beam using one-dimensional pulsed optical lattices created by fields with intensities in the 1012 W cm−2 range. We show that for the same pulse duration and lattice intensity the velocity of the molecules can be controlled by tailoring the lattice velocity. By utilizing the time-dependent oscillatory motion of the molecules within the lattice, we demonstrate the deceleration of nitric oxide from an initial velocity of 400 m s−1 to a final velocity of 290 m s−1 in a single 5.8 ns pulse. Using higher intensities, we measure the deceleration of benzene molecules from 380 m s−1 to 191 m s−1, representing a 75% reduction in the kinetic energy within the lattice over the same duration.

Narrow-band coherent Rayleigh scattering in a flame

We report on the application of coherent Rayleigh scattering (CRS) to the measurement of temperature in a flame using narrow bandwidth pump and probe fields. High resolution measurements of the line shape were used to derive flame temperature based on fits to the line shape. An uncertainty in the temperature of 3% was determined utilizing a CRS model that includes scattering from a multicomponent gas for the first time. This model was validated at room temperature for a mixture of atomic and molecular species.

Slowing cold molecules with pulsed optical lattices

This work presents the proposed schemes for decelerating cold molecules created in pulsed supersonic expansions using pulsed optical lattices. The first scheme relies on the application of a decelerating optical lattice with a dipole-potential well depth of approximately 1 K, created by rapidly chirping medium-intensity fields in the 10 W/cm/sup 2/ range. This scheme is an optical analog of the Start decelerator that has been successfully used to slow a range of polar molecules. A significant fraction (about 10%) of the very heavy I/sub 2 /molecules in an Ar buffer gas is shown to be slowed by using this method over sub-microsecond time scales. In the second technique, an optical lattice with larger well depth in the 100 K range travelling at half the supersonic beam velocity is used to trap a significant fraction of the cold, high-velocity molecules. This technique is developed based on the property of periodic motion of the trapped molecules in the optical lattice; the molecules reverse their initial (relative) velocities in the lattice reference frame after half a period. Using this method the cold molecules can be transferred from high speed to zero velocity on nanosecond time scales. As an example, 33% of a CO molecule beam (1 K) with a velocity of 230 m/s is slowed utilising optical intensities of less than 10/sup 12/ W/cm/sup 2/.

Filtered Thomson scattering in an argon plasma

A filtered Thomson scattering technique has been developed. This technique has successfully demonstrated the capability to detect Thomson scattered light from a plasma in the presence of strong scattered light and high plasma luminosity. It relies on a rubidium vapor filter cell to provide strong attenuation of stray scattered laser light at the central wavelength of the laser whilst simultaneously allowing the passage of the spectrally broad Thomson scattered light. An ASE filter was developed to obtain a high spectral purity for the laser (pulsed Ti-Sapphire at 780 nm) employed in this study. Successful experiments were performed to detect the Thomson signal which was obtained from an atmospheric pressure argon plasma. Information on the electron number density and the electron temperature was derived from the Thomson signal by fitting a model curve to the data. The measurement results gave an electron temperature of 0.82 ± 0.06 eV, an electron number density of 1.61×1016 ± 0.05 ×1016 electrons/cm3.

Focusing ground state xenon using large quasi-electrostatic potentials

We focus ground state xenon atoms using a high intensity (1012 W/cm2) optical field and map the atomic density at the focus using multiphoton ionization. The results are in agreement with a quasi-electrostatic model

An optical decelerator for cold molecules

We demonstrate a single stage optical Stark decelerator for neutral molecules which reduced the velocity of benzene molecules in a molecular beam by 25 m/s corresponding to a kinetic energy reduction of 15 %.

An optical micro-linear accelerator for molecules and atoms

Summary form only given. Acceleration of molecules within a time varying electric field produced by an optical traveling wave has been proposed as a means to accelerate neutral particles to high velocity. This technique is attractive because extremely large Stark forces can be produced by the high electric field gradients that can be created within an optical traveling wave. The electrodeless electric field gradient produced by focused laser beams can be orders of magnitude greater than electrostatic gradients, allowing acceleration of polar as well as polarizable molecules and atoms. This concept has already been used to accelerate ultracold atoms in a very weak optical periodic potentials, or lattices, and acceleration up to the velocities in the m/s velocity was observed. We report on the study of acceleration of polarizable particles to velocities in excess of 10 km/s range in an accelerated optical lattice, using high intensity pulsed fields.