We study the cooling of a dielectric nanoscale particle trapped in an optical cavity. We derive the frictional force for motion in the cavity field and show that the cooling rate is proportional to the square of oscillation amplitude and frequency. Both the radial and axial components of the center-of-mass motion of the trapped particle, which are coupled by the cavity field, are cooled. This motion is analogous to two coupled but damped pendulums. Our simulations show that the nanosphere can be cooled to e-1 of its initial momentum over time scales of hundredths of milliseconds.

The application of optical forces has allowed unprecedented control over the motion of atoms leading to laser cooling and trapping¹ and Bose–Einstein condensation². More recently, the manipulation of cold neutral polar molecules using electrostatic fields has been used to create slow cold molecules in the laboratory frame³. Here, we report on the controlled manipulation of molecules using deep periodic optical lattice potentials (22 K) created by intense optical fields (10¹¹ W cm⁻²). By using the oscillatory motion of nitric oxide molecules in these potentials, we have demonstrated rapid deceleration or acceleration in a molecular beam to well-defined velocities on a length scale of less than 535 nm. We reduce the kinetic energy of the molecules in a cold molecular beam by up to 50% in a single laser pulse (5.8 ns) demonstrating precise control of molecular-beam velocity and a new method for creating slow cold molecules using optical fields.

We report an experimental proof and full characterization of laser generation in molecular nitrogen in an argon-nitrogen gas mixture remotely excited at a distance above 2 m in a femtosecond laser filament. Filamentation experiments performed with near-infrared, 1-$\mu${}m-wavelength and midinfrared, 4-$\mu${}m-wavelength short-pulse laser sources show that mid-IR laser pulses enable radical enhancement of filamentation-assisted lasing by N2 molecules. Energies as high as 3.5 $\mu${}J are achieved for the 337- and 357-nm laser pulses generated through the second-positive-band transitions of N2, corresponding to a 0.5% total conversion efficiency from midinfrared laser energy to the energy of UV lasing.

A detailed physical model for asymmetric dielectric barrier discharge (DBD) in air at low voltages (1.5–2 kV) is developed. Modeling of DBD with an applied sinusoidal voltage is carried out in two dimensions. The leading role of charging the dielectric surface by electrons in the cathode phase is shown to be critical, acting as a harpoon that pulls positive ions forward and accelerates the gas in the anode phase. The positive ion motion back toward the exposed electrode is shown to be a major source of inefficiency in the sinusoidal or near-sinusoidal voltage cases. Based on understanding of the DBD physics, an optimal voltage waveform is proposed, consisting of high repetition rate, short (a few nanoseconds in duration), negative pulses combined with a positive dc bias applied to the exposed electrode.

We present an experimental and theoretical study of the coherent Rayleigh-Brillouin scattering in gases in the kinetic regime. Gas density perturbation waves were generated by two crossing pump laser beams through optical dipole forces. A probe laser beam was then coherently scattered from the perturbation waves. The line shape of the scattered light was modeled using kinetic theory. The model takes into account the internal energy modes of the gas particles and is applicable to both molecular and atomic gases. We discuss the implication of coherent Rayleigh-Brillouin scattering on kinetic theory and photon matter interaction.

Direct measurements of the dielectric surface potential and its dynamics in asymmetric dielectric barrier discharge (DBD) plasma actuators show that the charge builds up at the dielectric surface and extends far downstream of the plasma. The surface charge persists for a long time (tens of minutes) after the driving voltage has been turned off. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. The surface charging significantly affects DBD plasma actuator performance.