Ionization Processes In Air Research Articles

Self-Guiding of Long-Wave Infrared Laser Pulses Mediated by Avalanche Ionization.

Nonlinear self-guided propagation of intense long-wave infrared (LWIR) laser pulses is of significant recent interest, as it promises high power transmission without beam breakup and multifilamentation. Central to self-guiding is the mechanism for the arrest of self-focusing collapse. Here, we show that discrete avalanche sites centered on submicron aerosols can arrest self-focusing, providing a new mechanism for self-guided propagation of moderate intensity LWIR pulses in outdoor environments. Our conclusions are supported by simulations of LWIR pulse propagation using an effective index approach that incorporates the time-resolved plasma dynamics of discrete avalanche breakdown sites.

The role of barrier surface properties in barrier surface discharge behavior

Results of experimental investigation of a dielectric barrier surface discharge over barriers with different films deposited on their surface show evident dependence of the microdischarge structure, their intensity and their charge on the surface structure and chemical composition of the barrier surface. Measured profiles of barrier surface structures by means of a laser scanning microscope are used to calculate the electric field distribution in air in the vicinity of the barrier surface. The local electric field near the surface is shown to have strong dependence on the surface profile elements (highness of protrusions, curvature radii of their peaks and the distance between neighbor protrusions). It is shown that the values of local fields are sufficient for ionization processes in air and it is supposed that such additional ionization is one of the main factors to change the discharge behavior.

Pulsed digital micro-holography of femto-second order by double-wavelength recording

Double-wavelength recording used in a pulsed digital micro-holographic system to record ultra-fast processing of the order of femto-second is reported for the first time, where a BBO crystal is used to generate harmonic wave of the incident laser wave, and both of the basic and the frequency doubled waves are time-delayed and introduced to a Michelson’s interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD. In the experiment, an ultrafast dynamic process of air ionization induced by a single femto-second laser pulse is recorded with holography by this system, and both of intensity and phase difference images digitally reconstructed are obtained through Fourier transformation and digital filtering, which show clearly the dynamic process of formation and propagation of the plasma, with a time resolution of the order of femto-second.

Pulsed digital holographic recording of ultra-fast process of the femto-second order

In this paper, we report a pulsed digital micro-holography system for recording ultra-fast process of the order of femto-second. Two sub-pulse-train generators can be adjusted independently for generating reference beams with different spatial angles and object beams of the same angle, respectively, and the time delay between the sub-pulses can be adjusted from pico-senconds to femto-seconds. In the experiment, the ultra-fast dynamic process of air ionization induced by a femto-second laser pulse is recorded by the holographic recording system through spatially angular multiplexing, and both of the digitally reconstructed images in intensity and phase are obtained, which show the dynamic process of formation and propagation of the plasma with a time resolution of the order of femto-second.

Charge phenomena on technical boundary surfaces in air by D.C.-stress

The presented paper deals with the investigation of test samples in air with nonuniform potential distribution along the insulating boundary surface. The applied D.C. test voltage, the stressing time and the polarity have been varied as well as the relative air humidity (20% – 80%) for different insulator materials (epoxy resin, PMMA, PVC, kraftboard). The surface charge distribution was recorded by means of a computer controlled measuring system using an electrostatic probe. Increasing the voltage and stressing time as well as the surface resistivity of the insulator material increases the measured charge density, as expected. In contrast, especially two phenomena are observed as being considerable: 1. 1. An increase in humidity causes a partly enormous rise of the charge density. In case of a relatively high humidity, the measured charge distribution is always reproducible. In dry conditions the charge density is lower and the charge distribution is indeterminate. 2. 2. Charges may accumulate on the surface in the case of nearly uniform electrode configurations, i.e. without measurable partial discharges. Above a humidity of 30% the polarity of the charges always corresponds to the polarity of the D.C. voltage. Based on the assumption that the charge accumulation is attributed to ionization processes in air a model conception is derived. In spite of a larger attachment coefficient the influence of the humidity is traced back to a rise in the frequency of ionization events in air.