Experimental investigation of electrical breakdown in nitrogen and oxygen induced by focused laser radiation at 1.064 μ

Abstract

The characteristics of laser-induced breakdown in N2 and O2 at a wavelength of 1.064 μ were investigated using 10-nsec pulses for pressures ranging from 1 to 50 atm. The pressure dependence of the experimentally determined threshold field intensities for these two gases is essentially the same except at the lowest pressures where the O2 values are slightly lower than those for N2. Comparison of this data with existing microwave data can be accomplished most directly by means of a ’’universal plot’’ of the type used effectively in the latter case. The general trends of the microwave and optical data are essentially the same; however, actual numerical values for the optical data tend to be lower than the corresponding microwave values by a constant factor of roughly 0.5. The fact that the two sets of data correspond so closely in spite of the large difference in frequencies has to be regarded as providing substantial evidence supporting the validity at optical frequencies of the cascade theory of breakdown used to interpret microwave breakdown measurements. Time-resolved and time-integrated emission spectra were analyzed, from which the electron density and temperature were obtained for the initial stage of spark development. The spectral characteristics, the electron densities, and temperatures are similar to those determined previously by other investigators for air.

Optical emission spectroscopy of oxygen plasma induced by IR CO2pulsed laser

“…This pressure range is relatively limited due to the characteristics of the employed pyrex gas cell. Presumably, we suppose that the oxygen breakdown occurs in the high pressure range taking into account the experimental observations reported by Chan et al [22], Dewhurst [23], Stricker and Parker [24], Gamal [25] and Phuoc [26,27]. Therefore, starting from our experimental observations and calculations, we can conclude that although the measurements of the breakdown threshold intensity variation with the oxygen pressure (figure 10) reveal the weak pressure dependence, a characteristic of MPI, our calculations of MPI probability for O 2 give W MPI ∼ = 0 for the CO 2 laser at λ ∼ = 10 µm and I W ∼ = 6 GW cm −2 .…”

“…Breakdown thresholds of solids and liquids are usually lower than for gases. Several LIB threshold measurements have been reported for oxygen [22][23][24][25][26][27] using CO 2 [22] and Nd : YAG [23][24][25][26][27] lasers. The breakdown threshold was defined as the laser energy at which the gas would break down on more than 50% of the laser shots.…”

“…Several laser-induced breakdown threshold measurements have been carried out in oxygen [22][23][24][25][26][27]. However, very limited data are available on the laser-induced plasma emission spectrum in oxygen [24,28]. The LIBS oxygen spectrum recorded by Nordstrom [28] in the spectral region 350-950 nm is composed of O and O + atomic lines.…”

Measurements of Air Breakdown and Scaling to Microwaves Using 193 nm Focused Laser Radiation

“…Multi-photon ionization processes may also play a substantial role at 193 nm due to the high photon energies (6.4 eV). The breakdown threshold data for air at 193 nm is correlated with the microwave breakdown using the concept of universal scaling, for which extensive microwave breakdown data is available [1][2] and current microwave breakdown measurements are being obtained at Texas Tech University [3]. An extensive range of optical and spectroscopic diagnostics with fast gating and 13 µm ICCD resolution is utilized to characterize the plasma.…”

Measurements of Air Breakdown and Scaling to Microwaves Using 193 nm Focused Laser Radiation

“…Multi-photon ionization processes can also play a substantial role at 193 nm due to the high photon energies (6.4 eV). The laser breakdown threshold data for air at 193 nm is correlated with corresponding microwave breakdown values using the concept of universal scaling, for which extensive microwave data is available [1][2] and current microwave breakdown measurements are being obtained at TexasTech University [3]. An extensive range of optical and spectroscopic diagnostics with ns fast gating and 13 ptm ICCD resolution is utilized to characterize the plasma.…”