Atmospheric Pressure Plasma Jet in Organic Solution:Spectra,Degradation Effects of Solution Flow Rate and Initial pH Value

The organic compounds of p-nitrophenol （PNP） solution was treated by the active species generated in a stirred reactor by an atmospheric pressure plasma jet （APPJ）. The emission intensities of hydroxyl （OH）, oxygen （O）, nitric oxide （NO）, hydrogen （H） and molecular （N2） were measured by optical emission spectroscopy （OES）. The relations between the flow rates of the PNP solution and degradation, the degradation effects and initial pH value of the solution were also investigated. Experimental results show that there exist intense emissions of O （777.1 nm）, N（337.1 nm）, OH （306-310 nm） and NO band （200-290 nm） in the region of plasma. Given the treatment time and gas flow rate, the degradation increased as a function of discharge energy and solution flow rate, respectively. The solution flow rate for the most efficient degradation ranged from 1.414 m/s to 1.702 m/s, and contributed very little when it exceeded 2.199 m/s. This indicates the existence of diffusion-controlled reactions at a low solution flow rate and activation- controlled reactions at a high solution flow rate. Moreover, increasing or decreasing the initial pH value of neutral PNP solution （pH=5.95） could improve the degradation efficiency. Treated by APPJ, the PNP solutions with different initial pH values of 5.95, 7.47 and 2.78 turned more acidic in the end, while the neutral solution had the lowest degradation efficiency. This work clearly demonstrates the close coupling of active species, photolysis of ultraviolet, the organic solution flow rate and the initial pH value, and thus is helpful in the study of the mechanism and application of plasma in wastewater treatment.

Experimental investigation on pulse-contrast degradation caused by surface reflection in optical parametric chirped-pulse amplification

In this Letter, we experimentally explore the pulse-contrast degradation caused by surface reflection in optical parameter chirped-pulse amplification. Different pump-to-signal conversion efficiencies and post-pulses with different intensities are obtained by changing the seed-pulse or pump-pulse energy and inserting etalons with different reflection coefficients, respectively. The contrast measurements show that the generated first pre-pulse intensity is proportional to the product of the surface reflection intensity ratio and the square of the pump-to-signal conversion efficiency.