Atmospheric pressure plasma jets (APPJs) generally chara cterized by high concentration of radicals and low gas temper atures are suitable for many applications. The increasing inter est in the application of APPJs heightened the need for quanti fication of the main active species generated by APPJs. Laser -induced fluorescence (LIF) and two-photon absorption laserinduced fluorescence(TALIF) spectroscopy are the major tec hniques that have direct access to the ground state population s. They imply two or single photons excitation of the studied species from the ground to an excited state which is followin g by spontaneous emission (fluorescence) of a photon to an in termediate state. In the atmospheric pressure, quantitative detection of species of interest by LIF and TALIF involves co mplicated interpretation of the experimental results. The pres ent work uses the timeresolved LIF and TALIF spectroscopy to investigate the temporal behavior of laser excited states in t he atmospheric pressure RF plasma, sustained in Ar/0.3%H 2 O or 0.3%O 2 mixtures, with a special attention devoted to the proper interpretation of the LIF and TALIF results.The OH radicals was excited from the ground state (X 2 , ''=0) to the (A 2 + , '= ) state by laser through P (4) transitio n.The time-resolved LIF spectrum of OH (0 -0) band (308 nm) demonstrates that the vibrational and rotati onal relaxation substantially affect the population of OH (A) r otational states. In the APPJs, time and wavelength integrated LIF signal cannot be considered directly proportional to grou nd density of OH radicals but it is function of VET and RET processes. Both VET and RET have to be considered carefull y, especially when LIF signal decay time is used as a paramet er for absolute OH density calculations.In case of O atom excitation the working wavelength was f ixed at 225.65 nm corresponding to the two-photon excitation energy gap between the fine levels (2p 4 3 P 2 3p 3 P 2 ) of O. During and after the laser pulse, the time dependent evolution of the plasma spectral emission is successfully recorded by t he fast optical emission spectroscopy measurements with a nd 5 ns exposition time. Different from previous researches a nd theoretical predictions, in addition to the resonant emissio n of O 844 nm, the TALIF spectrum of the Ar+0.3%O 2 atmos pheric plasma is characterized by the spectral irradiance from O 777 nm and Ar lines.The distinct time-resolved behaviors between O (777 nm and 844 nm) and Ar lines emission intens ities can be attributed to the laser direct and indirect excitatio n process through collision effects.
Nonthermal and low temperature plasmas are a subject of great interest in different fields of science and applications. One of the attractive features of non-thermal atmospheric pressure plasma is the ability to produce a large amount of reactive species without the need for elevated gas temperature. Since the gas temperature in atmospheric pressure plasma remains relatively low, the plasma does not cause any thermal damage to the sensitive surface it comes in contact with. These properties make this type of plasma attractive for medical applications like electrosurgery, tissue engineering and surface modification of biocompatible materials. Generation of rf-DBD of a size of cm is strongly desirable f or many fields and can find an application in polymers modification and bio-medicine where uniform and fast treatment is required. In the present work rf-DBD plasma of 13.56 MHz generated in between two electrodes with a size of 50x50 mm at pressure range from sub-atmospheric (300 mbar) to atmospheric (1100 mbar) and power of 20-80 W is studied by optical emission spectroscopy (OES) and absorption spectroscopy (AS). The gas temperature and electron density is estimated f rom the OES measurement. AS is used to record the absolute density of Ar * metastable and resonance states by measuring absorption signal of 794.8, 800.8, 811.53, and 750.4 nm corresponding to excited states 1S 3 , 1S 4 , 1S 5 , and 1S 2 respectively.Atmospheric pressure plasma jets (APPJs) generally characterized by high concentration of radicals and low gas temperatures are suitable for many applications. The increasing interest in the application of APPJs heightened the need for quantification of the main active species generated by APPJs. Laser -induced fluorescence (LIF) and two-photon absorption laser-induced fluorescence(TALIF) spectroscopy are the major techniques that have direct access to the ground state population s. They imply two or single photons excitation of the studied species from the ground to an excited state which is following by spontaneous emission (fluorescence) of a photon to an intermediate state. In the atmospheric pressure, quantitative detection of species of interest by LIF and TALIF involves complicated interpretation of the experimental results. The present work uses the timeresolved LIF and TALIF spectroscopy to investigate the temporal behavior of laser excited states in the atmospheric pressure RF plasma, sustained in Ar/0.3%H 2 O or 0.3%O 2 mixtures, with a special attention devoted to the proper interpretation of the LIF and TALIF results.
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