The density of OH radicals in ground state is measured by laser-induced fluorescence (LIF) spectroscopy in the core of a micro-flow discharge in He, Ar and N 2 with a water electrode. The lines P 2 (6), P 1 (4) and P 2 (3) of the X 2 (v = 0) to the A 2 + (v = 1) transition are used for OH radical excitation. The density of the main quencher of OH radical in the core of the discharge is estimated based on the time decay of the LIF signal. It is revealed that the plasma core consists of a high amount of 8-10% of water vapour. The calculation of the absolute density of OH radical is carried out based on the model of LIF excitation including vibrational and translation energy transfer, and the results in different gases are presented for the discharge.

The inactivation of microbial biofilms using a low temperature atmospheric pressure argon plasma jet is investigated. The treatment of Staphylococcus aureus biofilms was the most effective; 78% population reduction was reached within 3 min. Higher reduction rates were found for smaller plasma‐sample distances and for longer exposure time. Employing a pretreatment of the samples with ascorbic acid suggests that oxygen radicals might play a role in the inactivation process. A novel method for the quantitative analysis of spectra is introduced. It points towards an important role of entrained nitrogen and shows that excited nitrogen species are created in large abundances. These species can be important carriers of excitation energy to the biofilms or may function as important intermediate reactive species.

The electron temperature in atmospheric argon plasmas created by a DBD jet is determined using a combination of Absolute Line Intensity (ALI) measurements and a collisional radiative model (CRM). The ALI measurements have been performed to determine the densities of the states in the 4p level. In addition, the ground state density is taken into account, which is found via the pressure and the gas temperature. The density ratio of the ground state and 4p state gives a value of the excitation temperature, which by means of the CRM is transformed into the electron temperature. With this method, the electron temperature in the active zone of a pure argon plasma is found to be 1.27 eV which is significantly higher than the experimental value reported by others. An error analysis shows that the relative error in the electron temperature obtained in this way is about 5%. In the afterglow, the temperature decreases gradually to about 0.88 eV. The addition of 2% O2 leads to a decrease in electron temperature of about 5%.

We present a method to determine the electron density, ne, of an argon plasma jet using the continuum radiation. The radiation measurements are calibrated with a standard tungsten filament lamp. Due to the filamentary nature of these plasmas, it is not possible to use the spectral radiance W m−2 nm−1 sr−1 as the radiometric quantity. Instead we work with the spectral irradiance W m−2 nm−1. As the ionization degree is low, the continuum radiation is predominantly generated by interactions of electron with atoms; the influence of electron–ion interactions can be neglected. The method provides ne values of about 7 × 1019 m−3 in the active zone for an argon plasma created by a sinusoidal peak to peak voltage of 10 kV. Comparison with the ne values determined via the current density shows a fair agreement; this comparison can only be done for the region between the electrodes. In the afterglow region, where the current‐density method cannot be applied, we can still use the continuum radiation to determine ne. It is observed that ne decreases in the afterglow direction down to 2 × 1017 m−3.

The effect of ion-channel guiding on saturation mechanism of a single pass free electron laser with electromagnetic wiggler is studied numerically. By using equations of motion of electron beam and field equations, a set of coupled nonlinear differential equation is derived in slowly varying envelope approximation. The electron beam propagates with a relativistic velocity, ions are assumed immobile and slippage is ignored. A comparison is made between thr result of propagation of the electron beam in an electromagnetic and magnetostatic wiggler 1 . Numerical simulations are performed with and without ion channel, for electromagnetic wiggler. Calculations are made for the saturation length, bunching parameter and output power.