We propose a method for diagnostics of the density of weakly magnetized plasma using a resonance microwave probe, which allows decreasing the minimum measurable value of the density by three orders of magnitude, thus expanding the dynamic range of the measuring system significantly. Within the framework of this method, measurements are performed at a fixed frequency corresponding to the resonance frequency of a microwave probe in the absence of plasma, while minor variations in the resonance frequency of the system within the limits of the width of the inherent resonance are recorded by the method of amplitude-phase measurements. The paper presents a theoretical model of the measurement method and its experimental verification.

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The kinetics of the processes occurring in an O 2 -I 2 -He -H 2 O gas flow in which photodissociation of molecular iodine at a wavelength close to 500 nm and excitation of atomic iodine on the 2 P 1/2 -2 P 3/2 transition by narrow-band radiation near 1315 nm are implemented successively has been analysed. It is shown that implementation of these processes allows one to form an oxygen -iodine medium with a high degree of dissociation of molecular iodine and a relative content of singlet oxygen O 2 (a 1 D) exceeding 10 %. Having formed a supersonic gas flow with a temperature ~100 K from this medium, one can reach a small-signal gain of about 10 -2 cm -1 on the 2 P 1/2 -2 P 3/2 transition in iodine atoms. The specific power per unit flow cross section in the oxygen -iodine laser with this active medium may reach ~100 W cm -2 .