Spectral Properties of Optical Discharge in Hollow-Core Optical Fibers

The phenomenon of optical discharge (OD) propagation along hollow-core optical fibers under the action of laser radiation was observed recently [1] , [2] . In this work the radiation spectra of optical discharge plasma in hollow-core fibers were measured and analysed for the first time. As hollow core fibers, we used the so-called revolver optical fibers (RFs) with reflecting cladding made of pure silica (see Fig. 1b , inset) [3] . The source of the single-mode radiation was a Nd:YAG laser. It operated in a combined Q-switch and mode-lock mode, generating nanosecond trains of picosecond pulses. The radiation power at the maxima of the picosecond pulses was ~ 1 MW. The maximum laser radiation intensities on the axes of the RF core during the picosecond pulses was up to 10 12 W/cm 2 . The wavelength of the Nd:YAG laser was in the transparency band of RF. After launching the laser radiation into the RF, the OD was initiated and then propagated through the fiber at an average speed of ~1 m/s. The OD looked like a bright spot in the visible wavelength range moving through the fiber towards the laser radiation source.