On a definition of positive and negative streamers observed optically in liquids

The conduction and breakdown phenomena in liquids have been studied by using optical methods such as shadow, Schlieren and interferometric techniques together with a high speed camera. In this case, the phenomena are recorded as the optical disturbance caused by the transport of charged particles such as electrons. From the time evolution of the optical disturbance produced by charged particles, the velocity of the positive and negative streamers in liquids has been estimated. The term of "streamer" was originally given to the development of a small discharge channel caused by the electron collision ionization in gases. The streamers in gases are characterized by luminescence, while those by optical disturbance. Therefore, a question arise concerning to the simultaneity between the charge movement and the resultant optical disturbance. From the point of view that the light is a kind of electromagnetic wave, the following experiment has been done. An electromagnetic wave of mm wavelength is irradiated to a spherical glass whose size is smaller than the wavelength in order to study the wave scattering phenomena. From the results, it is suggested that the optical disturbance might be a cloud of tiny bubbles which are produced by the transport of quasi-free electrons.