  Optical recording of avalanche-induced photons is an interesting tool for
studying basic physics processes in gaseous detectors. In this work we
demonstrate the potential of optical readout in avalanche-propagation
investigations in Thick Gas Electron Multipliers (THGEMs) operated with Ne/CF4
(95/5). We present the results of direct measurements, with single- and
cascaded-THGEM detectors irradiated with soft x-rays, of the hole-multiplicity
and avalanche asymmetry within holes, as a function of detector parameters.
Further study directions are discussed.

Instrumentation and Detectors