The detection of complex rare events requires efficient pattern recognition and background rejection. This can be reached by recording optically avalanche-induced photons. Following extensive studies carried out by us on optically-recorded UV-photon detectors for Ring Imaging Cherenkov Detectors (RICH), particle tracking and beta-autoradiography, an optical readout target-TPC (O-TPC) has been developed; it was built and operated with Gamma-ray beams at the HIgS facility (TUNL-Duke Univ.) in Nuclear Astrophysics experiments. The latest basic optical-readout studies, in cascaded avalanche detectors, included avalanche-induced light-emission optimization of selected oxygen-rich target-gases.