This paper presents a novel problem in laser dynamics, where two lasers using different active material with different frequency produce radiation interaction. In the first experiment, we performed a study on the effect of radiation coupling of the giant pulse ruby laser on the Nd3+-glass laser under normal oscillation. It was found that the sudden enchancement followed by the quenching of oscillation in the Nd3+-glass makes a short, intense pulse, which was one order of magnitude or more larger than usual oscillating spikes, after the excitation by the -switched ruby laser light. In order to explain this result, the fluorescence study of the Nd3+-glass in the range of the visible and near infrared spectrum was arranged by employing the giant pulse ruby laser as an exciting source. This measurement has led to valuable information on the energy levels of the Nd3+-ion in the glass host through the new observation of fluorescence lines in the visible spectral region. Hence it was found that the ruby laser radiation is properly responsible for two upward transitions from the ground state in the Nd3+-glass, and thereby such radiation coupling yields the sudden enhanced emission in the laser output.