A mains electricity (AC-powered) device assembly in which input energy (e.g., flashlamp, diode laser) is used to excite a doped glass/crystal medium to emit a high-power laser beam intended for endocardial ablation procedures for the treatment of atrial fibrillation; the therapeutic laser does not include frequency-doubling technology. It includes a laser generator with controls and monitor. It is intended to function with a laser beam-guide catheter (typically introduced to the pulmonary vein via transseptal access) and a flexible video angioscope for visualization during the procedure; the catheter and angioscope may be included.