In phase-change (PC) optical data storage, information bits are recorded as amorphous marks on a crystalline film of GeSbTe alloy (hereinafter referred to as GST). This is achieved by raising the local temperature of the film above its melting point (approximately 600°C) using a high power laser pulse, and allowing the film to cool down rapidly to below its glass transition temperature. The crystalline-to-amorphous transition (or vice-versa) is accompanied by a large change in the optical constants of the GST material, which provides a mechanism for optical readout. Thus, crystallization, melting, and amorphization of thin GST films are of fundamental significance in PC optical recording technology. Several such studies have been undertaken in the past, using a single laser beam to both trigger the transformation and monitor its progress. In the present paper we describe the results obtained in a novel, two-laser static tester, which allows real-time monitoring of the crystallization/amorphization processes both during the laser pulse and in the cooling period following the pulse.