CHANGES IN THE REFLECTION COEFFICIENT OF A HIGH-TEMPERATURE SUPERCONDUCTING CERAMIC NDCECUO IN THE VISIBLE SPECTRAL RANGE UNDER THE ACTION OF IR RADIATION PULSES

An IBM PC/XT computer was used to develop an automated method for meas uring the time dependence of the room-temperature reflection coefficie nt of a high-temperature superconducting ceramic Nd1.85Ce0.15CuO4-y ob served within the focal spot formed by laser radiation, The Excitation was provided by an electric-discharge gasdynamic laser emitting in th e wavelength range 16-18 mu m. The radius of the spot was similar to 0 .5 mm, the pulse duration was similar to 0.12 s, and the power was sim ilar to 1 W. Measurements of the reflection coefficient were made with the aid of an He-Ne laser generating linearly polarised light which w as reflected at the Brewster angle from the ceramic at the centre of t he spot illuminated by the gasdynamic laser. During an IR excitation l aser pulse the reflection coefficient rose by similar to 4.5%. A compa rison with the measured relative change in the reflection coefficient of the same ceramic caused by heating to 300 degrees C gave an estimat e of the temperature of the sample which was reached at the focus of t he laser spot. This temperature increased by 50 degrees C during one I R pulse, in agreement with the calculated value.