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 automated method based on an IBM PC/XT computer was developed for measuring the time dependence of the room-temperature reflection coefficient of a high-temperature superconducting ceramic Nd_1.85Ce_0.15CuO_4–y observed within the focal spot formed by laser radiation. The excitation was provided by an electric-discharge gasdynamic laser emitting in the wavelength range 16 – 18 μm. The radius of the spot was ~0.5 mm, the pulse duration was ~0.12 s, and the power was ~1 W. Measurements of the reflection coefficient were made with the aid of an He — Ne laser generating linearly polarised light which was reflected at the Brewster angle from the ceramic at the centre of the spot illuminated by the gasdynamic laser. During an IR excitation laser pulse the reflection coefficient rose by ~4.5%. A comparison with the measured relative change in the reflection coefficient of the same ceramic caused by heating to 300°C gave an estimate of the temperature of the sample which was reached at the focus of the laser spot. This temperature increased by 50°C during one IR pulse, in agreement with the calculated value.