IMPROVED APPARATUS FOR PICOSECOND PUMP-AND-PROBE OPTICAL MEASUREMENTS

We present an improved method for making pump-and-probe optical picose cond to nanosecond time range. In this type of measurement, a pump lig ht pulse is used to excite the sample and the resulting changes in the optical properties are investigated by means of a probe pulse that is time-delayed relative to the pump pulse. In most measurements of this type, a mechanical stage is used to introduce the variable time delay of the probe pulse. As a result of imperfections in the stage motion, alignment problems, and divergence of the probe beam, it has been dif ficult to make accurate measurements when the time delay of the probe relative to the pump is in the range above a few hundred picoseconds. To overcome these difficulties, we have developed an apparatus that ut ilizes a single-mode optical fiber. In order to demonstrate the perfor mance of this system, we present results of experiments in which the f low of heat from a thin film into a substrate has been measured. (C) 1 996 American Institute of Physics.