Development and characterization of a microscope based on pump probe spectroscopy : a valuable tool for the study of photoactivated drugs in cellulo This thesis presents the construction and characterization of a microscope based on pumpprobe spectroscopy and its application to observe and study the evolution of photoinduced reactions. As compared to the typical pump probe systems reported in the literature which utilizes either 1 kHz or 80 MHz pulse trains the developed microscope was fed by pump pulse trains at 125 kHz and probe pulse trains at 250 kHz repetition rates in order to perform transient absorption microscopy (TAM). The use of such intermediate repetition rate reduces the unnecessary exposure of the sample to input field leading to risk of photo induced damage and it also relaxes the use of lock in detection an unavoidable element for any MHz system which increases the cost and complexity of the system. This gives the possibility to perform microspectroscopic studies of micro structures with minimal photo induced damage a property that is especially important to the study of biological samples without the incorporation of lock in detection. Therefore the developed TAM system by itself is a proof of concept.