NANOSECOND & PICOSECOND TRANSIENT SPECTROSCOPY

纳秒光谱学已经证明了广泛的

Nanosecond spectroscopy has demonstrated a wide range of applications over the whole of biology. It permits the identification of intermediate species in optically triggered processes. This research involves the development and maintenance of a nanosecond absorption spectrometer. This device continues to provide high quality spectra from the nanosecond to second time scale, with a wide range of sample handling and improved kinetic analysis software. The apparatus can record absorption or gain spectra of transients excited by pulses from a YAG laser running at 20Hz. The probe source is a xenon flash transmitted to the sample with quartz optical fibers. The time resolution is achieved by a gated diode array. In addition, we have constructed a transient absorption system which is run with two NdYAG lasers which have been modified for "filled-in" beam profiles. In addition, we have incorporated an optical parametric oscillator (OPO) into this dual YAG setup which generates near and mid-IR frequencies in order to probe processes such as protein conformational dynamics. This OPO easily generates enough pulse energy to produce temperature jumps in aqueous solution of 25 to 300C, acting as an ultrafast trigger for protein folding dynamics measurements. Coupled to this system is a dye laser (pumped by second Nd:YAG laser) whose output can be doubled to 270-300 nm; this is used to pump fluorescent transitions in aromatic amino acids. The change in fluorescent quantum yield and ?max for emission are sensitive probes of conformational changes in protein and we have the capability of monitoring either property. This configuration will also allow for probing of transients with broadband light generated from fluorescent dyes which will significantly improve the S/N of the transient spectral measurements. A picosecond system which will generate stable amplified continuum for a wide range of pumping and probing wavelengths with an increased repetition rate (in the kHz domain) is being developed. This system can be coupled to the dual intensified diode array detection system for routine acquisition of spectra on a "user-friendly" basis.