Time-resolved Ultrafast Dynamics Study Of Coumarin 480,500,540 In High Pressure

Several techniques have been developed in the past years to generate ultrashort pulses. The availability of ultrafast lasers with a wide range of pulse widths, wavelengths, pulse energy, and pulse repetition rate makes it possible not only to investigate a broad range of physical phenomena using ultrafast optical spectroscopy, but also investigate practical applications of ultrafast technology. Many techniques have been developed to investigate linear and nonlinear optical properties of semiconductors using ultrafast lasers. Pump-probe spectroscopy is the most common form of ultrafast spectroscopy.Diamond anvil cell is the most powerful tool for generating ultrahigh pressure. Combined with many other measurements it could be used for many in-situ measurements at high temperature and high pressure. A fantastic development has been appeared on the research of high pressure properties of materials with the development and application of the DAC technique. People may obtain the information on materials, thus far many in-situ measurements have been conducted on DAC, such as structure,spectroscopy,light emission,light scattering and so on.To study the time-resolved ultrafast dynamics of Coumarin 480,500,540, we fall ultrafast laser pump-probe spectroscopy technique and high pressure technique together for the first time. Because of the limit of experiment condition, our high pressure equipment is gem anvil cell. Wavelengths of pump and probe pules both are 400nm, intensity of them are 1GW/cm2,0.1GW/cm2. The samples are coumarin 480,coumarin 500,coumarin 540, solvent is methanol, the concentration is 3.1×10-4mol/L.At 1 Atm, for these complexes, we observe a dynamical behaviour consisting of two components. After the initial spike due to a two–photon absorption effect, the generated bleach of the transition diminishes with a <200fs time constant. At longer delays a further decrease of the bleach is observed with a ps time constant for times up to a residual value. We owe the shorter time constant to hydrogen-bond dynamics. In other words, The time hydrogen-bond cleavage occurs in 200fs. We owe the longer time constant to solvation dynamics. At high pressure, we only observe hydrogen-bond dynamics. The larger the pressure, the slower the relaxation time. The decay of relaxation time fits a exponential function.Furthermore, we don't know the reason of the initial spike due to a two-photon absorption effect. We will be study this phenomena further more.