Simple approach to determining absolute Raman cross sections using an optical parametric oscillator

In the present investigation, it is shown that use of commercial optical parametric oscillators (OPOs) has allowed far a simple method of determining the absolute Raman cross sections utilizing the measurement of integrated intensity ratios. Standard curves for the absolute Raman cross sections of the commonly used internal standards (viz., acetonitrile 918 cm(-1) peak and nitrate 1045 cm(-1) band) have been developed from the relative Raman intensities measured in the wavelength range 450-650 nm. The absolute intensities are fitted to the A-term frequency dependence and found to be consistent with the available literature data. We have demonstrated that, using an OPO, one can develop a standard curve for any internal standard, in order to accurately determine absolute Raman cross sections for a given system. This approach, in general, avoids the use of precalibrated lamps or external standard methods which are cumbersome, in comparison to measuring the integrated intensity changes with respect to an internal standard.