Coherent anti-Stokes Raman spectroscopy

Coherent anti-Stokes Raman spectroscopy offers significant advantages over standard incoherent Raman spectroscopy. The advantages include 105 improvement in conversion efficiency, spectral and spatial discrimination against fluorescence, low incident average power, and no requirement for a monochromator. The potential disadvantages of signal scaling as power cubed and requirement for a high peak power tunable laser source are largely overcome by presently available tunable laser sources. The method appears particularly useful for investigating biological compounds where background fluorescence is a problem for conventional spontaneous Raman studies. We show that for low concentrations, the density-squared signal dependence becomes linear due to coherent mixing with an intense solvent Raman mode or the third-order background signal.