Relative phase control between two successive coherent anti-Stokes Raman-scattering signals for the recovery of spectral lines

We have controlled the relative phase between two successively generated coherent anti-Stokes Raman-scattering signals with a homemade phase-shifting unit, the thickness of which could be automatically adjusted as the wavelength of Stokes beam scanned in a wide spectral range. With this technique we have recovered the Q-branch spectrum of carbon monoxide distorted by a large nonresonant contribution from propane. Also, we have selectively recorded the spectrum of hydrogen chloride buried in the spectrum of propane.