Coherent anti-Stokes Raman-spectroscopy studies of nitric oxide

Coherent anti-Stokes Raman spectroscopy (CARS) of the $Q$ branch of NO has been performed with a resolution of 0.05 ${\mathrm{cm}}^{-1\mathrm{}}$ by means of a pulsed-dye-laser system. The two $Q$-branch series originating from the ${}_{}{}^2{}_{}{}^{}\mathrm{II}_{1/2}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{II}_{3/2}^{}{}_{}{}^{}$ electronic states could be resolved for higher $J$ values. CARS measurements were performed for various gas pressures in order to study the pressure dependence of the real and imaginary parts of the third-order nonlinear susceptibility ${\chi }^{\mathrm{}\left(13\right)\mathrm{}}$. Observed CARS spectra at a pressure of 1.33 × ${10}^4$ Pa allowed the determination of the ratio of the differential Raman-scattering cross sections for the two electronic states as ${\left(\frac{d\sigma }{d\Omega }\right)}_{{\Pi }_{\frac{1}{2}}}:{\left(\frac{d\sigma }{d\Omega }\right)}_{{\Pi }_{\frac{3}{2}}}=1.01\mathrm{}\pm 0.02$.