# 3.5: CARS (Coherent Anti-Stoke Raman Scattering)

- Page ID
- 304373

Used to drive ground state vibrations with optical pulses or cw fields.

- Two fields, with a frequency difference equal to a vibrational transition energy, are used to excite the vibration.
- The first field is the “pump” and the second is the “Stokes” field.
- A second interaction with the pump frequency lead to a signal that radiates at the anti-Stokes frequency: \(\omega_{sig}=2\omega_P-\omega_S\) and the signal is observed background-free next to the transmitted pump field: \(\bar k_{sig}=2\bar k_P-\bar k_S\).

The experiment is described by R_{1} to R_{4}, and the polarization is

\[\begin{aligned} R^{(3)} &=\bar \mu_{ev'} \bar \mu_{v'g} e^{-i\omega_{eg}\tau-\Gamma_{eg}\tau} \bar \mu_{gv} \bar \mu_{ve} +c.c. \\ &=\bar\alpha_{eg}e^{-i\omega_{eg}\tau-\Gamma_{eg}\tau}\bar\alpha_{ge}+c.c. \end{aligned} \nonumber\]

The CARS experiment is similar to a linear experiment in which the lineshape is determined by the Fourier transform of \(C(\tau)=\langle\bar\alpha(\tau)\bar\alpha(0)\rangle\).

The same processes contribute to Optical Kerr Effect Experiments and Impulsive Stimulated Raman Scattering.