Biharmonic Pumping Research Articles

Observation of the rotational spectrum of molecular hydrogen under stimulated Raman scattering conditions

An experimental investigation was made of simultaneous excitation of purely rotational S0(1), S0(3), and S0(5) transitions in the orthohydrogen molecule (T = 300 K) under stimulated Raman scattering conditions. More accurate values were found of the coefficients in the expansion of the energy of the rotational terms of the H2 molecule in powers of the rotational quantum number/of the ground vibrational state. The observed complex scattering spectrum was accounted for by biharmonic pumping in stimulated Raman scattering.

Spectral properties of resonant four-photon parametric oscillation

An investigation was made of the spectral properties of four-photon parametric oscillation when the frequency of the generated field is tunable near an atomic resonance line. An ω4 = ω1–ω2+ω3 generation process involving coherent anti-Stokes scattering in thallium vapor was achieved experimentally. Biharmonic pumping was provided by resonant excitation of a 6P1/2–6P3/2 two-photon transition at the frequency ω1–ω2. Measurements were made of the oscillation power when the frequency ω3 was tunable near the frequency of a 6P3/2–7D3/2 transition at various thallium vapor pressures. It was found that the spectral properties of resonant parametric oscillation depend strongly on the concentration of active-mixture atoms and also on various saturation effects.

The line shape of Coherent Antistokes Raman Scattering excited under resonance conditions

If Coherent Antistokes Raman Scattering (CARS) is excited by a biharmonic pump in resonance with one photon molecular transition, the Raman line shape is significantly changed compared to the case of nonresonant excitation. This is due to an essential alteration of the 3rd order susceptibility responsible for CARS. Aside from a considerable enhancement of the Raman signal (which makes it possible to detect dissolved molecules in concentration lower than 10 -4 mole/l) the most marked effects are a reversal of the spectral sequence of the Raman maximum and minimum in the CARS-spectrum and for a specially chosen concentration an enhanced contrast of the signal. The factors determining the CARS line shape are discussed theoretically and preliminary experimental results concerning resonance CARS spectra are reported.

Resonance coherent anti-stokes Raman spectroscopy

Conditions to get Coherent Anti-Stokes Raman Spectra for strong one-photon-resonance are given. The biharmonic pump was realized by a high power ns-ruby-laser and a broadband dye-laser, focussed together into a small sample cell. Resonance Raman spectra of an extension of some hundreds cm -1 are obtained during one laser shot, thus opening possibilities to investigate excited electronic states or short-living molecules.

Parametric amplifiers and converters with biharmonic pumping

Parametric amplifiers and converters with biharmonic pumping

Active spectroscopy of spontaneous Raman scattering of light by surface polaritons

A theoretical analysis is made of the spontaneous Raman scattering of a test wave by coherent surface polaritons, which are created by the difference frequency in biharmonic pumping. Formulas are obtained for the intensity of the scattering of the test wave. Numerical estimates show that this type of scattering produces much higher intensities than the scattering by noise surface polaritons.

Excitation of the coherent optical phonons of Eg‐type in calcite by means of the active spectroscopy method

AbstractThe results of an experimental investigation of the twofold degenerate vibrations in calcite (Eg‐type; phonon frequency ΩE/2πc = 721 cm−1) by means of active spectroscopy method, including a new modification of this method are reported. Beating of a biharmonic pump consisting of Nd: YAG laser radiation and tunable (narrow band or broad band) radiation from an optical parametric oscillator (OPO) was used to excite coherent optical phonons above the thermal level. Scattering of the second harmonic of Nd: YAG was used to detect these coherent vibrations. The components of the Raman scattering tensor for Eg phonons and the absolute sign of χ the component of the nonresonant cubic electronic susceptibility were measured.