Multimode Pump Laser Research Articles

Theoretical modeling of two-color coherent anti-Stokes Raman spectroscopy spectra measured with a frequency-doubled, multimode pump laser

We have theoretically modeled coherent anti-Stokes Raman spectroscopy spectra of nitrogen measured with a frequency-doubled Nd:YAG pump laser. The fluctuations of the multimode pump field are modeled using a field variable having non-Gaussian statistics derived from a functional dependence on a Gaussian field. Both isolated and multiple, overlapping transitions are treated. The model qualitatively predicts the non-Gaussian effects observed in experiments but somewhat overemphasizes the magnitude of these features.

Theoretical analysis of non-thermal pump effects in broadband CARS spectroscopy

The effect of finite-bandwidth multimode pump lasers in CARS is normally accounted for by an intensity convolution integral based on gaussian (thermal) pump sources. This paper presents a derivation of the convolution integral for non-gaussian pump sources derived from frequency doubling. The modified convolution integral makes it possible to identify regions of insensitivity to pump stochastic properties.

Single pulse CARS noise: a comparison between single-mode and multimode pump lasers

An investigation of single pulse coherent anti-Stokes Raman spectroscopy (CARS) noise, determined by the analysis of broadband nonresonant spectra, is described. It is shown that the use of a single-mode rather than a multimode pump laser leads to a significant reduction of CARS noise (40%), down to the level exhibited by the Stokes spectral profile itself. This reduction in noise is attributed to the minimization of the effects due to random variations in the laser temporal profiles by using temporally smooth single-mode laser pumps. A measurement of detector shot noise is presented and its effect on CARS noise is described. The advantages of using a single-mode pump laser in CARS spectroscopy are discussed.

The effect of weak dispersion on stimulated Raman scattering

The Raman gain of an undepleted plane-wave multimode pump laser is calculated. The Stokes and pump fields are represented as vector states in a Hilbert space, and the Dirac bracket notation is introduced to simplify the form of the equations. It is shown that in the absence of dispersion the Stokes vector component correlated with the pump grows exponentially with the monochromatic-pump gain, while all other Stokes components experience zero growth. Perturbation theory is used to second order to determine the gain decrease resulting from relative dispersion between pump and Stokes, and the results are compared with previous works.

Theory of the four-photon parametric oscillator

The quantum statistics of parametric oscillation in a medium with cubic polarization is investigated in parametric approximation. Starting from an effective hamiltonian containing Bose operators of the signal, idler and pump mode and their coupling to heat baths, we obtain a c-number Fokker-Planck equation and the stochastically equivalent Langevin equations. These equations are solved, below threshold, well above threshold and near threshold. The linewidth of the signal and idler wave and their autocorrelation and crosscorrelation functions are calculated, characteristic differences between the four-photon and the three-photon parametric oscillators are discussed. The solution of the Fokker-Planck equation near threshold for a multimode pump laser is also obtained.