Dynamics of a cw multimode dye laser

Abstract

The spectral and temporal dynamics of a multimode dye laser has been studied theoretically and experimentally. The analytical model includes quantum fluctuations as well as four-wave mixing due to population pulsations, stimulated Brillouin scattering, and Rayleigh scattering both in a standing-wave linear laser, and in a unidirectional ring laser. The nonlinearity found most important in the multimode dye laser is four-wave mixing due to pulsations of the population of the upper laser level. Numerical simulations show features that characterize this particular type of mode coupling: broadening of the emission spectrum, oscillations of the light flux in individual laser modes, suppression of certain beat notes. Observations of these features confirm population pulsations dominating the laser dynamics. Four-wave mixing due to population pulsations tends to arrange the phases of the laser modes such as to minimize the pulsations and to limit its own strength.

Glassy behavior of light in random lasers

“…by the time-constant of the off-diagonal density matrix elements, whose inverse is the "dipole dephasing rate" which is around 10 14 s −1 (see e.g. [34]). The latter time scale is the "elementary" time scale for the dynamics of the phases, that corresponds in molecular systems to the typical time scale of atomic vibrations τ 0 ∼ 10 −12 s. In a first approximation, the arrival of a pulse produces a fast variation of the "temperature" from T ∼ ∞ (before the pulse) to a value of T < T d (subsequently after the arrival of the pulse).…”

“…by the time-constant of the off-diagonal density matrix elements, whose inverse is the "dipole dephasing rate" which is around 10 14 s −1 (see e.g. [34]). The latter time scale is the "elementary" time scale for the dynamics of the phases, that corresponds in molecular systems to the typical time scale of atomic vibrations τ 0 ∼ 10 −12 s. The power density spectrum of the mode instantaneous frequency displays modulation sidebands; this corresponds to the transition from random-mode-phases to phase-locking in one the meta-stable states; the side-bands are due to small oscillations in these minima that result into frequency shifts of the mode resonances.…”

“…To perform the analytic continuation to n → 0 one has to make an ansatz on the structure of the matrices q and r. The free energy is then computed using the equation (34). Using the relation…”

“…Complex processes in laser physics, including nonlinear optics, are well known and studied (see e.g. [30,31]), up to recent investigations in multi-mode systems [32,33,34] and successful reformulations of standard laser thermodynamics [35,36,37,38,39]. The extension of these approaches to RL immediately leads to the application of the statistical theory of disordered systems, of which spin glass theory is a paradigm [40], and which is the subject of the present manuscript.…”

Mode-locking transitions in nanostructured weakly disordered lasers

“…The thermodynamic approach to multi-mode interactions in various physical frameworks is well established [7]. For example, it was recently applied to transverse-mode interaction in resonators [8,9], as well as to standard-laser mode-locking transition [10][11][12]. This transition can be described in terms of an effective temperature T , which encompasses the level of noise due to spontaneous emission and the amount of energy stored into each mode.…”