A new, first-principles derivation of the equations for a quantized single-mode laser field pumped by a semiclassical stochastic field in a four-level molecular pumping scheme is presented. Computer simulations are used to generate fits to measured correlation functions for a single-mode dye laser.
We examine from first principles the effects of a stochastic pump on the output fluctuations of a laser. The Hamiltonian for a four-level molecule interacting with a stochastic semiclassical pump field and quantized laser field is used to obtain density-matrix equations of motion. Noise from the pump field and from spontaneous emission is introduced systematically, as opposed to the ad hoc inclusion of random forces in the semiclassical equations. The relationship of this theory with previous quantum and semiclassical equations is described. New equations are derived on which computer simulations are performed to compare our theoretical results to experimental data for a single-mode dye laser.
Recent theoretical analyses of the single-mode laser with colored-noise pump fluctuations have allowed the detailed prediction of the short-time behavior of the intensity autocorrelations of such a laser. In particular, a rounding off of the intensity correlation function on the time scale of the correlation time of the pump fluctuations has been predicted. We present results from experiments performed on a single-mode dye-laser system that clearly confirm these predictions. Numerical simulations of the laser Langevin equations including the colored-noise pump fluctuations are used to fit the experimental results.
A single-mode dye-laser model incorporating pump white noise through gain-parameter fluctuations is analyzed. It includes a fluctuating saturation term. Intensity fluctuations, a first-order-like transition, and intensity correlation functions are calculated and discussed. It is found that effects previously claimed to be a consequence of the presence of colored noise in the context of loss-noise models can be also explained by white gain noise, except for the existence of two time regimes in the early decay of intensity correlation functions.
The probability distribution p(n) for the detection of n photons emitted by a single-mode dye laser in a short time at various excitations is measured, together with the distribution of time intervals between pairs of detected photons. The first measurement yields the probability density p(I) and the moments of the light intensity I, and the second one the two-time intensity-correlation function. Measurements are also performed at three different wavelengths. p(I) is found to have a two-component structure, and the relative intensity fluctuations $\frac{〈{(\ensuremath{\Delta}I)}^{2}〉}{{〈I〉}^{2}}$ grow, apparently without limit, as the excitation tends to zero, so that no thermal state is reached. A possible explanation in terms of pumping fluctuations is discussed. The correlation function has the form of a sum of three exponential functions, and the amplitudes and decay constants of the three components are derived. The effective decay-time constant exhibits a thirteenth-power-law dependence on frequency of the laser light.