Two-photon Loss Research Articles

Generalized EinsteinBcoefficients for coherently driven three-level systems

Generalized Einstein B coefficients for coherently driven closed three-level systems are introduced by means of the quantum-jump technique. The nonreciprocity between stimulated emission and absorption for both one-photon and two-photon gain and loss processes has been studied and quantified in terms of the rates of the particular incoherent processes present in each three-level system. Some general properties of these generalized Einstein B coefficients have been found. In particular, whenever the generalized Einstein B coefficient for one-photon gain overcomes that for one-photon loss then the generalized Einstein B coefficient for two-photon loss overcomes that for two-photon gain, and vice versa. Finally, we have obtained simple analytical expressions indicating the way to maximize the asymmetry between stimulated emission and absorption coefficients either for one-photon or for two-photon processes.

Femtosecond Z-scan and degenerate four-wave mixing measurements of real and imaginary parts of the third-order nonlinearity of soluble conjugated polymers

We investigated the third-order nonlinear optical properties of several soluble π-conjugated polymers with a goal of reliable determination of the parameters that characterize the nonlinearity, such as the real and imaginary parts of the nonlinear refractive index n2 and the one-photon loss and two-photon loss merit factors W and T, respectively. The measurements were performed at 800 nm with 100-fs pulses from an amplified Ti:sapphire system. We present results of investigations of several 2,5-substituted poly(p-phenylene vinylenes), including poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene] and a soluble ladder poly (p-phenylene) polymer. In particular, Z-scan measurements of polymer solutions were found to be useful for the determination of the complex nonlinear refractive index. The results could be verified by time-dependent degenerate four-wave mixing studies performed on thin films of the polymers. We found generally good agreement between the values of n2 determined from Z scan and those from degenerate four-wave mixing. The results indicate that the nonlinear refractive index of the order of 10-12 cm2/W can be readily obtained for various conjugated polymers. However, the two-photon merit factors T larger than unity are commonly encountered within the two-photon absorption ranges of these compounds.

Dispersion of the nonlinear refractive index of optical crystals

The nonlinear refractive indices of several important optical materials have been measured at the second and third harmonic wavelengths of the Nd laser using nearly degenerate four-wave mixing. Measurements made relative to the nonlinear index of fused silica have the highest accuracy. Absolute measurements were also made using the Raman cross-section of benzene as a nonlinear reference standard. The relative measurements are compared with a despersion model base on parameters fitted to the linear refractive indicies and also to a recently proposed model based on Kramers-Kronig transformation of the calculated, two-band, two-photon loss spectrum.

LANGEVINIAN THEORY OF TWO-PHOTON LASERS BY OPTICAL PUMPING

In this paper, a two-photon laser by optical pumping, with two-photon losses, is studied by means of the Langevinian theory, the langevinian equation is obtained. Then the steady-state average photon number, the frequency pulling, the linewidth and the dynamical Stark effect are obtained. From the analysis of the gain, it is shown that, for the incoherent pumping, only the two-step process of single-and two-photon gives contribution. And for the coherent pumping, in addition, the one-step process of single and two-photon also contributes. And two processes are confined by the negative-feedback and saturation. The linewidth is independent of the steady state average photon number.

A STUDY ON DISSIPATION MECHANISM IN TWO-PHOTON LASER

In this work, we have respectively investigated two-photon processes of a cascade three-level atom interacting with thermal and vacuum radiation fields by means of non-relativestic QED. We verified the important role of atomic thermal loss and two-photon transtion loss in the disspation processes. We proved the condition under which the thermal fluctuation can be neglected, and discussed, the character of laser cavity in which the two-photon laser can be produced.

Quantum simulations of nonlinear optical damping: An exact solution for the stochastic differential equations and an interpretation of "spiking"

This paper considers the ``positive-P'' description of nonlinear optical damping where one-photon and two-photon loss mechanisms are allowed. An exact solution of the corresponding stochastic differential equations is presented that graphically shows the breakdown of the positive-P representation found in earlier numerical-simulation work. The problem of ``spiking'' in simulations of nonlinear optical processes is then addressed, using the nonlinear damping process as an example. It is pointed out that although ``spiking'' can be exascerbated at high levels of quantum noise by numerical inaccuracy, the tendency to spike is in fact an analytic property of the stochastic variables.

Observation and density dependence of the Raman echo in atomic thallium vapor

Working on the 6P12−6P32 transition of atomic thallium vapor, we have observed Raman echoes generated by excitation and probe fields detuned from the 7S12 intermediate state by up to 50 cm-1. This constitutes the first time that echoes, generated by pure two-photon excitation, have been observed in an atomic system. The Raman echo intensity is found to increase roughly as the square of the thallium density at low densities, but at higher densities it peaks and subsequently declines. We suggest that two-photon absorption and loss of phase-matching resulting from excitation-pulse-induced population transfer are important in the high density degradation of the Raman echo signal.

Quantum theory of an inhomogeneously broadened two-photon laser

A quantum statistical analysis of a two-photon laser is presented in a generalization of the one-photon laser. A two-photon loss mechanism is assumed by taking detailed-balance considerations into account. The expressions for the photon statistical distribution exhibit the exact influence of the Doppler parameter and other relaxation parameters. In addition, the photon statistics can be studied as a function of the detuning. Threshold conditions for the laser action are noticed. The peak photon number and half-width of the photon distributions are obtained. It is found that the photon distribution can be written as a ratio of the one-photon laser-photon distribution to the Poisson distribution for photons.