A theoretical study is presented which permits the analysis of multiphoton processes in the presence of homogeneous, inhomogeneous, and power-broadening mechanisms. A method derived from the Markov model microfield theory is used. This is based on the statistics of the fluctuations of the interaction between the radiator and a perturbing environment. Application is made to velocity-changing collisions in Doppler-free spectroscopy and to homogeneous and inhomogeneous pressure broadening in two-photon absorption or resonance fluorescence.