No abstract

An analytic study is presented of the efficient multiphoton excitation and strong harmonic generation in three-level systems specified by a pair of nearly degenerate, strongly dipole-coupled excited states. Such systems are physically formed by the three lowest states in, e.g., the hydrogen atom or evenly charged homonuclear diatomic molecular ions under reasonably chosen laser intensities. As a detailed analytic result, we found that the laser pulse of photon energy 2.05 eV, duration 0.23 ps and intensity 5 · 10 13 W cm 2 is able to produce complete inversion of the initial population in the hydrogen atom through the 5-photon excitation. At the same photon energy, the pulse of duration 0.41 ps and intensity 3.44 · 10 14 W cm 2 was found to produce the same effect in the molecular ion but through the 9-photon excitation. We show that the accompanying scattering of light has very rich spectrum differing substantially from that of the two-level system.

Driving on an analogy with the technique of composite pulses in quantum physics, we propose a broadband Faraday rotator and thus a broadband optical isolator, which is composed of sequences of ordinary Faraday rotators and achromatic quarter-wave plates rotated at the predetermined angles.

We propose a broadband optical diode, which is composed of one achromatic reciprocal quarter-wave plate and one non-reciprocal quarter-wave plate, both placed between two crossed polarizers. The presented design of achromatic wave plates relies on an adiabatic evolution of the Stokes vector, thus, the scheme is robust and efficient. The possible simple implementation using fibre optics is suggested.

We generalize our analytic approach (Berent M and Parzyński R 2009 Phys. Rev. A 80 033834) to include the effect of strong depopulation of the initial state when considering the multiphoton population transfer and scattering of low-frequency light by a 3-level system in the lambda-type configuration. We discuss the quality of the approximations made, i.e., the adiabatic and generalized rotating-wave approximations.