Generation of vacuum-ultraviolet pulses with a Doppler-broadened gas utilizing high atomic coherence

We carry out the theoretical study for the generation of vacuum-ultraviolet pulses with a Doppler-broadened gas utilizing high atomic coherence. It is essentially a difference-frequency generation scheme induced by the two-photon near-resonant pump and probe pulses, where the key point is to generate high atomic coherence between the ground and two-photon near-resonant states through a variant of stimulated Raman adiabatic passage with a time-dependent detuning. The advantage of our scheme is that the degree of coherence is sensitive to neither the exact amount and even sign of the detuning, nor the exact timing between the pump, auxiliary, and probe pulses. Hence our scheme is practically insensitive to Doppler broadening. As a specific example, we consider the generation of picosecond Lyman-α pulses with a Kr gas, and quantitatively study the influence of Doppler broadening as well as the intensity and incident timing of the picosecond probe pulse with respect to the pump pulse. The numerical results indicate that our scheme has a certain advantage over the conventional scheme which utilizes two-photon resonant excitation.