We theoretically study propagation behavior of probe (signal) and Stokes (idler) pulses under a strong coupling beam. The analyses predict that both pulses are parametrically amplified and delayed by about a pulsewidth.
We have theoretically and experimentally analyzed the ultraslow matched-pulse propagation in a parametric amplifying medium, especially focusing on the delay-time behaviors of the input probe pulse (signal) and the generated Stokes pulse (idler) under a strong coupling beam. Theoretically, it is predicted that the Stokes pulse always propagates with a definite group velocity with some initial delay time. The probe pulse, on the other hand, propagates at a fixed delay from Stokes after some transient period. This additional delay time is positive (probe is behind Stokes) if the medium is opaque for probe and transparent for Stokes, or it can be negative (probe is ahead of Stokes), if otherwise. It is also shown that the delay times of probe and Stokes, including the order of the pulses, can be arbitrarily and independently controlled by external parameters. The theoretical predictions and numerical simulations have been compared with experimental observations using a hot sodium vapor and they had a very nice agreement.
We have investigated experimentally and theoretically four-wave mixing (FWM) in hot potassium vapor as a medium for producing slow and store light. Two pump and a single probe photon were mixed in double-Λ system, characterized by parametric amplification of coupled co-propagating probe and conjugate beams. We have observed very high gains of probe and conjugate, up to 60 and 80 respectively, at two photon Raman resonance, under large one photon detuning, and high K-cell temperature. Using an amplifying medium to alleviate the absorption and distortion of propagating pulses are important for slow-light propagation. We observed ultraslow propagation of probe and conjugate pulses under conditions when parametric amplification of twin beams is well below their maximum values. A fractional delays of close to 5 at a gain ∼1.5, for the probe pulse of 20 ns, have been achieved simultaneously for both probe and accompanying conjugate pulse. FWM mixing process under conditions of the experiment results in broadening of twin beams, close to observed delays.