Four-wave Mixing With A New Phase-matching Geometry

How to improve the degree and the bandwidth of the two-mode squeezed light in the four-wave mixing process caused by the interaction between atoms and the field in a double-Λ structure has always been a hot topic in the experimental and theoretical research.In the process of four-wave mixing when a single pump light is incident,the effective phase matching can only be satisfied in the range of refractive index of the probe light in the atomic medium np≥ 1 due to the restriction of the angle between the pump light and the probe light.The refractive index changes very fast in this region and the closer to the four-wave mixing,the larger the resonance absorption,so the gain bandwidth is narrower.We theoretically study the non-degenerate four-wave mixing process in which two pumping beams incident at a certain angle of θ0.Because of the new geometric phase matching in space,the projection of the two pump beams in the matching direction becomes smaller.When the angle between the probe light and the projection direction is less than or equal to θ0/2,the refractive index of the corresponding probe light should be np≤ 1 to satisfy the wave vector matching.In the np<1 region,the gain bandwidth is large because the absorption of the probe light is zero and the refractive index changes slowly,so the wide bandwidth intensity-squeezed light can be realized.Furthermore,the refractive index of the corresponding probe light np can be converted between greater than 1 and less than 1 by angle adjustment,which can be used to implement two different time order output pulses.By the inverse process the twin beams with frequency degenerated but separated spatial patterns can be realized when np<1 is satisfied.