Abstract
We demonstrate a second harmonic generation (SHG) of 116 mW at 461 nm in a periodically poled lithium niobate waveguide when the power of the 922-nm fundamental light is coupled into the waveguide was 350 mW. The waveguide is 12.5 μm wide, 12.0 μm thick, 22 mm long, and has a 1-mm-long slab window at the output facet of the waveguide. The temperature acceptance bandwidth of the phase-matching curve of the SHG is approximately 0.5 °C. The SHG system demonstrates good beam quality and is reliable for cold atom experiments, including research on optical lattice clocks.
We theoretically demonstrate cascaded fourth and second harmonic generation in a periodically-poled nonlinear crystal with a half-order of phase-matching period. We consider a cascaded process in which four photons of the fundamental harmonic firstly convert into an intermediate photon of the fourth harmonic, which parametrically decays into two photons of the second harmonic at the second stage. Phase-matching for this cascaded nonlinear conversion is provided by using an asymmetric periodical poling. We use the quantum spatial Heisenberg equations to describe light propagation and conversion inside the nonlinear crystal. With this approach, we calculate second and fourth harmonic average number of photons as a function of the nonlinear crystal length.
Broadening of the second-harmonic phase-matching bandwidth in a temperature-gradient-controlled periodically poled Ti:LiNbO3 channel waveguide