Observation of Wavelength Tuning Curves During Pump-Depleted Second Harmonic Generation

Abstract

Achieving nearly complete energy conversion (or, in the case of lossy systems, pump depletion) in second harmonic generation (SHG) is challenging. Only when the phase velocities of the fundamental (or pump) and second harmonic frequencies are precisely matched throughout the interaction does power flow unidirectionally to the second harmonic wave. We recently reported the observation of 99 % pump depletion in a single-pass, quasi-phasematched SHG experiment [1]. A plot of SHG efficiency as a function of pump wavelength is known as a tuning curve; the evolution of the shape of the tuning curve as a function of maximum depletion was predicted in the early days of nonlinear optics [2]. We present here wavelength tuning curves for SHG in the limit of strong pump depletion, where the interaction is quasi-CW in time and involves guided waves in space, allowing direct comparison with theory based on a CW plane-wave model. This is not possible with typical configurations involving Gaussian beams in space and averaging over pulses in time.