Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO 3 waveguides at 1.5??m

We retrieve intensity and phase profiles of 280?fs, 50?MHz optical pulses with 124?aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7×10?6?mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.