Ultrasensitive Nonlinear Measurements of Femtosecond Optical Pulses at 1.5 μm by Aperiodically Poled Lithium Niobate Waveguides

Ultraweak, ~300-fs pulses at 1.5 μm are measured by second-harmonic generation intensity autocorrelation and frequency-resolved optical gating using aperiodically poled LiNbO
₃
waveguides. Our reference-free scheme can retrieve complex fields with 120-aJ coupled pulse energy, corresponding to a sensitivity of 2 x 10
^-6
mW, ~5 orders of magnitude better than the previous record