Simultaneous second-harmonic generation, third-harmonic generation, and four-wave mixing microscopy with single sub-8 fs laser pulses

We demonstrate a compact pulse compression scheme that offers flexible chirp control for improved conversion efficiencies in high resolution nonlinear optical microscopy. An Er:fiber laser combined with a highly nonlinear optical fiber yields pulses centered at 1100 nm with a bandwidth of 500 nm. The compressed pulses with a duration of 7.6 fs enable simultaneous second-harmonic generation, third-harmonic generation, and four-wave mixing microscopy. The spectrum is tailored for an ideal compromise between conversion efficiency and spectral discrimination between the three types of broadband nonlinear signals. Distinct differences in structural contrast obtained from the simultaneous read-out of the three nonlinear signals are demonstrated in a biological sample.