Ultrafast pulse characterization for microscopy by spatially integrated intensity of auto-convolution measurements using nonlinear excitation signal generation

Ultrafast laser pulses, with durations on the order of hundreds of femtoseconds or less enable nonlinear microscopic imaging. Characterizing the spectral-phase of a pulse is particularly valuable to understand the pulses structure in time, however this typically requires additional experimental setup on an entirely separate arm of an optical system. We present a technique for characterizing the spectral phase and amplitude of an ultrafast laser pulse from sequential spectrally modulated non-linear energy measurements. The technique is demonstrated for coherent and incoherent energy from the focus of a microscope. A significant benefit to this technique is that the nonlinear signals are measured as a condensed set of integrated auto-convolution intensities instead of a relatively large collection of spectrum measurements. We demonstrate both an amplitude modulation setup using a spectral mask and a phase modulation setup using a spatial light modulator. Pulses are characterized using a second harmonic generation peak power meter and within a biological sample exhibiting two-photon excitation fluorescence.