Measurement of the intensity and phase of attojoule femtosecond light pulses using Optical-Parametric-Amplification Cross-Correlation Frequency-Resolved Optical Gating.

We use the combination of ultrafast gating and high parametric gain available with Difference-Frequency Generation (DFG) and Optical Parametric Amplification (OPA) to achieve the complete measurement of ultraweak ultrashort light pulses. Specifically, spectrally resolving such an amplified gated pulse vs. relative delay yields the complete pulse intensity and phase vs. time. This technique is a variation of Cross-correlation Frequency-Resolved Optical Gating (XFROG), and using it, we measure the intensity and phase of a train of attenuated white light continuum containing only a few attojoules per pulse. Unlike interferometric methods, this method can measure pulses with poor spatial coherence and random absolute phase, such as fluorescence.