Using photo-induced EMF to characterize femtosecond laser pulses

Summary form only given. Femtosecond pulses are usually characterized by measuring their autocorrelation functions. Intensity autocorrelation using second-harmonic generation (SHG) is the most commonly used technique, which gives information on the pulse shape directly. However, the intensity requirement for SHG is high, and group-velocity mismatch can distort the pulses in phase-matched SHG crystals. In addition, it cannot give information on the phase of femtosecond pulses, which is important in pulse characterization. Electric-field autocorrelation can be performed without nonlinear optical effects and can give the phase information. For transform-limited pulses, the pulse width can be obtained. In cross correlation, if the reference pulse is fully characterized, the pulse envelope of the signal pulse can be extracted. We propose and demonstrate a linear technique to detect the envelope of the electric-field correlation of femtosecond pulses, using a detector based on the photo-induced-EMF. Our experiment uses a mode-locked Ti:sapphire laser operating at 800 nm to write the intensity pattern in a PI-EMF photodetector.