Amplitude and phase measurement of mid-IR femtosecond pulses using XFROG

Summary form only given. Frequency-resolved optical gating (FROG) is a versatile technique for the measurement of ultrashort pulses across a wide range of wavelengths, and common approaches rely on using a detector array to record the spectrum of the second-harmonic autocorrelation signal of a pulse. Implementing an analogous method to measure mid-infrared pulses is inconvenient because the sensitivity of readily available silicon CCD devices is poor at the second-harmonic frequency of pulses with wavelengths longer than 2.1 /spl mu/m. In this work we demonstrate a technique which generates a cross-FROG (XFROG) trace by sum-frequency mixing a mid-infrared pulse with a time-delayed near-infrared pulse. By using an adapted version of the principal components generalised projections retrieval algorithm we have been able to characterise both pulses in amplitude and phase.