Fig.1 Interferometric autocorrelation/FROG setup.
Ultrafast femtosecond spectroscopies, where ultrashort pulses are used, require auxiliary pulse characterization techniques. This requirement is the consequence that there is no direct way to measure the duration of ultrashort pulses since the response of electronic devices occurs over durations of the order of nanoseconds (10-9 sec), which is 6 orders of magnitude longer than the duration of a femtosecond (10-15 sec) pulse. Therefore, indirect pulse characterization methods are normally used in virtually any ultrafast spectroscopy laboratory.
In 2DES laboratory, there are several pulse characterization techniques based on autocorrelation, crosscorrelation (or x-correlation) and frequency-resolved optical gating (FROG).
- Second-harmonic generation (SHG) autocorrelation and SHG FROG: used to characterize green/red/near-infrared optical pulses.
- Sum frequency generation (SFG) autocorrelation and SFG FROG: used for characterization of green/red/near-infrared optical pulses.
- Interferometric autocorrelation and interferometric FROG (iFROG): used to characterize red/near-infrared optical pulses (Fig. 1) .
- Difference frequency generation (DFG) x-correlation and DFG x-FROG: used to characterize deep ultraviolet (UV) pulses (200-300 nm central wavelength) of the duration longer than ~12 fs.
- Transient grating (TG) x-correlation and TG x-FROG: used to characterize deep-UV pulses of a duration longer than ~7 fs (Fig. 2).
Fig.2 Transient-grating cross-correlation/FROG setup.
 Pavel V. Kolesnichenko, Lukas Wittenbecher, and Donatas Zigmantas, “Fully symmetric dispersionless stable transmission-grating Michelson interferometer”. Optics Express 28(25), 2020, pp. 37752-37757 (https://doi.org/10.1364/OE.409185).