5. Practical considerations

The experimental setup generally used to generate four-wave mixing in hollow fibers is based on lasers delivering intense ultrashort pulses. A schematic diagram is shown in figure 10 a. Pump and signal pulses are generally derived from the same source to ensure synchronization and limit relative jitter. However, the two pulses must have different spectra, with their central wavelengths far apart (figure 10 b). In practice, one of the two pulses is often generated from non-linear phenomena. The spectrum of the main pulse from the laser can be shifted using an optical parametric amplifier based on nonlinear crystals