We present the application of the dispersion scan (d-scan) technique in order to fully characterize intensity and phase of ultrafast pulses compressed by a grating-prism (grism) compressor.
Ultrafast pulses are generated in an Yb-doped fiber oscillator, mode-locked by non-linear polarization evolution (NPE) and operating at a central wavelength of 1030 nm with a repetition rate of 50 MHz. These output pulses are stretched in a 150 m long fiber to roughly 50 ps and then amplified in an Yb-doped fiber to an average power of 150 mW. A grating-prism combination is used to compensate the second and third order dispersion that was applied to the pulse by the fiber material.
For the optimal compression of the pulse, information on its spectral and temporal phase is required. Therefore, the dispersion scan is applied. In this technique, second harmonic spectra of the pulse are generated and recorded for different amounts of dispersion compensation applied to the pulse by the grism compressor. Depending on the chirp of the pulse, the maximum of the generated second harmonic spectra shifts, leading to a characteristic trace.
The amount of dispersion is changed by varying the separation of the prisms within the compressor, while the relation of second and third order dispersion is kept almost constant. The separation is changed by a stepper motor in order to enable a fully automated recording of the spectra.
The spectral and temporal course and phase of the pulse are then retrieved from the d-scan trace by a genetic computer algorithm.