Fig. 1. Optical path of femtosecond pulse nonlinear compression system based on thin plate compression technology

Fig. 2. Experiment of measuring spectrum of cone-shaped emitted beam. (a) Schematic of state of light beam during near-steady propagation in medium-air unit; (b) optical path for cone-shaped emission measurement built by Yb³⁺-doped crystal femtosecond laser; (c) spectrum of annular cone-shaped emitted beam after separation; (d) spectrum of central beam after separation

Fig. 3. Nonlinear compression experiment results of Yb³⁺-doped femtosecond fiber laser. (a) Autocorrelation measurement result of output pulse of Yb³⁺-doped femtosecond fiber laser with pulse spectrum shown in inset; (b) pulse autocorrelation after first-stage compression system with first-order broadening result of spectrum shown in inset; (c) pulse autocorrelation after two-stage compression system with final spectral broadening result shown in inset; (d) pulse time-domain electric field after the second stage nonlinear compression restored by SHG-FROG with output beam quality of nonlinear compression system shown in inset

Fig. 4. Nonlinear compression experiment results of Yb³⁺-doped bulk femtosecond laser. (a) Autocorrelation measurement result of output pulse of Yb³⁺-doped bulk femtosecond laser with pulse spectrum shown in inset; (b) pulse autocorrelation after first-stage compression system with first-order broadening result of spectrum shown in inset; (c) pulse autocorrelation after two-stage compression system with final spectral broadening result shown in inset; (d) pulse time-domain electric field after the second stage nonlinear compression restored by SHG-FROG with output beam quality of nonlinear compression system shown in inset

Fig. 5. Spectral evolution of pulse after passing through different numbers of dielectric plates. (a) First-order broadening process; (b) second-order broadening process