Fig. 1. Experimental device diagram of Ti∶sapphire femtosecond oscillator

Fig. 2. Resonator cavity designed by ABCD matrix and intracavitary dispersion calculated by ray tracing method. (a) Spot radius of continuous light at flat mirror M4 versus distance between concave mirror C2 and crystal; (b) spot radius distribution in resonator; (c) relationship between stable region and optimal folding angle; (d) second-order dispersion in resonator

Fig. 3. Average output power and pulse duration versus pump power

Fig. 4. Spectra and pulse width measurement curve when average output power is 4.1 W. (a) Spectrum and corresponding Fourier transform limit pulse curve; (b) autocorrelation curver

Fig. 5. CW component gradually disappears as slit width decreases

Fig. 6. Measured mode-locking pulse trains at repetition rate of 74.15 MHz. (a) Time scale of 4 ns·div^-1; (b) time scale of 200 ns·div^-1

Fig. 7. Measurement results for spectrum, power stability, and beam quality. (a) Spectrum when repetition rate is 74.15 MHz and resolution is 5 Hz; (b) harmonics with resolution of 100 Hz; (c) power stability of mode-locked laser within 60 min; (d) beam quality at average output power of 4.1 W