Pulse-evolution dynamics and pulse-energy scaling in a SESAM-free dual-gain-chip traveling-wave butterfly-ring VECSEL

A SESAM-free self-mode-locked dual-gain-chip vertical external-cavity surface-emitting laser (VECSEL) with a traveling-wave butterfly-ring cavity is numerically investigated and experimentally demonstrated. A pulse-evolution model based on the mode-locking master equation was developed and solved using the split-step Fourier method. The simulation results that the dual-gain-chip configuration enables faster pulse buildup and yields a simulated output peak power of 1031 W, with a pulse width of 1.44 ps, a spectral width of 1.31 nm, and a repetition rate of approximately 252 MHz. Experimentally, stable fundamental self-mode locking was achieved at 254 MHz, producing pulses with a duration of 1.46 ps, a maximum average output power of 376.8 mW, corresponding to a calculated output peak power at the kilowatt level. The RMS power fluctuation of 0.28% over 60 min. Agreement in pulse duration, spectral width, and repetition rate supports the model and indicates that the proposed dual-gain-chip traveling-wave butterfly-ring cavity can support stable self-mode-locked operation and, compared with the single-gain-chip cavity, can increase the pulse energy and accelerate the pulse buildup process. This architecture is promising for optical amplification, nonlinear frequency conversion, and precision laser processing.