Widely tunable VECSEL-based laser system for multicontrast high-speed nonlinear imaging

We present a broadband laser system based on a passively mode-locked Vertical-External-Cavity Surface-Emitting Laser (VECSEL) designed for high-speed, multicontrast nonlinear imaging. The system generates a 300nm wide supercontinuum through a Photonic Crystal Fiber (PCF) and employs a Multiphoton Intrapulse Interference Phase Scan (MIIPS) scheme for advanced pulse shaping. This configuration enables precise spectral window selection and pulse compression to their transform-limited durations. Operating at a mode-locking repetition rate of 1.5 GHz, the frequency of the system matches the typical fluorescence lifetimes of many biological samples and commonly used fluorophores, making it an ideal light source for rapid bioimaging. The spectral range spans 900 to 1200 nm, covering key wavelengths essential for deep tissue imaging, offering great versatility in various biomedical applications. The ability to independently control the pulse amplitude, wavelength, and phase allows tailored excitation and an improved signal-to-noise ratio. Moreover, the high repetition rate inherently reduces the risks of photobleaching and photodamage, enhancing the overall imaging performance. The capability of the system to induce a non-linear response in biological samples is demonstrated using a multi-photon microscope, where Two-Photon Excitation of Fluorescence (2PEF) and higher-order harmonic generation are successfully detected.