Hyperspectral stimulated Raman scattering microscopy with a polarization and timing-stabilized tunable VCSEL

We demonstrate hyperspectral stimulated Raman scattering microscopy with a self-seeded, optically gain-switched MEMS-vertical-cavity surface-emitting laser (VCSEL). The VCSEL generates sub-100-ps pulses across a 94-nm tuning range centered at 1290 nm when optically pumped with a 1076-nm, 84-ps mode-locked ytterbium-doped fiber laser, increasing the peak power by over 10× from the maximum continuous-wave power. An inline self-seeding scheme suppresses pulse-to-pulse polarization switching and raises the polarization extinction ratio above 15 dB across the full tuning range. Automatic synchronization with the pump laser is achieved by virtue of the optical pumping, and a high-speed electronic delay compensation scheme maintains a pulse walk-off of less than 7 ps as the wavelength is swept. By sweeping the VCSEL wavelength at each pixel in a scanning confocal microscope, stimulated Raman scattering spectra spanning 553 cm−1 from 1306 to 1859 cm−1 with 4.5 cm−1 resolution are demonstrated in 24 ms (957 spectral points with a 25 μs spectral dwell time), limited by the power of the VCSEL. A 230 × 230 pixel hyperspectral image with 252 spectral frames and a 500 μs spectral dwell time is demonstrated in 2 h. With further VCSEL amplification and switchable pumping between additional VCSELs, this architecture is readily scalable to shorter acquisition times and broader spectral coverage.