Direct diode pumped Ti:Sapphire oscillator with novel ultrabroad tuning scheme optimized for non-linear optical microscopy

With the advent of femtosecond lasers, non-linear optical microscopy techniques have become powerful tools to image and study biological tissue. Ultra-fast Titanium Sapphire (Ti:sapphire) lasers have emerged as the gold standard in this field due their broad emission spectrum. Historically, the wider adoption of these imaging techniques outside of laboratory settings has been slowed by the complexity, cost and big footprint of femtosecond Ti:sapphire oscillators. However, in recent years, the new development of high power Gallium Nitride (GaN) based laser diodes has enabled direct diode pumping of Ti:Sapphire lasers, paving the way for drastic reductions in complexity, footprint and price. We present a compact, direct diode pumped, ultra-fast Kerr-lens Mode-Locked (KLM) Ti:sapphire oscillator with a novel tuning scheme based on a combination of a razor-edge slit and a single prism to minimize intracavity dispersion. This scheme allows for a 150 nm continuous tuning range while permitting sub-70 fs pulse duration at the sample plane over the full wavelength range including all optical components including microscope objective. The slit aperture and position are adjustable which allows for tuning of the central wavelength and bandwidth of the emission spectrum. To demonstrate the versatility of the laser for biological imaging, we show two-photon excited fluorescence microscopy and second harmonic generation images of various human tumor biopsies and ex-vivo sheep myocardium slices acquired at different wavelengths ranging from 750 nm to 900 nm.