We present an ultra‐low noise, near to mid infrared light source for a variety of multiphoton imaging and spectroscopy techniques. The system is based on an optical parametric oscillator (OPO) pumped by a femtosecond Ytterbium solid state oscillator with tens of megahertz repetition rate. This light source supplies three intrinsically synchronized light beams at wavelengths: 1040 nm, 1400-2000 nm (tunable) and 2200-4200 nm (tunable). Without active stabilization, the OPO preserves the shot-noise limited performance of the Yb-oscillator, along with a high long-term stability and a TEM00 beam profile. While this tuning range is already suitable for two- and three-photon microscopy, it now becomes possible to address vibrational modes and thus molecular specificity by employing further frequency conversion stages. Tailored frequency doubling provides either a narrow linewidth (0.5-1.2 nm) or a broadband (>40 nm) beam, tunable from 750-950 nm.
The fixed Stokes beam of the Yb-oscillator can directly be used as a pump source for coherent Raman scattering such as SRS or CARS spectroscopy/microscopy. To this end, we will demonstrate the capability of our system for both SRS imaging at video rate with a spectral precision of 13 cm-1 as well as SRS spectroscopy with more than 400 cm-1 bandwidth in a single shot. By further mixing the two output beams of the OPO, we are able to additionally produce mid-infrared light that is tunable from 4-16 µm. With the help of vibrational sum frequency generation, our system will allow us to cover a spectral range of 700-7000 cm-1.
We present mid-infrared supercontinuum sources based on chalcogenide, tellurite, and liquid-filled capillary fibers and sub-picosecond oscillator pumping. Depending on the fiber geometry and material, the experimentally achieved spectral bandwidths and output powers vary significantly. In As2S3 chalcogenide step-index fibers we achieve a maximum output power of 550 mW at a spectral width of 2 μm, covering the important transparent atmospheric window between 3 and 5 μm. In tellurite step-index fibers we attain an ultra-broadband spectrum ranging from 1.3 to 5.3 μm with an average power of 150 mW. The spectral behavior of the supercontinua is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. As pump source we use high repetition rate (42 MHz) optical parametric oscillators/amplifiers which deliver Watt-level pulses tunable between 1.4 – 4.1 μm. These supercontinuum sources promise to be excellent laboratory tools for high resolution spectroscopy owing to their high brilliance and near TEM00 spatial beam profiles.
We demonstrate a tunable and robust femtosecond supercontinuum source with a maximum output power of 550 mW and a maximum spectral width of up to 2.0 μm which can cover the mid-infrared region from 2.3 μm up to 4.9 μm by tuning the pump wavelength. As light source we use a synchronously pumped fiber-feedback OPO and a subsequent OPA which delivers femtosecond, Watt level idler pulses tunable between 2.5 μm and 4.1 μm. These pulses are launched into As2S3 chalcogenide step-index fibers with core diameters of 7 and 9 μm. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy owing to its high brilliance as demonstrated for the CS2- absorption bands around 3.5 μm.