Shot-noise limited tunable dual-vibrational frequency stimulated Raman scattering microscopy.

We present a shot-noise limited SRS implementation providing a >200 mW per excitation wavelength that is optimized for addressing two molecular vibrations simultaneously. As the key to producing a 3 ps laser of different colors out of a single fs-laser (15 nm FWHM), we use ultra-steep angle-tunable optical filters to extract 2 narrow-band Stokes laser beams (1-2 nm & 1-2 ps), which are separated by 100 cm. The center part of the fs-laser is frequency doubled to pump an optical parametric oscillator (OPO).

High-repetition rate, mid-infrared, picosecond pulse generation with µJ-energies based on OPG/OPA schemes in 2-µm-pumped ZnGeP.

We report on two different concepts to generate µJ-level mid-infrared laser pulses with sub-10 ps pulse duration via nonlinear parametric generation at high pulse repetition rates. Both schemes rely on the recent development of compact and efficient CPA-free, Ho:YLF-based 2-µm laser sources pumping the highly nonlinear crystal ZnGeP used for parametric amplification. The first concept comprises a simplified OPG/OPA scheme efficiently producing signal and idler radiation at fixed wavelengths of 3.

Background-suppressed SRS fingerprint imaging with a fully integrated system using a single optical parametric oscillator.

Stimulated Raman Scattering (SRS) imaging can be hampered by non-resonant parasitic signals that lead to imaging artifacts and eventually overwhelm the Raman signal of interest. Stimulated Raman gain opposite loss detection (SRGOLD) is a three-beam excitation scheme capable of suppressing this nonlinear background while enhancing the resonant Raman signal. We present here a compact electro-optical system for SRGOLD excitation which conveniently exploits the idler beam generated by an optical parametric oscillator (OPO).

Origin and suppression of parasitic signals in Kagomé lattice hollow core fibers used for SRS microscopy and endoscopy.

Hollow core fibers are considered as promising candidates to deliver intense temporally overlapping picosecond pulses in applications such as stimulated Raman scattering (SRS) microscopy and endoscopy because of their inherent low nonlinearity compared to solid-core silica fibers. Here we demonstrate that, contrary to prior assumptions, parasitic signals are generated in Kagomé lattice hollow core fibers. We identify the origin of the parasitic signals as an interplay between the Kerr nonlinearity of air and frequency-dependent fiber losses.

Real-time Raman and SRS imaging of living human macrophages reveals cell-to-cell heterogeneity and dynamics of lipid uptake.

Monitoring living cells in real-time is important in order to unravel complex dynamic processes in life sciences. In particular the dynamics of initiation and progression of degenerative diseases is intensely studied. In atherosclerosis the thickening of arterial walls is related to high lipid levels in the blood stream, which trigger the lipid uptake and formation of droplets as neutral lipid reservoirs in macrophages in the arterial wall.

Difference-frequency generation of ultrashort pulses in the mid-IR using Yb-fiber pump systems and AgGaSe(2).

We employ AgGaSe(2) for difference-frequency generation between signal and idler of synchronously-pumped picosecond / femtosecond OPOs at 80 / 53 MHz. Continuous tuning in the picosecond regime is achieved from 5 to 18 µm with average power of 140 mW at 6 µm. In the femtosecond regime the tunability extends from 5 to 17 µm with average power of 69 mW at 6 µm.

Difference-frequency generation of fs and ps mid-IR pulses in LiInSe(2) based on Yb-fiber laser pump sources.

Difference-frequency generation between signal and idler of Yb-fiber laser synchronously pumped femtosecond and picosecond optical parametric oscillators (SPOPOs) operating at 53 and 80 MHz, respectively, is investigated in the wide bandgap chalcogenide crystal LiInSe(2). Single pulse energies in excess of 1 nJ are demonstrated, and the continuous tuning extends from 5 to 12 μm.