A new picosecond light source for ultra-sensitive SRS microscopy allow imaging in the CH- and fingerprint region as well as of Raman labels. Its fast tuning of about one second enables easy multispectral SRS imaging.

Stimulated Raman Scattering (SRS) microscopy was developed for the label-free detection of molecular groups, addressing the speed limitations of spontaneous Raman microscopy. Standard SRS microscopy typically operates with laser sources at an 80 MHz repetition rate and a color-tuning speed of approximately 0.1 Hz to target different molecular groups. Here, we present a novel laser system that overcomes these speed limitations, achieving an order-of-magnitude improvement in both color-tuning and imaging speed. Our system features a reduced repetition rate of 40 MHz, enabling SRS imaging that is ten times faster than standard systems while maintaining the same average power at the sample. This is achieved through increased pulse energy and laser modulation at half the repetition rate. Furthermore, the system provides nearly ten times faster color-tuning across an extended range (660-1010 nm) by employing angle-tuning of nonlinear crystals instead of temperature-tuning. The improved performance is demonstrated in direct comparison with a standard SRS laser system, showcasing the potential for significantly enhanced imaging capabilities. ### Competing Interest Statement AE: Abberior Instruments GmbH (I), GS, PT, SP & IR: APE Angewandte Physik & Elektronik GmbH (E).

High energy of up to 800 nJ Vacuum UV pulses at 133 nm were generated by frequency tripling of second harmonic pulses of a Ti:sapphire amplifier in argon. Numerical simulations suggest six-wave-mixing as underlying nonlinear process.

Spectral fringes in the second harmonic of fs pulses under strong phase- and group-velocity mismatch are used to evaluate the refractive index of SrB 4 O 7 down to 160 nm, essential for random quasi-phase-matching in the VUV.

We consider second harmonic generation (SHG) of ultrashort pulses in the case of strong phase- and group-velocity mismatch. Spectral fringes appear in the second harmonic related to two delayed replicas of the fundamental pulse in the time domain. The fringe separation can be used to evaluate the group-velocity and refractive index of nonlinear crystals at extreme wavelengths. Experimental results with femtosecond pulses in SrB(4)O(7) (SBO) are used to refine the Sellmeier equation describing the n(c) refractive index down to 160 nm, essential for the use of this unique nonlinear crystal for random quasi-phase-matching in the VUV.

Tunable coherent radiation is generated in the vacuum ultraviolet down to 121 nm using random quasi-phase matching in strontium tetraborate, the shortest wavelength ever produced with a second-order nonlinear optical process in a solid-state material. Relevant properties of this radiation, the nonlinear process, and the nonlinear crystal are investigated.

We investigate non-adiabatic dynamics of NO molecules that are photo-excited in the vacuum ultraviolet photon energy range using time-resolved velocity map imaging. Highly excited valence and Rydberg states are populated with a tunable (147-151 nm) femtosecond laser pulse and then ionized by a time-delayed near-IR laser pulse. Three main contributions are observed in the photoelectron kinetic spectra with corresponding electron yields that show pronounced oscillations. Two oscillations are assigned to ro-vibronic coupling in the valence-Rydberg mixture of the B-'2 Delta (v = 7) and 4d delta N-2 Delta (v = 0) states and the B-2 Pi (v = 25) and 4p pi K-2 Pi (v = 1) states, respectively. We assign a third oscillation to originate from a coupling between two Rydberg states.

Generation of sub-45 fs vacuum UV (VUV) pulses tunable across the spectral range of 146-151 nm at 1 kHz repetition rate is reported. The pulses are produced using noncollinear difference-frequency four-wave mixing between the third-harmonic of an amplified Ti:sapphire laser and the signal wavelength of an infrared optical parametric amplifier (ω(VUV)=2ω(TH)-ω(IR)) in krypton and argon. The generated VUV pulses have energies as high as 90 nJ. Pulse duration measurements are realized by cross correlation between the VUV pulses and the laser fundamental wavelength using pump-probe ionization in xenon.

We report the generation of sub 20 fs UV pulses with 300 μJ energy at 1 kHz repetition rate by applying spectral broadening of the UV pulses during filamentation in argon.

Generation of sub-20-fs UV pulses with more than 300 μJ energy at 268 nm is reported. First, the UV pulses are produced by successive second-harmonic and third-harmonic (TH) generation of 805 nm pulses of a 1 kHz Ti:sapphire laser amplifier. The spectral broadening of TH pulses is realized in a filament, generated in argon. The produced pulses are compressed in a simple double-pass prism-pair compressor. Starting from 100 fs pulses, we achieve a fivefold pulse shortening.