Continuous beam scanning by transverse mode-locking in a Pound-Drever-Hall stabilized resonator.

Mode-locking, i.e., the phase-locked superposition of resonator modes, enables ultrafast laser beam dynamics.

Highly efficient and widely tunable SiN waveguide-based optical parametric oscillator.

We demonstrate an efficient and widely tunable synchronously pumped optical parametric oscillator (OPO) exploiting four-wave mixing (FWM) in a silicon nitride (SiN) waveguide with inverted tapers. At a pump pulse duration of 2 ps, the waveguide-based OPO (WOPO) exhibited a high external pump-to-idler conversion efficiency of up to -7.64 dB at 74% pump depletion and a generation of up to 387 pJ output idler pulse energy around 1.

Longitudinal to transversal conversion of mode-locked states in an empty optical resonator.

A longitudinal mode-locked state can be converted to a transverse mode-locked state by exploiting the spectral and spatial filtering of an empty optical resonator. Carrier and amplitude modulation sidebands were simultaneously transmitted by the conversion resonator, yielding phase-locked superpositions of up to five transverse modes. Equivalently, an amplitude-modulated beam was converted into a beam that periodically moved across the transverse plane.

Toward integrated tantalum pentoxide optical parametric oscillators.

We present a hybrid waveguide-fiber optical parametric oscillator (OPO) exploiting degenerate four-wave mixing in tantalum pentoxide. The OPO, pumped with ultrashort pulses at 1.55  µm wavelength, generated tunable idler pulses with up to 4.

Frequency modulation stimulated Raman scattering scheme for real-time background correction with a single light source.

A frequency modulation (FM) scheme for stimulated Raman scattering (SRS) is presented with a single fiber-based light source. Pulse-to-pulse wavelength-switching allows real-time subtraction of parasitic signals leaving only the resonant SRS signal with a noise reduction of up to 30 % compared to digital subtraction schemes, leading effectively to a contrast improvement by a factor of up to 8.3.

Toward integrated synchronously pumped optical parametric oscillators in silicon nitride.

We present a tunable, hybrid waveguide-fiber optical parametric oscillator (OPO) synchronously pumped by an ultra-fast fiber laser exploiting four-wave mixing (FWM) generated in silicon nitride waveguides. Parametric oscillation results in a 35 dB enhancement of the idler spectral power density in comparison to spontaneous FWM, with the ability of wide wavelength tuning over 86 nm in the O-band. Measurements of the oscillation threshold and the efficiency of the feedback loop reveal how an integration of the OPO on a single silicon nitride chip can be accomplished at standard repetition rates of pump lasers in the order of 100 MHz.

Multi-color stimulated Raman scattering with a frame-to-frame wavelength-tunable fiber-based light source.

We present multi-color imaging by stimulated Raman scattering (SRS) enabled by an ultrafast fiber-based light source with integrated amplitude modulation and frame-to-frame wavelength tuning. With a relative intensity noise level of -153.7 dBc/Hz at 20.

High-sensitivity frequency modulation CARS with a compact and fast tunable fiber-based light source.

Frequency modulation (FM) coherent anti-Stokes Raman scattering (CARS) is presented, using a compact as well as fast and widely tunable fiber-based light source. With this light source, Raman resonances between 700 and 3200 can be addressed via wavelength tuning within only 5 ms, which allows for FM CARS measurements with frame-to-frame wavelength switching. Moreover, the functionality for high-sensitivity FM CARS measurements was integrated by means of fiber optics to keep a stable and reliable operation.

Optical parametric amplification in silicon nitride waveguides for coherent Raman imaging.

We present tunable waveguide-based optical parametric amplification by four-wave mixing (FWM) in silicon nitride waveguides, with the potential to be set up as an all-integrated device, for narrowband coherent anti-Stokes Raman scattering (CARS) imaging. Signal and idler pulses are generated via FWM with only 3 nJ pump pulse energy and stimulated by using only 4 mW of a continuous-wave seed source, resulting in a 35 dB enhancement of the idler spectral power density in comparison to spontaneous FWM. By using waveguides with different widths and tuning the wavelength of the signal wave seed, idler wavelengths covering the spectral region from 1.

Higher-order mode supercontinuum generation in dispersion-engineered liquid-core fibers.

Supercontinuum generation enabled a series of key technologies such as frequency comb sources, ultrashort pulse sources in the ultraviolet or the mid-infrared, as well as broadband light sources for spectroscopic methods in biophotonics. Recent advances utilizing higher-order modes have shown the potential to boost both bandwidth and modal output distribution of supercontinuum sources. However, the strive towards a breakthrough technology is hampered by the limited control over the intra- and intermodal nonlinear processes in the highly multi-modal silica fibers commonly used.

Spontaneous four-wave mixing in silicon nitride waveguides for broadband coherent anti-Stokes Raman scattering spectroscopy.

We present a light source for coherent anti-Stokes Raman scattering (CARS) based on broadband spontaneous four-wave mixing, with the potential to be further integrated. By using 7 mm long silicon nitride waveguides, which offer tight mode confinement and a high nonlinear refractive index coefficient, broadband signal and idler pulses were generated with 4 nJ of input pulse energy. In comparison to fiber-based experiments, the input energy and the waveguide length were reduced by two orders of magnitude, respectively.

Rotational motion and rheotaxis of human sperm do not require functional CatSper channels and transmembrane Ca signaling.

Navigation of sperm in fluid flow, called rheotaxis, provides long-range guidance in the mammalian oviduct. The rotation of sperm around their longitudinal axis (rolling) promotes rheotaxis. Whether sperm rolling and rheotaxis require calcium (Ca ) influx via the sperm-specific Ca channel CatSper, or rather represent passive biomechanical and hydrodynamic processes, has remained controversial.

Portable all-fiber dual-output widely tunable light source for coherent Raman imaging.

We present a rapidly tunable dual-output all-fiber light source for coherent Raman imaging, based on a dispersively matched mode-locked laser pumping a parametric oscillator. Output pump and Stokes pulses with a maximal power of 170 and 400 mW, respectively, and equal durations of 7 ps could be generated. The tuning mechanism required no mechanical delay line, enabling all-electronic arbitrary wavelength switching across more than 2700  in less than 5 ms.

Photochemical preparation of gold nanoparticle decorated cyclodextrin vesicles with tailored plasmonic properties.

We report a photochemical strategy for the preparation of plasmonic vesicles by the in situ formation of gold nanoparticles at the surface of cyclodextrin host vesicle templates decorated with photoactive guest polymers. Upon irradiation with UV light, these carefully designed polymer shells undergo a Norrish type I reaction to generate reducing radicals for the in situ reduction of gold salts and simultaneously provide a stabilizing matrix allowing for a dense decoration with discrete gold seeds. In a highly controlled growth procedure the gold particle size can be adjusted between 3 and 28 nm resulting in an increasing interparticle plasmonic coupling as revealed by a pronounced redshift of the surface plasmon resonance (SPR) band and an enhanced absorption at wavelengths above 600 nm.

Density matrix study of ground state depletion towards sub-diffraction-limited spontaneous Raman scattering spectroscopy.

The suppression of Raman scattering is of high interest for the achievement of sub-diffraction-limited resolution in Raman scattering spectroscopy and microscopy. We present density matrix calculations of the suppression of spontaneous Raman scattering via ground state depletion in a level system based on the molecule tris(bipyridine)ruthenium(ii). This particular molecule has been earlier used for an experimental demonstration of the suppression of spontaneous Raman scattering, allowing us to successfully verify the validity of our numerical calculations by a comparison to the experimental results.

Low-power broadband all-optical switching via intermodal cross-phase modulation in integrated optical waveguides.

We demonstrate the potential of all-optical switches in integrated waveguides based on intermodal cross-phase modulation between transverse modes. For this purpose, the differential phase between two transverse modes of a probe beam was altered by cross-phase modulation with a control beam propagating only in the fundamental mode. A switching behavior was accomplished by spatially filtering the resulting multimode interference of the probe modes, which changed depending on the control beam power.

Rapid spectro-polarimetry to probe molecular symmetry in multiplex coherent anti-Stokes Raman scattering.

We present the simultaneous detection of the spectrum and the complete polarization state of a multiplex coherent anti-Stokes Raman scattering signal with a fast division-of-amplitude spectro-polarimeter. The spectro-polarimeter is based on a commercial imaging spectrograph, a birefringent wedge prism, and a segmented polarizer. Compared to the standard rotating-retarder fixed-analyzer spectro-polarimeter, only a single measurement is required and an up to 21-fold reduced acquisition time is shown.

Optical parametric chirped pulse oscillation.

A concept to flexibly adjust the spectral bandwidth of the output pulses of a fiber optical parametric oscillator is presented. By adjusting the chirp of the pump pulses appropriate to the chirp of the resonant pulses, the energy of the output pulses can be transferred into a user-defined spectral bandwidth. For this concept of optical parametric chirped pulse oscillation, we present numerical simulations of a parametric oscillator, which is able to convert pump pulses with a spectral bandwidth of 3.

Stabilization of High Oxidation State Upconversion Nanoparticles by N-Heterocyclic Carbenes.

The stabilization of high oxidation state nanoparticles by N-heterocyclic carbenes is reported. Such nanoparticles represent an important subset in the field of nanoparticles, with different and more challenging requirements for suitable ligands compared to elemental metal nanoparticles. N-Heterocyclic carbene coated NaYF :Yb,Tm upconversion nanoparticles were synthesized by a ligand-exchange reaction from a well-defined precursor.

Two-octave spanning supercontinuum generation in stoichiometric silicon nitride waveguides pumped at telecom wavelengths.

We demonstrate supercontinuum generation in stoichiometric silicon nitride (SiN in SiO) integrated optical waveguides, pumped at telecommunication wavelengths. The pump laser is a mode-locked erbium fiber laser at a wavelength of 1.56 µm with a pulse duration of 120 fs.

Near-infrared photoswitching of cyclodextrin-guest complexes using lanthanide-doped LiYF upconversion nanoparticles.

This communication reports a new type of supramolecular cyclodextrin-guest complexes using cyclodextrin coated upconversion nanoparticles as hosts and monovalent and divalent azobenzenes and arylazopyrazoles as guests. A potentially biocompatible photocontrol of the interaction by isomerization of the azobenzene or arylazopyrazole was achieved by laser irradiation at 980 nm and a very low light intensity of 0.22 W cm.

Ultrafast, all-optical control of modal phases in a few-mode fiber for all-optical switching.

The phase differences between the transverse modes of an optical fiber can be altered all-optically by intermodal cross-phase modulation. In this Letter, we experimentally demonstrate this effect with ultrashort laser pulses. An ultrashort probe pulse, guided in both modes of a two-mode fiber, is co-propagating and temporally overlapping with an ultrashort control pulse, guided in the fundamental mode only and centered at a separate wavelength.

Suppression of resonance Raman scattering via ground state depletion towards sub-diffraction-limited label-free microscopy.

We report on the first experimental demonstration of the suppression of spontaneous Raman scattering via ground state depletion. The concept of Raman suppression can be used to achieve sub-diffraction-limited resolution in label-free microscopy by exploiting spatially selective signal suppression when imaging a sample with a combination of Gaussian- and donut-shaped beams and reconstructing a resolution-enhanced image from this data. Using a nanosecond pulsed laser source with an emission wavelength of 355 nm, the ground state of tris(bipyridine)ruthenium(II) molecules solved in acetonitrile was depleted and the spontaneous Raman scattering at 355 nm suppressed by nearly 50 %.

Electronically and rapidly tunable fiber-integrable optical parametric oscillator for nonlinear microscopy.

We present a fiber-based optical parametric oscillator (FOPO) pumped by a fiber-coupled laser diode. The FOPO consisted of a photonic crystal fiber to convert the pump pulses via four-wave mixing and a dispersive resonator formed by a single-mode fiber. Via dispersion filtering, output pulses with a bandwidth of about 3 nm, a temporal duration of about 8 ps and a pulse energy of up to 22 nJ could be generated.

Light source for narrow and broadband coherent Raman scattering microspectroscopy.

We present a light source that is well adapted to both narrow- and broadband coherent Raman scattering (CRS) methods. Based on a single oscillator, the light source delivers synchronized broadband pulses via supercontinuum generation and narrowband, frequency-tunable pulses via four-wave mixing in a photonic crystal fiber. Seeding the four-wave mixing with a spectrally filtered part of the supercontinuum yields high-pulse energies up to 8 nJ and the possibility of scanning a bandwidth of 2000  cm(-1) in 25 ms.