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In contrast to spontaneous Raman scattering, coherent Raman scattering techniques, such as femtosecond stimulated Raman scattering (FSRS), show advantages for many applications. Besides an enhanced signal strength, FSRS is free of a nonresonant background but is affected by cross-phase modulation (XPM). The resulting artifacts in FSRS become relevant for high pulse intensities (GW/cm2-regime) and ultrashort pulses (

We demonstrate a waveguide-based OPO exploiting the emerging Ta2O5 platform and investigate its feasibility for integration. Pumped synchronously at 1.55 µm wavelength, the OPO provided up to 6 pJ pulse energy, tunable by ±20 nm around 1.46 µm wavelength.

Transverse mode-locking is achieved by matching the transverse mode spacing of an optical cavity to the spacing of phase-locked longitudinal modes of an incident beam.

Generating visible light with wide tunability and high coherence based on photonic integrated circuits is of high interest for applications in biophotonics, precision metrology and quantum technology. Here we present the first demonstration of a hybrid-integrated diode laser in the visible spectral range. Using an AlGaInP optical amplifier coupled to a low-loss Si3N4 feedback circuit based on microring resonators, we obtain a spectral coverage of 10.8 nm around 684.4 nm wavelength with up to 4.8 mW output power. The measured intrinsic linewidth is 2.3$\pm$0.2 kHz., Comment: 8 pages, 6 figures

We present multicolor coherent Raman imaging (CRI) with enhanced sensitivity by a novel fiber optical parametric oscillator (FOPO). The FOPO combines a rapid and wide tunability for accessing Raman bands between 700 and 3500 cm-1 within only 5 ms with a frequency modulation (FM) at 20 MHz for enhancing CRI sensitivity by at least two orders of magnitude.

Silicon nitride (Si 3 N 4 ) waveguides offer a versatile on-chip platform, on which nonlinear processes such as four-wave mixing (FWM) can be driven very efficiently due to the high nonlinearity [1] . Therefore, lower pump energies and shorter interaction lengths are necessary in comparison to fibers [2] . We experimentally exploit these advantages in a tunable waveguide-based optical parametric amplifier (WOPA) by stimulated FWM in Si 3 N 4 waveguides for narrowband coherent anti-Stokes Raman scattering (CARS) imaging.

Optical parametric oscillators (OPOs) are ubiquitous sources for efficient frequency conversion and have evolved into robust fiber technology [1] . However, integrated waveguides offer in contrast to photonic crystal fibers a higher nonlinearity resulting in lower necessary pump energies and shorter interaction lengths [2] . Therefore, OPOs would require smaller footprints on a chip with additionally improved stability [3] . Here, we present a waveguide-based OPO (WOPO) exploiting four-wave mixing (FWM) in silicon nitride (Si 3 N 4 ) waveguides, with the potential to be fully integrated.

Supercontinua are of high interest due to their broad bandwidth and high brightness enabling a broad range of applications, e.g., optical coherence tomography or frequency metrology. During soliton-driven supercontinuum generation (SCG), a higher-order soliton (HOS) forms, generating a sufficiently broad spectrum prior to the HOS’ fission to radiate phase-matched dispersive waves (DWs) [1] .

The conversion of transverse mode-locked (TML) laser beams from a Hermite-Gaussian (HG) to a Laguerre-Gaussian (LG) mode set using a cylindrical lens mode converter was demonstrated experimentally. By changing the spatial symmetry of the beams new spatio-temporal dynamics for TML lasers were enabled. In particular, the fast linear motion of an oscillating laser spot, generated by a TML laser based on HG modes, was translated into the circular motion of a TML laser beam based on LG modes. The mode conversion was demonstrated successfully for different average mode orders. Apart from an average ellipticity of about $$6\%$$ 6 % , the converted beam profiles remained circular over the propagation from the near- into the far-field. The remaining ellipticity seemed to be introduced by astigmatism of the incident HG TML beam, which could be compensated before conversion. Due to their radial symmetry and high scanning speed TML laser beams based on LG modes are well suited for precision applications like STED or Minflux microscopy.

Hybrid integration of semiconductor optical amplifiers with frequency-selective feedback circuits, implemented using low-loss Si3N4 waveguides, enables robust chip-sized lasers with outstanding properties. Deploying ring resonators as a tunable feedback filter provides single-mode operation over a wide wavelength range. Moreover, these rings resonantly enhance the cavity length, which results in ultra-narrow intrinsic linewidth, as low as 40 Hz. Here, we present an overview on state-of-the-art developments regarding these lasers. We compare linewidth and tuning results for different feedback circuit configurations. Finally, we report on the first demonstration of a hybrid-integrated semiconductor laser that operates in the visible wavelength range.

We present high-speed multicolor stimulated Raman scattering imaging (SRS) enabled by an all-fiber light source. With a relative intensity noise level of -157 dBc above 10 MHz the light source is shot-noise limited up to a detector current of 0.75 mA. Compared to other fiber-based light sources optimized for SRS, the presented system is tunable in under 5 ms per arbitrary step between 700 and 3530 wavenumbers. The compact and environmentally stable system is predestined for fast multicolor assessments of medical or rapidly evolving samples with high chemical specificity.

We present multicolor coherent Raman imaging (CRI) with two orders of magnitude enhanced sensitivity accomplished by a frequency modulation (FM) at 20 MHz of a portable fiber optical parametric oscillator (FOPO). The FM is combined with a rapid and wide tunability for accessing Raman bands between 700 and 3500 1/cm within only 5 ms. This development constitutes an important step for advancing CRI microscopy in terms of portability and sensitivity for applications in medical diagnostics or environmental sensing.

We demonstrate dispersive wave generation in a low-intensity transverse mode on account of intermodal cross-phase modulation driven by an orthogonal mode excited with a high-intensity pulse.

We present dispersive wave generation via intermodal cross-phase modulation. The interaction between a higher-order soliton in one transverse mode and an orthogonal, low-intensity mode causes the latter to radiate a dispersive wave.

Transverse mode-locking in an end-pumped solid state laser by amplitude modulation with an acousto-optic modulator was investigated. Using the stochastic parallel gradient descent algorithm the modal power coefficients and the modal phases of the transverse mode-locked (TML) laser beam were reconstructed from the measured spatial and spatio-temporal intensity distributions, respectively. The distribution of the reconstructed modal power coefficients revealed that the average mode order of the transverse mode-locking process could be increased by a factor of about 8 compared to previous works, corresponding to an increase in the normalized oscillation amplitude by a factor of about 3. Furthermore, we found that besides a non-Poissonian modal power distribution, strong aberrations of the modal phases occurred in the experiment, resulting in a deformation of the oscillating spot. Additionally, we demonstrated the generation of up to four spots oscillating simultaneously on parallel traces by operating the TML laser on a higher mode order in the orthogonal direction to the transverse mode-locking process. TML lasers are of interest, e.g., for beam scanning purposes, as they have the potential to enable spot resolving rates in the multi-GHz regime.

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. The idler and residual pump pulses were used for CARS measurements, enabling chemically selective and label-free spectroscopy over the entire fingerprint region, with an ultrafast fiber-based pump source at 1033 nm wavelength. The presented simple light source paves the path towards cost-effective, integrated lab-on-a-chip CARS applications.

When an ultrafast optical pulse with high intensity is propagating through transparent material a supercontinuum can be coherently generated by self-phase modulation, which is essential to many photonic applications in fibers and integrated waveguides. However, the presence of dispersion causes stagnation of spectral broadening past a certain propagation length, requiring an increased input peak power for further broadening. We present a concept to drive supercontinuum generation with significantly lower input power by counteracting spectral stagnation via alternating the sign of group velocity dispersion along the propagation. We demonstrate the effect experimentally in dispersion alternating fiber in excellent agreement with modeling, revealing almost an order of magnitude reduced peak power compared to uniform dispersion. Calculations reveal a similar power reduction also with integrated optical waveguides, simultaneously with a significant increase of flat bandwidth, which is important for on-chip broadband photonics., Comment: Main text and supplementary information

We present a rugged all-fiber optical parametric oscillator (FOPO) for coherent Raman imaging (CRI). The FOPO shows ideal performance for hyperspectral video-rate coherent Raman imaging with pulse durations of 7 ps at 40 MHz and switching times of less than 5 ms from 700 to 3530 wavenumbers. Due to our patented all-fiber setup the FOPO runs on a regular laboratory cart. We present shock measurements that resemble typical situations in a clinical environment as well as long-term stability measurements. The presented robust fiber laser system is ideally suited to allow easy access to hyperspectral, high-speed CRI for translational research.

Silicon nitride waveguides offer a high nonlinear refractive index and tight mode confinement, ideal for efficient four-wave mixing (FWM) processes. We present a light source for coherent anti-Stokes Raman scattering (CARS), with the potential to be set up as an all-integrated device, based on spontaneous FWM in silicon nitride waveguides with only a single ultrafast fiber-based pump source at 1030 nm wavelength. Broadband signal and idler pulses are generated with only 5 nJ input pulse energy, such that the idler and residual pump pulses can be used for CARS measurements, enabling chemically-selective and label-free imaging over the entire fingerprint region.

A concept for nonlinear pulse compression is presented, which relies on alternating the dispersion sign by repeatedly splicing segments of normal to anomalous dispersion fibers. This approach accomplishes to limit temporal defocusing by repetitive recompression of the broadened bandwidth, resulting in few-cycle pulses without the need of soliton formation or free-space compressors. We show the compression of 80 fs pulses down to 25 fs pulses, which are nearly bandwidth-limited by using a special dispersion compensating fiber. Besides further scaling of pulse duration, we show a stability and scaling analysis regarding the input conditions and the highly coherent few-cycle output.

Visible diode lasers with wide wavelength tunability and narrow spectral linewidth are of high importance in bio-photonics and metrology. Hybrid integrated diode lasers, using waveguide circuits for spectrally selective feedback, provide wide tunability and sub-100-Hz intrinsic linewidths in a robust chip format. So far, these lasers have only been realized at infrared wavelengths. Here we present the first operation of a hybrid integrated diode laser in the visible. The laser, formed by a diode amplifier which is hybrid integrated with a Si3N4 ring-resonator based feedback circuit, is tunable over 11 nm around 685 nm and delivers 5 mW output power.

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 (Ca2+) influx via the sperm‐specific Ca2+ channel CatSper, or rather represent passive biomechanical and hydrodynamic processes, has remained controversial. Here, we study the swimming behavior of sperm from healthy donors and from infertile patients that lack functional CatSper channels, using dark‐field microscopy, optical tweezers, and microfluidics. We demonstrate that rolling and rheotaxis persist in CatSper‐deficient human sperm. Furthermore, human sperm undergo rolling and rheotaxis even when Ca2+ influx is prevented. Finally, we show that rolling and rheotaxis also persist in mouse sperm deficient in both CatSper and flagellar Ca2+‐signaling domains. Our results strongly support the concept that passive biomechanical and hydrodynamic processes enable sperm rolling and rheotaxis, rather than calcium signaling mediated by CatSper or other mechanisms controlling transmembrane Ca2+ flux., Live‐cell imaging unexpectedly reveals that Ca2+ influx via the CatSper channel is dispensable for rheotactic steering of sperm.

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.

The cholesterol concentration in lipid membranes is an important parameter that influences signaling processes as well as the structure of membranes. We show that the cholesterol content in giant unilamellar vesicles from binary lipid mixtures of cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine can be quantitatively assessed with spontaneous Raman scattering spectroscopy. An analytical model employing correlation analysis is introduced, which can be applied for the determination of the actual cholesterol content in unilamellar lipid membranes of lipid compositions that are unknown or, because of external effects, deviant from the weighed-in values.

Die Stabilisierung von hochoxidierten Nanopartikeln mit N-heterocyclischen Carbenen wird beschrieben. Solche Nanopartikel reprasentieren eine wichtige Untergruppe im Feld der Nanopartikel. Sie stellen andere Anforderungen an geeignete Liganden als elementare Metallnanopartikel. Durch die N-heterocyclischen Carbene stabilisierte NaYF4:Yb,Tm-Upconversion-Nanopartikel wurden mittels einer Ligandenaustauschreaktion ausgehend von einer wohldefinierten Vorstufe synthetisiert. Dieses neue photoaktive Material wurde umfassend charakterisiert und in der Aktivierung von photoresponsiven Molekulen durch Nahinfrarot-Licht (980 nm) mit niedriger Intensitat angewendet.

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 NaYF4:Yb,Tm upconversion nanoparticles were synthesized by a ligand-exchange reaction from a well-defined precursor. This new photoactive material was characterized in detail and employed in the activation of photoresponsive molecules by low-intensity near-infrared light (λ=980 nm).

We demonstrate an improved concept for nearly bandwidth-limited nonlinear pulse compression down to the few-cycle regime in a fiber chain with alternating sign of dispersion. Whereas the normally dispersive fiber segments generate bandwidth via self-phase modulation, the anomalously dispersive fiber segments recompress the broadened spectral bandwidth by an appropriate amount of group velocity dispersion. Nonlinear pulse compression from 80 fs input pulses to nearly bandwidth-limited 25 fs pulses at 1560 nm was achieved, resulting in a pulse compression factor of 3.2. The use of a specific dispersion-compensating fiber eliminated the impact of higher-order dispersion, such that a high spectral coherence was ensured. We show that nonlinear Schrödinger equation simulations were in good agreement with the experimental results and investigated the transfer of input fluctuations to the output. The concept is transferable to longer input pulse durations, resulting in compression factors of 83 for 10 ps input pulses.

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser., 25 pages, 16 figures

We present a scheme for a sub-diffraction-limited Raman microscope. The scheme combines the concept from stimulated depletion microscopy with femtosecond stimulated Raman scattering. The suppression of the Raman signal in a three-beam setup with only two involved wavelength-components was accomplished by the saturation of the Raman scattering. A reduction of the Raman signal of up to 79% could be measured with only a single Raman resonance involved. Based on this signal suppression, a resolution enhancement by a factor of 2 could be verified in a first proof-of-concept measurement, opening up a pathway toward label-free sub-diffraction-limited imaging.

Supercontinuum generation (SCG), a process that generates a wide and coherent bandwidth of light, has become foundational in emergent optical technologies in a plethora of fields, such as optical coherence tomography (OCT), metrology (e.g., integrated photonic Kerr combs) and precision sensing. As advanced applications of SCG emerge, the requirements on the spectral bandwidth, the coherence, its temporal compressibility, and the quality of the optical spectral content (e.g., a uniformly flat spectral profile) are increasing. Moreover, as these technologies need not be restricted to the lab, the spectral conversion efficiency of SCG must increase from current technology that functions, e.g., in the tens of nJ pulse energy, to sub nJ levels.

The excitation of transverse laser modes, can be achieved by a cavity-internal amplitude or phase modulation of the laser light. For this purpose typically additional cavity-internal components are applied, which can result in increased losses and a limited resonator internal power [1]. Therefore, gain shaping based methods [2], where the selective mode excitation is achieved via a cavity-external modulation of the pump beam are of great interest, as they require no modification of the laser cavity itself. However, the so far presented gain shaping methods are strongly limited with respect to the number of modes that can be excited, as they apply pump beams of a fixed spatial shape. Here, we present a spatial gain shaping method that applies a digital micromirror device (DMD) as a shaping tool for the pump beam, enabling a high degree of freedom for the gain distributions that can be generated. We demonstrate the advantage of our approach by exciting nearly 1000 different single Hermite-Gaussian (HG) modes in an end-pumped Nd:YVO 4 laser, increasing the number of excitable HG modes by at least a factor of five in comparison to other excitation methods [2, 3].

Integrating diode laser sources in the visible range into photonic circuits, for controlling wavelength tuning or for reducing the spectral linewidth, can enable, e.g., chip-sized multicolor light engines for life-science applications or drive multiple narrow-linewidth transitions in portable optical clocks. Current approaches with grating feedback and bulk or fiber optical beam combining lead to devices of appreciable size, restricted spectral control and suffer from mechanical perturbations. Hybrid integrated lasers, formed by a diode laser amplifier and a low-loss waveguide feedback circuit can avoid these disadvantages, but have only been realized at telecom wavelengths. We present our approach for realizing a first hybrid integrated diode-SiN laser in the visible, to generate light around 690 nm via optical feedback from an integrated micro-ring Vernier filter.

The detection and stabilization of laser beam pointing is of great interest for multiple high precision applications, e.g., interferometric measurements [1]. Beside the typically applied beam pointing detection based on quadrant photodiodes [2] an alternative detection method based on the superposition of the deflected beam with a higher order mode has been demonstrated [3]. However, in the so far presented approach the beam pointing detection was realized by the superposition of two modes at the same frequency in a homodyne detection setup, requiring multiple detectors. Here, we present that with an alternative approach the tilt and displacement of the deflected beam can also be reconstructed from a radio-frequency beating signal generated by the deflected beam superimposed with a frequency-shifted higher-order mode on a single detector. Numerical and analytical descriptions of the beam pointing detection concept are compared, and we present a first proof-of-principle experimental realization of an one-dimensional beam stabilization which can be extended into a two-dimensional approach by the superposition with two higher-order modes with different frequency shifts.

Sub-diffraction limited imaging schemes have become widely used in fluorescence microscopy [1]. However, the need for labeling with fluorescent dyes remains a major downside of fluorescence microscopy. The size, availability, toxicity as well as photo-bleaching of the used dyes can complicate measurements [2]. In contrast, Raman imaging is inherently label-free. Unfortunately, the super-resolution schemes used in fluorescence microscopy are currently not transferable to Raman microscopy. This paper presents the development of a scheme for the suppression of coherent Raman scattering through the depletion of probe photons, inspired by the work of M. Cho et al. [3, 4], who showed the suppression of coherent Raman scattering using laser pulses at three different wavelengths and two Raman resonances. In our case, probe depletion is achieved through saturated stimulated Raman scattering in a three-beam setup with only two colors involved. Fig. 1 (a) describes the working principle: in the unsuppressed case, the combination of pump and probe pulse induces stimulated Raman scattering at the Raman resonances, leading to stimulated Raman loss (SRL) of the probe and and stimulated Raman gain (SRG) of the pump. The Raman spectrum then results from the difference between two spectra, recorded with pump on and off, respectively. In the suppressed case a second strong pump pulse, working as a depletion pulse, depletes the probe pulse via stimulated Raman scattering (SRL D ) and induces a shortage of the probe photons at the Raman resonances, saturating the stimulated Raman scattering. Thus, only a small amount of additional SRLSup is induced by the original pump. If SRL is detected in addition to the spectral change, induced by the depletion pulse, the SRL will be reduced resulting in SRL Sup < SRL.

Fiber-based pulse shaping is a topic of current research for any application scenario requiring robust, alignment-free all-fiber systems. However, the spatial domain, which could enable a spatial degree of freedom in fiber sensing applications like lab-on-a-tip scenarios, has not been accessed yet [1]. Here, we demonstrate with a numerical study that few-mode fibers can offer spatial as well as temporal pulse shaping capabilities by exploiting intermodal cross-phase modulation (intermodal XPM) and use its analytical description to derive a simplified numerical model in order to significantly reduce calculation times for such a device from hours to seconds [2].

We present multi-color coherent Raman imaging (CRI) with a frame rate of 8 Hz and rapid wavelength tuning within only 5 ms between successive images, enabled by a novel fiber optical parametric oscillator (FOPO). In CRI the limited tuning speed of conventional laser systems (>1 s) prevents the acquisition of successive images per second at more than one vibrational resonance and is considered as a bottleneck for multi-color assessments of medical specimen and rapidly evolving samples, such as living cells. Recent approaches to CRI with wavelength switching on a timescale of (sub-) milliseconds were based on two synchronized oscillators [1], being limited to two resonances, and parallel laser amplifiers [2] or spectral focusing techniques [3], both the latter with a limited tuning bandwidth of less than 300 cm−1. In contrast, the energy difference of the pump and Stokes pulses, emitted by the here presented FOPO, is tunable across the wide spectral range between 865 and 3050 cm−1 within only 5 ms. Assuming an equal time span for tuning and acquisition, up to 100 user-selectable vibrational components could be imaged per second, when imaging with 100 frame/s. The rapid tuning was achieved by a novel tuning concept for OPOs, based on the dispersive matching of the repetition frequency change of the pump pulses to the associated repetition frequency change of the resonant signal pulses in the FOPO. No alteration of the FOPO, e.g., via a mechanical delay line [4], was required for tuning the signal wavelength and the light source could be composed of all-spliced fiber components. Compared to previously presented FOPOs, the system runs at a high repetition rate of 40 MHz. The pump and Stokes pulses exhibit equal durations of 7 ps and an average power of 500 and 200 mW, respectively. As a first proof-of concept of the CRI capabilities, Fig. 1 shows three images of a sample consisting of water, oil and beads of PMMA and PS, taken successively with an acquisition time of 125 ms for each frame, limited only by the sampling rate of our detection setup. The energy difference was tuned in a frame-by-frame manner between 2850, 2950 and 3050 cm−1 in a time of 5 ms, a negligible time span compared to the acquisition time.

We present a mechanical delay-free tuning concept for optical parametric oscillators (OPO) removing the main barrier for high-speed switching between arbitrary wavelengths. The concept is based on dispersive matching of the repetition frequency change occurring during wavelength tuning of the pump laser to the associated change of repetition frequency in the OPO.

Transverse modes in optical fibers have gained increasing interest in the recent years. For the measurement of the modal amplitude and modal phase in a fiber, several techniques exist examining the spatial distribution of the light exiting the fiber end facet [1,2]. However, such techniques are not suitable for inline monitoring of the modal content in an all-fiber application, like lab-on-a-tip sensing applications, where the distal end of the fiber is not accessible. Here, we present an inline-measurement technique for modal phase differences and experimentally demonstrate the direct measurement of all-optically induced changes of the modal phase difference by intermodal cross-phase modulation (intermodal XPM) [3].

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. This unique combination of cyclodextrin vesicles capable of specifically recognizing guest molecules with a plasmonic particle shell displaying multiple interparticle gaps acting as electromagnetic hotspots shows great potential for surface-enhanced Raman scattering (SERS) applications.

Raman scattering has become a powerful method in analytic spectroscopy and label-free imaging to study the chemical composition of a sample. Especially coherent Raman scattering (CRS) techniques such as stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) are developed further and show a great potential, due to their amplified signal in comparison to spontaneous Raman scattering. In CRS the interaction of light pulses with molecular vibrations are investigated, typically resulting in a characteristic molecular spectrum. However, especially CARS spectra are effected by the non-resonant contribution to the Raman scattering signal, resulting in a non-specific background and a distortion of the lineshape. SRS is free of a non-resonant background but is affected by two-photon absorption, cross-phase modulation (XPM) [1], and thermal scattering (temperature-induced refractive index change) [2]. The resulting artefacts in SRS become relevant for high pulses energies and ultra-short pulses. One example, where high pulse energies and ultra-short pulses are needed, is the field of spatial resolution enhancement in CRS. All techniques to overcome the diffraction limit by Abbe are based on depleting one of the scattering resources, as for example the pump or probe photons [3]. High pulse energies in the order of up to 200-300 nJ are needed, leading to also unwanted spectral distortions through XPM [4].

We present a new approach that increases bandwidth of supercontinuum generation by alternating the sign of dispersion along the interaction length, bypassing mechanisms that limit bandwidth in typical approaches. The method should be particularly suited for fiber and integrated optical waveguides.

We present high-speed multicolor coherent Raman imaging (CRI) with rapid wavelength tuning within only 5 ms between successive images, enabled by a novel fiber optical parametric oscillator (FOPO). In CRI the limited tuning speed of conventional laser systems (at least several seconds per wavelength change) hinders the rapid acquisition of successive images at multiple vibrational frequencies and is a bottleneck for fast assessments of medical specimens or rapidly evolving samples. The output pulses of the presented FOPO are tunable across the vibrational spectrum between 865 and 3550 wavenumbers within only 5 ms. Therewith, the wavelength can be tuned in a frame-by-frame manner adequate for an image acquisition with up to 200 frames/s. Tuning of the FOPO is achieved by synchronized changes of both wavelength and repetition rate of the pump pulses, allowed by a novel fiber-integrated pump laser working without a mechanical delay. Based on this tuning mechanism, the FOPO resonator can be composed of all-spliced fiber components. Compared to previously presented FOPOs, the system exhibits short pulse durations of 7 ps and operates at a high repetition rate of 40 MHz to allow short pixel dwell times as low as 25 ns. The pump (

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 1.1 µm up to 1.6 µm can be generated. The versatility of the chip-based FWM light source is demonstrated by acquiring CARS images.