Nonlinear Optics and Applications XIII

Infrared (IR) detectors suffer from limited performances compared to their visible counterparts. Recent studies have shown interest to convert IR signals into the visible before their detection. Especially, sum frequency generation (SFG) is actively studied in order to perform active IR imaging. The conversion, performed in a periodically-poled lithium niobate (PPLN) crystal by mean of a pump laser fulfill the nonlinear conversion laws: the energy conservation and the phase matching condition. These laws result in limited field of view and resolution. Several attempts in increasing imaging performances resulted in solutions hardly conceivable in practice. The use of a pump laser as mediator for the conversion opens the way to new degrees of freedom. In this work, we focus on the spatial shape of the pump beam. Particularly, we study the possibilities offered by a flat-top beam shaped by a Spatial Light Modulator (SLM).

Digital holography is an imaging technique that enables a 3-dimensional reconstruction of the electromagnetic field scattered by an object in both amplitude and phase. Since Second Harmonic Generation (SHG) is a coherent process, SHG light can also be used to generate interferences and holograms. We apply SHG holography to nonlinear nanostructured samples made of dielectrics or metals to obtain single-shot measurements of their second harmonic 3D radiation pattern and to map intensity and phase variations near the sample. Thus, we realize a complete 3D tomographic reconstruction of the SHG emission from a sample.

Inelastic electron-light scattering between electrons and optical modes renders ultrafast transmission electron microscopes an ideal platform for investigating optical properties on the nanoscale. Building on this technique, we demonstrate the spatial and spectral characterization of the intracavity field of a photonic chip-based, high-Q silicon nitride microresonator by means of free electron light interaction. By combining optical and electron spectroscopies, we probe the emergence of various nonlinear intracavity states, including dissipative Kerr solitons. This novel combination of nonlinear integrated photonics and electron microscopy promises new schemes in electron beam manipulation as well as electron-based probing of optical microresonator states.

We study the effects of annealing temperature on oxide charge trapping near the SiO2/Si interface using time-dependent second harmonic generation (TD-SHG), which is sensitive to charge separation near the interface. The TD-SHG signals are measured in plasma enhanced tetraethyl orthosilicate (PE TEOS) and high density plasma (HDP) oxide films deposited on silicon, respectively, which are typically used as intermetal dielectric (IMD) layers in 3D NAND. After annealing at temperatures ranging from 550 °C to 850 °C, the initial slopes of the TD-SHG signals at t=0, related to the charge trap density, decrease with increasing annealing temperature for PE TEOS, while the signals from HDP oxides show relatively flat curves independent of temperature even in the as-deposited state due to the reduced charge traps. The direction of the interfacial electric field resulting from the charge separation can be interpreted from the sign of the measured slopes. In PE-TEOS oxides annealed above 800 °C, the slope changes to the opposite sign, indicating the dominance of negative charges rather than positive charges. The observed TD-SHG results support previous suggestions that the electron trapping occurs in the carbon-related center of TEOS and appears to be dominant after high temperature annealing.

Photonics and spintronics represent a great promise to overcome the fundamental limits of electronics since light and spins are simultaneously much faster and less dissipative of electrons. In this framework, the quest for energy-efficient data processing and storage functionalities led great attention to the field of femtomagnetism, the study and control of magnetism using ultrashort light pulses. However, our knowledge of magnetic phenomena and ultrafast light-matter interactions in nanoscale magnetic materials is extremely limited. In this work, we introduce a time-resolved magneto-optical pump-probe spectroscopy scheme enabling to access both the thermal and nonthermal spin (and charge) dynamics with sub-15 fs temporal resolution. We test the capabilities of our system on archetypical magnetic and magnetoplasmonic materials, such as Ni thin films and Ni nanodisks.

Nonlinear light propagation inside the medium can be analyzed using the concept of nonlinear refractive index. Unique and popular nonlinear media with enhanced nonlinearity are photonic crystal fibers (PCFs). To numerically simulate nonlinear light propagation inside a PCF it is necessary to properly evaluate the fiber’s nonlinear refractive index at different wavelengths. This work presents a new method to measure nonlinear refractive index in optical fibers, which allowed to estimate the nonlinear refractive index of PCF over a broad range of wavelengths. This work has received funding from European Regional Development Fund (project No. 01.2.2-LMT-K-718-03-0004) under grant agreement with the Research Council of Lithuania (LMTLT).

The irradiation conditions in the high-power laser systems are extreme for critical optical elements, thus, often leading to a long-term degradation effect and eventually failure. The phenomena behind the interaction between extreme laser light and dielectric optic are typically associated with nonlinear absorption in the mirror, antireflective, polarizer or other coatings. The nonlinear response makes these components optically unstable, however, the knowledge about the nonlinear properties of most of the dielectric coatings is very limited. Furthermore, nonlinear features of the multilayer dielectric coatings are even less investigated. To study these effects a set of single- and multi-layer HfO2, ZrO2 and Al2O3 dielectric coatings was produced. The nonlinear absorption was investigated for different wavelengths. In order to measure the nonlinear absorption we employed a common-path interferometry (PCI) method in combination with a high energy and a high average power laser source operating at 1MHz repetition rate. During the presentation we will share the preliminary results of our study.

We propose a dispersion-engineered Silicon nitride (Si3N4) based vertical dual-slot silicon waveguide structure that exhibits an ultra-flat dispersion profile with four zero-dispersion wavelengths (ZDWs). Furthermore, we present a theoretical analysis describing the generation of efficient broadband cascaded four-wave mixing (CFWM) products in the mid-IR range, while two intense continuous wave pump fields are propagation through the hybrid waveguide structure. We investigate the effect of input pump power, pump wavelength detuning, and other waveguide parameters on CFWM products under a dual-pump scenario.

We propose and theoretically analyze a novel device with a simple architecture for high-power mid-wave and long-wave infrared beam generation by employing a realistic model that takes the diffraction of the beams into account. The device is a seeded optical parametric generator (OPG) based on an aperiodic orientation-patterned GaAs (OP-GaAs) grating in which two optical parametric amplification (OPA) processes, OPA-1 and OPA-2, are simultaneously quasi-phase-matched along the full length of the crystal. When pumped by a high-repetition-rate nanosecond-pulsed pump laser operating at 2.1 µm and a low-power continuous-wave seed source at a wavelength of 2.74 µm (signal), OPA-1 in this crystal generates a long-wave infrared beam output at a wavelength of 8.8 µm (idler) whose power conversion efficiency is enhanced by means of OPA-2 compared to what is achievable with a single OPA process. OPA-2 occurs as signal photons are down-converted to idler photons and difference-frequency (DF) photons at a wavelength of 3.98 µm. These wavelengths have important applications in the fields such as infrared laser projector technologies, countermeasures against heat seeking missiles, remote sensing, and spectroscopy.

Within the last decade, research and development in the field of silicon microring resonators have been accelerated due to their potential in a wide range of applications. In this study, we experimentally characterize the self-pulsing dynamics in active silicon ring cavities under the effects of varying the optical power, detuning, and free-carrier lifetime. Self-pulsing is measured by coupling a single laser source into the microring resonator’s input port. The light collected from the output grating is fiber coupled and sent to a photodetector, oscilloscope, power meter, and optical spectrum analyzer (OSA) for both time and frequency domain measurement.

Subnanosecond pulse duration optical parametric generator (OPG) based on fan-out grating design MgO:PPLN crystal is demonstrated. In a fan-out grating design crystal, the effective grating period and thus quasi-phase-matching (QPM) conditions change continuously throughout the width of the crystal. We show that the OPG, based on a fan-out periodically poled crystal and pumped by a micro-laser system, permits a compact and effective subnanosecond coherent light source that could be rapidly, widely, and continuously tunable in the near-infrared spectral region (1.4- 4.4 μm) just by laterally displacing the crystal with up to 50% conversion efficiency. Full characterization of the OPG is performed and the feasibility of broadband OPG output is evaluated with the addition of numerical calculations based on a nonlinear model. This work has received funding from European Regional Development Fund (project No. 01.2.2-LMT-K-718-03-0004) under grant agreement with the Research Council of Lithuania (LMTLT).

The laser is the most promising man-made invention that has strong usage in research and the public sector due to its unique properties such as coherence, monochromaticity, energy density, and directionality. The laser creates new optical effects like nonlinear polarization, nonlinear absorption, nonlinear refraction, nonlinear scattering, etc. Accidental or direct exposure to intense laser radiation causes severe injury to humans and other optical components within a short period of time. As a result, safety devices or optical moderators are required to protect ourselves and optical components from exposure. In this instance, the optical limiters are excellent defenders to safeguard against optical hazards. Recent research has discovered that the remarkable light absorption and broadband emission of graphene oxide (GO) and reduced graphene oxides (rGO) due to the extended π-conjugate system have shown significant attention for their potential uses in laser damage-protecting devices. Further, the combinations of reduced graphene oxides with Fe2O3 derivatives possess better nonlinear optical properties with stability. Based on these facts, the present work is focused on finding a superior composite material with high nonlinear optical properties. The reduced graphene oxide decorated with gold (Au) ferric oxide (Fe2O3) showed enhanced nonlinear optical behavior. The complex Au- Fe2O3 systems exhibit optical limiting action under ultrafast (800 nm, 80 MHz, 150 fs) and (532 nm, 50 mW) laser excitation. Among the investigated systems, Au-Fe2O3-(15 wt%) rGO demonstrated the highest nonlinear optical coefficients and optical limiting action, as well as the highest thermal stability. The detailed investigation shows that the combined contribution of rGO and metal ions present in the Fe2O3 system is responsible for the improvement of NLO coefficients and optical limiting action. Thus, the present work is an investigation into the enhancement of nonlinear optical properties through nanocomposite formation and the possibility to utilize them as optical limiters for laser safety devices.

State-of-the-art multi-Petawatt laser facilities coming online include the Zettawatt Equivalent Ultrashort pulse laser System (ZEUS), a user facility being commissioned at the University of Michigan. The 3-PW pulses will make ZEUS the highest power laser in the USA. This talk will describe the various experimental approaches that can be used to produce ultrashort particle beams and light-sources, as well as their application to study strong-field plasma physics and beyond. One area of interest is to create extremely strong magnetic fields within the hot plasma in the laboratory, so we can study the microphysics likely to be occurring around the most energetic objects in the universe.

Laser Plasma Accelerators (LPA) rely on our ability to control finely the electrons motion with intense laser pulses. Such manipulation allows to produce giant electric fields with values in the TV/m exceeding by more than 3 orders of magnitude those used in current accelerator technology. Controlling the collective electrons motion permit to shape the longitudinal and radial components of these fields that can be optimized for delivering high quality electrons beam or energetic photons. To illustrate the beauty of laser plasma accelerators I will explain the fundamental concepts we recently discovered, and I’ll show the maturity of our approach in delivering particle and radiation beams for societal applications including for radiotherapy with the ebeam4therapy EIC project.

On December 5th, 2022, the National Ignition Facility in Livermore, California, USA performed the first experiment demonstrating controlled fusion ignition in the laboratory. With a 2.05MJ UV laser drive energy delivered to the target, a neutron yield of 3.15MJ was released by the fusion reactions in the capsule, providing a net target gain of ~1.5×. The results of this experiment will be discussed, along with the decades-long developments in optical materials, laser architectures, target fabrication, and target diagnostics enabling this recent accomplishment. We will discuss the next steps for NIF and provide an outlook on future applications and technologies, including the reinvigorated pursuit of Inertial Fusion Energy.

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions. To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy. We use it to exemplify how deep learning can be employed for a broad range of applications, from particle localization, tracking and characterization to cell counting and classification. Thanks to its user-friendly graphical interface, DeepTrack 2.1 can be easily customized for user-specific applications, and, thanks to its open-source object-oriented programming, it can be easily expanded to add features and functionalities, potentially introducing deep-learning-enhanced video microscopy to a far wider audience.

We demonstrate experimentally a nonlinear plasmonic metasurface that exhibits strongly asymmetric second-harmonic generation (SHG), depending on the illuminating direction: when the metasurface is illuminated from one side, it produces a significant SHG signal, whilst this nonlinear response is strongly reduced (approx. 10 dB), upon illumination from the opposite side. This surprising behavior stems from the bianisotropic response of the system, as confirmed by a homogenization analysis and the extraction of the effective susceptibility tensor. At first sight, it could be tempting to interpret this asymmetric response as a non-reciprocal phenomenon, but we will show that actually it is time-reversal asymmetric.

In this work, we analyze operating speed of photonic integrated circuit (PIC) with microring resonator by transfer function model. The transfer function is obtained from single microring resonator and waveguide, further modified for complex circuits with multiple microring resonators and waveguides. The model was run in Matlab without running time, while indicating influence of change in PIC parameters to the output. The simulation showed large coupling coefficient (k>0.2) and small radius (R< 8 um) of microring increases operation speed to 30 Gbps, but decreases quality factor below 1500. The model is recommended for designing PIC at early stage with small time.

Complex photonic lattices are suitable for the investigation of many physical phenomena from solid-state to atomic physics with easier experimental realization. Light transport in complex optical systems is a rich and fascinating topic of research. Nondiffracting beams are highly relevant in optics and atom physics, particularly because their transverse intensity distributions propagate unchanged for hundreds of diffraction lengths. Four different fundamental families of propagation invariant light fields, distinguish in the underlying real space coordinate system, exist: Discrete, Bessel, Mathieu, and Weber nondiffracting beams. We present a numerical investigation for the realization of photonic lattices with waveguides arranged in elliptical geometry. We compound two Mathieu beams of a particular order and appropriate a parameter of ellipticity at different offsets to create a two-dimensional structure appropriate for the realization of complex photonic lattices in which waveguides will be arranged along two connected ellipses. We demonstrate that changing the horizontal separations of Mathieu beams we are able to control the creation of different environments between two ellipses of waveguides, that significantly influences control and manipulation of light in such structures. If there are no waveguides between two ellipses, light expands less than if there are some waveguides between them. For all lattices, we investigate how various input beam positions of a probe beam influence light diffraction, and we observe that beam expansion depends on the refractive index modulation.

Flat optics has been recently unveiled as a powerful platform to perform data processing in real-time, and with small footprint [1, 2, 3]. So far, these explorations have been limited to linear optics, while arguably the most impactful operations stem from nonlinear processing of the incoming signals. In this context, here we add a new twist and depth to analog optical computing: we demonstrate that nonlinear phenomena combined with engineered nonlocality in flat-optics devices can be leveraged to synthesize Volterra kernels able to perform complex operations on incoming images in real-time. Metasurfaces have already introduced a paradigm shift for nonlinear optics enabling stronger nonlinearities in thin films and manipulation of the nonlinearly-generated wavefront [4, 5, 6]. In this framework, here we show that it is possible to exploit nonlocal nonlinearities as a powerful tool for analog computing with light waves. We show that using nonlinear nonlocality in flat optics we can realize analog image processing with previously not accessible functionalities. By exploring the simple scenario of a uniform χ2 thin sheet, we demonstrate edge detection operation with exciting potentials. In our proposed nonlinear flat-optics solution, the non-resonant nature of the nonlinear interaction involved in image processing allows edge detection over a broadband spectrum with ultra–high contrast and superior resilience to noise. Our results indicate that Volterra kernels of nonlinear nonlocal flat optics can open new opportunities in applications such as image processing, item recognition for computer vision, and high-contrast, high-resolution microscopy. References 1. Solli, D.R., Jalali, B., Nature Photonics 9(11), 704–706 (2015). 2. Silva, A., Monticone, F., Castaldi, G., Galdi, V., Alù, A., Engheta, N., Science 343(6167), 160–163 (2014). 3. Overvig, A., Alù, A., Laser & Photonics Reviews 16(8), 2100633 (2022). 4. Vabishchevich, P., Kivshar, Y., Photon. Res. 11, B50-B64 (2023) 5. Schlickriede, C., Waterman, N., Reineke, B., Georgi, P., Li, G., Zhang, S., Zentgraf, T., Advanced Materials 30(8), 1703843 (2018). 6. Gigli, C., Marino, G., Artioli, A., Rocco, D., De Angelis, C., Claudon, J., Gerard, J.-M., Leo, G., Optica 8(2), 269–276 (2021).

The present contribution provides a link between optical pumping with polarized light and polarized optical injection in a Quantum-Dot (QD) Vertical-Cavity Surface-Emitting Lasers (VCSEL). Based on the sensitivity of the QD spin-VCSEL to the stability state before the injection and the rich dynamic behaviour induced by optical injection we perform an analysis of optimized parameters for the demonstration of extended chaotic regions. The proposed scheme aims at ultrafast random bit generation (RBG) reducing the complexity of well established systems based on VCSELs to generate high-quality chaos signals. Our investigations reveal that inside these regions an enhancement of chaotic bandwidth up to 50 GHz can be achieved, exceeding the state of-the-art performance of conventional VCSELs under continuous wave (CW) optical injection. We show that in addition to exhibiting enhanced polarization chaos, QD spin-VCSELs enable 240 Gbit/s RBG thus allowing future exciting routes for cryptography and secure communications.

Grating is the most suitable for excitation of the SPP because grating coupling is more compatible than prism coupling for the active PICs devices. But traditional gratings are not able to selectively excite SPP waves at single interfaces of the metallic waveguides. Traditional gratings usually excite SPP wave at the interface where they are or, for thin metallic nanostrips, at both interfaces. But the reduction of the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunneling of the light towards the substrate, increasing the losses and reducing the coupling efficiency. Through numerical simulations, I optimized the effective parameters for the coupling of the SPP waves, such as the angle of incidence, the thickness of the metal layer in the grooves of the buried lattice and in the upper cover, as well as the width and depth of the grooves. As a result of the optimization process, the efficiency of light coupling in the SPP wave increased at the lower interface with the substrate and the transmitted tunneling light was effectively suppressed compared to an equivalent conventional lattice. The attenuation of the transmitted tunneling light favours the use of SPP for a nonlinear medium.

Light confinement in nanoscale regime has opened new doors to the miniaturisation of optical materials required for future integrated photonics. Recently, Tamm Plasmons (TP) have attracted research interest as they possess various advantages over conventional surface plasmons. They are characterized by sharp resonances in the transmission spectrum and low degree of loss, making them ideal and versatile platform for nonlinear applications. In this work, we report the enhanced nonlinear optical response of gold@carbon (Au@C) core-shell nanostructures aided by a TP cavity. The spacer layer containing Au@C is sandwiched between gold film and a DBR made of TiO2 and SiO2 layers. The photonic bandgap of the DBR is centred around 534 nm and the final structure is characterized by a prominent transmittance peak around 532 nm, indicating the TP cavity mode. The observed TP mode is sufficiently large to induce nonlinear effects at low input intensities. This is confirmed from the open aperture z-scan results, which shows a decreased transmittance at the focus characteristic of Reverse Saturable Absorption (RSA) behaviour, which becomes steeper for the TP cavity structure compared to the bare core-shell reference film. The effective nonlinear absorption coefficient obtained for the TP structure is 37 times larger than the reference film containing core-shell nanoparticles. This giant enhancement in absorptive nonlinearity arises from the enormous energy concentrated in the spacer layer due to the presence of localized TP mode allowing stronger light-matter interaction.

Ultrafast control of light-matter interactions is fundamental in view of new technological frontiers, for instance in light-driven information processing and nanoscale photochemistry. In this framework, we explore metal-dielectric nanocavities to achieve all-optical modulation of the light reflectance at a specific wavelength. Without the need of driving higher order effects, our system is based on linear absorption, provides large relative modulation exceeding 100% and switching bandwidths of few hundred GHz at moderate excitation fluence. This archetypical system becomes even more interesting if the “gain medium” is an inorganic van der Waals bonded semiconductor, like a transition metal dichalcogenide (TMD). TMDs are subject of intense research due to their electronic and optical properties which are promising for next-generation optoelectronic devices. In this context, understanding the ultrafast carrier dynamics, as well as charge and energy transfer at the interface between metals and semiconductors is crucial and yet quite unexplored. By employing a pump-push-probe scheme, we experimentally study how thermally induced ultrafast charge carrier injection affects the exciton formation dynamics in bulk WS2, opening up excellent opportunities also in nano-chemistry. In fact, if an electronic transition strongly interacts with the light modes of a resonator, we can tailor the energetics and the morphology of a molecular state. By combining quantum mechanical modelling and pump-probe spectroscopy, we shed light on the ultrafast dynamics of a hybrid system composed of photo-switchable dye molecules coupled with optically anisotropic plasmonic nanoantennas, which allow us to selectively switch between two regimes where the light-matter interaction is either weak or strong. Our synergistic approach is instrumental to devise new strategies for tailoring electronic states by using plasmons for applications in polaritonic chemistry on femtosecond timescales.

In recent years whispering gallery mode (WGM) resonators have attracted interest due to their various potential passive (filters, resonators, sensors) and active (lasers, four-wave mixing) applications. By choosing an appropriate material with very low absorption, and fabricating a very smooth surface, WGM resonators can reach ultra-high quality (Q) factors. Additionally, the surface of the WGM resonator can be functionalized with nanoparticles or nanomaterial layers, which can enhance optical properties. Recently, we have been interested in the functionalization of the WGM resonator surface for active applications. WGM resonators are suitable for nonlinear optical interactions due to their ultra-high Q factors, significantly lowering necessary pumping power. WGM resonators can be used to generate optical frequency combs (OFCs), which have many applications in optical clocks, spectroscopy, and communications. After coating WGM resonator with quantum dots, besides the OFC generation, we have observed the third harmonic generation. Functionalization with erbium ions leads to the observation of lasing.

Voigt effect is a nonlinear magneto-optical phenomenon originating from the rotation and ellipticity of linearly-polarized light as it travels in optically active media. In this study, the detailed features and capabilities of a newly developed ultra-sensitive Voigt rotation device consisting of a GaN-based diode emitting light of wavelength range 400 – 480 nm as the light source. A transverse 1 T magnetic field is used to trigger the optical media response. A sensitive and fast semiconducting detector is employed to detect the finest rotation in light polarization. The detector is also coupled with an electronic circuit board which is configured to record changes in the polarization direction of the transmitted light relative to the reference polarizer, in addition to measuring the absolute magnetic field strength. The device sensitivity and modes of operation will also be presented. Moreover, a theoretical model to simulate polarized light transmission through optically active media will be presented and compared with experimental results.

We present a comparative study of supercontinuum generation in sapphire, YAG and KGW crystals with 200 fs, 1035 nm pulses from Yb:KGW laser. We demonstrate that KGW crystal has the lowest supercontinuum generation threshold and exhibits damage-free long-term operation at 2 MHz repetition rate. Our results prove that KGW crystal is an excellent nonlinear material for high average power infrared supercontinuum generation and for seeding high repetition rate fundamental harmonics-pumped ultrafast optical parametric amplifiers.

The development of new services and the expansion of legacy services are constantly increasing the demands on access networks. Passive optical networks can meet these increasing demands by develop a new standard and improve existing optical networks. Currently, next generation passive optical networks provide sufficient transmission capacity while allowing legacy standards to coexist. One way to improve already deployed optical networks is to use higher order modulation formats together with coherent detection and digital signal processing. Phase-based modulation formats can provide sufficient performance improvement by phase noise compensation. First implemented phase noise algorithm exhibits potential improvement in bit error rate more than 6 orders of magnitude for 4-QAM with compared to QPSK and DQPSK. The second algorithm significantly achieves improvement in bit error rate but has comparable results in compensating for phase noise according to the number of symbols in constellation diagram.

Harmonic frequencies, 2nd, 3rd, 4th, and 5th, generated from the picosecond beams of the diode-pumped Yb:YAG thin-disk lasers PERLA B (1.7 ps pulse duration, 10 W average output power, 1 kHz repetition rate) and PERLA C (1.2 ps pulse duration, 75 W average output power, 100 kHz repetition rate), are presented together with their application in user experiments. Nonlinear crystals used for the second and third harmonic generation, as well as for the sum frequency generation are LBO and CLBO. The user experiments have been performed at the HiLASE Centre in Dolni Brezany, Czech Republic.

A compact optical delay line optoelectronic oscillator is designed to fit in a volume of less than 1 litre. It consists of a 1.55 µm wavelength laser, a modulator, a resonant element or an optical fiber acting as a delay line, a photodetector, a X-band microwave amplifier and a driving coupler.This oscillator must be stable in terms of nominal frequency delivered. In addition, its elements must be less sensitive to environmental and mechanical disturbances. Compactness is evaluated in terms of efficiency and the signal is characterized in terms of power delivered and stability of the nominal frequency. We rely on the measurement of phase noise carried out using a bench developed in the laboratory and we give an approximation of the specifications measured according modern appproach, by enriching the work done on the oscillators.

A physical model of compact generator of infrared surface plasmon polaritons based on a planar waveguide structure to produce short pulses with a controllable repetition rate is proposed. The pulse generation is produced by modulation instability of continuous surface plasmon polariton waves in a film structure with graphene sheets (two graphene sheets spatially separated by a dielectric layer).

Harmonically mode-locked (HML) fiber lasers delivering pulses with pulse repetition rate (PRR) in the GHz range have become a valuable alternative to semiconductor and solid-state lasers ensuring high beam quality, reliability, user-friendly light output, inherent to laser configurations in all-fiber format. The main drawback of HML laser technology is the noise-induced irregularities of the time interval between pulses known as the HML timing jitter. Ensuring low-level supermode noise and precise pulse repetition rate tuneability in all-fiber-integrated harmonically mode-locked laser sources establishes a new level of their versatility and extends areas of their applications. We report on new techniques enabling both the mitigation of supermode laser noise and highly precise setting of the PRR in a soliton fiber laser harmonically mode-locked by nonlinear polarization evolution. The principle of operation relies on resonant interaction between the soliton pulses and a narrow-band continuous wave (CW) component cooperatively generated within the same laser cavity.

Brillouin amplification, the most prominent effect implemented with Brillouin dynamical gratings, enables exponential narrowband gain that is Stokes-shifted by some value in the GHz range. In this process, the interaction of the counterpropagating pump and Stokes waves through a BDG they produce causes an increase of the Stokes-shifted wave amplitude and decrease of the pump wave amplitude during their propagation through the fiber. Here, we report on a similar effect that could be implemented in rare-earth-doped fibers with the population inversion dynamical gratings. The effect is the most pronounced in a bidirectional rare-earth-doped optical fiber amplifier. Two monochromatic optical signal waves are introduced into the fiber from opposite ends and experience amplification (if the fiber is pumped) or attenuation (if the fiber is unpumped) as they propagate through the fiber. The signal waves are coherent on a sub-kHz level and slightly detuned. In terms commonly accepted in stimulated Brillouin scattering these counterpropagating signal waves correspond to what is referred to as "pump" and "Stokes" waves. However, in contrast to the Brillouin process, their interference inside the rare-earth-doped fiber creates not acoustic, but the population inversion dynamical gain grating. Then interaction between the signal waves and created population inversion dynamical gratings cause a strong power transfer from one signal wave to another.

We demonstrate deep label-free multicolor microscopy in streptomyces bacterial communities. Using a single ultrafast Yb:fiber laser, a superior signal-to-background ratio is obtained for 3-photon excited blue autofluorescence compared to 2-photon excited green, orange and red fluorescence. We observe that the superior nonlinear background suppression offered by 3-photon excitation allowed to achieve high quality imaging of blue fluorescence of relevant compounds deep in the streptomyces mycelium structure. 3P- excitation allowed for generating stable blue fluorescence deep in the sample without the detrimental photobleaching effects that limited imaging with confocal microscopy to only a few micrometers below the surface.