Search

openaire: EC/H2020/820423/EU//S2QUIP | openaire: EC/H2020/965124/EU//FEMTOCHIP | openaire: EC/H2020/834742/EU//ATOP The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of similar to 14.8 mu m length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by similar to 48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m(-1) W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such asfrequency combs and quantum light sources.

We present novel waveguide writing concepts in bulk PMMA. The writing relies on laser induced modification tracks that are completely surrounding a waveguide core. We found the optimal parameters to construct highly reproducible, single-mode waveguides with minimal propagation losses down to 0.6 dB ${\rm cm}^{-1}$ . Employing the best geometry, we demonstrate 2D and 3D Y-splitters that are the building blocks for creating complex optical networks such as sensors or lab-on-chip devices in polymer materials.

Metal nanomaterials have attracted increasing attention due to their outstanding nonlinear optical and photonic properties, making them as potential saturable absorber (SA) candidates for realizing ultrafast photonic devices. In this article, we demonstrate the generation of mode-locked dual-wavelength pulse trains in an Ag nanoplates (AgNPTs)-based Yb-doped all-fiber laser for the first time to the best of our knowledge. The AgNPTs are synthesized by seed-mediated growth and then integrated into a fiber ferrule by optical deposition, which serve as SA in the ring laser cavity. The plasmonic properties of such nanoplates are measured by absorption spectrophotometry and their nonlinear optical properties are characterized by Z-scan. The measured nonlinear saturable absorption of the AgNPTs-based SA is 6.4%. In our laser, the dual-wavelength synchronous mode-locking is achieved at the center wavelengths of 1031.92 and 1033.24 nm with 3-dB spectral bandwidth of 0.52 and 0.46 nm, respectively, where 293-ps pulse trains with a repetition rate of 11.43 MHz are obtained at the pump power of 350 mW. The results demonstrate that the solution-processed AgNPTs are promising SA candidates for achieving stable and low-cost pulsed laser sources which could be used for spectroscopy and ultrafast photonics.

Recent advancements in photonic-electronic integration push towards denser multichannel fiber to silicon photonic chip coupling solutions. However, current packaging schemes based on suitably polished fiber arrays do not provide sufficient scalability. Alternatively, lithographically-patterned fused silica glass interposers have been proposed, allowing for the integration of fanout waveguides between a dense array of on-chip silicon waveguides and a cleaved fiber ribbon. In this paper, we propose the use of femtosecond laser inscription for the fabrication of the fused silica glass interposer, allowing for a monolithic integration of waveguides and V-grooves for fiber alignment. The waveguides obtained by Femtosecond Laser Direct Writing (FLDW) have a propagation loss of 0.88 dB/cm at 1550 nm. The mode-field diameter is 12.8 $\pm$ 0.4 $\mu$ m, allowing for a coupling loss of 1.24 $\pm$ 0.32 dB when coupling to a standard single mode optical fiber, passively aligned to the fused silica waveguide by insertion in a V-groove created by Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). The average surface roughness of the etched waveguide facet is 160 $\pm$ 5 nm. Scattering loss when coupling to fiber is reduced by use of an index-matching adhesive for fiber fixation. A polished out-of-plane coupling mirror at an angle of 41.5 $^{\circ }$ injects the light into standard grating couplers, providing a quasi-planar fiber-to-chip package. The excess loss of the proposed solution is limited to 2 dB per interface, including mirror, waveguide and fiber coupling losses.

This paper presents a method of reel-to-reel femtosecond laser direct writing that enables the continuous inscription of low-loss and high-temperature stable Rayleigh scattering centers inside the core of single-mode optical fibers for distributed temperature sensing up to 1000°C. By examining the correlation between the Rayleigh backscattering profile and the cross-section morphology of femtosecond laser-induced nanograting in fiber cores, this paper reveals the mechanisms that underlie the fabrication of high-temperature stable distributed fiber sensors with low loss. By fine-tuning laser exposure conditions, the femtosecond laser-fabricated Rayleigh scattering enhanced section could achieve an optimized propagation loss of 0.01 dB/cm with an increased signal-to-noise ratio of over 35 dB for meters of lengths. Long-term high-temperature stability of the Rayleigh scattering enhanced section was successfully demonstrated, with improved thermal stability and signal-to-noise ratio. The fabrication method presented here provides a promising technique to improve the performance of Optical Frequency-Domain Reflectometry based distributed sensing for harsh environment applications.

The complete polarization state of second harmonic (SH) light was measured and characterized by collagen type I and skeletal muscle fiber using a Stokes vector-based SHG microscope. The polarization states of the SH signal are analyzed in a pixel-by-pixel manner and displayed through two dimensional (2D) Stokes vector images. Various polarization parameters are reconstructed using Stokes values to quantify the polarization properties of SH light. Also, the measurements are extended for different input polarization states to investigate the molecular structure of second harmonic generation (SHG) active molecules such as collagen type I and myosin.

Yb:CaGdAlO4, or Yb:CALGO, a new laser crystal, has been attracting increasing attention recently in a myriad of laser technologies. This crystal features salient thermal, spectroscopic and mechanical properties, which enable highly efficient and safe generation of continuous-wave radiations and ultrafast pulses with ever short durations. More specifically, its remarkable thermal-optic property and its high conversion efficiency allow high-power operation. Its high nonlinear coefficient facilitates study of optimized mode locking lasers. Besides, its ultrabroad and flat-top emission band benefits the generation of complex structured light with outstanding tunability. In this paper, we review the recent advances in the study of Yb:CALGO, covering its physical properties as well as its growing applications in various fields and prospect for future development.

Energetic, few-fs pulses in the deep-UV region are highly desirable for exploring ultrafast processes on their natural time scales, especially in molecules. The deep-UV source can be generated from gas media irradiated with few-cycle near-infrared laser pulses via a third-order frequency conversion process, which is a perturbative mechanism in a relatively weak field regime. In this work, we demonstrate that the deep-UV generation process is significantly affected by also even higher nonlinear processes, such as the ionization depletion of gas and plasma-induced spatiotemporal distortion of propagating light. In the experiment, by optimizing the deep-UV (3.6–5.7 eV) generation efficiency, the highest deep-UV energy of 1 μJ was observed from a moderately ionized 0.8-bar Ar gas target. The observed UV spectra exhibited frequency shifts depending on the experimental conditions—gas type, gas pressure, and the gas cell location—supporting the importance of the highly nonlinear mechanisms. The experimental observations were well corroborated by numerical simulations.

Standing on the potential for high-speed modulation and switching in the terahertz (THz) regime, all-optical approaches whose response speeds mainly depend on the lifetime of nonequilibrium free carriers have attracted a tremendous attention. Here, we establish a novel bi-direction THz modulation experiment controlled by femtosecond laser for new functional devices. Specifically, time-resolved transmission measurements are conducted on a series of thin layers Bi2Se3 films fabricated straightforwardly on Al2O3 substrates, with the pump fluence range from 25 μJ/cm2 to 200 μJ/cm2 per pulse. After photoexcitation, an ultrafast switching of THz wave with a full recovery time of ~10 ps is observed. For a longer timescale, a photoinduced increase in the transmitted THz amplitude is found in the 8 and 10 quintuple layers (QL) Bi2Se3, which shows a thickness-dependent topological phase transition. Additionally, the broadband modulation effect of the 8 QL Bi2Se3 film is presented at the time delays of 2.2 ps and 12.5 ps which have a maximum modulation depth of 6.4% and 1.3% under the pump fluence of 200 μJ/cm2, respectively. Furthermore, the absorption of α optical phonon at 1.9 THz shows a time-dependent evolution which is consistent with the cooling of lattice temperature.

Direct femtosecond writing is the simplest and most economical way to create waveguides in various media, which also allows the creation of complex waveguide networks. When considering materials, polymers are of particular interest because polymers provide unlimited variations of special compositions. Writing waveguides in polymers is not an easy task that cannot be directly compared with writing schemes in materials such as fused silica [2] . In recent times, successful laser writing schemes using complex parameter selection in polymers have been reported [3] , but further investigation is required research to get deeper insight into physical mechanisms and explore various aspects of undisclosed optical properties.

The analogy existing between spatial and temporal optics has motivated many studies to interpret spatial phenomena in the domain of ultrafast optics [1] . Indeed, dispersion and one-dimensional diffraction may share the same mathematical formalism. Temporal analogues of common optical systems have been proposed such as lenses, imaging systems, diffraction gratings, which opens up a whole range of new possibilities for ultrafast photonics.

International audience; The time profile of the lasing signal at 391.4 nm emitted by a weakly ionized gas of nitrogen molecules at low pressure is measured under double excitation with intense femtosecond laser pulses at 800 nm. An abrupt decrease of the emission occurs at the time of arrival of the second pulse. It is explained by a transfer of population from ground to first excited ionic level and by a disruption of coherence, terminating the conditions for lasing in a V-scheme without population inversion.

Patch-clamp technique is the gold standard for cellular electrophysiological measurements, which is capable of measuring single ion transport events across the cell membrane. However, the measurement possesses significant complexity, and it requires a high level of expertise, while its experimental throughput is nevertheless considerably low. Here, we suggest and experimentally demonstrate a laser-assisted method for performing cellular electrophysiological measurements. Femtosecond laser pulses, coupled to an optical microscope, are used to form a sub-micrometer hole on a thin polymer membrane separating two electrodes, where a nearby cell is subsequently placed onto the hole by negative pressure. Afterwards, the cell is punctured using subsequent laser exposure, revealing the cell membrane over the hole for electrophysiological recording. This system could be used to increase the output amount of the electrophysiological measurements substantially., 4 pages, 4 figures

Modern ultrafast lasers are enabling better operative performances in micro and nano-fabrications of materials, benefited from their ease of use, robustness, and reliability. The purpose of this paper is to bridge the gap between the knowledge of ultrafast optics and the modern industrial applications. The paper introduces main phenomena in ultrafast laser-matter interactions by reviewing relevant theoretical models and simulation techniques. The operation of ultrafast lasers is based on nonlinear optics phenomena, fully described only in the framework of quantum-mechanics. Current trends in the development of modern ultrafast system are given. It also presents a review of the latest advances in ultrafast laser-based manufacturing processes, some of the most interesting industrial applications, and a discussion on future trends and challenges.

We present a combined gain media Kerr-lens mode-locked laser based on Tm-doped sesquioxide materials. Pulses as short as 60 fs were obtained with an average output power of 52 mW at 2.1 μm.

We review our recent results on fiber lasers with distributed feedback based on π-shifted or random fiber Bragg gratings, and random index structures inscribed by femtosecond pulses in singlemode or multicore/multimode fibers.

International audience; We present an ultrafast thin-disk based multipass amplifier operating at a wavelength of 1030 nm, designed for atmospheric research in the framework of the Laser Lightning Rod project. The CPA system delivers a pulse energy of 720 mJ and a pulse duration of 920 fs at a repetition rate of 1 kHz. The 240 mJ seed pulses generated by a regenerative amplifier are amplified to the final energy in a multipass amplifier via four industrial thin-disk laser heads. The beam quality factor remains ∼ 2.1 at the output. First results on horizontal long-range filament generation are presented.

The temporal characterization of ultrafast laser pulses has become a cornerstone capability of ultrafast optics laboratories and is routine both for optimizing laser pulse duration and designing custom fields. Beyond pure temporal characterization, spatio-temporal characterization provides a more complete measurement of the spatially-varying temporal properties of a laser pulse. These so-called spatio-temporal couplings (STCs) are generally nonseparable chromatic aberrations that can be induced by very common optical elements -- for example diffraction gratings and thick lenses or prisms made from dispersive material. In this tutorial we introduce STCs and a detailed understanding of their behavior in order to have a background knowledge, but also to inform the design of characterization devices. We then overview a broad range of spatio-temporal characterization techniques with a view to mention most techniques, but also to provide greater details on a few chosen methods. The goal is to provide a reference and a comparison of various techniques for newcomers to the field. Lastly, we discuss nuances of analysis and visualization of spatio-temporal data, which is an often underappreciated and non-trivial part of ultrafast pulse characterization., Comment: 37 pages, 22 figures. This is the version of the article before peer review or editing, as submitted by an author to Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it

We report on the first active surface Y-branch waveguide in the ~2 μm spectral range. Depressed-cladding rectangular-cross-section surface waveguides with a splitting ratio of 1 × 2 are fabricated by femtosecond direct laser writing in a thulium (Tm 3+ ) doped monoclinic double tungstate crystal. Confocal laser microscopy and μ-Raman spectroscopy reveal well preserved crystallinity of the waveguide core. Under high-brightness laser pumping at 0.8 μm, a simultaneous continuous-wave laser operation in both arms is achieved resulting in a total output power of 0.46 W at ~1.84 μm with a slope efficiency of 40.6% and a laser threshold of 0.28 W. The laser output is linearly polarized and spatially multimode (TE12/TE22) with a power splitting ratio between arms of 52.1/47.9%). The waveguide propagation losses at 1.84 μm are ~1.6 dB/cm and the loss from the Y-junction is 0.1 dB. The fabricated waveguides represent a route towards advanced photonic micro-structures such as a Mach-Zehnder interferometer for bio-sensing at ~2 μm., This work was supported in part by the Spanish Government (Projects No. MAT2016-75716-C2-1-R (AEI/FEDER,UE), TEC 2014- 55948-R, FIS2017-87970-R), in part by Junta de Castilla y León (Project No. SA287P18), in part by Generalitat de Catalunya (Project No. 2017SGR755), and in part by the Ministry of Science and Higher Education of the Russian Federation (Goszadanie no. 2019-1080). The work of E. Kifle was supported by the Generalitat de Catalunya under Grant 2016FI_B00844, Grant 2017FI_B100158 and Grant 2018FI_B200123.

We give an overview of experimental results on mid-IR femtosecond lasers and frequency combs based on polycrystalline Cr$^{2+}$: ZnS providing access to few-cycle pulses in the spectral range 2–$;3\mu \mathrm{m}$. We also discuss the techniques for generation of multi-octave coherent femtosecond continua with Cr$^{2+}$: ZnS lasers.

Hot carrier cells offer the potential for very high efficiencies if slowed carrier cooling can be demonstrated effectively. Various mechanisms of phonon interaction have been identified that can lead to such slowed cooling with classes of materials exhibiting long hot carrier lifetimes. The exact reasons for these are not completely clear, but a study and comparison of the materials and mechanisms will give greater insight into constructed robust hot carrier absorber materials.

Fermi level dependence of ultrafast optical responses of single-layer graphene has been investigated using sub-10-fs pump-probe spectroscopy under bias voltages. We observe the ultrafast thermalization of photoexcited carriers, whose dynamics can be modulated via bias-induced change of the Fermi level. The relaxation time and the amplitude of the electronic response are maximized when the Fermi level reaches approximately half of the excitation photon energy. From the analysis of the pump-pulse-induced optical conductivity change, we find that the bias-induced blocking of the relaxation pathways and the pump-induced change of the electronic temperature and the Fermi level significantly contribute to the observed ultrafast optical modulation. The results demonstrate the controllability of the ultrafast optical responses in single-layer graphene, which could be useful for future ultrafast electro-optic graphene devices.

Nanoscale electron pulses are increasingly in demand, including as probes of nanoscale ultrafast dynamics and for emerging light source and lithography applications. Using electromagnetic simulations, we show that gold plasmonic lenses as multiphoton photoemitters provide unique advantages, including emission from an atomically at surface, nanoscale pulse diameter regardless of laser spot size, and femtosecond-scale response time. We then present fabrication of prototypes with sub-nm roughness via e-beam lithography, as well as electro-optical characterization using cathodoluminescence spectromicroscopy. Finally, we introduce a DC photogun at LBNL built for testing ultrafast photoemitters. We discuss measurement considerations for ultrafast nanoemitters and predict that we can extract tens of pA photocurrent from a single plasmonic lens using a Ti:Sa oscillator. Altogether, this lays the groundwork to develop and test a broad class of plasmon-enhanced ultrafast nanoemitters.

We report on the design and fabrication of straight and S-curved waveguides in neodymium-doped yttrium aluminate (Nd:YAP) crystal by using direct femtosecond laser writing. These S-curved channel waveguides are based on the hexagonal optical-lattice-like and depressed cladding geometry. For each type waveguide, S-curves with three lateral offsets of 50 μm, 100 μm, and 150 μm are implemented. These waveguides are with good guiding properties and low bending losses. With S-curved waveguide as laser cavity, dual-wavelength, 31.6 GHz waveguide laser operating at 1064 nm and 1079 nm have been demonstrated based on MoS2 as a saturable absorber. This work paves the way to develop new on-chip ultrafast laser sources based on femtosecond laser inscribed S-curved waveguides., This work was supported in part by the National Natural Science Foundation of China under Grant 61775120 and Grant MINECO FIS2017-87970-R, in part by the Major Program of Shandong Province Natural Science Foundation under Grant ZR2018ZB0649, and in part by the Ministerio de Economía y Competitividad de España under Grant MAT2016-75362-C3-1-R

We utilize ultra-fast laser inscription to fabricate photorefractive type III waveguides in Fe:LiNbO3 along the crystal c-axis. We demonstrate the ability to write transmission and reflection gratings into these waveguides with losses of 2.5 dB cm-1 and 48 dB cm-1 respectively.

We show the capability of plasmonic lenses for next-generation ultrafast electron sources. Using electromagnetic simulations, we design structures capable of femtosecond, nanoscale electron pulses. Plasmonic properties of template-stripped gold prototypes are characterized using cathodoluminescence spectromicroscopy.

We study a combination of subradiant states’ access and embedding into an optical cavity to enable very efficient excitons’ transport in chains of quantum emitters. Localization in the presence of disorder can additionally be prevented.

A machine learning-based model was trained on beam propagation simulation data of a femtosecond laser direct written 1-D waveguide array structure with varying refractive indices, to predict the refractive index difference of laser-induced waveguide.

We demonstrate a fully integrated alignment free, femtosecond Yb:fiber laser operating in the stretched pulse regime. After compression, the laser provides a long-term stable output of 104 fs pulses at 76 MHz repetition rate.

The layered MoS2 has recently attracted significant attention for its excellent nonlinear optical properties. Here, the ultrafast nonlinear optical (NLO) absorption and excited carrier dynamics of layered MoS2 (monolayer, 3–4 layers, and 6–8 layers) are investigated via Z-scan and transient absorption spectra. Our experimental results reveal that NLO absorption coefficients of these MoS2 increase from–27 × 103 cm/GW to–11 × 103 cm/GW with more layers at 400-nm laser excitation, while the values decrease from 2.0 × 103 cm/GW to 0.8 × 103 cm/GW at 800 nm. In addition, at high pump fluence, when the NLO response occurs, the results show that not only the reformation of the excitonic bands, but also the recovery time of NLO response decreases from 150 ps to 100 ps with an increasing number of layers, while the reductive energy of A excitonic band decreases from 191.7 meV to 51.1 meV. The intriguing NLO response of MoS2 provides excellent potentials for the next-generation optoelectronic and photonic devices.

Coherent optical fiber links recently demonstrate their ability to compare the most advanced optical clocks over a continental scale. The outstanding performances of the optical clocks are stimulating the community to build much more stable time scales, and to develop the means to compare them. Optical fiber link is one solution that needs to be explored. Here, we are investigating a new method to transfer time based on an optical demodulation of a phase step imprint onto the optical carrier. We show the implementation of a proof-of-principle experiment over 86-km urban fiber, and report time interval transfer stability of 1 pulse per second signal with sub-ps resolution from 10 s to one day of measurement time. Prospects for future development and implementation in active telecommunication networks, not only regarding performance but also compatibility, conclude this paper.

Fiber Bragg gratings (FBGs) are written using an infrared (IR) femtosecond laser and a phase mask into pure silica microstructured optical fiber having a cladding region comprised of random air-lines (RAL). Scanning electron microscopy measurements of the IR irradiated RAL fiber samples shows the presence of subwavelength nanograting structures associated with thermally stable type II Bragg gratings. High temperature annealing testing shows that although the RAL FBGs have a high degree of stability even at 1000 °C, they are less stable than similar FBGs made in single mode telecom fiber (SMF-28).

We report on the fabrication of waveguide arrays based on depressed-cladding structures produced by femtosecond laser direct inscription in a Nd:YAG crystal. The arrays consisted of seven divergent hexagonal waveguides with different separations between the waveguides at the exit of the crystal. Optical characterization in the visible (633 nm) and near infrared (800 nm) was performed. The obtained modal profiles show multimodal behavior in the visible and nearly single-mode at 800 nm. The propagation losses were measured to be 1.6-3.0 dB/cm in all the cases. Microluminescence maps were obtained showing the presence of defects only at the damage tracks and a residual stress that slightly affects the waveguide core in the vicinity of the tracks. This affected area is responsible for a modal profile distortion that can be clearly seen at 633 nm, but does not modify the modal profiles in the near infrared. Our results show a very good performance of the fabricated structures and suggest a promising potential use in photonic applications (i.e., photonic lanterns) that can be easily implemented in other transparent materials., This work was supported in part by Junta de Castilla y León (Projects UIC016, SA046U16), MINECO (FIS2013-44174-P, FIS2015-71933-REDT), and in part the Spanish Ministerio de Educación y Ciencia (MAT2013-47395-C4-1-R and MAT2016-75362-C3-1-R). The work of L. Labrador-Páez was supported in part by the Universidad Autónoma de Madrid for the “Formación de Personal Investigador (FPI-UAM)” program.

We present a novel cavity design for vertical external cavity surface emitting lasers (VECSELs) enabling multiple interactions with the gain structure under different angles in a single round trip. This allows for a low round-trip group delay dispersion (GDD) despite using high-gain resonant VECSEL structures possessing pronounced resonances in their reflective GDD profile. Femtosecond-regime pulses with an average output power of 1.14 W and record peak intensities for mode-locked VECSELs of 6.3 kW are presented with simulations demonstrating the GDD compensating mechanism employed in this scheme.

Graphene is a gapless material with a linear energy–momentum dispersion relationship. Because of its unique band structure, graphene has been demonstrated as an ultra-broadband photon absorption material from the visible to terahertz frequency ranges. Here, we study the reverse process: photon emission from graphene. Using silica microsphere structures and femtosecond laser pulse excitation, photon emission enhancement at visible, near infrared, and terahertz ranges were achieved. These results help to promote graphene as a new type of light generation material, which can overcome the restriction that the emission wavelength is determined by the material bandgap. It is also found that the graphene's electrical properties, such as the nonlinear conductivity, changed significantly with the enhancement of the absorption during the ultrafast process.

[EN]Inscription of optical waveguides by direct femtosecond laser irradiation has become a very versatile tool for the development of integrated photonic devices, such as waveguide lasers, frequency converters or photonic lanterns, among many others. The potential application of such devices for the control and manipulation of ultrashort pulses requires the precise knowledge of the temporal distortions that may be induced in the pulse propagation. Currently, research in this topic is scarce, and to our knowledge there is no previous experimental study on the spatio-temporal characterization at the output of waveguides inscribed inside crystals. Here, we have firstly fabricated depressed-cladding waveguides with different modal behavior in YAG crystal by direct femtosecond laser irradiation. Then, we implemented an experimental method based on the fiber coupler assisted spectral interferometry technique, that allows obtaining: (1) the temporal dispersion of a pulse at the output of an inscribed waveguide and, (2) full spatio-spectral and spatio-temporal characterization of the output of single-mode and multi-mode waveguides. Our results suggest that the main contribution to the pulse dispersion is due to the material dispersion. Moreover, we found that multimodal waveguides may induce an appreciable inhomogeneity in the temporal features of the pulses that needs to be taken into account in the design of complex devices. This work was supported by Junta de Castilla y León (Project SA046U16 and SA287P18) and MINECO (Projects FIS2017-87970-R, EQC2018-004117-P). M.M.-V. acknowledges support from Junta de Castilla y León grant (No. SA046U16) and from Generalitat Valenciana, Spain, under project CDEIGENT/2018/024.

Nitrogen molecules are promoted to excited neutral states during femtosecond laser pulse filamentary propagation in atmosphere, leading to a characteristic UV fluorescence. Using a laser-induced fluorescence depletion technique, we measure the formation dynamics of these excited neutral nitrogen molecules with femtosecond time resolution. We find that the excited neutral molecules are formed in an unexpected ultrafast timescale of $\ensuremath{\sim}4\text{ }\text{ }\mathrm{ps}$ at 1 bar and $\ensuremath{\sim}120\text{ }\text{ }\mathrm{ps}$ at 30 mbar pressure. From this observation we deduce that the excitation of neutral ${\mathrm{N}}_{2}$ occurs via multiple collisions with hot free electrons. Numerical simulations based on rate equations reproduce well this ultrafast formation time and its dependence on gas pressure, and thus support this interpretation.

International audience; It is shown in this communication that a LT-GaAs photomixer based on an optically resonant cavity is able to generate peak output powers above 2 mW up to 320 GHz when it is driven by optical pulses of 5 ns width at a repetition rate of 10 MHz.

International audience; We study the optical response of multilayer graphene quantum dots at THz frequencies. We fabricate 73 nm diameter graphene quantum dots in an array of ~1mm 2 size. We demonstrate optical absorbance of these graphene quantum dots from 0.85 to 4.7 THz and study the absorption dependence with the temperature from 4K to 300 K.

The graded-index fiber lens was used to couple probe light into the multimode sapphire fiber containing a Bragg grating (SFBG). It improved the spectral resolution of the SFBG and facilitated the packaging of the SFBG as a fiber sensor for applications in high temperature environments., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

[EN]We report on a one-step fabrication method of horizontal dual-line waveguides supporting TE guidance in LiTaO 3 crystal utilizing multiple refocusing mechanisms of the femtosecond laser. Through the nonlinear process, multiple foci can be formed spontaneously with the interval of a few micrometers along the laser propagation direction. The number and the separation of focal spots, even the entire length of laser-induced tracks, could be modulated by varying the laser parameters. Taking advantage of this spontaneous phenomenon, we further implemented the multi-scan technique to write two parallel damage lines along transverse direction, realizing stress-induced waveguides by horizontal light confinement. Moreover, using this method, one-step two-channel guidance could also be demonstrated by adjusting the pulse energy. The fabrication details and waveguiding performances were studied by both experimental and computational methods. This paper opens the alternative way to construct complex integrated platforms in LiTaO 3 crystal by using femtosecond laser writing., This work was supported in part by the National Natural Science Foundation of China under Grant 61775120 and Grant 11874239, in part by the Ministerio de Economía y Competitividad under Grant FIS2017-87970-R, in part by the Ministerio de Economía y Competitividad de España under Grant MAT2016-75362-C3-1-R, and in part by the Autónoma de Madrid under Grant B2017/BMD-3867RENIM-CM.

This article offers an extensive survey of results obtained using hybrid photonic-crystal fibers (PCFs) which constitute one of the most active research fields in contemporary fiber optics. The ability to integrate novel and functional materials in solid- and hollow-core PCFs through various postprocessing methods has enabled new directions toward understanding fundamental linear and nonlinear phenomena as well as novel application aspects, within the fields of optoelectronics, material and laser science, remote sensing, and spectroscopy. Here the recent progress in the field of hybrid PCFs is reviewed from scientific and technological perspectives, focusing on how different fluids, solids, and gases can significantly extend the functionality of PCFs. The first part of this review discusses the efforts to develop tunable linear and nonlinear fiber-optic devices using PCFs infiltrated with various liquids, glasses, semiconductors, and metals. The second part concentrates on recent and state-of-the-art advances in the field of gas-filled hollow-core PCFs. Extreme ultrafast gas-based nonlinear optics toward light generation in the extreme wavelength regions of vacuum ultraviolet, pulse propagation, and compression dynamics in both atomic and molecular gases, and novel soliton-plasma interactions are reviewed. A discussion of future prospects and directions is also included.Optical fibers provide much more than a means to transport light between different locations. This article reviews how integration of functional fluid, solid, and gaseous materials in photonic-crystal fibers enables control of their linear and nonlinear properties with applications in optoelectronics, sensing, and laser-matter interactions.

Frontiers in Physics, 7, ISSN:2296-424X

We study the interaction of swift electrons with laser and solids using a numerical approach, and specifically show that low-energy electrons can be used to map the time-resolved response of a Fermi gas.

The first chapter has pointed out important breakthroughs of solid-state laser architectures. In particular Ti:sapph lasers have revolutionized frequency metrology and ultrafast optics. The introduction has also emphasized the potential of the thin-disk technology to become the foundation of the upcoming power-scalable laser oscillator generation.

Journal of synchrotron radiation 26(3), 899 - 905 (2019). doi:10.1107/S160057751900345X, Wavefront-propagation simulations have been performed to complete the design of a monochromator beamline for FLASH2, the variable-gap undulator line at the soft X-ray free-electron laser in Hamburg (FLASH). Prior to propagation through the beamline optical elements, the parameters of the photon source were generated using the GENESIS code which includes the free-electron laser experimental data. Threshold tolerances for the misalignment of mirror angles are calculated and, since diffraction effects were included in the simulations, the minimum quality with respect to the slope errors required for the optics is determined., Published by IUCr, Chester

The widespread applications of ultrafast fiber lasers in various fields are due to their inherent advantages of compact configuration, excellent pulse quality, and extraordinary stability. The combination of optical passive device and two-dimensional materials is a promising approach of improving the fiber laser’s performance. Here, we demonstrate a versatile optical device with MoTe2 mode-locker and a simplified ultrafast laser based on the proposed device. The proposed device can greatly improve the environmental stability of two-dimensional MoTe2 mode-locker, and provide a new method of incorporating two-dimensional materials into ultrafast optics application. The versatile device with MoTe2 mode-locker has important application in ultrafast fiber laser. The simplified laser has great commercial value in various fields like optical communication, optical sensing, and materials processing.

Ultrafast optics and ultra-intense laser technology, which are important frontiers in the fields of optics and lasers, are expected to promote fundamental science discoveries and high-technology developments. In this paper, the current status and future trends of ultrafast optics and ultra-intense laser technology are introduced briefly, including the applications of ultrafast and ultra-intense lasers in particle acceleration, attosecond science, ultrafast nonlinear optics, micro/nano-fabrication, broadband optical frequency combs, etc. The future prospects and key techniques for generating ultra-intense and ultra-short laser pulses with higher performance are also described.

The waveguide beam splitters with diverse configurations in LiNbO 3 crystal have been produced by direct femtosecond laser writing of a family of optical-lattice-like cladding structures. By on demand design of the lattice tracks with “defect” lines, the efficient beam guiding and tailoring have been implemented in the structures. With a family of three-element integration of structures, three-dimensional (3-D) 1 × 3 beam splitting at the telecommunication wavelength of 1550 nm was realized. Different from the Type I modification of LiNbO 3 waveguides, the guiding cores of the optical-lattice-like cladding waveguide structures we fabricated locate in regions that are surrounded by the laser-induced-tracks. This paper opens the alternative way to construct complex integrated platforms in LiNbO 3 crystal by using femtosecond laser writing., The work was supported by National Natural Science Foundation of China under Grant 11274203, and Ministerio de Econom´ıa y Competitividad (Project FIS2013-44174-P), Spain