We report on the fabrication of inverted Yablonovite-like three-dimensional photonic crystals by nonlinear optical
nanolithography based on two-photon polymerization of a zirconium propoxide hybrid organic-inorganic material with
Irgacure 369 as photo-initiator. Advantage of this material is ultra-low shrinkage that guaranty high fabrication fidelity.
Images of the fabricated structure are obtained with a scanning electron microscope. The photonic crystal consists of
three sets of nearly cylindrical structural elements directed along the three lattice vectors of the fcc lattice and cross each
other at certain angles to produce inverted Yablonovite geometry. To investigate photonic properties of the inverted
Yablonovite structures, we calculate the photonic band structure for ten lowest-frequency electromagnetic modes. In
contrast to the direct Yablonovite structure that has a complete photonic band gap between the second and third bands,
we find no complete photonic band gaps in the inverted Yablonovite lattice. This situation is opposite to the case of fcc
lattice of close-packed dielectric spheres in air that has a complete photonic band gap only for the inverted geometry.
Excitation, focusing, and directing of surface plasmon polaritons (SPPs) with curved chains of bumps located
on a metal surface is investigated both experimentally and theoretically. We demonstrate that, by using a
relatively narrow laser beam (at normal incidence) interacting only with a portion of a curved stripe or chain
of nanoparticles, one can excite an SPP beam whose divergence and propagation direction are dictated by the
incident light spot size and its position along the structure. It is also found that the SPP focusing regime is
strongly influenced by the chain inter-particle distance. Extensive numerical simulations of the configuration
investigated experimentally are carried out for a wide set of system parameters by making use of the Green's
tensor formalism and dipole approximation. Comparison of numerical results with experimental data shows
good agreement with respect to the observed features in SPP focusing and directing, providing the guidelines
for a proper choice of the system parameters. It was found that the focusing regime of SPPs is strongly
influenced by the chain inter-bump distance, so that the focusing and directing effects with optimal properties
can be obtained only when the chain inter-bump distance is smaller than the SPP wavelength. Following the
experimental conditions, we have studied the role of the size of light spot exciting SPPs. Spectral dependence
of the focusing waist is also numerically studied for gold surface taking into account the ohmic loss.
Rapid advance of nanostructuring technologies offers new possibilities for flexible and low-cost fabrication of plasmonic
components and devices. In this contribution, we study applications of laser-based nonlinear lithography for the fabrication of dielectric surface-plasmon-polariton (SPP)-structures. These structures can be used for localization, guiding, and manipulation of SPPs on a subwavelength scale. Effective excitation of SPPs on dielectric structures and focusing of the generated SPPs are studied. The characterization of the SPP structures is performed by plasmon leakage radiation microscopy. Laser-based nonlinear lithography,
e.g. two-photon polymerization technique, allows the
fabrication of dielectric waveguides, splitters, and couplers directly on metal surfaces. The fabricated dielectric structures
on metal films are demonstrated to be very efficient for the excitation of SPPs. Using these structures, excitation,
focusing, and guiding will be demonstrated.
One of the rapidly advancing femtosecond laser technologies is three-dimensional micro- and nanostructuring by two-photon
polymerization (2PP) technique. This technique allows the fabrication of any computer-generated 3D structure by
direct laser "recording" into the volume of a photosensitive material. Because of the threshold behavior and nonlinear
nature of the 2PP process, a resolution beyond the diffraction limit can be realized by controlling the laser pulse energy
and number of applied pulses. Many different applications of 2PP technique are discussed.
Renewed and growing interest in the field of surface plasmon polaritons (SPPs) comes from a rapid advance of
nanostructuring technologies. The desired nanostructures are usually fabricated by electron- or ion-beam lithography. An
alternative approach is the application of two-photon polymerization (2PP) or nonlinear lithography. Both these
technologies are based on nonlinear absorption of near-infrared femtosecond laser pulses. With 2PP, the fabrication of
three-dimensional micro-objects and photonic crystals with a resolution down to 100 nm is possible. In this contribution,
we study applications of advanced femtosecond laser technologies for the fabrication of SPP structures. We demonstrate
that resulting structures can be used for excitation, guiding, and manipulation of SPPs on a subwavelength scale.
Characterization of these structures is performed by detection of the plasmon leakage radiation (LR). 2PP allows the
fabrication of dielectric waveguides, splitters, and couplers directly on metal surfaces. The fabricated dielectric structures
are also very efficient for the excitation of SPPs. Using these structures, excitation and focusing of the resulting plasmon
field can be achieved.
We study the application of two-photon absorption of near infrared femtosecond laser pulses and nonlinear maskless femtosecond laser lithography for the fabrication of dielectric and metallic SPP-structures, being used for localization, guiding, and manipulation of SPPs on a subwavelength scale. Resolutions down to 100 nm are already achievable. Characterization of these structures is performed by detection of the plasmon leakage radiation. Nonlinear lithography allows the fabrication of dielectric waveguides, splitters, and couplers directly on metal surfaces, e. g. by two-photon polymerization. The dielectric structures on metal films are demonstrated to be very efficient for the excitation of SPPs. Using these structures, excitation and focusing of the resulting plasmon field can be achieved. Results on the fabrication and characterization of metallic SPP-structures and components on dielectric substrates fabricated by nonlinear femtosecond laser lithography will be presented and discussed.
Infrared, femtosecond laser pulses are ideal for the fabrication of 3D structures in transparent media. Due to the low
absorption cross-section, 2 or more photons are necessary for absorption. This multi-photon effect limits the affected
volume to the focal area allowing for sharp features on the order of the wavelength of light. One possible multi-photon
reaction is the photo-destruction (ablation, decomposition, etc.) or photo-polymerization of materials. Using these
techniques, 3D photonic components can be realized.
A photonic band gap template has been created with a monodisperse polystyrene (PS) spheres (diameter ~ 624 nm).
We have used ultrafast laser pulses to remove spheres (introduce defined defects) at the surface to gain a fuller
understanding of the laser-material interaction. To optimally focus inside the bulk, an index matching material must be
infiltrated. By using a photosensitive material, two-photon polymerization can be used to harden the material
surrounding the spheres and insert defects inside the bulk. With proper placement of defects, 3D photonic components,
i.e., waveguides, splitters, and filters, can be created.
The science of surface plasmon polaritons (SPPs) has attracted a lot of attention in the last years. In this contribution, we study applications of two-photon absorption of femtosecond laser radiation for the fabrication of dielectric and metallic SPP-structures, which can be used for localization, guiding, and manipulation of SPPs. Dielectric SPP components, e.g. waveguides, bends and splitters are fabricated on gold films. SPP properties are investigated by scanning optical near-field microscopy (SNOM), indicating guiding and reflection of SPPs by polymer lines. SPP excitation on dielectric line and point structures is observed by far-field microscopy. Results on plasmon focussing and on the fabrication and characterization of metallic SPP-structures and components on dielectric substrates will be presented and discussed.
In this contribution, we demonstrate multi-photon femtosecond laser lithography for the fabrication and rapid prototyping of plasmonic components. Using this technology different dielectric and metallic SPP-structures can be fabricated in a low-cost and time-efficient way. Resolution limits of this technology will be discussed. Investigations of the optical properties of the fabricated SPP-structures by far-field leakage radiation microscopy will be reported.
We observed and investigated self-starting quasi-periodic pulsation in Er-doped fiber laser at 30 - 100 mW pump power. Pulse with duration of 10 - 50 ns and peak power of 50 - 200 W are generated at a quite stable repetition rate in the range of 300 - 500 microsecond(s) . In contrast with previous experiments the pump level in our experiment is significantly lower. At this low pump power we found no nonlinear effect except SBS influencing on the laser dynamics. The experimental results were explained by a theoretical model based on cooperative dynamics of Rayleigh backscattering and Stimulated Brillouin Scattering (SBS). Using digital oscilloscope, we traced in details different stages of Q-switching pulse formation process: growth of the spontaneous radiation, lasing due to Rayleigh backscattering, appearance and growth of the first order SBS Stokes radiation and the second order Stokes radiation, lasing suppression due to saturation of the population inversion in Er-doped fiber by the SBS Stokes radiation. Good agreement between theory and experiment have been demonstrated.
We demonstrate for the first time that pulse-to-pulse amplitude fluctuations occurring in the rational-harmonic repetition-rate-doubling regime of actively mode-locked fiber laser are eliminated when modulation frequency is properly tuned. Irregularity of the pulse position in the train is found to be the only drawback of this technique. The irregularity can be reduced to value acceptable for applications by a proper laser design.
Bragg gratings were written in H2-loaded polarization- maintaining fiber (PM-FBGs) and inserted in an actively mode-locked Er-doped fiber laser. The use of PM-FBG in sigma laser cavity allows to effectively build all polarization- maintaining fiber laser. Long term stabilization of the laser was ensured by a feedback loop that controlled the cavity length. Peak wavelengths, reflection bandwidths and reflectivity values of the grating were equal to 1545.5 nm and 1540.5 nm, 1.6-nm and 0.8-nm, of 99% and 90%, respectively. At a 3-GHz repetition rate, pulses of 9.4-ps and 27.9-ps duration were generated with first and second gratings, respectively. By inserting additional long piece of dispersion-shifted fiber in the cavity, nonlinear pulse shortening was observed due to formation of average soliton inside the cavity. In this case, pulses of 7.8-ps and 22.7- ps duration were generated with first and second gratings, respectively. With the first grating, generated pulses were close to transform limit for hyperbolic secant pulse shape. Longer pulse duration obtained with second grating is attributed to narrower bandwidth and residual chirp of the grating.
Recently a new mechanism for passive Q-switching in fiber lasers based on cooperative dynamics of linear Rayleigh backscattering (RS) and Stimulated Brillouin Scattering (SBS) has been reported in Yb- and Er-doped fiber lasers with high pump powers (greater than 2 W). At such high pump levels, the intensity of the light generated inside the fiber laser cavity exceeds considerably the SBS threshold, so that the conditions for passive Q-switching due to nonlinear backscattering are easily achieved and, for this reason, no special optimization of the laser configuration is required. Here, we report on experiments in Er-doped fiber lasers with low pump power levels. The Q-switching operational mode of Er-doped fiber lasers was observed at pump power levels in the range of 30 - 100 mW. Throughout the experiments, we traced in details different stages of Q-switching pulse formation process: growth of the spontaneous radiation, lasing due to Rayleigh backscattering, appearance and growth of the first order SBS Stokes radiation and the second order Stokes radiation, lasing suppression due to saturation of the population inversion in Er-doped fiber by the SBS Stokes radiation. In general, the process was slower in comparison with previous experiments at high pump power level. The output pulse duration was in the range of 10 - 20 ns and the peak power of the pulses was less than approximately 100 - 200 W. For this reason, all nonlinear processes except SBS did not influence the pulse formation process. The experimental results are well explained by a theoretical model based on RS-SBS dynamics.
Generation of picosecond pulses at two distinct wavelengths is interesting for wavelength-division-multiplexing, fiber communication and sensing. For this purpose, we achieved harmonic active mode locking simultaneously at two wavelengths separated by about 15 m in an Erbium-doped fiber laser. Dual- wavelength lasing was obtained with two wide-bandwidth (greater than 1 nm) nonchirped high-reflectivity fiber Bragg gratings inserted in the laser cavity. The fiber Bragg gratings were written with 275-nm light from an Ar laser in hydrogen-loaded fibers. Optical path lengths and losses were carefully adjusted at each wavelength to obtain perfect mode locking at both wavelengths. Total cavity dispersion was set in the anomalous dispersion regime and optimized at each wavelength independently to generate solitons. Pulses at 3-GHz repetition rate were obtained at two wavelengths simultaneously with pulse widths of 16 ps and 13 ps, at 1547 nm and 1562 nm respectively. Time-bandwidth products of 0.37 and 0.34 respectively confirmed that the pulses were nearly transform-limited at each wavelength.
Stokes field demonstrated unusually narrow-spectrum and non- Gaussian statistics for SBS in 300m single-mode optical fiber with enhanced Rayleigh losses. We show that SBS lasing takes place withing the fiber. The effect is explained by dynamic distributed feedback, due to double Rayleigh scattering of the Stokes field. Results of numerical simulation of the cooperative SBS-RS process in fiber are in agreement with experimental results.
Backward light scattering processes always take place in fiber lasers. They create additional feedback in laser resonator changing qualitatively the laser operation. We have described for the first time the mechanisms of their influence on lasing in number of fiber configurations. The understanding of the mechanisms allows us to get several important scientific results suitable for rapid practical applications in the process of elaboration of new fiber sources of light.
An in-line scheme of an Er3+-doped fiber laser with self-starting passive mode locking using the effect of polarization ellipse self-rotation is suggested. The laser has been studied experimentally. For the pump radiation with a power of 150 mW and wavelength of 532 nm, a self-starting generation of pulses with 3 - 3.5 ps duration has been obtained.
Theoretical investigation of four- and three-level fiber amplifiers based on Nd3+- and Er3+- doped silica fibers has been carried out. Analytical expressions for the gain factor and the power of the output signal saturating the gain factor are obtained. We have showed that the corresponding choice of the refractive index profile allows to increase essentially the power of signal saturating the gain.
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