Lasing Regime Research Articles

Synthesis of magnetic nanoparticles by laser ablation in a liquid and verification of their antibacterial properties

Nickel nanoparticles were obtained by nanosecond laser ablation in deionized water and in air in different laser regimes. The nanoparticles were characterized by scanning electron microscopy, method of dynamic light scattering, and optical spectroscopy. Solutions with the highest concentration of nanoparticles were tested for antibacterial activity. The antibacterial properties of nickel nanoparticles were demonstrated on gram-positive (S. aureus) and gramnegative (P. aeruginosa) bacteria using the LIVE/DEAD method.

Thermo-optic effects mediated self focusing mechanism and optical power limiting studies of ZnO thin films deposited on ITO coated PET substrates by RF magnetron sputtering under continuous wave laser regime

In this work, ZnO thin films are deposited on ITO coated PET substrates employing RF magnetron sputtering technique. The evolution of crystallites orientation on (002) plane with increasing thickness of the films is unveiled from XRD patterns. Further, the appearance of (103) plane in the highest thickness film (183 nm) is attributed to the formation of surface layer during sputtering process. The smooth and homogenous natures of the films are displayed by the interference pattern in transmittance spectra. The presence of defect level emission in the luminescence spectra is ascribed to compressive stress in the films. The exhibition of orange-red emission confirms the excess oxygen in the sputtered films (89 nm and 183 nm). The dominance of thickness on the third-order nonlinear optical parameters is revealed by single beam Z-scan measurements. The lower thickness ZnO film (42 nm) shows an interesting self focusing behavior under closed aperture Z-scan measurements. A transition from self focusing to self defocusing behavior is noticed with increasing thickness values from 42 nm to 183 nm. The self focusing property is attributed to the combination of presence of large dipole moments at the substrate-film interface as result of large energy gap gradients and thermo-optic effects.

Bio-inspired synthesis of silver nanoparticles using Hibiscus Tiliaceus L. flower extracts for improved optical characteristics

In this work, we report a simple, facile, environment friendly and green approach to synthesize silver nanoparticles using aqueous flower extracts of Hibiscus Tiliaceus L. The morphology (shape/size) and crystal structure of as-synthesized silver nanoparticles (NPs) were determined by transmission electron microscopy and x-ray diffraction. The UV–Vis spectroscopy was used to record the surface plasmon resonance peak, while spectro-fluorophotometry was used to examine the fluorescence emission spectra of silver NPs. Moreover, the optical nonlinearities of silver NPs were investigated using z-scan technique with low power argon laser beam at wavelengths 488 nm and 514 nm in continuous-wave regime and at 532 nm in the pulsed laser regime. Our results indicate that the nonlinear absorption in silver NPs is reverse saturation absorption of the order of 10–3 cm/W and the negative nonlinear refractive index was determined as of the order of 10–8 cm2/W. Moreover, the optical nonlinear properties were used to demonstrate optical limiting abilities of the synthesized silver NPs. The results presented in this study indicate that bio-synthesized silver NPs are excellent candidates as a nonlinear material and can be widely used for waveguide applications.

Sub-100 fs Bound State Solitons and Period-Doubling Bifurcations in a Mode-Locked Fiber Laser

We investigate on bound-state mode-locking in the close-to-zero dispersion regime of an Er-fiber laser. A two-soliton bound state with 82 fs pulse duration and 0.58 ps pulse separation is achieved. Compound 2+1 type bound state solitons with ~100 fs pulse duration has also been observed. Both the double-pulse and the 2+1 type bound states could experience period-doubling bifurcations and exhibit the pumping hysteresis characteristics as the single pulse. To the best of our knowledge, this work provides the first observation of sub-100 fs bound solitons in a fiber laser. Such ultra-short bound state solitons show potential applications of multilevel coding unit for high-capacity telecommunication systems.

Stable-, period-N- and multiple-soliton regimes in a mode-locked fiber laser with inconsistently filtered central wavelengths

We systematically study the stable-, period-N- and multiple-soliton regimes in an Erbium-doped fiber laser effectively mode-locked by nonlinear polarization rotation technique. In the stable mode-locked regime, an invariant soliton with 497 fs pulse duration and 6.9 nm optical spectrum are obtained. With a larger pump power of 180 mW, the period-N state (in which the pulse intensity returns to its original value after N cavity-roundtrips) emerges, accompanied by sub-sideband generation on the first Kelly sideband and spectrum shift. Considering the inconsistent central wavelengths between gain and polarization-dependent isolator (PD-ISO) firstly, to our knowledge, the numerical results are in good agreement with the experiment and reveal the composite filtering of gain and PD-ISO takes major responsibility for spectrum shift, which causes group velocity offset simultaneously. Further study shows the continued increase of pump power can lead to the laser operating in the unstable multi-pulse state and the narrow spectral width contributes to stabilizing the multi-pulse state. Our work can promote the understanding of soliton dynamics and filtering in ultrafast fiber lasers.

Er-doped crystalline active media for ~ 3 μm diode-pumped lasers

Lasers based on erbium ions using 4I11/2 ​→ ​4I13/2 transition can generate laser radiation in the spectral range from 2.7 ​μm to 3 ​μm. Since the strong absorption peak of water is located at 3 ​μm, there has been an effort to develop a suitable laser source for various medical applications, e.g. dentistry, dermatology, urology, or surgery. Laser radiation from this wavelength range can also be used in spectroscopy, as a pumping source for optical parametric oscillators, or for further mid-infrared conversion.This paper represents an overview of the erbium-doped active media (e.g. Er:YAG, Er:YAP, Er:GGG, Er:SrF2, Er:YLF, Er:Y2O3, Er:KYW, etc.) for laser radiation generation in the spectral range 2.7–3 ​μm. In the first part of this paper, the particular active media are discussed in detail. On the other hand, the experimental results summarized absorption and emission cross-section spectra together with decay times at upper (4I11/2) and lower (4I13/2) laser levels of all tested Er-doped samples at room temperature. Moreover, laser results in CW and pulsed laser regime with tunability curves, achieved in recent years, are presented, too.

Investigating material modification in a heretofore unexplored laser regime

Beyond the critical power for self-focusing, ultrashort pulses unexpectedly yield stable bulk modifications in silica, including photonics-relevant densification.

Localized Photon Lasing in a Polaritonic Lattice Landscape

Periodic photonic structures have attracted much interest due to their versatility for controlling light propagation. The dispersion of photon modes in photonic lattices exhibits an energy band structure analogous to the electronic one in crystals. An important consequence of the photonic band structure is the localization of light in a band gap, which can be engineered by breaking the translational symmetry introducing a defect in the lattice. Here, we demonstrate experimentally the localization of light in a two-dimensional periodic system of polaritons confined in a patterned microcavity. We generate a self-trapping of light by optically inducing a local breaking of the strong-coupling regime of excitons to photons. In the photon lasing regime we show the existence of confined modes that can be controlled by the shape of the generated defect. We demonstrate single on-site localization with lasing mode at the edge of the Brillouin zone similar to a gap soliton. Our results pave the way for useful tools to optically control localization and propagation of light towards the generation of microlasers.

Conventional Soliton and Noise-Like Pulse Generated in an Er-Doped Fiber Laser with Carbon Nanotube Saturable Absorbers

Conventional soliton (CS) and noise-like pulse (NLP) are two different kinds of pulse regimes in ultrafast fiber lasers, which have many intense applications. In this article, we experimentally demonstrate that the pulse regime of an Er-doped fiber laser could be converted between conventional soliton and noise-like pulse by using fast response saturable absorbers (SA) made from different layers of single-wall carbon nanotubes (CNT). For the monolayer (ML) single-wall CNT-SA, CS with pulse duration of 439 fs at 1560 nm is achieved while for the bilayer (BL) single-wall CNT, NLP at 1560 nm with a 1.75 ps spike and a 98 ps pedestal is obtained. The transition mechanism from CS to NLP is investigated by analyzing the optical characteristics of ML and BL single-wall CNT. The further theoretical simulation illustrates that CNT-SA enables the switching between CS and NLP in anomalous dispersion regime in Er-doped fiber lasers.

Spectral and third-order nonlinear optical characteristics of natural pigment extracted from coriandrum sativum

Abstract The present study focuses on determination of spectral and third-order nonlinear optical (NLO) properties of a natural pigment chlorophyll-a have been extracted from the leaves of coriandrum sativum (coriander). The extraction was carried out by a column chromatography technique, is a sensitive method for isolating the natural pigment chlorophyll-a from coriandrum sativum. The spectral characteristics of the natural pigment were examined by UV–Vis absorption, emission and FT-IR spectra, respectively. The concentration of chlorophyll-a in coriandrum sativum was measured to be 48.6 mg/g using UV–Vis absorption spectra. A peak tailed by a valley curve was noted in closed aperture Z─scan technique due to self-defocusing and open aperture Z─scan curve signifies the reverse saturable absorption (RSA) behavior. The existence of RSA in chlorophyll-a was ensured by ground and excited state absorption cross-section. The real and imaginary parts of the third-order NLO susceptibility of chlorophyll-a were found to be the order of 10─15 m2/V2. The natural pigment exhibits a low optical limiting (OL) threshold of 4.22 × 102 W/cm2 under continuous wave laser regime. The experimental results revealed that the natural pigment chlorophyll-a extracted from the leaves of coriandrum sativum is a potential material for photonics and optoelectronics applications.

Infrared Laser Effect on Healthy and Ossified Costal Cartilage: The Development of Stable Load-Bearing Autoimplants.

The laser-induced stress relaxation provides new prospects to obtain stable long fragments of costal cartilage for autoimplantation avoiding the risk of spontaneous deformation and poor engraftment. However, the age-related alterations of cartilage may sufficiently influence its interaction with infrared (IR) laser radiation and disrupt the effectiveness and safety of the technique. The aim of the work is to study the influence of the structural quality of costal cartilage on its interaction with IR laser and efficiency of obtaining of curved implants for trachea surgery. Healthy costal cartilage was taken from pigs and human. Ossified costal cartilage was taken from humans of age 65 ± 7. The cartilage slices with a mean thickness of 3 mm were mechanically curved and processed to stress relaxation by laser irradiation with the wavelength 1.56 µm. The structure and mineral content were studied by X-ray microtomography and element analysis. The optical measurements included the study of the propagation of IR radiation, speckle interferometry, and IR radiometry. The aged cartilage demonstrates a high level of heterogeneity in structure and properties and decreased water content. The presence of dense inclusions consisting of amorphous calcined volumes makes the tissue more fragile and less elastic. The IR radiation propagation intensity for aged cartilage is at least twice higher than that for healthy cartilage. The thermal-induced motion of scatterers in aged cartilage is slower. X-ray microtomography showed the cartilage-like and the bone-like structures within the ossified samples. The main challenge for laser reshaping of aged cartilage is the presence of ossifications. However, the new stable curvature can be obtained with adjustment of laser power. To obtain the satisfying stable curvature of an implant the ossified volumes should be avoided The laser-induced stress-relaxation mechanism for aged cartilage can be particularly different from that of healthy tissue and the optimal laser regimes should be specified. Lasers Surg. Med. © 2020 Wiley Periodicals, Inc.

Triggering of different pulsed regimes in fiber cavity laser by a waveguide electro-optic switch.

A novel practical method for electronic triggering of essentially different pulsed regimes in fiber cavity lasers is introduced. The method relies on electronic control of complementary transmission characteristics of a fiber-coupled LiNbO3 waveguide electro-optic switch (WEOS) which plays the role of the variable output coupler in a fiber cavity. The method was studied using a testbed laser configuration comprised of a semiconductor optical amplifier (SOA) and an all-fiber cavity. Modulation of the WEOS-based output coupling in the fast gain recovery configuration allowed not only high-quality mode locking and harmonic mode-locking at certain pulse repetition rates determined by the cavity round trip time, but it also allowed nanosecond pulsed output of the same quality to be yielded by cavity dumping at widely and continuously tunable repetition rate (ranging from kHz to MHz). Thus, WEOS-based electronically variable output coupling allows uniquely high flexibility for lasing regimes and characteristics within a single all-fiber cavity configuration.

Bond assessment of resin modified glass ionomer cement to dentin conditioned with photosensitizers, laser and conventional regimes.

To assess different conditioning regimes on shear bond strength (SBS) of resin modified glass ionomer cement (RMGIC) bonded to dentin MATERIAL AND METHODS: Fifty non carious intact maxillary molars were cleaned, isolated and randomly divided into five groups (n = 10). Before randomization, dentin surface was exposed and finished. Samples in group 1 were conditioned with methylene blue photosensitizer (MBP) 50 mg/l and activated by photodynamic therapy (PDT), Group 2: surface treated with Er,Cr:YSGG (ECL), Group 3: surface conditioned with polyacrylic acid (PAA) (control), Group 4: surface conditioned with 17 % Ethylenediaminetetraacetic acid (EDTA), Group 5: surface conditioned with total etch (Optibond solo Plus). For SBS testing the samples were placed in universal testing machine. Fracture analysis of debonded surfaces were evaluated using stereomicroscope at 40x magnification. Means and standard deviations were calculated using analysis of variance (ANOVA) and Tukey's post hoc test at a significance level of (p < 0.05). The maximum bond strength was found in group 5 conditioned with Optibond solo plus total etch (23.15 ± 3.21 MPa). Whereas, the lowest bond values were observed in group 1 treated with MBP (15.25 ± 1.54 MPa). Moreover, samples in group 2, group 3 and group 4 resulted in comparable bond strength (p > 0.05). MBP at 50 mg/l is not recommended to condition dentin prior to RMGIC application. Moreover, ECL has a potential to be suggested for dentin conditioning compared to PAA.

Simulation of the analytical solution of lasing output power for Yb 3+: YAG thin disk laser regime in a fundamental mode operation

A theoretical model is established to derivation equation of output Laser power for multi-pass pumping for a quasi-three level thin-disk laser, A numerical solution of this equation for Yb3+:YAG thin-disk laser, which pumped at wavelength (940 nm) and lasing emission at wavelength (1030 nm), regime in fundamental transverse mode (M2=0.95) at room temperature were performed by calculated the variation of (Nt),(d),(Mp),(R2),(T) and (Pp) on the output Laser power and find the typical value of these parameters are used to obtain high output Laser power.

Wave plate-dependent lasing regimes transitions in an all-normal-dispersion fiber laser mode-locked by nonlinear polarization rotation

We address the transitions between three different working regimes of an all-normal-dispersion pulsed fiber laser, mode-locked by nonlinear polarization rotation (NPR). In particular, we investigate numerically the dynamics and study in details the transitions induced by solely rotating the cavity wave plates. We analyze the phemomenon by putting forward a model for all-normal-dispersion NPR-moded-locked fiber laser, based on the coupled Ginzburg-Landau equations and Jones matrix. Numerical results show that depending on the values of the cavity parameters, the transitions between the dissipative soliton regime and amplifier similariton one, or the transition between the dissipative soliton regime and the splitting pulse one may be realized by simply rotating the cavity wave plates. We found that the transitions are intrinsically related to the NPR mode-locking mechanism by explicitly evaluating the polarization states across the pulse at different locations of the cavity. Our numerical results are in very good agreement with experimental results reported in the relevant literature, and provide evidence that besides gain saturation and spectral filtering, the orientations of wave plates may be exploited as a suitable degree of freedom to obtain the desired pulse regimes in all-normal-dispersion fiber lasers.

Multi-Shuttle Behavior Between Dissipative Solitons and Noise-Like Pulses in an All-Fiber Laser

A multi-switchable generation between dissipative solitons (DSs) and noise-like pulses (NLPs) in a fiber laser is demonstrated. A 45° tilted fiber grating is applied as an effective in-line all-fiber polarizer to realize the nonlinear polarization rotation (NPR) mechanism. With the fixed orientations of polarization controllers, the operation regimes of the fiber laser can be alternatively switched between DS and NLP by monotonically increasing pump power only. We observed five switching stages between DS/NLP regimes with the pump power elevating from 200 to 660 mW. Remarkably, the whole procedure could be precisely controlled forwardly and backwardly. This multi-shuttle behavior between the two distinct types of output pulse can be attributed to the transmission of NPR mechanism together with the gain filtering effect. To the best of our knowledge, this is the first report on the multi-shuttle behavior between DS and NLP in a fiber laser under monotonic change of pump power. Our findings may contribute to in-depth understanding of nonlinear dynamics and laser physics.

Features of fused silica ablation by laser induced carbon microplasma

The features of surface structuring on the transparent material by laser-induced microplasma were studied and the intensity of its microplasma was measured. The formation of micro-relief by a series of nanosecond pulsed laser induced carbon microplasma in confinement mode on the surface of fused silica were investigated and the measured intensity was compared with the features of micro-relief. The dependence of depth of formed relief and track on the laser regime was determined. It is shown that the mechanism of microstructure formation is dependent on multifactor and associated with the ablation on the surface of fused silica by the microplasma, which exists quite long time after the pulses.

Analysis of time, frequency and time-frequency domain features from acoustic emissions during Laser Powder-Bed fusion process

Sensor integration for in situ monitoring during additive manufacturing promises to enhance control over the process and assures quality in the fabricated workpieces. Acoustic emissions from the process zone of the laser powder-bed fusion process carry information about the events and failure modes of the printed workpiece. Analysis of acoustic signals emitted during different laser regimes, such as conduction, keyhole, etc. in time, frequency and time-frequency domains could provide quantitative information about the underlying physical mechanisms. This article reports a statistical analysis of the features in acoustic signals to perceive the characteristics of failure modes occurring during layering of stainless steel 316L. The visualization of the feature space distribution that corresponds to different failure modes shows the potentials of applying machine learning for in situ classification. The paper also proposes strategies in terms of data acquisition and preprocessing for building a comprehensive monitoring system.

Эффект насыщающегося поглотителя в длинноволновых вертикально-излучающих лазерах, реализованных по технологии спекания

Vertical-cavity surface-emitting lasers emitting at the spectral range of 1.55 µm based on heterostructures with a buried tunnel junction (BTJ) with a height step of 15 nm are studied. The devices are realized using wafer fusion technique of heterostructures grown by molecular beam epitaxy and demonstrate a single-mode lasing regime at the 8 μm BTJ-diameter. With a decrease in the BTJ-diameter, a sharp increase in the threshold current, accompanied by an abrupt increase in the output optical power and resonance frequency at the lasing threshold are observed. Stable single-mode lasing is due to the smoothing of the boundary of the overgrown surface relief, which leads to a smooth change in the profile of the effective refractive index in the lateral direction, while maintaining effective current confinement, which makes it possible to significantly reduce the transverse optical confinement factor for high-order modes even at large BTJ-diameter. However, at small BTJ-diameter, it also leads to the formation of a saturable absorber in the non-pumped parts of the active region.

HILITE – A well-defined ion target for laser experiments

SynopsisWe present a Penning-trap-based setup for the study of light-matter interactions in the high-power and/or high-intensity laser regime, such as multi-photon ionization and field ionization. The setup applies ion-cloud formation techniques to highly charged ions to the end of specific target preparation, as well as non-destructive detection techniques to identify and quantify the interaction educts and products.