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Two-dimensional (2D) violet phosphorus (VP) plays a significant role in the applications of photonic and optoelectronic devices due to its unique optical and electrical properties. The ultrafast carrier dynamics and nonlinear optical absorption properties were systematically investigated here. The intra- and inter-band ultrafast relaxation times of 2D VP nanosheets were measured to be ~6.83 ps and ~62.91 ps using the pump–probe method with a probe laser operating at 1.03 μm. The nonlinear absorption coefficient βeff, the saturation intensity Is, the modulation depth ΔR, and the nonsaturable loss were determined to be −2.18 × 104 cm/MW, 329 kW/cm2, 6.3%, and 9.8%, respectively, by using the Z-scan and I-scan methods, indicating the tremendous saturable absorption property of 2D VP nanosheets. Furthermore, the passively Q-switched Nd:YVO4 laser was realized with the 2D VP nanosheet-based SA, in which the average output power of 700 mW and the pulse duration of 478 ns were obtained. These results effectively reveal the nonlinear optical absorption characteristics of VP nanosheets, demonstrating their outstanding light-manipulating capabilities and providing a basis for the applications of ultrafast optical devices. Our results verify the excellent saturable absorption properties of 2D VP, paving the way for its applications in pulsed laser generation. [ABSTRACT FROM AUTHOR]

Optical waveguides covered with thin films, which transmittance can be controlled by external action, are widely used in various applications from optical modulators to saturable absorbers. It is natural to suggest that the losses through such a waveguide will be proportional to the absorption coefficient of the covering material. In this letter, we demonstrate that under certain conditions, this simple assumption fails. Instead, we observe that the reduction of the material loss of the film can lead to an increase in the propagation losses through the waveguide. For this, we use a side polished fiber covered with a single-walled carbon nanotube thin film whose absorption can be attenuated either by a short pulse illumination (due to absorption saturation) or with electrochemical gating. For the films thicker than 50 nm, we observe saturable absorption to turn into optical limiting with nonmonotonic dependence on the incident power. With a numerical simulation, we identify that this nontrivial behavior comes from mode reshaping due to changes in the absorption coefficient of the covering film. We demonstrate the applicability of the observed effect by fabricating the device which nonlinear optical response can be controllably switched between saturable absorbing and optical limiting. Finally, we utilize an analytical approach to predict the required parameters and corresponding nontrivial shapes of the nonlinear absorbance curves. These results provide new perspectives for engineering complex reconfigurable nonlinear optical responses and transmittance dependences of nanomaterial covered waveguides. [ABSTRACT FROM AUTHOR]

The nonlinear absorption coefficient and reverse saturable absorption on optical limiting threshold behavior was exhibited by 1-((E)-(2,5-dichlorophenylimino)methyl)naphthalen-2-ol (E25DCM) under the Nd: YAG nanosecond laser (532 nm, 9 ns, and 10 Hz) excitation. E25DCM crystal was grown by the slow evaporation technique at ambient temperature. The crystal structure was identified using the single crystal X-Ray diffraction analysis E25DCM belongs to Orthorhombic system with space group P212121. The Fourier Transform Infrared Spectroscopy, 1H-NMR Spectroscopy, and 13C-NMR Spectroscopy have all been well correlated with E25DCM structure. The thermal behavior indicates that E25DCM stable up to 160 °C. Surface analysis explains the irregular arrangement of E25DCM. The UV–Visible spectrum showed the absorption of E25DCM at 325 and 340 nm, and moderate transmittance is observed at the level of 62%. The optical band gap, which results in blue emission, is shown in the fluorescence spectrum at a value of 3.97 eV. The efficiency of crystal has significantly improved in the Second Harmonic Generation (SHG).Based on the Nonlinear absorption coefficient and optical limiting value of E25DCM, this crystal can be classified as an excellent NLO material and also a best contender for the use in developed laser safety devices. [ABSTRACT FROM AUTHOR]

In this work, we report single- and two-photon absorption (TPA) induced transmission and resonance modulation in a multilayer gallium selenide (GaSe) integrated silicon nitride (Si3N4) waveguide and ring resonator operating in the 700–800 nm wavelength range. Intensity dependent saturable absorption at low optical powers followed by TPA at higher power levels in GaSe integrated Si3N4 waveguides is observed at 785 nm pulsed laser excitation. A TPA coefficient of 0.117 cm/GW for the GaSe–Si3N4 composite waveguide and a three-photon absorption coefficient of 7.876 × 10−6 cm3/GW2 for the bare Si3N4 waveguide are extracted from intensity dependent transmission measurements. The single-photon absorption process induced by a blue laser incident on the multilayer GaSe transferred on top of the Si3N4 ring resonator is used for all-optical resonance tuning through the free-carrier refraction effect. A strong blue shift of the resonance by ∼12.3 pm/mW combined with resonance broadening is observed due to the free-carrier induced refractive index and absorption modulation. The TPA in the GaSe integrated Si3N4 ring resonator is also shown to result in a blue shift of the resonances excited using a 785 nm pulsed laser. This work demonstrates the all-optical control of 2D material integrated Si3N4 guided-wave structures operating in the shorter near-infrared wavelength range with potential applications in integrated quantum photonics, miniaturized sensing devices, and biomedical imaging. [ABSTRACT FROM AUTHOR]

The use of tin disulfide ( SnS 2) as a candidate material for saturable absorption in nonlinear optical devices is investigated in this article. A dual-wavelength soliton mode-locked fiber laser is demonstrated using a fabricated SnS 2 thin film as a saturable absorber within an erbium-doped fiber laser cavity. The laser generates two peaks centered at 1536.7 and 1562.6 nm, with a pulse width of 5.3 ps. The experimental results indicate that the SnS 2 thin film has the required absorption characteristics to realize good mode-locked operation. Thus, we confirm that SnS 2 has great potential to be used in multiwavelength ultrafast fiber laser applications. [ABSTRACT FROM AUTHOR]

Two thiophene based low band gap conjugated copolymers P(EDOT‐NA)] and P(PRDOT‐NA) were designed and synthesized via direct arylation polymerization. The copolymers were characterized by UV‐Vis, IR, Photoluminescence and NMR spectroscopic techniques. HOMO‐LUMO energy levels of the copolymers were theoretically calculated by two levels of DFT theories, HSE06 and B3LYP using a 6‐31G (d,p) basis set. Thermal properties were evaluated by thermogravimetric analysis. Optical properties of the copolymers showed solvatochromic behavior in different tolune/acetonitrile mixtures. P(EDOT‐NA) exhibited a negative solvatochromism in both absorption and emission spectra with a Stoke's shift of 6761 cm−1 to 7218 cm−1. P(PRDOT‐NA) was observed with a negative solvatochromism in absorption and positive solvatochromism in emission with Stoke's shift of 7265 cm−1 to 7891 cm−.1. Third‐order non‐linear optical properties of the copolymers were evaluated using the open‐aperture Z‐scan technique at 532 nm in DMSO solvent. OA Z‐scan behavior and optical limiting effect of the copolymers P(EDOT‐NA) and P(PRDOT‐NA) were studied at 81 μJ, 165 μJ and 300 μJ. Both copolymers exhibited reverse saturable non‐linear optical absorption with positive non‐linear absorption coefficient β (m/W) in the range of 10−10. The optical limiting threshold values obtained for the polymers at 81 μJ were 0.026 GW/cm2 and 0.033 GW/cm2. [ABSTRACT FROM AUTHOR]

Pure and (1–9 wt%) copper doped niobium pentoxide nanostructures were prepared by a simple solution processed method and the influence of Cu doping on structural, morphological, vibrational, linear and nonlinear optical properties of Nb 2 O 5 was analysed. X-ray diffraction unveiled that the samples possess an orthorhombic crystal structure with a notable preference for growth along the (001) plane. Raman spectroscopy and X-ray photoelectron spectroscopy provided insights into the vibrational modes and oxidation states of Nb 2 O 5 respectively, showcasing distinct alterations with varying Cu contents. Furthermore, FESEM observations highlighted the transformation of Nb 2 O 5 from agglomerated multifaceted cuboids to nanorod like structures upon adjusting the Cu concentrations. Energy dispersive X-ray spectroscopy confirmed the expected elemental makeup of the prepared samples. Absorbance pattern revealed the characteristic absorption in UV–visible range that favors the opportunity for two-photon absorption under green laser excitation. Notably, absorbance band edge experienced a red shift due to morphological changes induced by increasing Cu doping. Demonstration of reverse saturable absorption and optical limiting behaviour in Nb 2 O 5 and Cu:Nb 2 O 5 was scrutinized by open aperture Z-scan technique using Nd:YAG laser (532 nm, 9 ns, 10 Hz). Intensity dependent open aperture Z-scan shows the variation of nonlinear absorption coefficient with on-axis input intensity (1.23–4.92 GW/m2) that confirm the existence of excited state absorption involved sequential two-photon absorption. Notably, 7 wt% Cu doped Nb 2 O 5 exhibited higher two-photon absorption coefficient (2.50 × 10−10 m/W) with lower onset optical limiting threshold (1.52 × 1012 W/m2) due to synergistic effects like enhanced light-matter interaction from nanorod like morphology, copper induced band structure modifications and improved excited state absorption. These effects suggest its potential as a probable candidate for producing protective laser goggles against most delicate and commonly used nanopulsed green lasers. [Display omitted] • Cu doping impacts the morphology of Nb 2 O 5 , thereby influencing the nonlinear optical response. • 7 wt% Cu doped Nb 2 O 5 exhibited higher two-photon absorption coefficient with lower onset optical limiting threshold. • Cu doped Nb 2 O 5 can be a probable candidate for fabricating protective laser goggles against nanopulsed green lasers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation strategy of integrated W-P/MoS 2 was developed by utilizing W doping engineering induced S v. • Modulating the photoelectric properties of MoS 2 via defect and doping engineering were analyzed. • DFT investigated the defect energy levels of S v introduced by tungsten doping in MoS 2. • The nonlinear optical and OL performance of W-P/MoS 2 was obtained at femtosecond time domain. Modulating the photoelectric properties of molybdenum disulfide (MoS 2) through defect engineering and heterometal doping is crucial for its potential applications in electronic and optoelectronic devices. Herein, a comprehensive overview is provided on the advancements of two-dimensional materials with a ternary structure comprising sulfur (S), molybdenum (Mo), and tungsten (W) in the field of optoelectronic device. A ternary W-P/MoS 2 (P: direct current target power) nanomaterial was designed and synthesized using W interior doping engineering induced S vacancies. The experimental results reveal that the introduction of W metal causes lattice distortion in MoS 2 , leading to the formation of S vacancies within W-P/MoS 2. Compared to pure MoS 2 , W-P/MoS 2 with S vacancies demonstrates enhanced reverse saturable absorption and optical limiting. Density functional theory calculations suggest that the S vacancies introduced by W doping in MoS 2 introduce defect energy levels, which are believed to be the reason for the improved nonlinear optical (NLO) performance of W-P/MoS 2. Furthermore, transient absorption spectroscopy reveals the photophysical model of carrier relaxation and presents an explanation for the optimized NLO properties of W-P/MoS 2. This work provides a novel strategy for the design and synthesis of ternary transition metal dichalcogenides and modulating the NLO properties by doping transition metal-mediated vacancies. [ABSTRACT FROM AUTHOR]

• DCBB crystal was grown by solvent evaporation and it confirms monoclinic crystal system. • The band gap value is 3.84 eV. • Thermal stability was 125°C and it belongs to soft material category. • Z-scan shows reverse saturable absorption induces optical limiting behavior. New organic 2,4-dichlorobenzoic acid benzamide co-crystal (DCBB) was successfully grown using slow evaporation solution growth technique. The formation of new DCBB co-crystals was taken and their structure and crystallinity were analyzed by single crystal and powder X-ray diffraction analyses. It shows that DCBB material in monoclinic structure with centrosymmetric space group of P21/c. The different vibrations, chemical bonding and chemical configuration of the co-crystal was studied through FTIR, Raman and 1H NMR spectroscopy. Optical transmittance is the basic requirement for the nonlinear optical application with a lower cutoff wavelength of about 320 nm as well as optical band gap value E g is 3.84 eV. Photoluminescence spectrum showing two emission peaks of 403 and 550 nm by means of an excitation wavelength of 290 nm. The compound's thermal stability was up to 125 °C was analyzed by the thermal analysis. Vickers's micro hardness test was used for evaluating mechanical properties of DCBB, and the results showed that the material was classified as soft category (n = 2.54). Nonlinear optical characteristics of the sample under pulsed laser stimulation by Q-switched Nd:YAG laser with 532 nm wavelength. The presence of reverse saturable absorption peak exhibits 2-photon absorption process was confirmed by varying its intensity shows saturation intensity I S), nonlinear absorption coefficient (β) under pulse laser excitation. The optical limiting threshold determined by three different intensities were found to be 3.02×1012 (W/m2), 2.85×1012 (W/m2) and 1.44×1012 (W/m2) respectively. Theoretical investigations like density functional theory using B3LYP to calculate as well as determining non-linear optical characteristics of the DCBB complex. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The authors controlled the reduction of three graphene oxide (GO) saturable absorber (SA) thin films by controlling the exposure time under a solar simulator and afterwards, incorporated them into an Er‐doped fibre laser in order to investigate their effect on ultrashort pulse. The authors also hypothesized that the controlled reduction would result in a controlled absorption, and ultimately, a controlled modulation depth. A larger modulation depth would lead to stronger pulse shaping and shorter pulse duration. Sample A was left unreduced, whereas samples B and C were exposed for 15 and 30 min, respectively. Afterwards, their modulation depths were measured using twin‐detector method and determined to be 0.69%, 1.2% and 1.94%, respectively. When used as an SA in an Er‐doped fibre laser, the result showed pulse duration shortening; from 670 to 520 fs, as well as spectral broadening; from 4.22 to 6.73 nm. In addition, we also observed changes in repetition rate, output power and time‐bandwidth product (TBP). The result of this paper shows the feasibility of controlling the modulation depth of a GO SA and conclusively shows the effect of modulation depth on ultrashort pulse.

The linear absorption in erbium-doped fiber (EDF) contributes to its excellent role in EDF amplifiers and lasers. A nonlinear optical contribution in the absorption of EDF is responsible for optical bistable action when it is present in a laser cavity. To quantify this effect, the variation of absorption coefficient is measured at different signal powers at multiple wavelengths in the C-band for different EDF lengths, and saturable absorption parameters such as the saturation power are extracted. Then the modification in the output characteristics of EDF ring laser with change in fiber length and in the presence of self-induced saturable absorption effect within the gain medium, which leads to optical bistability, is measured. By comparing the measured parameters obtained from saturable absorption in EDF and optical bistability in EDF ring laser, we estimated the length of the gain medium which acts as the saturable absorber inside the cavity of the laser. This is useful in constructing bistable lasers with optimized conditions. The temporal evolution of cavity loss and gain with the intra-cavity power and up- and down-thresholds helps in understanding why the down-threshold will be lesser than the up-threshold in bistable laser systems. [ABSTRACT FROM AUTHOR]

We develop the Z-scan technique on a saturable absorber under the excitation of radially polarized beams. It is shown that the sensitivity of the Z-scan measurements on a saturable absorber using radially polarized beams has the great improvement compared with those using the scalar light beams such as Gaussian beams, Laguerre-Gaussian beams, and top-hat beams. As the experimental evidence, we investigate the saturable absorption properties of layered WS2 nanosheets in aqueous suspension by performing the radially polarized-beam Z-scan measurements with femtosecond laser pulses in the near infrared region. [ABSTRACT FROM AUTHOR]

Fully microscopic many-body calculations are used to study the influence of strong sub-picosecond pulses on the carrier distributions and corresponding optical response in saturable absorbers used for mode-locking--semiconductor (quantum well) saturable absorber mirrors (SESAMs) and single layer graphene based saturable absorber mirrors (GSAMs). Unlike in GSAMs, the saturation fluence and recovery time in SESAMs show a strong spectral dependence. While the saturation fluence in the SESAM is minimal at the excitonic bandgap, the optimal recovery time and least pulse distortion due to group delay dispersion are found for excitation higher in the first subband. For excitation near the SESAM bandgap, the saturation fluence is about one tenth of that in the GSAM. At energies above the bandgap, the fluences in both systems become similar. A strong dependence of the saturation fluence on the pulse width in both systems is caused by carrier relaxation during the pulse. The recovery time in graphene is found to be about two to four times faster than that in the SESAMs. The occurrence of negative differential transmission in graphene is shown to be caused by dopant related carriers. In SESAMs, a negative differential transmission is found when exciting below the excitonic resonance where excitation induced dephasing leads to an enhancement of the absorption. Comparisons of the simulation data to the experiment show a very good quantitative agreement. [ABSTRACT FROM AUTHOR]

Nonlinear optical absorption and optical power limiting properties of Fe2O3 hexagonal nanomorphotype are investigated using open aperture Z-scan technique with the 5 ns and 100 fs laser pulses, at 532nm and 800 nm excitation domains. At relatively low pulse energies (below 5 μJ), sample shows saturable absorption (SA), but on going to the higher energies an interesting switchover from saturable absorption to effective two photon absorption is observed in both excitation domains. The magnitude of effective two photon absorption coefficients is calculated to be in the range of 10-10 m/W for nanosecond and 10-15 m/W for femtosecond laser pulse energies, respectively. XRD and TEM study reveals the polycrystalline nature, hexagonal morphology, and size of the nanostructure. The luminescence emission property is examined by photoluminescence spectroscopy (PL). It is found that some strange features exist in the luminescence spectra that are consistent with the nanoparticles size distribution. The PL emission lines are explained as originated from various optical band edges due to the size induced quantum confinement and band gap resonant PL absorption/emission behavior of semiconductor nanostructures. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2) is a nonlinear optical material with graphene-like structure. In order to further improve the nonlinear optical performance of MoS 2 and expand the application fields of MoS 2 , we report a simple in-situ self-growth method to functionalize MoS 2 nanosheets with metal-organic framework (MOF) for the first time to pursuit excellent reverse saturable absorption performance and optical limiting performance. Firstly, defective MoS 2 nanosheets was obtained by chemical etching with H 2 O 2 and cysteamine was inserted into the sulfur vacancies under ultrasound to obtain MoS 2 –NH 2. Then 5,10,15,20-Tetra (4-carbomethoxyphenyl) porphyrin (TCPP) as MOF active growth sites were grafted on MoS 2 –NH 2 by amido linkage to obtain MoS 2 -TCPP in mild conditions. Finally, flower-like porphyrin-based CuMOF was grown on MoS 2 -TCPP by solvothermal method to obtain MoS 2 -CuMOF with stable structure. The third order nonlinear optical performance of MoS 2 -CuMOF were studied by Z-scan technique. It was found that the third order nonlinear absorption coefficient of MoS 2 -CuMOF was significantly improved compared with MoS 2. Under the same energy of laser irradiation, the third order nonlinear absorption coefficient of MoS 2 -CuMOF nanocomposite in solution was 6 × 10−10 m/W about 2.3 times of the pristine MoS 2 (2.6 × 10−10 m/W). After blending the above materials with polymethyl methacrylate (PMMA) to prepare a solid device, the third order nonlinear absorption coefficient of MoS 2 -CuMOF/PMMA was 18 × 10−10 m/W about 3.6 times of the MoS 2 /PMMA (5 × 10−10 m/W). And MoS 2 -CuMOF/PMMA had better optical limiting ability than MoS 2 /PMMA. The significant improvement in the performance of the composites can be attributed to the energy transfer between MoS 2 and CuMOF, and porphyrin aggregation was inhibited by PMMA after the preparation of devices. Energy transfer can be proved by fluorescence spectroscopy. This work not only provided an example for the covalent functionalization of MoS 2 , but also offered a new method for designing materials with excellent nonlinear optical performance. [Display omitted] • MOF was grown on MoS 2 by a simple in-situ self-growth method to prepare MoS 2 -CuMOF. • MoS 2 -CuMOF had larger third-order nonlinear absorption coefficient. • MoS 2 -CuMOF had excellent properties through energy transfer between components. • MoS 2 -CuMOF can be prepared into PMMA-based optical limiter. [ABSTRACT FROM AUTHOR]

High pressure-high temperature (HP-HT) nanodiamonds and detonation nanodiamonds have unique optical properties and are promising materials for various applications in photonics. In this work, for the first time, comparative studies of the nonlinear optical properties of aqueous suspensions of HP-HT and detonation nanodiamonds under femtosecond laser excitation are performed. Using the z-scan technique, it was found that for the same laser pulse parameters HP-HT nanodiamonds exhibited optical limiting due to two-photon absorption while detonation nanodiamonds exhibited saturable absorption accompanied by short-term optical bleaching, revealing the different electronic-gap structures of the two types of nanodiamonds. The saturable absorption properties of detonation nanodiamonds are characterized by determining the saturable and non-saturable absorption coefficients, the saturation intensity, and the ratio of saturable to non-saturable losses. The nonlinear absorption in HP-HT nanodiamonds is described with the nonlinear absorption coefficient that decreases with decreasing concentration of nanoparticles linearly. The results obtained show the possibility of using aqueous suspensions of nanodiamonds for saturable absorption and optical limiting applications. [ABSTRACT FROM AUTHOR]

Happach, M., +, JQE Feb. 2020 2000107 InP Membrane on Silicon (IMOS) Photonics. van der Tol, J.J.G.M., +, JQE Feb. 2020 6300107 JQE Special Virtual Issue Dedicated to the 21 st European Conference on Integrated Optics (ECIO). Arefin, R., +, JQE Aug. 2020 6300309 InP Membrane on Silicon (IMOS) Photonics. van der Tol, J.J.G.M., +, JQE Feb. 2020 6300107 Sensitivity Enhancement Factor for Gain-Assisted Cavity Enhanced Spectroscopy. Tong, Y., +, JQE Feb. 2020 8400107 Special issues and sections JQE Special Virtual Issue Dedicated to the 21 st European Conference on Integrated Optics (ECIO). Arefin, R., +, JQE Aug. 2020 6300309 InP Membrane on Silicon (IMOS) Photonics. van der Tol, J.J.G.M., +, JQE Feb. 2020 6300107 Micron and Nano-Dimensioned Silicon LEDs Emitting at 650 and 750-850 nm Wavelengths in Standard Si Integrated Circuitry. Hamad, W., +, JQE Feb. 2020 2400111 InP Membrane on Silicon (IMOS) Photonics. van der Tol, J.J.G.M., +, JQE Feb. 2020 6300107 MEMS-Enabled Silicon Photonic Integrated Devices and Circuits. [Extracted from the article]

Recent advances in the practical applications of metallophthalocyanines (MPcs) in different technological fields have stimulated us to design and synthesize a new asymmetric AB3-type trimeric zinc(II)-phthalocyanine (1). This bulky and high molecular weight compound was characterized by elemental analysis, 1H, 13C DEPT, and 1H-1H NOESY NMR, HR MALDI-TOF mass spectrometry, UV-vis, and FT-IR (ATR) techniques. In-depth electrochemical studies show that 1 displays quasi-reversible three one-electron reductions and two one- or two-electron oxidation processes, rather than any redox processes including the transfer of three-electrons in one-step. Besides this, in situ spectroelectrochemical measurements suggest the good application potential of 1 as an electrochromic material in display technologies. A study of the nonlinear optical properties (NLOs) of 1 reveals that the poly(methylmethacrylate) (PMMA) composite film displays a much larger nonlinear absorption coefficient and a lower saturable absorption threshold for optical limiting when compared to the same Pc molecules in solution. Ultrafast transient absorption measurements reveal the intersystem crossing mechanism. Density functional theory (DFT) was used for the geometry optimizations and time dependent-DFT (TD-DFT) for HOMO/LUMO energies and electronic transitions for 1. [ABSTRACT FROM AUTHOR]

This study experimentally demonstrates a Q‐switched fibre laser using a new tungsten tri‐oxide (WO3)‐based saturable absorber (SA). Using the drop and casting approach, we managed to prepare a thin film that contained WO3 powders in polyvinyl alcohol. A small bit of the film was used to form an SA which was placed in a ytterbium‐doped fibre laser cavity to generate a Q‐switched laser. The laser, operating at 1063.78 nm, was realised at the threshold pump power of 85 mW with a repetition rate of 23.87 kHz and a pulse width of 5.56 μs. At the pump power of 147 mW, the laser produced the maximum pulse energy of 625 nJ, signal‐to‐noise ratio of 59 dB, the repetition rate of 39.79 kHz and pulse width of 2.37 μs. To the best of our knowledge, this is the first demonstration of using WO3 SA to generate the pulse laser in the 1 μm region. [ABSTRACT FROM AUTHOR]

The authors experimentally demonstrated the generation of mode‐locked pulses from all‐fibre erbium‐doped fibre laser cavity by using organic material, Alq3, as a saturable absorber (SA). The SA film was integrated into a ring fibre laser cavity to act as a mode‐locker. A mode‐locking operation was achieved in three different experiments with pulse width/repetition rate of 1.26 ps/3.36 MHz, 970 fs/3.36 MHz and 820 fs/4.9 MHz by using cavity length/optical coupler (OC) of 61.5 m/80:20 OC, 61.5 m /95:5 OC and 42 m/80:20 OC, respectively. All the experiments produced a soliton and a very stable mode‐locking operation at central wavelength of ∼1561 nm. The experiments confirmed that organic material can readily be used as SA for a mode‐locked operation in the 1.5 μm region. This demonstration might shed new insights into the potentials and techniques for developing ultrafast fibre lasers by using organic materials as SAs. [ABSTRACT FROM AUTHOR]

Chromophores in azo dyes are optically active and play an important role in modifying the optical nonlinear properties. Methyl orange (MO), an azo dye, has been chosen to dope with l‐arginine monohydrochloride (LAHCl), in order to tune the nonlinear optical properties. Pristine and MO doped LAHCl single crystals are grown by slow solvent evaporation method at ambient conditions. The grown crystals are confirmed by powder X‐ray diffraction and Fourier transform infrared studies. The crystals are subjected to linear and nonlinear optical characterizations. Decrease in optical band gap with increase in refractive index and birefringence are attributed to the increase in net macro‐polarizability of the doped LAHCl. Both pristine and MO doped crystals exhibit reverse saturable absorption (RSA) in Z‐scan measurements. The samples show optical limiting behavior under laser irradiation at 650 nm. The chromophore of MO has a significant role in enhancing RSA and optical limiting behavior of LAHCl. [ABSTRACT FROM AUTHOR]

We demonstrate herein a passively Q-switched continuous wave (CW) Nd:YVO4 laser at 1064 nm with gold nanocages (GNCs) as the saturable absorber (SA). The performance has been systematically investigated using two output couplers with transmittance of 4.0 and 10.8%. The shortest pulse width is 143 to 240 ns, the repetition rate is 440 to 467 kHz and the maximum average output power is 211 to 372 mW, depending on the transmittance of the output coupler. [ABSTRACT FROM AUTHOR]

Generation and control of the reverse saturable absorption (RSA) and optical limiting (OL) are investigated in a four-level Y-type quantum system. It is demonstrated that the applied laser fields induce the RSA and it can be coherently controlled by either intensity or frequency of the applied laser fields. The effect of the static magnetic field on the induced RSA is studied and we obtain that it has a constructive role in determining the intensity range in which the OL is established in the system. In addition, we find that the transmission of the suggested optical limiter can be decreased either by increasing the length of the medium or by getting the atomic system denser. Finally, the Z-scan technique is presented to confirm our theoretical results. The proposed scheme can be used in designing the coherent optical limiters with controllable threshold and intensity range of the OL. [ABSTRACT FROM AUTHOR]

Layered transitional metal dichalcogenides (TMDs) are drawing significant attentions for the applications of optics and optoelectronics. To achieve optimal performances of functional devices, precisely controlled doping engineering of 2D TMDs alloys has provided a reasonable approach to tailor their physical and chemical properties. By the chemical vapor transport (CVT) method and liquid phase exfoliation technique, in this work, we synthesized WS1.76Te0.24 saturable absorber (SA) which exhibited high-performance of nonlinear optics. The nonlinear saturable absorption of the WS1.76Te0.24 SA was also measured by the open aperture Z-scan technique. Compared to that of the binary component WS2 and WTe2, WS1.76Te0.24 SA has shown 4 times deeper modulation depth, 28% lower saturable intensity and a much faster recovery time of 3.8 ps. The passively Q-switched laser based on WS1.76Te0.24 was more efficient, with pulse duration narrowed to 18%, threshold decreased to 28% and output power enlarged by 200%. The promising findings can provide a method to optimize performances of functional devices by doping engineering. [ABSTRACT FROM AUTHOR]

The study of nonlinear absorption has potential applications as saturable absorption and optical limiting character in scientific and engineering technology. In this work, we report on the Gaussian vortex beam z-scan to study the saturable absorption in the two-level model. For a given material and laser beam parameters, even though vortex beam shows less saturable absorption nature than the conventional Gaussian beam but not much appreciated. The open aperture z-scan peak is narrower for Gaussian vortex beam as compared with Gaussian beam. Also, in the presence of pico- and femto-second laser pulses, the central dark core of Gaussian vortex beam can provide a stable and accurate z-scan profile with avoiding thermal and other nonlinear optical effects at the beam waist of z-scan in the saturable absorber characterization. With including above mentioned points, we have shown how the Gaussian vortex z-scan is superior to the conventional Gaussian beam z-scan for saturable absorber characterization. Though discussed for single-photon absorption, it may extend to multi-photon absorption. [ABSTRACT FROM AUTHOR]

A passively Q‐switched erbium‐doped fibre laser was demonstrated by using tris‐(8‐hydroxyquinoline)aluminium (Alq3) organic material as a passive saturable absorber (SA). The SA was fabricated by a drop casting technique at room temperature and incorporated into a laser cavity by inserting it between two optical fibre ferrules. The Q‐switched fibre laser operates at a centre wavelength of 1559 nm with a full‐width half maximum of 1 nm. The generated pulse train is stable and has a pulse width decreased from 6.65 to 1.2 µs and the pulse repetition rate increased from 31.65 to 144.5 kHz as the pump power increased from 20 to 122 mW. The maximum pulse energy obtained is 63.89 nJ. This work indicates that the Alq3 as SA has a great potential to be utilised for pulsed laser generation. To the best of the authors' knowledge, this is the first time an organic material is utilised as a SA device for generating a stable Q‐switched laser pulse. [ABSTRACT FROM AUTHOR]

Abstract Proton transfer complex of Picolinium Tartrate Monohydrate (PTM) was synthesized and structure was confirmed by single crystal X-ray diffraction technique and 1H &13C NMR analysis. The molecular structural investigations by Hirshfeld surface, NBO and AIM analyses reveals that the picolinium cation and tartrate anion are interconnected through water molecule via strong N+-H ....O− and O+-H...O− hydrogen bonds. The harmonic wavenumber is computed with DFT/B3LYP/6–31++G(d,p) method and compared to the experimental FT-IR and FT-Raman with the help of Normal Coordinate Analysis (NCA) following scaled quantum mechanical force field methodology results the red shifting of N H and O H stretching vibrations due to the proton transfer. The solid state and solvent assisted photoluminescence spectrum shows that luminescence is at the blue region with appreciable lifetime. Third order nonlinear optical properties like self-defocusing, saturable absorption and optical limiting at 532 nm are identified by Z-scan analysis. The field dependent nature of first and second order hyperpolarizabilities and luminescence properties suggest that PTM crystal is a potential candidate for non-linear optical and OLED applications. The correlation between proton transfer, hole-electron transport and charge transfer interaction explores in this study. Graphical abstract Image 1 Highlights • Proton transfer mechanism within the molecule enhances NLO activity: investigates with experimentally and theoretically. • Field dependent First & Second order Hyperpolarizability enhanced compared to their pristine molecules. • Optical absorption and solvent assisted photoluminescence spectra revels its applications for blue light emitting devices. • Z-scan studies confirm third order nonlinear optical property. [ABSTRACT FROM AUTHOR]

Highlights • The iron oxide nanoparticles is synthesized via chemical co-precipitation method. • The self-Q-switched operation can be presented with the absence of polarizer controller. • The shortest pulse duration is 896 ns. Abstract All fiber Q-switched laser with its advantages of high energy, compact structure and high stability boosted the growing demand in many applications. We synthesized the regular iron oxide nanoparticles (IONP) in size of 12–15 nm via the chemical co-precipitation method. Using the IONP-PVA film as SA, high stable polarization-insensitive Er-doped Q-switched fiber laser was demonstrated. The prepared IONP SA exhibits saturation intensity of 13.44 MW/cm2. The shortest pulse duration was achieved to be 896 ns and the single pulse energy was up to 100 nJ with the maximum pump power of 500 mW. In particular, the polarization controller is unnecessary in our experiments, so the ring cavity can be compacted into a smaller size with 80 dB signal-to-noise ratio for the output pulse sequence. Such a compact, low cost and high stability Q-switched laser maybe expected to have the more extensive application prospect. [ABSTRACT FROM AUTHOR]

Highlights • Two cavity geometries are proposed for SESAM passively modulated Nd:YVO 4 laser. • Stable mode locking is achieved for the cavity with stronger focusing on the SESAM. • Nd:YVO 4 mode locked (ML) laser performance is analyzed for two distinct SESAMs. • SESAM parameters influence the ML laser performance and operation regime. • 12.5 ps pulses are yielded, at 158 MHz repetition rate and 13.4 nJ pulse energy. Abstract In this work we report on the output performances of a Nd:YVO 4 picosecond (ps) laser oscillator that was passively modulated by different semiconductor saturable absorber mirrors (SESAMs). The laser emission characteristics are given for SESAM used in Z-type and W-type cavities under similar pumping conditions. Q-switch mode-locking (QML) regime was obtained in the Z-type resonator whereas the W-type oscillator enabled stable mode-locking (ML) operation. For the W-type cavity ML performances are reported for two SESAMs with distinct parameters. Thus the use of a SESAM with 10 ps long recovery time allowed ML operation with pulses of 11.1 nJ energy and 15 ps duration (0.74 kW peak power) at 158 MHz repetition rate; the average power at 1.06 μm was 1.75 W for 5.17 W pump power at 809 nm. Employing a second SESAM with 0.5 ps short recovery time, the Nd:YVO 4 laser yielded pulses with increased 13.4 nJ pulse energy and shorter, 12.5 ps, duration (1.1 kW peak power) at 158 MHz repetition rate, corresponding to 2.11 W average power; the pump power was 5.09 W. The results highlight the significant role of the SESAM parameters as well as of the implemented cavity design for the construction of a ps laser source of high performance. [ABSTRACT FROM AUTHOR]

Highlights • Thermal modified g-C 3 N 4 samples with diverse etching temperatures were fabricated. • Temperature-depended photoelectric properties of modified g-C 3 N 4 were reported. • A nanosecond pulse laser at 1 μm was obtained by using modified g-C 3 N 4 as SA. Abstract A facile thermal modification method based on thermal oxidation etching was successfully developed as an effective way of improving the photoelectric properties of graphite carbon nitride (g-C 3 N 4), and the as-prepared modified g-C 3 N 4 was employed as the saturable absorber (SA) for a passively Q-switched Nd:LLF laser at 1.06 μm to improve the laser performance. Under the incident pump power of 7.68 W, a pulsed laser output with 110 ns pulse width at 95.5 kHz pulse repetition rate was achieved, which was the narrowest among the g-C 3 N 4 materials used as SAs around 1 μm. [ABSTRACT FROM AUTHOR]

Highlights • A novel SA for generating giant pulse laser at ∼3 μm. • Easy to fabricate for the SA. • Compact structure. • High repetition frequency and narrow pulse width. Abstract We demonstrate a passively Q-switched Er3+: ZBLAN fiber laser using gold nanobipyramids (gold-NBPs) as a saturable absorber. The gold nanobipyramids aggregate film is formed by casting gold nanobipyramids aqueous sample onto an Au-coated mirror and hot inducing rapid drying in the oven with a temperature of 100 °C. A reflection-type saturable absorber mirror (SAM) is fabricated and inserted linear laser cavity of Er3+: ZBLAN fiber laser. The maximum average output power of 485 mW is obtained with the pulse width 612 ns and the pulse repetition rate 130 kHz. The corresponding peak power and pulse energy is 6.1 W and 3.7 μJ respectively. [ABSTRACT FROM AUTHOR]

Abstract We report on a highly efficient, compact, passively Q-switched Yb:KLu(WO 4) 2 laser, with few-layer MoS 2 or WS 2 acting as saturable absorber. A maximum output power of 2.45 W was generated at a repetition rate of 2.52 MHz, with 6.49 W of pump power absorbed in passively Q-switched operation induced by MoS 2 ; the largest pulse energy, shortest duration, and highest peak power were, respectively, 1.27 μ J, 43 ns, and 29.5 W. With WS 2 as saturable absorber, the output power attainable in stable Q-switched operation was 1.87 W, produced with an optical-to-optical efficiency of 37% and a slope efficiency of 71%. The minimum pulse duration obtained was 39 ns; while the largest pulse energy and highest peak power were 1.19 μ J and 30.5 W. Highlights • Power scaling to 2-W level is demonstrated for Yb:KLuW/MoS 2 (WS 2) laser. • Pulse repetition rates up to 2.5 MHz are reached in stable passively Q-switched action. • Shortest pulse duration of 39 ns is achieved. [ABSTRACT FROM AUTHOR]

Abstract Nonlinear optical properties, vibrational features, optical and electronic properties of organic dye Disodium 8-Hydroxy-5,7-Dinitro-2-Naphthalenesulfonate Hydrate have been studied. Spectral and electronic properties were studied by FT-IR, FT-Raman and UV–visible spectroscopic technique combined with density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods respectively. The intramolecular charge transfer interactions leading to nonlinear optical response have been analyzed by natural bond orbital analysis. The kinetic stability, chemical reactivity and electrophilicity index were studied by frontier molecular orbital analysis. The first- and second hyperpolarizabilities were calculated at DFT level using B3LYP and CAM-B3LYP hybrid functional. The third-order nonlinear optical performance of the compound have been investigated experimentally by open and closed aperture Z-scan techniques. Z-scan measurements were performed using Q-switched Nd: YAG laser with 5 ns pulses at 532 nm with different dye concentrations and intensities. The Z-scan results confirm the sign of nonlinear absorption and refraction are positive. The optical limiting threshold and laser damage threshold were measured. The obtained results promote the title compound can be considered as a promising candidate for developing future optoelectronic and photonic devices. Graphical abstract Image 1 Highlights • Experimental spectroscopic characterization has been compared with theoretical DFT/TD-DFT results. • Second order hyperpolarizability was computed theoretically and compared with the experimental result. • Third-order nonlinear optical parameters were measured at different concentrations and intensities using the Z-scan technique. • Optical limiting property and Laser damage threshold were studied. [ABSTRACT FROM AUTHOR]

Abstract A quality saturable absorber for the integration of a practical laser product with long-term stability and sustainability is of utmost importance to be delivered to end-users. Graphene/polymethyl-methacrylate saturable absorber is proposed with the advantage of gapless material characteristic for ultra-broadband wavelength operation. This saturable absorber possesses stability over 24-hour continuous mode-locked laser operation at 105.2 mW pump power, as well as sustainability over four consecutive observation weeks with the preservation of 670 fs pulse duration within the experimental period. Last but not least, the proposed saturable absorber shows excellent long-term stability and sustainability for the formulation of practical seed mode-locked fiber laser source. Highlights • 670 fs mode-locked laser generated with graphene/PMMA saturable absorber. • High stability saturable absorber over 24-hours continuous mode-locked laser operation. • High sustainability saturable absorber with constant pulse duration over four consecutive weeks. [ABSTRACT FROM AUTHOR]

We report on the response of graphene to high intensity mid-IR radiation and show that graphene exhibits saturable absorption and significant two-photon absorption in the spectral region of 1.55 μm to 3.50 μm (0.35 eV to 0.80 eV). We find that the effective modulation depth of multilayer graphene is limited by two-photon absorption, which will affect its performance as a laser mode-locking element. The measured saturation intensities of femtosecond pulses were found to depend on the third power of photon energy when we combined our results with others reported in the literature, while those of longer pulses were found to have a square root dependence. [ABSTRACT FROM AUTHOR]

Abstract Wet-chemical sol-gel spin coating technique was considered to fabricate ZnO thin films on bare glass substrates with different thickness values (30 nm, 90 nm, 110 nm, 150 nm). The XRD reflections showed a transition from semi-polar crystal growth orientation to polar crystal growth orientation when the thickness was reduced to 30 nm. The nonlinear characteristics of prepared nano-films were quantized by performing open aperture and closed aperture Z-scan measurements under a continuous wavelength regime. The open aperture Z-scan transmittance curves showed a remarkable transition from normalized valley to normalized peak in 30 nm thick ZnO film. The presence of normalized valley and peak were attributed to reverse saturable absorption (RSA) and saturable absorption (SA) behavior respectively. The RSA behavior was attributed to well known two-photon absorption (TPA) mechanisms and the SA behavior was due to the reduction in electron-hole wave function overlapping along c-axis. The closed aperture Z-scan measurement of 30 nm thick ZnO film revealed the violation of two parabolic band (TPB) and Kramer-Kronig relations by exhibiting self-focusing mechanism. The self-focusing mechanism was attributed to thermal effects due to the smaller thickness of ZnO. However, self-defocusing behavior was observed in 90 nm, 110 nm, and 150 nm thick ZnO films. Graphical abstract Image 1 Highlights • ZnO thin films of different thickness values are prepared using sol-gel spin coating technique. • Dominant single c-axis oriented ZnO exhibit SA behavior. • RSA is observed in semipolar crystal growth oriented ZnO films. • Thermo-optic effects are observed under continuous wavelength laser. [ABSTRACT FROM AUTHOR]

We demonstrate the generation of Q-switching pulse train in thulium-doped fiber laser (TDFL) cavity by employing titanium-based saturable absorber (Ti-SA). The Ti-SA was fabricated by depositing titanium particles molecules using electron beam evaporation on the surface of a polyvinyl alcohol (PVA) film. Subsequently, stable Q-switched pulses were obtained within the 1,552 nm pump power range from 272.1 to 467 mW, with repetition rate tuned from 21.8  to 39.1 kHz. At the maximum pump power, the TDFL showed that the pulse duration of 2.22 μs and the maximum pulse energy of 124 nJ. [ABSTRACT FROM AUTHOR]

Abstract The feasibility of using rhenium diselenide (ReSe 2) as the saturable absorber for the broadband passively Q-switched (PQS) thulium solid-state lasers was demonstrated in this paper. In the short wavelength of 2 μm region, the combination of Tm:YLF and ReSe 2 was used to achieve the PQS operation with multi-wavelength around 1900 nm. A maximum average output power of 862 mw, a shortest pulse width of 527.9 ns and a repetition rate of 54 kHz were obtained. In the long wavelength of 2 μm region, a ReSe 2 -based PQS multi-wavelength Tm:Y 2 O 3 laser around 2050 nm was realized, generating a maximum average output power of 1.04 W, a shortest pulse width of 727 ns and a repetition rate of 106 kHz. The output performance of the ReSe 2 -based pulsed laser is competitive among these PQS thulium solid-state lasers using the emerging two-dimensional materials as SAs, indicating that ReSe 2 is a promising broadband SA for the 2 μm solid-state lasers. Highlights • The results demonstrate the possibility of generating 2 μm nanosecond pulses by using ReSe 2 as broadband saturable absorbers. • The ReSe 2 -based output mirror combines the function of passive Q-switching and output coupling. • The output performance of the ReSe2 passively Q-switched Tm solid-state lasers is competitive. [ABSTRACT FROM AUTHOR]

Exploring new saturable absorber (SA) materials is important for the advancement fibre laser technology especially in the improving the performance of Q-switched and mode-locked fiber lasers, which have tremendous applications in areas such as material processing, telecommunications, biomedical imaging, and scientific research. Here, we prepared a layer of Neodymium Oxide (Nd 2 O 3) film as a nonlinear optical device to obtain the Q-switched and mode-locked pulses in the Erbium-doped fiber laser (EDFL) cavity. The developed Nd 2 O 3 film recorded excellent optical properties with the saturable absorption of 2.8%, saturation intensity of 0.8 MW /cm2 and non-saturable loss of 59.0%. By integrating the Nd 2 O 3 film into a simple ring EDFL's cavity, a stable and robust Q-switched laser operating at 1558 nm was realized as the pump power is set between 45 and 92 mW. The average output power improved from 4.70 to 9.57 mW as the strength of the pumping was raised from 45 to 92 mW. The repetition rate and pulse width are tunable from 71 to 89 kHz and 3.48–2.56 µs, respectively as the pump power is escalated within the same range. The fundamental frequency of electrical signal exhibits signal-to-noise ratio (SNR) of 62 dB and this signifies the excellent stability of the Q-switching operation. In an extended EDFL cavity, the Nd 2 O 3 SA can produce a mode-locked soliton pulse operating at 1559.29 nm. The laser run at repetition rate of 1.89 MHz and pulse duration of 3.73 ps while recorded the highest peak power of 1.7 kW at pump power of 97.62 mW. [ABSTRACT FROM AUTHOR]

Highlights • A 1.3 μm Q-switched laser based on ReS 2 saturable absorber was demonstrated. • The performance of the passive Q-switching laser has been investigated. • The average output power of 78 mW and the pulse width of 403 ns were obtained. Abstract A novel two-dimensional saturable absorber, few-layered rhenium disulfide (ReS 2), was prepared by liquid phase exfoliation method successfully. Moreover, for the first time, it was successfully employed in passively Q-switched bulk Nd:YAG lasers at 1.3 μm in this paper. The maximum average output power of 78 mW was obtained with the shortest pulse width of 403 ns and the repetition rate of 214 kHz, corresponding to single pulse energy and pulse peak power of 0.42 µJ and 0.9 W, respectively. The results indicate that ReS 2 has the potential to be used for passive Q-switching laser generation at 1.3 μm wavelength. [ABSTRACT FROM AUTHOR]

Highlights • All-fiber 2 μm Thulium-doped mode-locked fiber laser based on MoSe 2 -saturable absorber. • A MoSe 2 -polyvinyl alcohol saturable absorber film is fabricated by liquid phase exfoliation (LPE) as effective saturable absorber (SA). • The laser is centered at 1943.35 nm with a 3 dB bandwidth of 4.38 nm and a pulse duration of 980 fs. Abstract We demonstrate an all-fiber passive mode-locking laser operating in the 2 μm region that is implemented using a MoSe 2 -based saturable absorber (SA). A MoSe 2 -polyvinyl alcohol (PVA) SA is prepared with a modulation depth of 4.98%, a saturation intensity of 168.6 MW/cm2 and a nonsaturable loss of 29.6%. When the MoSe 2 -PVA SA was inserted into the fiber laser cavity, highly stable self-starting soliton pulse trains were generated with a center wavelength of 1943.35 nm and a 3 dB bandwidth of 4.38 nm. The pulse waveform has a sech2 profile with pulse duration of 980 fs. The fundamental repetition rate is 23.53 MHz and the signal-to-background ratio of the fundamental frequency ranges up to 65 dB. The production of stable and robust pulses using this laser indicates that the MoSe 2 -PVA SA is suitable for generation of 2 μm femtosecond ultrashort pulses. [ABSTRACT FROM AUTHOR]

Highlights • The GaSe saturable absorber is formed and characterized. • The mode-locked Er-doped fiber laser with GaSe saturable absorber is demonstrated. • A GaSe-PVA based saturable absorber (SA) is prepared by liquid-phase stripping method. Abstract A GaSe-PVA based saturable absorber (SA) is prepared by liquid-phase stripping method. The linear and nonlinear transmission spectrum, AFM, SEM and Raman spectrum are used to characterize the SA, the modulation depth of 6.4% and the saturation intensity of 72 MW/cm2 indicated that the GaSe nanosheets can be employed as SA for mode-locked (ML) operation in Er-doped fiber laser (EDFL). The passively mode-locked operation with the output power of 29.1 mW, pulse width of 4.3 ps and repetition rate of 8.849 MHz can be obtained by GaSe-PVA based SA. [ABSTRACT FROM AUTHOR]

An advanced full-wave time-domain numerical model for reverse saturable absorption (RSA) is presented and verified. Rate equations describing atomic relaxations and excitation dynamics are coupled to the Maxwell equations by using a Lorentzian oscillator, which models the kinetics-dependent light–matter interactions. The presented novel technique provides a versatile multiphysics framework for designing complex structures and integrating diverse material models that were not previously possible. The multiphysics framework allows capturing the behavior of the RSA materials embedded in artificial photonic nanostructures that cannot be analyzed with established techniques such as the Beer–Lambert law. To showcase the importance of the full-wave RSA analysis coupled to carrier kinetics, we analyze two plasmon-enhanced optical limiters: a metal grating and a Fabry–Perot cavity-like structure where we decrease the unenhanced limiter threshold by a factor of 3 and 13, respectively. This is a promising approach for developing RSA devices operating at reduced illumination levels and thereby significantly expanding their area of applicability to areas such as protective eyewear and automatically dimmed windows. By exploring the dynamic behavior of a given RSA system, this framework will provide critical insights into the design of transformative photonic devices and their complementary optical characterization, and serve as an invaluable utility for guiding the development of synthetic absorbing materials. We believe that our multiphysics models are crucial enabling tools that lay a necessary foundation for the numerical machinery required for the realization and optimization of optical limiting and all-optical switching systems. [ABSTRACT FROM AUTHOR]

In this paper, we fabricated a PMMA sandwiched Bi2Te3 self-assembly layer as a saturable absorber device, which was used as a passive mode locker for ultrafast pulse generation at the telecommunication band. Nanosheets of Bi2Te3 as a bulk topological insulator were successfully synthesized through a solvothermal treatment and self-assemble method to form a thin film at a water-air interface. In order to transfer the Bi2Te3 self-assembly layer to the optical fiber end, we design a construction of two PMMA layers sandwiched self-assembly layer. By incorporating this saturable absorber into an erbium-doped fiber laser, femtosecond mode-locking operation was experimentally demonstrated. The output pulse width is about 505 fs. Our results indicate that PMMA sandwiched topological insulator layer structure could be an improvement technology in traditional PMMA transfer method and could be used as a long-term stable saturable absorber for the passively mode locking lasers. [ABSTRACT FROM AUTHOR]

Abstract We firstly used THz-TDS to characterize the 2D-material (SnSe 2) saturable absorber (SA) with nondestructive and high resolution. In addition, the application of the SnSe 2 SA for dual-wavelength Q-switched laser is demonstrated. The highest dual-wavelength output power of 438 mW with the optical to optical efficiency of 9.7%. The minimum pulse width is 237 ns at the repetition rate of 72 kHz can be obtained. This results indicate that the THz transmission spectrum could be used to characterize the SAs and the tin diselenide SA also shows good features used in dual-wavelength solid state lasers. [ABSTRACT FROM AUTHOR]

Abstract Sb 2 Te 3 thin films are very promising candidates for nonlinear optics and several applications including super-resolution and nano-photoinscription. This work aims to offer a detailed study of the preparation of the thin films and their nonlinear optical properties under nanosecond laser excitation. Thin Sb 2 Te 3 films have been deposited by the electron beam deposition technique. The films have been protected by a thin silica layer, then annealed in order to enhance their nonlinearities by material crystallization. The annealing has been optimized by simultaneously recording the X-Ray diffraction diagrams. After this optimization, the annealing could be safely performed by heating in an oven. The nonlinear optical properties of the Sb 2 Te 3 thin films have been studied by means of the Z-scan technique employing 11 ns laser pulses at 1064 nm and 532 nm. High nonlinear absorption has been found showing the possibility to employ these materials for super-resolution, mode-locking and other applications. Highlights • Structure optimization of Sb 2 Te 3 thin films to enhance the optical nonlinearities. • Significant nonlinear absorption has been detected by means of the Z-scan technique. • The samples can be used for super-resolution at the visible and the NIR. [ABSTRACT FROM AUTHOR]

Nonlinear optical effect such as saturable absorption (SA) and reverse saturable absorption (RSA) play a key role for all-optical logic gates, in which transition between them is a challenging issue for the optoelectronic applications. Herein, we find MoTe 2 nano-films fabricated with liquid-phase exfoliation and a vacuum filtration method which demonstrate both SA and RSA with different thicknesses and pump intensity. The SA nonlinear optical susceptibility for thick film (100 nm) is Imχ (3)  ∼ 10 −11 esu. However, the thin film (30 nm) exhibited RSA with the Imχ (3) as high as ∼9.96 × 10 −11 esu. The different nonlinear optical response with the thickness is due to the interlayer coupling effect. Under high pump intensity, the thick MoTe 2 film also demonstrates transition from SA to RSA. The four energy-level model is employed to analyze the competition between the ground-state and excited-state absorption. We found that the conversion of SA to RSA depends not only on pump intensity but also on the absorption cross-section and transition probability between energy level. The transition properties of SA and RSA for MoTe 2 films can be used in all-optical logic gates, fast optical switch, optical limiter, mode storage and so on. [ABSTRACT FROM AUTHOR]

A Ho:SSO crystal was employed as an efficient saturable absorber Q switch for the pulsed Ho:YAG laser for the first time. The characteristics of the passive Q-switch Ho:YAG laser were studied with different incident pump power and different laser energy density around the Ho:SSO. The single pulsed energy varied from 8.3 μJ to 76.6 μJ with the increasing of the incident power from 2.2 W to 8.2 W. The maximum repetition rate was 42.1 kHz, and the minimum pulsed duration was 48 ns. The maximum single-pulse peak power was 1.53 kW. The output center wavelength shifted from 2090.1 nm (the continuous-wave mode) to 2091.3 nm (the passive Q-switch mode). [ABSTRACT FROM AUTHOR]