Saturable Absorption Performance Research Articles

Passively mode-locked Yb-doped all-fiber oscillator operating at 979 nm and 1032 nm with the single wall carbon nanotubes as SA

We report on an all-fiber passively mode-locked ytterbium-doped (Yb-doped) fiber laser with single polymer composite saturable absorber (SA) based on the single wall carbon nanotubes (SWCNTs) with diameters of 0.8 nm. The SWCNTs are mixed with sodium carboxymethylcellulose (NaCMC) to form SWCNTs SA film. The non-saturable absorption coefficient, modulation depth and saturable intensity of the SWCNTs SA are measured to be 29%, 12% and 0.12 MW/cm2, respectively. By using the SWCNTs as SA, a passively mode-locked Yb-doped fiber laser has been achieved at 979 nm with pulse duration of 228 ps and repetition rate of 15.47 MHz. To our knowledge, this is the first time ever reported in an all-fiber Yb-doped mode-locked fiber laser using SWCNTs as SA at 980 nm, which overcome the difficulties of low gain and serious re-absorption effects in the quasi-three-level system. In order to verify the saturation absorption performance of the SWCNTs, mode-locking experiment in quasi-four-level system is also carried out around 1030 nm and the stable and uniform mode-locked pulses are obtained. A mode-locked fiber laser at 1032 nm is realized with a pulse width of 485 ps and repetition rate of 8.78 MHz. It is sufficiently manifested that SWCNTs with diameters of 0.8 nm have excellent saturable absorption performance as optical mode-locking elements in ultrafast photonic applications.

Nonlinear absorption properties of CdSe/ZnS quantum dots and the application: passively Q-switched Nd:GdVO4 laser at 1.06 μm

The nonlinear optical properties and the saturable absorption performance of CdSe/ZnS quantum dots (QDs) were experimentally investigated. The experimental results revealed strong saturable absorbed properties of CdSe/ZnS QDs at λ = 1.06 μm, which guarantee QDs passively Q-switched lasers. Subsequently, as an application, CdSe/ZnS QDs as saturable absorber passively Q-switched Nd:GdVO4 laser at 1.06 μm was demonstrated. The Q-switched pulse train with a duration of 233 ns at a repetition rate of 556.2 kHz was generated.

Promotion impact of thermal oxidation etching to saturable absorption performance of g-C3N4

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-C3N4), and the as-prepared modified g-C3N4 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-C3N4 materials used as SAs around 1 μm.

Linear and Nonlinear Optical Constants of Potassium Acid Phthalate crystal

Single crystals of potassium hydrogen phthalate (KAP) are grown by solution growth technique. Linear optical constants are evaluated from UV/VIS/NIR spectrum. The Z scan technique is used to elucidate the third order nonlinearity in the material. The results indicate that the compound exhibits reverse saturable absorption (RSA) and self-defocusing performance. The second harmonic generation (SHG) efficiency of the crystal evaluated by Kurtz and Perry technique is compared with that of the standard KDP crystal. Attempt is made to correlate the SHG efficiency with the crystalline perfection in the material. Full Text: PDF ReferencesMiniewicz.A, Barkiewics.S, "On the electro‐optic properties of single crystals of sodium, potassium and rubidium acid phthalates", Adv.Mat.Opt.Elect,2,157(1993). CrossRef Comeretto.D, Rosy.L, "Optical properties of potassium acid phthalate", J.Mat.Res, 12, 1262(1997). CrossRef Krajewski.T, Breczewski.T, "Dielectric and pyroelectric properties of TGS crystals doped with nitroaniline molecules", Ferroelectrics, 25, 547 (1980). CrossRef N. Kejalakshmy, K. Srinivasan, "Growth, optical and electro-optical characterisations of potassium hydrogen phthalate crystals doped with Fe3+ and Cr3+ ions", Opt. Mater. 27,389–394A, (2004). [5] CrossRef Ester. G.R, Price.R, Halfpenny. P.J, "An atomic force microscopic investigation of surface degradation of potassium hydrogen phthalate (KAP) crystals caused by removal from solution", J.Cryst.Growth, 182, 95(1998). CrossRef Hiroyuki Toda, Carl M. Verber "Simple technique to reveal a slow nonlinear mechanism in a z-scanlike n2 measurement", Opt. Lett. 17(19) 1379(1992). CrossRef K.J. Arun, S.Jayalekshmi, "Investigations on the nonlinear optical properties of glycinium oxalate single crystals", Optoelectron. Lett. 7(2), 136, (2011). CrossRef K.J.Arun, S.Jayalekshmi, "Third order nonlinear optical constants of L-alaninium oxalate", Phot. Lett. Poland 7(3), 81-83 (2015) CrossRef

High-power passively Q-switched 2 μm all-solid-state laser based on a Bi_2Te_3 saturable absorber

By using the ultrasound-assisted liquid phase exfoliation method, Bi2Te3 nanosheets are synthesized and deposited onto a quartz plate to form a kind of saturable absorber (SA), in which nonlinear absorption properties around 2 μm are analyzed with a home-made mode-locked laser. With the as-prepared Bi2Te3 SA employed, a stable passively Q-switched all-solid-state 2 μm laser is successfully realized. Q-switched pulses with a maximum average output power of 2.03 W are generated under an output coupling of 5%, corresponding to the maximum single-pulse energy of 18.4 μJ and peak power of 23 W. The delivered shortest pulse duration and maximum repetition rate are 620 ns and 118 kHz under an output coupling of 2%, respectively. It is the first presentation of such Bi2Te3 SA employed in a solid-state Q-switched crystalline laser at 2 μm, to the best of our knowledge. In comparison with other 2D materials suitable for pulsed 2 μm lasers, the saturable absorption performance of Bi2Te3 SA is proved to be promising in generating high power and high-repetition-rate 2 μm laser pulses.

Construction and nonlinear optical characterization of CuO quantum dots doped Na2O–CaO–B2O3–SiO2 bulk glass

The spherical shape copper oxide (CuO) quantum dots (QDs) were successfully fabricated via copper basic calcium sodium borosilicate (Na2O–CaO–B2O3–SiO2) precursor obtained with a facile sol–gel technique. The microstructural analysis of doped QDs are systemically characterized, such as transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photo-electron spectroscopy. And the results reveal that the CuO QDs with the small size are well dispersed doped in sodium calcium borosilicate glass. Remarkably, the CuO glass materials exhibit the good third-order optical nonlinear susceptibility χ(3) (1.379 × 10−12 esu), which was investigated by femto-second Z-scan technique at the wavelength of 1550 nm, pulse duration of 50 fs, repetition rate of 50 MHz. The glass hybrids displayed a reverse saturable absorption and self-focusing refraction performance. And the mechanism to explain the third-order nonlinearity of CuO glass may be predominantly originated from the surface plasmon resonance effect, the quantum confinement effect and partly from the thermal effect. Besides, it is interesting that the glass hybrids have significant nonlinear absorption effects that endow the material to the potential value of the application of optical limiting device.

Nonlinear Optical Properties of Novel Polypyrrole Derivatives Bearing Different Aromatic Segments

Polypyrrole (PPy) and its derivatives containing different were synthesized by the interfacial polymerization reaction using ammonium per sulfate as oxidant, and were characterized by using Fourier transform infrared, Ultraviolet/visible absorption, and Raman spectroscopic techniques. The third-order nonlinear optical properties of all samples were measured by using nanosecond Z-scan measurements at 532 nm. At the identical mass concentration of 0.15 mg·mL-1, all PPy derivatives exhibited an obvious reverse saturable absorption performance, while the saturable absorption response was observed for PPy. In addition, significant differences in their nonlinear optical performances were observed, highlighting the influence on optical nonlinearity of the aromatic segments of conjugated polymers.

Synthesis, growth, structure and characterization of 1-Ethyl-2-(2-p-tolyl-vinyl)-pyridinium iodide (TASI) – An efficient material for third-order nonlinear optical applications

A new organic stilbazolium derivative, 1-Ethyl-2-(2-p-tolyl-vinyl)-pyridinium iodide (TASI), was grown from methanol:acetonitrile (1:3) mixed solvent by slow evaporation technique. Single crystal X-ray diffraction analysis revealed that TASI crystallizes in triclinic system with a centrosymmetric space group P-1. The molecular structure and the presence of expected functional groups of TASI were confirmed by 1H NMR and FT-IR spectroscopic studies. The HOMO and LUMO energies influence the charge transfer takes place within the molecule. The grown crystal was thermally stable up to 210 °C as determined by TG/DTA analysis. UV-Vis-NIR spectral study showed that the grown crystal was transparent in the wavelength range of 438–1100 nm. Mechanical behaviour and surface laser damage threshold were studied to find the suitability of the grown crystal for device fabrication. Studies of its third-order nonlinear optical properties using a Z-scan technique demonstrates that TASI crystal is capable of exhibiting reverse saturable absorption and self-focusing performance with the second-order molecular hyperpolarizability (γ) 4.983 × 10−34 esu. The third-order nonlinear susceptibility of TASI was found to be 8.931 × 10−6 esu, which is higher than a few other stilbazolium derivative crystals.

End-to-End Self-Assembly of Gold Nanorods in Water Solution for Absorption Enhancement at a 1-to-2 μm Band for a Broadband Saturable Absorber

The redshift of the long wavelength plasmonic absorption band is essential to the use of gold nanorods (GNRs) for the implementation of the infrared broadband saturable absorbers (SAs). A common method to obtain the GNR-based SAs with a substantially broad absorption bandwidth from 1 to 2 μm is to use GNRs with a large aspect ratio. Here, a simple self-assembly technique is demonstrated, which enables us to obtain a significant redshift of the long wavelength plasmonic absorption peak of GNRs with a small aspect ratio, together with substantial spectral broadening of the absorption band. The proposed technique is based on an end-to-end self-assembly of the GNRs through hot air induced rapid drying of the GNRs in a deionized water solution, which makes the GNRs reassemble by attaching to one another by their ends. Using the proposed end-to-end self-assembly method for GNRs with an aspect ratio of 5.1, a single broadband SA that can operate from 1.5 to 1.9 μm was fabricated on a fiber ferrule based sandwich platform. The saturable absorption performance was tested by incorporating the fabricated GNR-based SA into two different optical fiber based ring cavities: One was based on an erbium-doped fiber and the other was a thulium–holmium codoped fiber. Our fabricated single SA readily produced stable Q-switched pulses from both the cavities.

Near‐Infrared Saturable Absorption of Defective Bulk‐Structured WTe2 for Femtosecond Laser Mode‐Locking

Mono‐ and few‐layer transition metal dichalcogenides (TMDCs) have been widely used as saturable absorbers for ultrashort laser pulse generation, but their preparation is complicated and requires much expertise. The possible use of bulk‐structured TMDCs as saturable absorbers is therefore a very intriguing and technically important issue in laser technology. Here, for the first time, it is demonstrated that defective, bulk‐structured WTe2 microflakes can serve as a base saturable absorption material for fast mode‐lockers that can produce femtosecond pulses from fiber laser cavities. They have a modulation depth of 2.85%, from which stable laser pulses with a duration of 770 fs are readily obtained at a repetition rate of 13.98 MHz and a wavelength of 1556.2 nm, which is comparable to the performance achieved using mono‐ and few‐layer TMDCs. Density functional theory calculations show that the oxidative and defective surfaces of WTe2 microflakes do not degrade their saturable absorption performance in the near‐infrared range, allowing for a broad range of operative bandwidth. This study suggests that saturable absorption is an intrinsic property of TMDCs without relying on their structural dimensionality, providing a new direction for the development of TMDC‐based saturable absorbers.

MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons.

Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources.

Chemical Wet Etching of an Optical Fiber Using a Hydrogen Fluoride-Free Solution for a Saturable Absorber Based on the Evanescent Field Interaction

We propose a chemical wet etching technique that does not make use of toxic Hydrofluoric solution to produce cladding-etched optical fiber intended for use as a platform for a fiberized saturable absorber. The wet etching technique is based on the use of a mixed solution of NH4F and (NH4)2SO4, which is not toxic, and a small, specially-devised etching cradle to achieve precise control of the etched fiber length. A fiberized saturable absorber was implemented by depositing the graphene oxide particles on top of the residual cladding for our cladding-etched fiber by using the drop & dry method. The saturable absorber was incorporated into an erbium-doped fiber ring cavity to test its suitability as a mode-locker with a modulation depth larger than 4.3%. Femtosecond pulses with a temporal width of ∼615 fs were readily obtained at a repetition rate of ∼17.09 MHz. The saturable absorption and laser performance of our saturable absorber were compared to those of an absorber on a core-etched fiber platform prepared through the formation of microdroplets of HF and surface tension-driven flow, as in [57] .

Reverse saturable absorption and nonlinear refraction of ultrathin ZrS3 nanobelts.

The nonlinear optical (NLO) properties of a ZrS3 nanobelt were measured with a 6.5 ns pulse laser at 532 nm. Its optical response to the incident light exhibits good optical absorptive and refractive effects, with the nonlinear absorption coefficient β = 4.42 × 10(-10) m W(-1) and the nonlinear refraction coefficient γ = 5.86 × 10(-17) m(2) W(-1) for the ZrS3 nanobelt in ethanol dispersions at an input energy of 34.25 μJ. In addition, the β values and γ values have dependence on input energy. Results show that the ZrS3 nanobelts have an excellent reverse saturable absorption (RSA) performance in nanosecond pulses, demonstrating that ZrS3 nanobelts are an extraordinarily promising novel optical power limiting material. Meanwhile, compared to the pure ZrS3, graphene oxide (GO) and reduced graphene oxide (RGO), composites (ZrS3/GRO) exhibit an enhanced nonlinear absorption response at the same input energy.

Slow and fast absorption saturation of black phosphorus: experiment and modelling.

According to the excited-state decay time, a slow saturable absorber model was employed to obtain the ground-state absorption and excited-state absorption cross sections σgs and σes of black phosphorus (BP) nanosheets, which are (1.25 ± 0.07) × 10-16 cm2 and (2.97 ± 0.21) × 10-17 cm2 at 515 nm, and (5.95 ± 0.17) × 10-18 cm2 and (5.19 ± 0.71) × 10-19 cm2 at 1030 nm, respectively. In comparison, the σgs and σes of MoS2 and graphene were also obtained with the same model. The ratio σes/σgs of BP is the smallest (only 0.24 ± 0.03 at 515 nm and 0.09 ± 0.01 at 1030 nm) among the three two-dimensional layered materials both at 515 nm and 1030 nm. Relatively large ground-state transition probability and weak loss of excited-state absorption result in good saturable absorption performance. In comparison with MoS2 and graphene, the much lower saturation intensity of BP can be well explained from this perspective.

Stable, Ultrafast Pulse Mode-Locked by Topological Insulator <inline-formula> <tex-math notation="TeX">${\rm Bi}_{2}{\rm Se}_{3} $</tex-math></inline-formula> Nanosheets Interacting With Photonic Crystal Fiber: From Anomalous Dispersion to Normal Dispersion

We demonstrate two kinds of stable ultrafast fiber lasers mode-locked by topological insulator (TI) Bi 2 Se 3 nanosheets interacting with photonic crystal fiber (PCF). The saturable absorber (SA) produced by drying TI solution filled in 5.5 cm PCF provides a modulation depth of 5%, and its damage threshold is highly enhanced due to the large evanescent field interaction length. When the SA is incorporated in an erbium-doped fiber ring cavity with anomalous dispersion, a conventional soliton with 908-fs duration is obtained, and no wave-breaking and SA damage is ever shown, even for pump power at 900 mW. Through tuning polarization controller, as high as tenth harmonic mode-locking, namely, 202.7 MHz, is obtained, and it operates stably for 8 hours under lab conditions. Dissipative soliton with a duration of 7.564 ps is generated when the dispersion of cavity changes from anomalous to normal, which can be further compressed to 245 fs by additional 15-m single mode fiber, and a maximum average output of 75 mW is obtained. This TI nanosheets-PCF structure possesses advantages of stable saturable absorption performance, high damage threshold, and freedom from special package, which make it an effective choice for a passively mode-locked laser.

Facile fabrication of wafer-scale MoS2 neat films with enhanced third-order nonlinear optical performance.

Wafer-scale MoS2 neat films with controllable thicknesses were successfully fabricated by vacuum filtering liquid-exfoliated MoS2 dispersions. The obtained MoS2 filtered thin films were systematically characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). It was found that the fabricated scalable MoS2 films have a smooth surface and high optical homogeneity verified by AFM and a collimated 532 nm beam, respectively. We investigated the ultrafast nonlinear optical (NLO) properties of the filtered films by an open aperture Z-scan method using 515 and 1030 nm femtosecond laser pulses. Saturable absorption was observed at both 515 and 1030 nm with the figure of merit (FOM) values as ∼3.3 × 10(-12) esu cm and ∼3.4 × 10(-14) esu cm, respectively. The observation of ultrafast NLO performance of the MoS2 filtered films indicates that vacuum filtration is a feasible method for the fabrication of optical thin films, which can be expanded to fabricate other two-dimensional films from the corresponding dispersions. This easy film fabrication technology will greatly enlarge the application of graphene analogues including graphene in photonic devices, especially of MoS2 as a saturable absorber.

Synthesis, crystal structure and third-order non-linear optical properties of a two-dimensional coordination network [Cd(AcO)2(L)2(H2O)

A novel two-dimensional (2-D) Cd(II) coordination network [Cd(AcO)2(L)2(H2O)] 1 (AcO=acetate, L=4-(1,2,4-triazol-1-yl) benzoic acid ethyl ester) has been synthesized by low-temperature solid-state reaction and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra and UV–visible spectra. The molecules of the complex are interconnected into layers by O–H⋯O and C–H⋯O hydrogen bonds in which participate AcO−, L and H2O ligands. The intermolecular hydrogen-bonds interactions are the most significant factors controlling the novel supramolecular sheet fashion packing of the title compound in the crystal state. The third-order non-linear optical (NLO) properties of the title compound 1 were also investigated and they exhibit the reverse saturable absorption and self-defocusing performance with modulus of the hyperpolarizability (γ) 2.30×10−30esu for 1 in a 2.15×10−4moldm−3 DMF solution.

Growth, spectral, optical, thermal, surface analysis and third order nonlinear optical properties of an organic single crystal: 1-(2-Methyl-6-nitro-4-phenyl-3-quinolyl) ethanone

Single crystal of 1-(2-Methyl-6-nitro-4-phenyl-3-quinolyl) ethanone was grown using slow evaporation solution growth technique. Single crystal X-ray diffraction study reveals the lattice parameters of the grown crystal. The modes of vibration of different molecular groups present in 2M6NQE were identified by FTIR spectral analysis. Its optical behavior was examined through UV–vis–NIR absorption and PL emission spectrum. They signify that the crystal has transparency in the region between 383 and 1100nm. The PL spectrum of the title compound shows green emission in the crystal. From the thermal analysis, 2M6NQE has found to be thermally stable up to 263°C, and the melting point of the material is 170°C. The estimations of third order non-linear optical properties like non-linear absorption coefficient (β), non-linear refractive index (n2) and susceptibility [χ(3)] were calculated using Z-scan technique. It has observed that, crystal exhibits reverse saturation absorption and self-defocusing performance. Etching study was carried out for the grown crystal using different solvents.

Growth and characterization of 4-methyl benzene sulfonamide single crystals

Single crystals of 4-methyl benzene sulfonamide (4MBS) were successfully grown from aqueous solution by low temperature solution growth technique. The grown crystal was characterized by single crystal XRD and powder XRD methods to obtain the lattice parameters and the diffraction planes of the crystal. UV–vis–NIR absorption spectrum was used to measure the range of optical transmittance and optical band gap energy. The optical transmission range was measured as 250–1200nm. FTIR spectral studies were carried out to identify the presence of functional groups in the grown crystal. The thermal behavior of the crystal was investigated from thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC) study. The absence of SHG was noticed by Kurtz and Perry powder technique. The third order NLO behavior of the material was confirmed by measuring the nonlinear optical properties using Z-scan technique and it was found that the crystal is capable of exhibiting saturation absorption and self-defocusing performance.

Tuning Optical Nonlinearity of Laser‐Ablation‐Synthesized Silicon Nanoparticles via Doping Concentration

Silicon nanoparticles at different doping concentrations are investigated for tuning their optical nonlinear performance. The silicon nanoparticles are synthesized from doped silicon wafers by pulsed laser ablation. Their dispersions in water are studied for both nonlinear absorption and nonlinear refraction properties. It is found that the optical nonlinear performance can be modified by the doping concentration. Nanoparticles at a higher doping concentration exhibit better saturable absorption performance for femtosecond laser pulse, which is ascribed to the free carrier absorption mechanism.