Open-aperture Z-scan Method Research Articles

Theoretical and experimental investigations on Nb2CT x MXene Q-switched Tm:YAP laser at 2 μm for the nonlinear optical response

In this paper, the Nb2CT x MXene nanosheets were fabricated and the corresponding microstructures were investigated. The nonlinear optical response was illustrated by open aperture Z-scan and I-scan methods. The ground and the excited state absorption cross-sections of 2D Nb2CT x MXene were also investigated. As the saturable absorber (SA), the Nb2CT x MXene was applied in the passively Q-switched Tm:YAP laser. 1.96 μs Q-switched pulses with 3.97 W peak power were achieved at the repetition frequency of 80 kHz. Further theoretical model was built by using the coupled rate equations in simulating the dynamic process of the passively Q-switched Tm:YAP laser. The numerical simulation results are fundamentally in agreement with the experimental results, which proves the Nb2CT x MXene can be a good potential nanomaterial for further optoelectronic applications.

Enhanced two-photon absorption of sandwich-like coordination complexes based on squaraine and metallomacrocycle derivatives

Covalent or noncovalent multi-chromophore structures have expanded the discovery of appreciable nonlinear optical (NLO) materials. We present here a report of how drastic changes in two-photon absorption (2PA) coefficients can enhance from slight changes of electronic delocalization through coordination interaction. Experimental results illustrate that 2PA is the dominant phenomenon contributing to the NLO properties of the complexes recorded in the range of 750–1550 nm by open aperture Z-scan method. The values of degenerate 2PA cross sections (δ2PA) can be enhanced obviously by coordination interactions assisted by steric effect and intermolecular charge transfer, not showing a simply sum of the nonlinear parameters of the starting components. Importantly, the complexes feature high δ2PA values up to 12,700 GM at 1400 nm in the second near-infrared region. Both complexes with large 2PA coefficients and multiple excitation wavelengths may offer a novel avenue for creating useful nonlinear absorbing materials.

A study on the electrical, magnetic and optical limiting behaviour of Pure and Cd-Fe co-doped CuO NPs

Copper Oxide (CuO) Nanoparticles (NPs) in pure and doped form (cadmium (Cd) - iron (Fe)) co-doped (2 & 4 wt%)) were developed via employing simple co-precipitation method. PXRD pattern shows that there is no impurity in the single-phase monoclinic structure. The agglomeration of needle-like, flake-like and spherical-like morphologies for undoped and Cd-Fe (2 & 4 wt%) co-doped CuO NPs are examined through SEM analysis. From UV–Vis DRS spectra, the obtained optical band gap of the synthesized materials was found to be 2.38, 2.62 and 2.77 eV for undoped and Cd-Fe (2 & 4 wt%) co-doped CuO NPs. PL spectrum confirms the slight variation in emission wavelength compared to undoped CuO NPs. At different temperatures, electrical conductivity measurements of synthesized samples are estimated by the dielectric constant, dielectric loss and ac conductivity with different frequencies. VSM analysis exhibits a maximum saturation magnetization (0.02159 emu/g) for Cd-Fe co-doped CuO NPs (4 wt%), which reveals the synthesized samples can be a probable candidate for optoelectronics and spintronic device fabrication. The nonlinear absorption and optical limiting properties were investigated by using open aperture Z-scan method under nano pulsed green laser excitation. With increased Cd-Fe concentration, the two-photon absorption coefficient increases from 3.0×10−10W/m to 4.8×10−10W/m. Both undoped and Cd-Fe co-doped CuO NPs exhibit two-photon absorption induced optical limiting action with lower onset optical limiting threshold and thus can be used for the development of the laser protection devices against widely used high power nano pulsed green laser.

Plasmon enhanced linear and nonlinear optical properties of natural curcumin dye with silver nanoparticles

The interactions between silver nanoparticles and bio molecules have potential significance in many interesting applications like sensing, imaging etc. In the present work, the variation in the fluorescence emission and nonlinear optical response of natural Curcumin dye extracted from the Curcuma longa with laser synthesized silver nanoparticles was studied. The formation and optical properties of silver nanoparticles and Curcumin dye solutions were analyzed using UV–Visible absorption spectroscopy, fluorescence emission spectroscopy and fluorescence life time studies. The third order nonlinear optical behavior of the Curcumin dye samples with incorporation of varying concentration of silver nanoparticles were investigated using open aperture Z-scan method. A substantial enhancement was observed for the entire optical behavior such as non-linear optical response, optical limiting properties and fluorescence emission of the Curcumin samples with silver nanoparticles, which progressively improved with the concentration of the silver nanoparticles incorporated into the system.

Broadband saturated absorption properties of bismuthene nanosheets.

The nonlinear absorption properties of two-dimensional bismuthene nanosheets have great value for application in the photonics field. In this work, bismuthene nanosheets with a thickness of around 4 nm were prepared using the liquid phase exfoliation (LPE) method. The infrared waveband nonlinear absorption properties of bismuthene nanosheets were investigated using the open aperture Z-scan technique with four wavelengths of 950, 1064, 1200, and 1500 nm, respectively. Bismuthene nanosheets exhibited broadband saturated absorption (SA) properties at the infrared band. The lower saturated intensity indicated the advantages of bismuthene as a saturated absorber in the application of ultra-fast lasers in the infrared band.

Visible nonlinear optical properties of tellurium and application as saturable absorber

Tellurium, a novel two-dimensional (2D) Group-VI material, has attracted much attention benefitting from its excellent electrical and optical properties. In this contribution, tellurium nanosheets were directly dispersed in toluene in the existence of polymer and were easily fabricated into flexible thin films. The nonlinear optical absorption properties of tellurium film at the visible band were studied by the open-aperture Z-scan method. For the application of laser modulation, we realized the passively Q-switched Pr: YLF laser over the spectrum of orange (605 nm), red (639 nm), deep red (721 nm) with tellurium film as the saturable absorber (SA). Furthermore, we also realized the passively Q-switched mode-locked laser at 639 nm with the tellurium SA. The research results indicate the tellurium thin film has remarkable nonlinear optical absorption properties and could be a promising optical modulator in the visible domain.

2 µm passively Q-switched all-solid-state laser based on a Ta2NiSe5 saturable absorber

In this paper, a novel 2D ternary chalcogenide Ta2NiSe5 is fabricated into a saturable absorber by using the liquid phase exfoliation (LPE) method and successfully applied to the passive Q-switching experiment of Tm:YAP all-solid-state laser at 2 µm. The nonlinear optical absorption (NOA) properties of Ta2NiSe5 at 2 µm was measured by using an open-aperture Z-scan method, showing saturation fluence and modulation depth of 400 µJ/cm2 and 24%, respectively. By using Ta2NiSe5 as saturable absorber, the shortest pulse width of 740 ns and maximum repetition frequency of 71 kHz are obtained, respectively. This results prove that the Ta2NiSe5 is an excellent saturable absorber to achieve passively Q-switched laser at 2 µm, for the first time to the best of our knowledge.

Starting monomer of graphdiyne–hexakis[(trimethylsilyl)ethynyl]benzene: a superior nonlinear absorption material

Graphdiyne (GDY) is an emerging carbon allotrope consisting of sp- and sp2-hybrid carbon atoms. The sp-hybrid carbon–carbon triple bond structure with strong d–π interaction has endowed GDY special nonlinear absorption (NLA) properties, which is different from graphene. As a starting monomer for synthesizing GDY, hexakis[(trimethylsilyl)ethynyl]benzene (HEB-TMS) also owns the carbon–carbon triple bond (sp-) and the benzene ring (sp2-) structures (similar to GDY), which stimulates us to explore the NLA properties of HEB-TMS. In this work, two-dimensional (2D) nanosheets of HEB-TMS are successfully prepared using a liquid-phase exfoliation method with the thicknesses of 3.49 ~ 4.47 nm. And the broadband NLA properties are researched using an open-aperture Z-scan method (from ultraviolet to infrared waveband). The results demonstrate that HEB-TMS owns excellent NLA characteristics in visible light waveband. The excellent optical limiting properties of HEB-TMS provide the possibility of application in the protection of human eyes and precision optical component in visible light.

Optimization of Nonlinear Optical Response of One-Dimensional Nanostructured Sodium Titanate Through Morphological Control

Nanostructured nonlinear optical (NLO) materials are attracting increasing interest as optical limiters for various applications. In this study, one-dimensional nanostructured Na2Ti3O7 was synthesized by a typical hydrothermal method and systematically characterized. The results showed that one-dimensional nanostructured Na2Ti3O7 has good crystallinity and thermal stability. Its morphology can be easily controlled to form nanotubes, nanobelts and nanorods by altering the amounts of added NaOH. The robustness of the NLO properties of one-dimensional nanostructured Na2Ti3O7 in broadband optical limiting (OL) applications was investigated by the open-aperture Z-scan method. At laser wavelengths of 532 nm and 1064 nm, the effective nonlinear extinction coefficients showed nonmonotonic dependence on the morphology; nanotubes gave the maximum value. The results confirmed that the NLO and OL responses of one-dimensional nanostructured Na2Ti3O7 can be effectively optimized by tailoring the morphology. In addition, the nonlinear extinction coefficients of these three types of one-dimensional nanostructured Na2Ti3O7 are better than those of multi-walled carbon nanotubes, a benchmark one-dimensional OL material, at 532 nm and 1064 nm; they therefore have potential applications in nonlinear optics. Nonlinear scattering and photothermal effect measurements showed that the OL shown by one-dimensional nanostructured Na2Ti3O7 can be mainly attributed to nonlinear scattering and free-carrier absorption at both irradiation wavelengths. The fabrication of one-dimensional nanostructured Na2Ti3O7 with different morphologies via this simple approach paves the way for the synthesis and tuning of new one-dimensional materials with desirable photonic properties for various applications.

Nonlinear optical absorption properties of InP nanowires and applications as a saturable absorber

Indium phosphide (InP) nanowires (NWs) have attracted significant attention due to their exotic properties that are different from the bulk counterparts, and have been widely used for light generation, amplification, detection, modulation, and switching, etc. Here, high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method. We thoroughly studied their nonlinear optical absorption properties at 1.06 μm by the open-aperture Z-scan method. Interestingly, a transition phenomenon from saturable absorption (SA) to reverse saturable absorption (RSA) was observed with the increase of the incident laser intensity. In the analysis, we found that the effective nonlinear absorption coefficient ( β eff ∼ − 10 2 cm / MW ) under the SA process was 3 orders of magnitude larger than that during the RSA processes. Furthermore, the SA properties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q -switched Nd : YVO 4 solid-state laser at 1.06 μm, where the shortest pulse width of 462 ns and largest single pulse energy of 1.32 μJ were obtained. Moreover, the ultrafast carrier relaxation dynamics were basically studied, and the intra-band and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps, respectively, were measured by a degenerate pump–probe method with the probe laser of 800 nm. These results well demonstrate the nonlinear optical absorption properties, which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.

2D tellurene/black phosphorus heterojunctions based broadband nonlinear saturable absorber

Abstract Two-dimensional (2D) mono-elemental materials (Xenes) show remarkable potential in the fields of fundamental science and technology, have been regarded as a wide range of building blocks for electronic technologies due to their unique chemical, physical, electrical, and optical properties. Here, 2D tellurene/black phosphorus (Te/BP) heterojunctions are successfully fabricated through liquid-phase exfoliation (LPE) method. Their nonlinear optical absorption properties at 1.0, 2.0, and 2.8 μm have been studied by an open-aperture Z-scan method. The results revealed the excellent broadband saturable absorption responses of the prepared BP/Te heterojunctions, which are further confirmed by using them as saturable absorbers (SAs) for passively Q-switched all-solid-state lasers operating at 1.0, 2.0, and 2.8 μm, respectively. In particular, 1.04 μm continuous-wave (CW) mode-locked lasers with a pulse width of 404 fs is realized for the first time, to our best knowledge. Our work indicates that 2D Xenes especially 2D Xenes based heterojunctions have great potential in the fields of pulsed laser generation/modulation and other optoelectronic and photonic devices.

Switch of Optical Nonlinear Absorption in Black Phosphorous

Nonlinear absorption of multi-layer black phosphorus nanosheets (BPs) were investigated using open aperture Z-scan method with 6 ns nanosecond laser pulses at 532 nm. It was found that, at lower intensities, BPs behave as saturable absorbers, but at higher intensities a shift from saturable absorption to reverse saturable absorption occurs. The transition process was analyzed in terms of the bleaching of ground-state and the excited-state absorption. We investigate the ultrafast dynamics by using pump − probe technique. The investigation implies that BPs has great potential applications in both mode-locking and optical liming in the visible range for ultrafast laser pulses.

Optical limiting property and ultrafast pump-probe study of two X-shaped oligomers with anthracene unit as a core

Two X-shaped multi-branched oligomers based on anthracene unit were studied by open-aperture Z-scan and ultrafast pump-probe methods to elucidate the nonlinear optical absorption properties as well as intramolecular charge transfer properties of typical X-shaped oligomers. Significant enhancement on the nonlinear optical absorption property was observed for the oligomer with triphenylamine groups as terminal end of each branch. Obvious optical limiting property was observed for these X-shaped oligomers and the mechanism was attributed to the two-photon absorption process. The ultrafast dynamic of these X-shaped oligomers exhibited a fast process about several ps to build an intramolecular charge transfer state, followed by a slow process longer than 100 ps which reflecting the evolution of the intramolecular charge transfer state.

Electronic Nature of Neutral and Charged Two-Photon Absorbing Squaraines for Fluorescence Bioimaging Application

The electronic properties of neutral 2,4-bis(4-bis(2-hydroxyethyl) amino-2-hydroxy-6-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenyl)squaraine (1) and charged 2-((3-octadecylbenzothiazol-2(3H)-ylidene)methyl)-3-oxo-4-((3-(4-(pyridinium-1-yl)butyl)benzo-thiazol-3-ium-2-yl)methylene)cyclobut-1-enolate iodide (2) squaraine derivatives were analyzed based on comprehensive linear photophysical, photochemical, nonlinear optical studies (including two-photon absorption (2PA) and femtosecond transient absorption spectroscopy measurements), and quantum chemical calculations. The steady-state absorption, fluorescence, and excitation anisotropy spectra of these new squaraines revealed the values and mutual orientations of the main transition dipoles of 1 and 2 in solvents of different polarity, while their role in specific nonlinear optical properties was shown. The degenerate 2PA spectra of 1 and 2 exhibited similar shapes, with maximum cross sections of ∼300–400 GM, which were determined by the open aperture Z-scan method over a broad spectral range. The nature of the time-resolved excited-state absorption spectra of 1 and 2 was analyzed using a femtosecond transient absorption pump–probe technique and the characteristic relaxation times of 4–5 ps were revealed. Quantum chemical analyses of the electronic properties of 1 and 2 were performed using the ZINDO/S//DFT theory level, affording good agreement with experimental data. To demonstrate the potential of squaraines 1 and 2 as fluorescent probes for bioimaging, laser scanning fluorescence microscopy images of HeLa cells incubated with new squaraines were obtained.

Unleashing the potential of Ti2CTx MXene as a pulse modulator for mid-infrared fiber lasers

The strong light–matter interaction in two dimensional (2D) materials portends an untapped potential for fiber lasers in the long sought-after terahertz to mid-infrared spectral range. Here, the broadband nonlinear optical properties of zero-gap 2D Ti2CTx MXene—a class of 2D transition metal carbides that exhibit high laser damage threshold—is discussed. Using the open aperture Z-scan method, for the first time the broadband saturable absorption properties of Ti2CTx in the 800–1560 nm spectral range are demonstrated. Specifically, it is shown that the high absorption and low saturation intensity of Ti2CTx make it an ideal saturable absorber for mode-locked fiber lasers operating at 1565 and 1051 nm, which exhibited pulse widths of 5.3 ps and 164 ps, respectively. Additionally, a Ti2CTx saturable absorber was used as a Q-switcher to realize a pulsed fiber laser operating at 2.8 µm, which showed excellent nonlinear absorption performance in the mid-infrared regime. This study significantly broadens the scope of materials available for non-linear optical applications in the near and mid-infrared regimes.

Impact of the Subunit Arrangement on the Nonlinear Absorption Properties of Organometallic Complexes with Ruthenium(II) σ-Acetylide and Benzothiadiazole as Building Units §

In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C≡CPh)(C≡C)(dppe)2 (dppe = Ph2PCH2CH2PPh2) as electron donor (D) and 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole as electron acceptor (A) units in two different arrangement, i.e., A–D–A and D–A–D, are presented. They were measured in solution by the femtosecond open-aperture Z-scan method. The complexes show moderate two-photon absorption cross-sections σ(2) of several hundred to one thousand GM (here 1 GM = 10−50 cm4 s molecule−1 photon−1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D–A–D arrangement are six times higher than that of the A–D–A one. This difference can be explained by the number of metal cores (one or two ruthenium centers), the geometrical configurations of the complexes (more or less planar), and the resonance enhancement by lowering the intermediate state.

Tin diselenide-based saturable absorbers for eye-safe pulse lasers

Eye-safe pulse lasers have attracted increasing attention due to their potential wide application in many fields. However, optical modulators with excellent nonlinear optical absorption properties in the range of 1.4–2.1 μm are still very scarce. In this study, tin diselenide (SnSe2), a newly-developed 2D layered semiconductor material with facile processability and low cost, was investigated. The nonlinear optical response of SnSe2 was investigated using the open aperture Z-scan method at 1500 and 1800 nm. Using SnSe2 as the saturable absorber, a passive Q-switched solid-state laser was realized at 1.3 and 1.9 μm for the first time. This study proved SnSe2 to be an effective optical modulating material for the eye-safe waveband.

Enhanced nonlinear absorption and ultrafast carrier dynamics in graphene/gold nanoparticles nanocomposites

The nonlinear optical response of gold nanoparticles/reduced graphene oxide (AuNPs/rGO) nanocomposites prepared by laser ablation method was studied using a femtosecond laser open-aperture (OA) Z-scan method, and an enhanced nonlinear absorption effect was observed. Using the femtosecond time-resolved pump-probe measurements, the nonlinear response mechanism in the hybrid was studied. When graphene was excited by an ultrashort laser pulse, the bleaching of valence band (VB) and the filling of conduction band (CB) took place, causing a saturable absorption (SA) effect. When decorated with gold nanoparticles, the excited carriers from the CB of graphene could transfer to the sp band of the metal before returning to the VB of graphene. This process would take place in a much longer time scale (∼50 ps) than the direct relaxation in pure graphene, causing the enhancement of the SA effect. The excited carrier dynamics were further demonstrated using femtosecond time-resolved transient absorption spectroscopy, and the interband relaxation of the excited electrons from the sp band of AuNPs to the CB of graphene was observed, resulting in the further filling of the CB of graphene and enhancement of the SA effect.

MoSSe Saturable Absorber-Based High-Power Passively Q-Switched <inline-formula> <tex-math notation="LaTeX">$2.0~\mu$ </tex-math> </inline-formula>m Bulk Laser

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range.

Ternary chalcogenide Ta2NiS5 as a saturable absorber for a 1.9 μm passively Q-switched bulk laser.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta2NiS5 with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9μm has been realized with the Ta2NiS5 SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1W, 313ns, 22.0μJ, and 71.0W, respectively. This is the first demonstration of the saturable absorption property of Ta2NiS5, to the best of our knowledge. The results indicate well the promising potential of Ta2NiS5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.