Ultrafast Nonlinear Optical Properties Research Articles

Surface Enhanced Raman Scattering-Based Sensing and Ultrafast Nonlinear Optical Properties of Silver-Hexagonal Boron Nitride Nanocomposites Achieved by Femtosecond Laser Ablation

This study investigated the surface-enhanced Raman spectroscopy (SERS) properties and nonlinear optical (NLO) behavior of silver nanoparticles (Ag NPs) decorated hexagonal boron nitride (hBN) nanocomposites. Although Ag NPs are known for their excellent plasmonic properties, their susceptibility to oxidation in ambient conditions significantly reduces SERS activity. To overcome this, a femtosecond laser-assisted single-step novel approach is developed for synthesizing hybrid Ag-hBN nanocomposites via ablating Ag target in a solution of exfoliated hBN nanosheets, forming uniformly embedded Ag NPs on hBN nanosheets. The morphological characteristics and elemental compositions were validated by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). TEM analysis revealed that Ag NPs averaged 15 nm in size, while hBN nanosheets had lateral dimensions of approximately 250 nm. The SERS activity of the prepared nanocomposites was investigated using dye and explosive molecules, achieving detection sensitivities of 1 μM and 100 μM, respectively, with high reproducibility. These detection sensitivities are significant as they demonstrate the potential of the Ag-hBN nanocomposites for sensitive and reliable detection of trace amounts of analytes. Notably, the Ag-hBN nanocomposites showed enhanced SERS activity compared to pure Ag NPs, with a 2.5-fold improvement for Nile blue, 3.6-fold for methylene blue, and 2.4-fold for RDX. The current study also demonstrates that hBN prevents Ag NPs’ oxidation and preserves the SERS functionality even at elevated temperatures. Furthermore, the NLO properties of the nanocomposites were investigated using the standard Z-scan technique, revealing two-photon and three-photon absorption coefficients of 3×10−4 cm/GW and 6.5×10−5 cm3/GW2, respectively. The findings highlight the potential of Ag-hBN nanocomposites to enhance SERS and NLO devices, enabling future applications in sensing and photonics.

Structural and ultrafast third-order nonlinearities of methyl and methoxy substituted anthracene chalcones: Z-scan, four-wave mixing, and DFT approaches

We report on the structural, thermal, linear, and ultrafast third-order nonlinear optical (NLO) properties of two novel anthracene chalcones: (2E)-1-(anthracen-9-yl)-3-(5-methylthiophen-2-yl)prop-2-en-1-one (5ML2SANC) and (2E)-1-(9-anthryl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-one (245TMANC). The chalcones were synthesized by Claisen-Schmidt condensation reaction, and the single crystals were grown by the solvent evaporation method. The molecular structure was confirmed by FTIR and NMR spectroscopy, while the crystal structure was determined using the single crystal XRD. Both crystals belong to centrosymmetric monoclinic crystal system with space group P21/n. The Hirshfeld surface was analyzed to understand intermolecular interactions, and the band structures - including HOMO-LUMO levels, excited state energies, GCRDs and MEPs-were studied using DFT. The ultrafast third-order NLO properties were investigated by Z-scan and degenerate four-wave mixing (DFWM) techniques using Ti: Sapphire amplifier laser delivering ∼50 fs pulses at 800 nm (1 kHz, ∼4 mJ, 2 W). Two-photon absorption, positive nonlinear refraction, optical limiting and optical switching behaviors were observed by Z-scan measurements. The time-resolved DFWM show that the decay time of 5ML2SANC is ∼127 fs, while for 245TMANC it is ∼142 fs. The second hyperpolarizability (γ) measured by Z-scan, DFWM and the estimations from the DFT theory are found to be in good agreement (∼10−34 esu). The ultrafast optical response, significant NLO properties and thermal stability of the synthesized chalcones demonstrate their potential suitability in optical limiting and switching applications.

Push-Pull Carbazole-Based Dyes: Synthesis, Strong Ultrafast Nonlinear Optical Response, and Effective Photoinitiation for Multiphoton Lithography.

The present work reports on the ultrafast nonlinear optical (NLO) properties of a series of D-π-Α and D-A push-pull carbazole-based dyes and establishes a correlation between these properties and their efficiency for potential photonic and optoelectronic applications such as multiphoton lithography (MPL). The ultrafast NLO properties of the studied dyes are determined by two distinct experimental techniques, Z-scan and pump-probe optical Kerr effect (OKE), employing 246 fs laser pulses at 515 nm. The results indicate that chemical functionalization of the carbazole moiety with various strong electron-donating and/or electron-withdrawing groups, such as benzene, styrene, 4-bromostyrene, nitrobenzene, trimethyl isocyanurate, methyl, and indane-1,3-dione, can result in a controlled and significant enhancement of the NLO absorptive and refractive responses. In the context of potential applications, the efficiency of carbazole-based organic materials as photoinitiators (PIs) for MPL applications is demonstrated. The fabricated woodpile microstructure using chemically functionalized carbazole as a PI demonstrates improvements in both feature size and MPL efficiency compared to that using unfunctionalized carbazole as a PI. This is attributed to the efficient charge transfer resulting from chemical functionalization, which leads to a substantial increase (approximately 1 order of magnitude) in the values of the imaginary part of the second-order hyperpolarizability (Imγ) and the two-photon absorption cross section (σ). The achieved feature size of 280 nm is comparable to that obtained with other widely used PIs in MPL applications. Additionally, owing to the strong NLO properties of the studied functionalized carbazole, they could also be promising candidates for further applications in photonics and optoelectronics.

Nonlinear Optical Saturable Absorption Properties of 2D VP Nanosheets and Application as SA in a Passively Q-Switched Nd:YVO4 Laser.

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.

Ultrafast nonlinear optical response of layered violet phosphorus for femtosecond noise-like pulse generation

As a new member of two-dimensional (2D) phosphorene, 2D layered violet phosphorus (VP) has unique optoelectronic properties and good environmental stability, showing its huge advantages in optoelectronic applications. In this paper, the ultrafast nonlinear optical (NLO) properties of layered VP nanosheets at 1 µm band were explored, which exhibit an obvious saturable absorption response with a modulation depth of ∼1.97%. Meanwhile, the fast and slow carrier lifetimes of VP nanosheets at 1µm band were also determined as 295.9 fs and 2.36 ps, respectively, which are much shorter than that of most reported 2D materials. The excellent saturable absorption response combined with ultrashort carrier lifetimes indicate the prospect of layered VP nanosheets as a fast saturable absorber (SA) for ultrafast laser modulation. Then we demonstrated a Yb-doped fiber laser based on the VP-deposited taper-shaped fiber (TSF) SA, which delivers stable Q-switched mode-locked (QSML) pulses, dual-wavelength mode-locked pulses and 404-fs noise-like pulses. This work fully demonstrates the great potential of 2D VP materials for 1 µm ultrashort laser pulse generation.

Emerging PbSnS2 pulse modulators for ultrafast and high repetition frequency photonic applications

Two-dimensional ternary metal sulfides receive growing concern due to the diverse physicochemical properties and broad application potential. In this study, ultrafast nonlinear optical properties of two-dimensional lead tin sulfide (PbSnS2) nanosheets are demonstrated. PbSnS2 nanosheets with the thickness less than 3 nm were fabricated by liquid-phase exfoliation, and PbSnS2 nanosheets based saturable absorber (SA) was constructed by photodeposition. The nonlinear optical absorption properties such as modulation depth (21 %) and saturation intensity (14.2 MW/cm2) of PbSnS2-SA were investigated. Dispersion management was applied to Er3+-doped fiber laser (EDFL) coupled with PbSnS2-SA. The EDFL with net dispersion −0.36 ps2 outputs 928 fs mode-locked pulses. With a cavity dispersion of −0.58 ps2, tunable 1st to 9th order harmonic mode-locked (HML) is realized by tuning the pump power only. The EDFL (net dispersion −0.98 ps2) produces the highest repetition frequency at 362.59 MHz (corresponding to 80th order HML). The results indicate that two-dimensional PbSnS2 may be widely used as ultrafast photonics material for photonics and engineering applications research.

Influence of Diketopyropyrole spacer on the Ultrafast Non-Linear Optical Properties and Excited state dynamics of Dimeric Zinc Porphyrin Molecules

Zinc porphyrins (ZnP) are an important class of small molecule donors that have gained significant attention in the domain of organic photovoltaics. In this work, we investigate and correlate various...

Violet phosphorene as a saturable absorber for controllable soliton molecule generation in a mode-locked fiber laser

Controllable soliton molecules were generated in a Er-doped mode-locked fiber laser with a few-layered violet phosphorene saturable absorber.

Ultrafast nonlinear optical properties of MTe2 (M = V and Ta) and their application as broadband saturable absorbers

Two novel saturable absorbers based on MTe2 (M = V and Ta) were successfully fabricated and the nonlinear optical response of these materials was thoroughly investigated.

Exotic femtosecond nonlinear optical properties of laser ablated MoS2 quantum dots

Molybdenum disulfide (MoS2) quantum dots (QDs) of sizes 2.05–4.40 nm were synthesized using the femtosecond pulse laser ablation in liquid (PLAL) method. The optical and ultrafast nonlinear optical (NLO) properties of MoS2 QDs were comprehensively studied using photoluminescence and femtosecond Z-scan method. We synthesized these QDs in ethanol (Et) and DI water (DW) with varying ablation times of 20 min and 10 min; the sample names are Et20 and Et10, DW20, and DW10, respectively. The nonlinear absorption (NLA) coefficients [three-photon absorption (3PA)], nonlinear refractive index, etc., of these QDs, were studied using the fs Z-scan method. Interestingly, Et20 possessed saturable absorption (SA) followed by reverse saturable absorption (RSA) due to the free carrier absorption (FCA) with FCA cross-section values of – (0.61–0.89) × 10−18 cm2. While for Et10, DW20, and DW10, we found 3PA, a rare finding for MoS2 QDs. The estimated values of the second hyperpolarizability of these samples were found to be ∼10−30 esu. Due to the strong NLA phenomena, these samples have the optical limiting (OL) onset values in the range of ∼ (5.11–8.43) mJ/cm2, proving the optical limiting application potential of these QDs. The obtained optical, NLO parameters, and Kane energy values of laser-ablated MoS2 QDs suggest that these can be suitable material systems for optoelectronic, NLO switching, logic gates, and other photonic applications.

Large enhancement of nonlinear optical absorption and refraction in planar chalcone structure with terminal substitution

The ultrafast nonlinear optical (NLO) properties of novel planar π-conjugated chalcone derivatives, (E)-3-(4-nitrophenyl)-1-(3-bromo-4-fluorophenyl) prop-2-en-1-one (1503) and (E)-3-(4-nitrophenyl)-1-(phenothiazin-2-yl) prop-2-en-1-one (1526) are investigated and compared. The effect of intramolecular charge transfer on NLO absorption and refraction is discussed without changing the planar structural properties of the chalcone molecules. Transient absorption experiments are used to observe the evolution of 1526 from local excited (LE) state to the intramolecular charge transfer (ICT) state. In the Z-scan experiments, 1526 exhibits respectively different nonlinear absorption (NLA) mechanisms (reverse saturable absorption and two-photon induced excited state absorption) at 532 nm (4 ns, 22ps, 190 fs) and 700–900 nm, 190 fs. The NLA and nonlinear refraction (NLR) phenomena of 1526 are observed and discussed in the POPP experiments. The experimental results indicate that the chalcone derivative can become the potential materials for laser protection.

Ultrafast nonlinear optical properties of Ag-CdTe thin films by co-sputtering in the near-infrared region

Metal-doped CdTe has become a heated topic in recent years due to its ultrafast nonlinear optical properties. Herein, Ag-CdTe thin films with different doping amount (1W, 3W and 5W) and pure CdTe thin films were fabricated on quartz substrates by magnetron sputtering. The effects of Ag doping on the morphology, optical band gap and nonlinear optical properties of the thin films were systematically investigated. The nonlinear optical properties were investigated by femtosecond(fs) Z-scan technique under 800 nm. The results indicated that the Ag-CdTe thin films exhibit good nonlinear optical properties in the near-infrared region due to free carrier absorption and two-photon absorption. The results showed that the dopant content and the variation of the incident laser energy can control the RSA intensity, the nonlinear absorption coefficient, and the nonlinear refractive index of Ag-CdTe thin films. These results can provide new support for their applications in the field of nonlinear optoelectronic devices.

Tunable, efficient, ultrafast broadband nonlinear optical properties of TiO2–loaded complex phosphate glasses

On account of their excellent optical transparency from ultraviolet to far infrared spectral regions, phosphate glasses have become interesting nonlinear optical (NLO) materials for photonic nonlinear devices. However, small NLO coefficients tend to limit the usage of phosphate–based glasses in nonlinear photonic devices. Herein, we explored the NLO tunability in multicomponent phosphate glasses by increasing the coordination of orthophosphate (PO4)3– structural units with a great number of AlO4 groups through the addition of titanium dioxide (TiO2) in the composition. The NLO absorption and refraction characteristics were ascertained using open and closed–aperture Z–scan configurations respectively in a broadband spectral region ranging from 400 nm to 1200 nm under an ultrafast regime. The Z–scan results illustrate the increase of nonlinear susceptibility of glasses with titanium dioxide content in the composition due to the formation of non–π–conjugated orthophosphate groups which are in connection with AlO4 units. Typically, at 400 nm excitation, the NLO susceptibility improved by 119.91% upon addtion of 5 mol% of TiO2. The outcomes of the study acknowledge a new approach for conceiving highly NLO active phosphate glasses while maintaining deep–ultraviolet transparency through the polymerization of (PO4)3−groups. Consequently, the strategy explored in this work might pave the way for achieving the high NLO features of phosphate–based glasses to excel in their usage in data storage, signal transmission, optical limiting, and harmonic generation functionalities.

Ultrafast dynamic processes and nonlinear optical properties of Platinum(II) fluoren-acetylides

Two N-(4-ethylnylphenyl)-9H-fluoren-9-imine (EFT)arylacetylides (1, 2) and three EFT based Platinum(II) arylacetylides (3, 4, 5) were synthesized. The ultrafast dynamic processes after excitation and the nonlinear optical properties for picosecond lasers were investigatedusing femtosecond transient absorption and Z-scan techniques. The influence of conjugated length and Pt(II) content percentage on the properties ofthese moleculeswas discussed in detail. For compounds 1 and 2, two dynamic decay processes are observed after excitationby the pump laser beams. The first process is an ultrafast singlet (first singlet excited state, S1S*) → singlet state (ground state, GS), followed by a geometric twisting charge transfer state (CTS*) of the fluoren units relative to the central arylacetylide plane. For 3, 4, and 5, three dynamic decay processes are observed. The first process is the same as those of 1 and 2. However,the geometric twisting of 3, 4, and 5 is easier than 1 and 2 due to the presence of Pt atoms in the molecular skeleton of 3, 4, and 5, which makes a fast S1S* → geometric twisting state (TS*) occurred before the charge transfer occurring, and then a subsequent geometric twisting state (TS*) to geometric twisting charge transfer state (CTS*) occurs. The nonlinear optical properties of these compounds, studied using the open aperture Z-scan technique (λ = 532 nm, pulse width 23 ps), show that the values of the title compounds are around tens of cm/GW, which are comparable to newly reported porphyrin-based MOF materials and much better than Ru(II) terpyridine complexes..The mechanism of the nonlinear optical properties is attributed to the excited state absorption based on S1S*, TS*, and CTS* states, according to the femtosecond transient absorption and Z-scan results. The increase of Pt content percentage does not benefit the nonlinear absorption of Pt-containing compounds for the picosecond pulse laser. This is because the increase of the intersystem crossing rate weakly contributes to the nonlinear optical properties.

Carrier density tuning in CuS nanoparticles and thin films by Zn doping via ion exchange.

Copper sulphide (covellite) nanoplatelets have recently emerged as a plasmonic platform in the near-infrared with ultrafast nonlinear optical properties. Here we demonstrate that the free-carrier density in CuS, which is an order of magnitude lower than in traditional plasmonic metals, can be further tuned by chemical doping. Using ion exchange to replace Cu with an increasing content of Zn in the nanoparticles, the free-hole density can be lowered, resulting in a long-wavelength shift of the localised plasmon resonances from 1250 nm to 1750 nm. The proposed approach provides new opportunities for tuning the plasmonic response of covellite nanocrystals as well as the carrier relaxation time which decreases for lower free-carrier densities.

Novel metallated imidazole phthalocyanines: synthesis, ultrafast excited-state carrier dynamics and multiphoton absorption properties

Herein we report a comprehensive investigation of ultrafast photophysics and nonlinear optical properties of novel metallated imidazole phthalocyanines.

Tunable ultrafast near-infrared nonlinear optical properties of Eu3+ and silver nanoparticles doped alkali borate glasses

Achieving strong optical nonlinearities in vitreous nanocomposites is imperative for the advancement of futuristic telecommunication and photonic technologies. In this regard the borate materials (vitreous) are deemed to be important and currently available commercial hosts. In the current work, we demonstrate the tuning of the third-order nonlinear optical (NLO) attributes of borate-based glass samples doped with metal nanoparticles (NPs) and rare earth ions through annealing process. The NLO attributes, such as nonlinear optical absorption and refraction have been analysed by the sensitive Z-scan approach in the open and closed aperture configurations, respectively. The NLO features were examined in the near-infrared spectral region using ultrafast laser pulses fired at a high repetition rate from a Ti: sapphire laser oscillator. The open aperture data unveiled the existence of two-photon absorption whilst closed aperture indicated the occurrence of self-focusing nonlinear refraction. The NLO coefficients improved with heat treatment duration but the nonlinear absorption coefficient reduced at longer heat treatment schedules. The enhancement in the NLO coefficients is ascribed to the local field enriched by metallic silver NPs in the proximity of the rare earth ions when high-energy laser pulses irradiate the hosts. The results suggest the glasses routed with rare earth ions and metallic silver NPs annealed for 40 hrs at 450 °C are beneficial for optical communication and nonlinear photonic device applications, including optical limiting functionalities.

Nonlinear optical properties of MXene and applications in broadband ultrafast photonics

As a typical kind of two-dimensional transition metal carbides, nitrides and/or carbonitrides (MXene), Ti 3 C 2 T x has attracted extensive attention in optoelectronic field owing to their outstanding thermal, optoelectronic, and nonlinear optical properties. Ti 3 C 2 T x has been widely used as saturable absorber (SA) for achieving ultrafast pulses, whereas the influence of recovery time on its nonlinear optical properties as SA in laser needs further exploration. Herein, the ultrafast dynamics and nonlinear optical properties of Ti 3 C 2 T x are investigated by the methods of transient absorption and balanced twin-detector measurements. According to the experimental results, Ti 3 C 2 T x has a bleaching recovery time more than 160 ps, resulting in a low saturation intensity. The prepared Ti 3 C 2 T x is utilized as SA to achieve Q-switched pulses at 1- and 1.5- μ m bands. This study demonstrates that ultrafast dynamics has a significant impact on adjusting and optimizing nonlinear optical parameters of MXenes, as well as designing new photonic devices. • Optical properties and applications of Ti 3 C 2 T x as saturable absorber (SA) in 1- and 1.5- μ m lasers were studied. • Effect of carrier dynamics of Ti 3 C 2 T x on saturable absorption performance was discussed. • Ti 3 C 2 T x as SA in lasers was quantitatively analyzed, benefiting for realizing customized SA. • Large-energy Q-switched pulses were realized in 1- and 1.5- μ m bands owing to low saturable intensity.

Interfacial charge transfers and ultrafast nonlinear optical response via constructing electronic structure-induced MoS2/ZnO heterostructure

The molybdenum disulfide (MoS 2 ) and ZnO composite system have reported as micro-nano photonic crystals in integrated optics. Based on interface engineering, their tunable nonlinear absorption (NLA) and photoelectric characteristics offer a flexible design strategies for saturation absorber and optical limiters. Nevertheless, the mechanism leading to the tunable NLA behavior has not been clearly elucidated, which were attribute to complex charge transfers and carrier regulation characteristics. In this article, MoS 2 /ZnO heterostructures with excellent nonlinear properties composed of ZnO nanorods (NRs) wrapped with MoS 2 nanosheets were prepared by magnetron sputtering (MS) synthesis of MoS 2 on highly stacked ZnO NRs. The MoS 2 /ZnO heterostructures exhibit an interesting brush-like morphology with abundant heterointerfaces base on optimizing sputtering time and temperature, which was beneficial to provide efficient charge transfer pathways. Due to the uneven distribution of the lowest nucleation free energy, MoS 2 nanosheets possess a hybrid mode of parallel (C // ) and perpendicular orientations (C ┴ ) on surface of ZnO NRs, which tends to form the bending and vertical growth of layered MoS 2 nanosheets. From electron-photon coupling effect, MoS 2 nanosheets, ZnO NRs and MoS 2 /ZnO heterostructures possess favorable saturation absorption (SA), reverse saturation absorption (RSA) and coexisting absorption behavior, respectively. In addition, a changeover from RSA to SA could be realized in MoS 2 /ZnO heterostructures by increasing the sputtering time. The NLA coefficient of MoS 2 /ZnO heterostructures are in the order of 10 −10 cm/W, which are about 2 times larger than those of the ZnO NRs. Thus, the MoS 2 /ZnO heterostructures with excellent NLA properties will be promising candidates in optoelectronic devices. • The interfacial charge transfers and carrier regulation characteristics of MoS 2 /ZnO composite have been studied. • The ultrafast nonlinear optical properties of MoS 2 /ZnO composite were analyzed. • The mechanism of growth and nonlinear absorption for MoS 2 /ZnO composite is analyzed.

Ultrafast intramolecular charge transfer dynamics and nonlinear optical properties of phenothiazine-based push–pull zinc porphyrin

Comprehensive investigations of the ultrafast photophysical properties and charge injection dynamics (adsorbed on mesoporous TiO2) of phenothiazine-functionalized push–pull Zinc porphyrin (LG6) utilizing a benzothiadiazole (BTD) as an acceptor unit is presented herewith. This includes density functional theory (DFT) calculations, fluorescence measurements, time-dependent fluorescence measurements, and femtosecond transient absorption (fs-TA) spectroscopy measurements. The charge injection dynamics of LG6 were compared with another porphyrin, LG5, with a similar molecular structure but thiophene as the acceptor unit instead of BTD. The multicomponent electron injection analysis from different excited electronic energy levels reveals ultrafast electron injection times of 434 fs and 336 fs for LG6 and LG5, respectively, revealing the impact of acceptor units on charge injection times. Further, femtosecond nonlinear optical (NLO) properties were characterized using the femtosecond Z-scan measurements with 70 fs, 800 nm pulses. The analysis of Z-scan open aperture data has been performed by solving three-level rate equations incorporating excited-state lifetimes calculated from the target/global analysis of fs-TA data set. The estimated NLO parameters and ultrafast NLO response times of LG6 indicated the strong potential for optical limiting and optical signal processing applications. The second hyperpolarizability was estimated to be γ=2.5×10-31esu, which was found to be in close agreement with the theoretically calculated value of 0.4×10-31e.s.u.