Z-scan Technology Research Articles

Nonlinear absorption of CsPbBr3/antimonene blend materials prepared by laser ablation in liquid

Recently, through the continuous research on perovskite materials, the excellent nonlinear optical properties of perovskite have been shown to the world. Nevertheless, people still try their best to improve its optical nonlinearity to make it better applied to nonlinear optical devices. In this work, the nonlinear optical performance of the perovskite quantum dot (PQD) has been studied and tested, and its reverse-saturable absorption property and optical limiting potential have been discovered. On this basis, we tried to further improve the nonlinearity of the PQD by compounding other materials that has excellent optical properties especially highly nonlinearity. It is found that the new two-dimensional (2D) Group-VA material antimonene He meets our needs. Although antimonene has excellent nonlinear optical performance, its dispersibility is poor and not easy to store. Here, we tried to incorporate PQD and antimonene to further improve its nonlinear optical performance. With the method of laser ablation in liquid (LAL), CsPbBr3/antimonene blend materials (CPBAB) with stronger nonlinear absorption and higher dispersibility were successfully prepared. The nonlinear absorption properties of CPBAB with different ablation time were studied by Z-scan technology. It was found that by adjusting the laser ablation time parameters, CPBAB with higher optical limiting ability could be prepared. In addition, this CPBAB can be encapsulated in a polymer for curing, which improves its practical application to protect human eyes and optical equipment from high-power laser damage.

Ultrafast nonlinear absorption properties of Ag/Sb2Se3 composite films in the near-infrared region

To explore the nonlinear absorption(NLA) properties of the Sb2Se3 composite system, Ag/Sb2Se3 composite films were prepared by magnetron sputtering at room temperature, and part of the films were annealed under 300 °C. The NLA properties were investigated using femtosecond(fs) Z-scan technology under 800 nm. The results showed that Ag/Sb2Se3 and annealed-Ag/Sb2Se3 composite films exhibited reverse saturated absorption(RSA) and saturated absorption(SA), respectively. The results indicated that annealing could tunable the NLA types of composite films. Furthermore, Ag can strengthen the NLA properties of the Ag/Sb2Se3 composite films compared with the single Sb2Se3. By increasing Ag sputtering power and incident laser energy, the NLA properties of composite films are enhanced. This study provides a new perspective for the application of Ag/Sb2Se3 composite films in optoelectronic devices.

Nonlinear optical properties of Au@Ag coreshell nanospheres excited by femtosecond laser

The nonlinear optical properties and ultrafast dynamics process of Au@Ag coreshell nanospheres (NSs) are reported in this paper. We researched the optical nonlinear absorption property of Au@Ag coreshell NSs excited by 800 nm laser at different energies by open-aperture Z-scan technology. The experimental results demonstrated that the Au@Ag coreshell NSs exhibited two-phone absorption (TPA) behavior, the degree of which was intensity-dependent. The TPA coefficients of Au@Ag coreshell NSs excited by different energies were obtained by fitting. By using pump-probe technology, we studied the ultrafast dynamics process of Au@Ag coreshell NSs. The results indicated that the relaxation process contained a fast and a slow process, which depended strongly on the laser intensity. By numerical fitting, we got the relaxation times of the sample excited at different laser powers.

Tin selenide: A promising black-phosphorus-analogue nonlinear optical material and its application as all-optical switcher and all-optical logic gate

All-optical technique is an effective method to breakthrough the speed limitation of electric devices. Due to the strong nonlinear optical properties, two-dimensional materials have been concerned. As a potential nonlinear two-dimensional material, SnSe has been applied in the field of ultrafast laser generation. The measurement of nonlinear refractive index of SnSe and its nonlinear application is rare. In this paper, SnSe nanosheets are fabricated by a facial Li intercalation-assisted liquid exfoliation method. The nonlinear optical parameters are measured by the Z-scan technology. The SnSe-coated microfiber acted as a nonlinear device to achieve an all-optical switch and an all-optical AND gate. The wavelength-tuning and long-term stability results confirm that SnSe materials are excellent nonlinear optical medium. It is anticipated that SnSe has potential applications in nonlinear photonics devices toward high-performance all-optical signal processing.

Influences of CO2 laser modification on the surface morphology and optical absorption of graphene thin films

Abnormal optical absorption phenomena were observed in as-modified few-layer graphene thin films by 10.6-μm CO2 laser under ambient conditions. Saturable absorption (SA) responses were measured using z-scan technology. The graphene samples showed SA before laser modification, whereas they exhibited reverse SA behavior after laser modification due to the effects of thinning and damage to samples. The shift of 2D peak and appearance of D peak from Raman scattering spectra further confirm the effects of laser irradiation on graphene.

Third-order nonlinear optical responses of CuO nanosheets for ultrafast pulse generation

As a representative transition metal oxide, cupric oxide (CuO) has attracted a lot of interest in miscellaneous fields. In the present work, the prominent third-order nonlinear optical (NLO) features of CuO nanosheets were demonstrated via the typical Z-scan technique at 1 μm. The open-aperture (OA) Z-scan measurements at different intensities clearly showed that CuO nanosheets possessed the saturable absorption (SA), reverse saturable absorption (RSA) and optical limiting behaviors. The closed-aperture (CA) Z-scan technology was implanted to investigate the nonlinear refractive index and the third-order nonlinear susceptibility. In virtue of the strong nonlinear optical absorption properties of CuO nanosheets, a stable all-solid-state mode-locked laser with the as-prepared CuO nanosheets as saturable absorber at 1.06 μm was realized for the first time. Our work confirmed that CuO nanosheets exhibited outstanding NLO properties, which might stimulate the development in ultrafast photonics and nonlinear optics.

Measurements of Linear and Nonlinear Optical Properties for Iraqi Heavy Crude Oil Samples

In this work, linear and nonlinear optical properties of two types of Iraqi heavy crude oil extracted from fields in southern Iraq were determined. The nonlinear optical properties were measured utilizing Z-scan technology with He-Ne laser at 632.8 nm. It was found that nonlinear refractive index (NLR) values for the Basra and Kut heavy crude oil samples are 6.34381×10-4 and 8.25108×10-4 cm2/mW, respectively, while those for the nonlinear absorption coefficient (NLA) are 2.68942×10-5 and 2.58874×10-5 , respectively. These results showed that the two samples with linear and nonlinear optical properties can be used in optics field applications as optical limiter devices at a wavelength of 632.8 nm.

Enhanced broadband nonlinear optical response of TiO2/CuO nanosheets via oxygen vacancy engineering

Abstract Cupric oxide (CuO), as a transition metal oxide (TMO) semiconductor, has attracted tremendous attention for various applications. In the present work, we synthesize the CuO nanosheets modified by TiO2 nanoparticles via a facile, non-toxic two-step method. Subsequently, the morphology and the structures of CuO and TiO2/CuO nanocomposites are investigated. By utilizing the common Z-scan technology, broadband nonlinear optical (NLO) properties of the as-prepared CuO nanosheets and TiO2/CuO nanocomposites are demonstrated, elucidating the enhancement on the NLO response via the TiO2 dopant, which is attributed to the more oxygen vacancies and the formed p-n junctions. Furthermore, CuO nanosheets and TiO2/CuO nanocomposites are implemented to the passively Q-switched bulk lasers operating in the near-infrared (NIR) region, generating broadband ultrastable pulses. Ultimately, TiO2/CuO nanocomposites were intergrated in a passive mode-locking bulk laser for the first time, achieving stable mode-locked pulses and verifying its ultrafast optical response potential. Our results illustrate the tremendous prospects of the CuO nanosheets modified by oxygen vacancy engineering as a broadband NLO material in ultrafast photonics field.

Enhanced Q-switching performance of magnetite nanoparticle via compositional engineering with Ti3C2 MXene in the near infrared region

In this work, we reported a new strategy to improve the nonlinear saturable absorption performance of magnetite (Fe3O4) nanoparticles (FONPs) via the compositional engineering with the Ti3C2 MXene in the near-infrared (NIR) region. Based on the DFT simulation, the band structures and work function were significantly modified by the Ti3C2 MXene doping. By using the open-aperture Z-scan technology, the nonlinear optical features of the FONPs@Ti3C2 nanocomposite were significantly improved, showing the great potential as the saturable absorber in the pulsed laser. With the nanocomposite as the saturable absorber, the passively Q-switched Nd:GdVO4 lasers emitted much shorter pulse durations when compared with the pristine FONP saturable absorber. These findings indicated that FONPs@Ti3C2 heterostructure was a promising saturable absorber for the short pulse generation in the NIR region.

不同核心尺寸及壳层厚度CdTe/CdS量子点非线性光学及超快动力学特性

CdTe core-shell semiconductor quantum dots are being widely explored due to their special nonlinear optics and ultrafast dynamics characteristics that include solar cells, optoelectronic devices, biological labeling, and optics fiber sensing fields. In this work, the six kinds of CdTe/CdS core-shell quantum dots were researched in the different core sizes and shell thicknesses for the nonlinear optics and ultrafast dynamics characteristics. The nonlinear absorption and refraction coefficients of the samples were measured by using Z-scan technology under the action of 400 nm wavelength and 130 fs laser pulse width. The experimental results show that the shell thickness of CdTe/CdS core-shell quantum dots affects the nonlinear absorption and refraction characteristics, in which the nonlinear absorption and refraction coefficients increase with the shell thickness. And the core size mainly affects the nonlinear absorption characteristics, while the nonlinear absorption coefficient decreases with the increase of the core size. At the same time, femtosecond time-resolved transient absorption spectroscopy technology was used to measure the ultrafast dynamics characteristics of the samples under the conditions of 400 nm wavelength, 130 fs pulse width, 1 kHz frequency, and 400 nJ single-pulse energy. The transient absorption spectra and ultrafast dynamics curves were obtained. The results suggest that the rising time of bleaching signal increases with the shell thickness. The decay time of the fast process increases with the shell thickness and core size. The decay time of the slow process increases with the shell thickness. The research reveals the influence of the core size and shell thickness of CdTe core-shell quantum dots on the nonlinear optics and ultrafast dynamics, providing a theoretical basis for the preparation of core-shell quantum dots and the research of the photophysical properties.

Large-scale monolayer molybdenum disulfide (MoS2) for mid-infrared photonics

Abstract Mid-infrared (MIR) photonics has attracted tremendous interest because of its broad applications at atmospheric windows. In this work, we report high-performance MIR photonics based on large-scale and good-quality monolayer molybdenum disulfide (MoS2). The open-aperture Z-scan measurement on the nonlinear saturable absorption features shows that the as-grown monolayer MoS2 possesses a modulation depth of 26% and a low saturable intensity of 271 kW/cm2, enabling its application as an excellent saturable absorber for the MIR pulse generation. This is further evident by the measured high effective nonlinear absorption coefficient β eff (−16 cm/MW). In addition, the two-photon absorption coefficient and the nonlinear refractive index of monolayer MoS2 are also determined by the closed-aperture Z-scan technology. As an application, we demonstrate a passively Q-switched Tm,Ho:CaLu0.1Gd0.9AlO4 (Tm,Ho:CLGA) disordered crystal laser at 2.1 μm by using the monolayer MoS2 as the saturable absorber for the first time, producing a minimum pulse width of 765 ns and a pulse repetition rate of 36 kHz. Our results demonstrate that large-scale monolayer MoS2 is a promising candidate for the MIR photonic applications.

Two-Dimensional Black Arsenic Phosphorus for Ultrafast Photonics in Near- and Mid-Infrared Regimes.

Black arsenic phosphorus (b-AsP), as one kind of novel two-dimensional (2D) materials, bridges the band gap between black phosphorus and graphene. Thanks to its great advantages, including high carrier mobility, excellent in-plane anisotropy, and broad tunability band gap, b-AsP has aroused great interest in fields of photonics and photoelectronics. In this paper, ultrathin 2D b-AsP nanomaterials were fabricated by the liquid-phase exfoliation method, and their strong broadband linear and nonlinear absorptions were characterized by ultraviolet-visible-infrared and Z-scan technology. The experimental determination of the nonlinear absorption coefficient and low saturation intensity of b-AsP were -0.23 cm/GW and 3.336 GW/cm2, respectively. Based on density functional theory, the partial charge density and band structure at the conduction band minimum and valence band maximum were calculated, which further proves the excellent optical properties of 2D b-AsP. By first using 2D b-AsP as a novel saturable absorber in both erbium-doped and thulium-doped fiber lasers, mode-locked soliton pulses can stably operate at 1.5 and 2 μm. The laser pulses generated by 2D b-AsP possess higher stability to resist self-splitting than those generated by other 2D material-based mode-lockers. These experimental results highlight that 2D b-AsP has great application potential as a novel optical material in ultrafast photonics from near- to mid-infrared regimes.

Nonlinear absorption-induced transparency and extinction of boron nanosheets

Abstract Two-dimensional (2D) materials exhibit interesting nonlinear optical properties, and they have been used in bioimaging, ultrafast photon and all-optical switch devices. Boron nanosheets is a recently emerging 2D material that has attracted the attention of a large number of researchers. In this work, the saturation absorption (SA) effect of boron nanosheets has been investigated through a typical z-scan method, it is demonstrated that the nonlinear absorption coefficient and the quality factor are greatly improved compared with the other 2D materials such as black phosphorus, MoS2 and Ti3C2Tx. By combining the all-optical modulation and z-scan technology, the competition between the laser intensity-dependent SA and nonlinear scattering in boron nanosheets are revealed, and hence the optically-induced transparency and optically-induced extinction in nanosecond regime have been confirmed. Based on this competitive effect, an effective modulation of continuous light (λ = 671 nm) by nanosecond pulses (λ = 532 nm) has been realized, the maximum modulation depth of 5.5 dB is obtained.

Synthesis, structure and ultrafast nonlinear absorption properties of ZnO-time/MoS2 films

In this paper, ZnO, MoS2 and ZnO-time/MoS2 films with excellent nonlinear absorption (NA) properties were successfully prepared by single/two-step magnetron sputtering. The morphology, structure and NA property of the samples were studied. The scanning electron microscope results show that cluster-like MoS2 have different morphology. This phenomenon can be attributed to the fact that the multi-directional growth of the ZnO base films causes the original growth orientation of MoS2 to be changed. The NA characteristics under different excitation intensities are studied by Z-Scan technology. The material exhibits the reverse saturation absorption characteristic caused by two-photon absorption. Furthermore, the order of magnitude of NA coefficient for samples was determined to be 10−6 cm/W. The ZnO-time/MoS2 films display excellent NA characteristics, which are desirable for field of optical switch, optical limiting, optical communication and integrated optics.

INVESTIGATING THE NONLINEAR OPTICAL PROPERTIES OF CuS THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION USING Z-SCAN TECHNIQUE

CuS thin films were participated onto glass substrate by using chemical Bath Deposition method at (75οC) for (1hr) with different concentrations (0.03,0.05 and 0.08)M of Thiourea (TU) and Copper Chloride with molar ratio (0.01 ) have been used for solution preparation. As deposition and annealed films were studied. Non-linear absorption coefficient is measured by using Z-Scan technology and it consists of two sections. The first section is closed opening were located before detector to calculate the non-linear refractive index. Whereas the second section, were aperture located before the detector (the open aperture) is taken to calculate the non-linear absorption coefficient. Both cases are done with a CW laser with a wavelength of 650 nm and a power of 50 MW

Passively Q-switched Tm:CaLu0.1Gd0.9AlO4 laser at 2 µm with hematite nanosheets as the saturable absorber.

We report the first passive Q-switching operation at 1.95 µm utilizing the disordered Tm:CaLu0.1Gd0.9AlO4 (Tm:CLGA) crystal and the hematite (α-Fe2O3) nanosheets as the saturable absorber. The nonlinear saturable absorption properties of the hematite nanosheets were investigated by the conventional Z-scan technology. The modulation depth of 14.3% with the low saturation intensity of 205 kW/cm2 was obtained, indicating that the hematite could be a suitable saturable absorber for the mid-infrared pulse generation. Using the disordered Tm:CLGA crystal as the gain medium, the passive Q-switching operation could be realized with the hematite nanosheets as the saturable absorber, producing the shortest pulse duration of 402 ns with a repetition rate of 76 kHz. The experimental results convinced us that the hematite nanosheets could be of great interest in the optical pulse generation in the mid-infrared region.

Control of third-order nonlinear optical properties by coordination metal change based on a series of metal organic chains

The research on the third-order nonlinear optics (NLO) materials have attracted more and more attention. In this work, an organic ligand (H2L) containing azo phenyl group and coordination N atom is selected. The presence of NN increases the fluidity of electrons in the azo molecule, which greatly improves the third-order nonlinearity. Furthermore, we synthesized three H2L-based metal complexes [Mn(L)(H2O)4]n (1), [Zn(L)(H2O)2]n (2) and [Cd(L)(H2O)4]n (3) and their nonlinear performances was also measured using Z-scan technology. The results show that the coordination bond between metal ions and the ligand changes the delocalization of the whole systems, resulting in changed the nonlinear performances. The calculation of density functional theory (DFT) confirms that the Mn2+ and Zn2+ addition is not obvious to influence NLO, and the addition of Cd2+ makes the non-linear signal weaken. The reason may result from the valence layer electron configuration of the different metal ions.

Passively Q-switched near-infrared lasers with bismuthene quantum dots as the saturable absorber

Bismuthene quantum dots (Bi-QDs) were synthesized via the liquid phase exfoliation (LPE) method for the passive Q-switching operation in near-infrared (NIR) region. The nonlinear optical properties of the prepared Bi-QDs were investigated by the open-aperture Z-scan technology. The modulation depths were 18.1% and 5.1% at 1.06 and 1.34 µm, respectively. Based on the Bi-QDs saturable absorber, passively Q-switched Nd:GdVO4 lasers operating at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 transitions were demonstrated, showing the wideband optical modulation in NIR regime. For the 4F3/2 → 2I13/2 transition lasing at 1.34 µm, the shortest pulse duration of 155 ns was obtained with a repetition rate of 457 kHz. With respect to the 4F3/2 → 2I11/2 transition at 1.06 µm, the minimum pulse duration was 150 ns with a repetition rate of 424 kHz, leading to a single pulse energy of 261 nJ and a peak power of 1.68 W. In addition, the ground state absorption cross section and the excited state absorption cross section of Bi-QDs were also investigated for the first time. The impact of the excited state lifetime on the output parameters was numerically stimulated by the coupled rate equations. Our work confirmed that the trap state in Bi-QDs played an important role in the pulse generation mechanism.

Interference rings induced by ultrafast laser pulse in GaAs crystal

Gallium arsenide (GaAs) is an important semiconductor material with direct bandgap and clear-cut absorption edge. High-quality crystal is available, which has excellent performances in the field of high power transmission and luminescence because of high laser damage threshold and high thermal conductivity. Nonlinear optics is of great significance for developing the laser technology, spectroscopy, and optoelectronic devices. The Z-scan technology is a nonlinear measurement method based on the analysis of single beam transmittance. Previous studies mainly focused on the measurement of the nonlinear absorption coefficient of the sample by open-aperture configuration of Z-scan and the nonlinear refractive index of the sample by shut-aperture configuration of Z-scan. We build a dual-channel Z-scan system with variable optical path difference, equipped together with a high speed camera, to observe the spatial distribution of transmitted light. Besides, we find the interference rings induced by nonlinear absorption in semiconductor GaAs crystals. Using three kinds of lasers (continuous-wave laser, 80 MHz femtosecond pulsed laser, 1 kHz femtosecond pulsed laser) to illuminate the GaAs crystal separately, multi-level interference rings come out only when a GaAs crystal wafer is illuminated by a femtosecond pulsed laser. In the single-channel Z-scan experiment, we observe that the interference rings contract or expand regularly when changing pulsed laser intensity incident on the surface of GaAs crystal. The higher the intensity of pulse, the more interference rings appear, and the maximum exiting angle becomes larger. Nonlinear effect of high intensity femtosecond pulsed laser locally changes the refractive index of GaAs crystals, resulting in optical path difference (Kerr lens effect). However, the Kerr lens generated by ultrafast light pulse in GaAs crystal cannot focus a beam as done by an ideal thin lens, leading the transmitted light to form interference rings instead. By analyzing the variation of the interference rings, the nonlinear absorption coefficient and refractive index of GaAs crystal can be obtained. In the dual-channel Z-scan experiment, different interference rings are induced in the GaAs crystal as the path difference between the two pulses changes, as done by the nonlinear transmission power. Thus we obtain the formation time of the interference rings and ascribe it to the ultrafast relaxation process of GaAs carriers.

Efficient Construction of Near-Infrared Absorption Donor–Acceptor Copolymers with and without Pt(II)-Incorporation toward Broadband Nonlinear Optical Materials

Organic nonlinear optical (NLO) materials have attracted immense scientific interest in various fields. Broadband NLO response extending to near-infrared (NIR) region is extremely important and remains challenging. Herein, two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A)-type π-conjugated copolymers with and without Pt(II) incorporation are rationally designed and synthesized toward broadband NLO response materials. The broad intramolecular charge transfer (ICT) absorption reaching 1000 nm due to the strong D-A interaction is well demonstrated by photophysical characterizations. The NLO properties of copolymers are studied using Z-scan technology. Owing to their extended π-conjugated D-A systems and near-infrared ICT absorption properties, both copolymers exhibit laser-induced NLO response to nanosecond as well as picosecond laser pulses upon the wavelengths of 532 and 1064 nm. Interestingly, introducing Pt(II) into the copolymer backbone can evidently improve the NLO property or unexpectedly switch the NLO response from saturable absorption to reverse saturable absorption. Meanwhile, both copolymers are successfully employed as optical limiting materials and exhibit broadband optical limiting abilities. Therefore, we present an efficient strategy toward broadband NLO materials, which may significantly facilitate the understanding of organic molecular structure-property relationship and promote their practical application.