Nonlinear Absorption Properties Research Articles

2D Ti4AlN3 (MAX): An excellent infrared nonlinear absorption material

Two-dimensional (2D) materials have drawn more attention since the discovery of graphene. The exploration of the nonlinear optical (NLO) properties of 2D materials has become more urgent. In this work, Ti4AlN3 nanosheets with a thickness of about 1.7–1.9 nm were prepared using the liquid phase exfoliation (LPE) method, and the open aperture (OA) Z-scan technique was used to explore the broadband nonlinear absorption (NLA) properties of 2D Ti4AlN3 nanosheets at three wavelengths, namely, 355, 532, and 1064 nm. According to the results, 2D Ti4AlN3 nanosheets exhibited excellent optical limiting (OL) behavior in all three bands, especially in the infrared (IR) band. The large two-photon absorption (TPA) coefficient and low OL excitation threshold indicated that Ti4AlN3 had great potential as OL material in the IR band for applications such as optical filters, protection of the human eye, laser protection, etc.

Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications

Nonlinear absorption properties of PbMo0.75W0.25O4 single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo0.75W0.25O4 single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo0.75W0.25O4 single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (β eff ) increased from 7.24 × 10−10 m W−1 to 8.81 × 10−10 m W−1 with increasing pump intensity. At higher intensities β eff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo0.75W0.25O4 single crystal at the lowest intensity was determined as 3.45 mJ/cm2. Results show that the PbMo0.75W0.25O4 single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.

Stress and interfacial/surface synergistically modulated charge transfer mechanism and nonlinear absorption properties in Ti3C2(-O)/MoS2 heterostructure

Here, Ti3C2(-O)/MoS2 with two interface contacts were obtained by two-steps of hydrothermal (HT)/HT and HT/magnetron sputtering (MS) technique. The visualizing orientation-controlled interlayer interconnection and vertical/lateral contact modes for interface properties and light-matter coupling effect have been analyzed. The Raman spectra of Ti3C2(-O)/MoS2(HT) verified that the redshift of characteristic peak for Ti3C2(-O) was dominated by interfacial stress. The results of Ti3C2(-O)/MoS2(MS) revealed that the overall blue shift of the characteristic peak for Ti3C2(-O) and the redshift of the characteristic peak for MoS2 can be attributed to the interface charge transfer of MoS2 to Ti3C2(-O). The exciton quenching of Ti3C2(-O) and the enhancement of the C exciton transition luminescence for MoS2 were observed in the photoluminescence result. It is proved that the high-excited electrons of Ti3C2(-O) transfers to the vibration level of the conduction band of MoS2 under photoexcitation. The nonlinear absorption and transient absorption properties of Ti3C2(-O)/MoS2 heterojunction were studied by Z-scan and pump–probe technology. An additional interfacial charge transfer signal in the hybrid spectra represents the efficient interfacial charge transfer of Ti3C2(-O)/MoS2(HT) and Ti3C2(-O)/MoS2(MS). This work also provides a basic theory for the emerging heterojunctions, which is conducive to developing the potential optoelectronic devices in energy environment field.

Saturable absorption properties and ultrafast photonics applications of HfS3.

In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS3 nanosheets. We prepared two-layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS3-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS3 material. Furthermore, we utilized the two-layer HfS3 materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices.

Introducing Optical Nonlinearity in PDMS Using Organic Solvent Swelling

The feasibility of introducing optical nonlinearity in poly-dimethyl siloxane (PDMS) using organic solvent swelling was investigated. The third-order nonlinear refraction and absorption properties of the individual materials, as well as the PDMS/solvent compounds after swelling were characterized. The well-established Z-scan technique served as characterization method for the nonlinear properties under picosecond pulsed laser excitation at a 532 nm wavelength. These experiments included investigations on the organic solvents nitrobenzene, 2,6-lutidine, and toluene, which showed inherent optical nonlinearity. We showed that nitrobenzene, one of the most well-known nonlinear optical materials, has proven suboptimal in this context due to its limited swelling effect in PDMS and comparatively high (non)linear absorption, resulting in undesirable thermal effects and potential photo-induced damage in the composite material. Toluene and 2,6-lutidine not only exhibited lower absorption compared to nitrobenzene but also show a more pronounced swelling effect in PDMS. The incorporation of toluene caused a weight change of up to 116% of PDMS, resulting in substantial nonlinear optical effects, reflected in the nonlinear refractive index of the PDMS/toluene composite n2=3.1×10−15 cm2/W.

Tunable third‐order NLO properties of acene derivatives with molecular structural modification

AbstractThe substitution of heteroatoms and the expansion of π‐conjugated units have significant effects on the photoelectric properties of polycyclic aromatic hydrocarbons (PAHs). In this study, based on the experimental molecule PBC, 10 acene derivatives containing the pyrrole group were designed by three strategies: (1) changing the connection position of the pyrrole group, (2) exchanging the position of the N atom, and (3) increasing the length of the π‐linker. Density functional theory (DFT) was used to optimize the molecular geometric structure. Time‐dependent density functional theory (TD‐DFT) was used to calculate the relevant parameters of the excited states. The results show that both of the pyrrole group and the N atom in the para‐position, and the addition of the π‐linker can reduce the energy gap, cause redshift of the linear absorption peak, and increase the two photon absorption (TPA) cross‐section. The analyses of the charge density difference (CDD) and the charge‐transfer matrix (CTM) proved that the electron transfer is mainly concentrated in the π‐linker. Moreover, the participation of the multi‐ring skeleton on both sides decreases gradually with the increase of the length of the π‐linker. The length of the π‐linker changes the dominant transition channel and intramolecular charge‐transfer (ICT) characteristics of TPA, thus affecting the transition dipole moments and nonlinear absorption properties. The second hyperpolarizability of the designed molecule PBI5‐p5 is also significantly superior to that of similar materials reported. It is expected that the above molecular design strategies and comprehensive analysis of nonlinear optical (NLO) properties could provide theoretical support for the research on acene derivatives.

Nonlinear refraction and absorption properties of optical materials for high-peak-power long-wave-infrared lasers

Optical materials transparent in the CO2 laser wavelength range have been evaluated regarding their suitability for components in ultrashort-pulse (≤ a few ps), high-peak-power (≥ a few TW) long-wave infrared (LWIR) lasers. We provide values for the nonlinear refractive index (n2) for seventeen materials, and onsets for nonlinear absorption for eleven materials. Characterizations were performed using a 2 ps laser pulse at λ=9.2μm. This paper methodically presents the newly acquired data in conjunction with existing literature on linear optical properties, establishing it as a comprehensive reference for designing high-peak-power LWIR laser systems.

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.

Carbon nanodots derived from organo-templated zeolites for femtosecond mode-locked fiber laser

Carbon nanodots (CNDs) have been widely investigated due to their physicochemical and optical properties. However, the nonlinear saturable absorption property and its application in laser technology is rarely reported. Here, we report the CNDs as an ideal saturable absorber (SA) for ultra-stable femtosecond mode-locked fiber laser at a wavelength of 1.5 μm. The mono-sized CNDs of 2 nm are fabricated from a dipropylamine-templated zeolite precursor calcination with a temperature of 380 °C. The nonlinear saturable absorption property of the as-synthesized CNDs is investigated by using a balanced twin-detector measurement system. The modulation depth and saturable intensity are measured to be 33 % and 3.1 MW/cm2, respectively. By inputting the CNDs SA into the erbium-doped fiber laser (EDFL) ring cavity, a highly stable mode-locked EDFL with pulse width of 388 fs and single-to-noise ratio (SNR) of 84.4 dB can be obtained. In addition, stable soliton pairs with single-pulse width of 422 fs and SNR of 84.1 dB can also be achieved. These findings demonstrate that the carbon dots can be used as an ideal SA and has promising applications in ultrafast photonics.

Enhanced nonlinear absorption and photoluminescence properties of Zn, Fe, Cu, V and Ni doped MoO3 transition metal oxide thin films

Abstract In this study, the effect of the dopant element on the linear, nonlinear absorption and optical limiting properties of ultrasonically sprayed MoO3 thin films is presented. The linear optical results showed an increase with the density of the defect states in the bandgap with doping, in conjunction with a decrease in bandgap energy and an increase in Urbach energy. Broad photoluminescence emissions are detected in the range of 350 and 600 nm, decreasing in intensity by doping. To reveal the defect states effects’ on the nonlinear absorption (NA) behavior, OA Z-scan data were analyzed with two theoretical models considering only two photon absorption (2PA) (model 1), and one photon absorption (OPA), 2PA and free carrier absorption (model 2). The NA behavior is observed and found to get enhanced by increasing input intensity and doping atoms due to generation of new oxygen vacancies and formation of further defect states. The NA coefficient values of the thin films in model 2 are 100 times higher than that of 2PA coefficient values in model 1. This result revealed the strong effect of defect states on the NA behavior. Among the investigated dopant atoms, Cu resulted in enhanced NA due to the higher density of defect states. While the genuine 2PA is the dominant NA mechanism for V and Fe doped MoO3 thin films, OPA and 2PA are the dominant NA mechanisms for the Ni, Zn and Cu doped MoO3 thin films due to their higher concentration of defect states. Cu-doped MoO3 thin film has a lower optical limiting threshold of 0.026 mJ/cm2 due to its enhanced NA behavior. Considering the results obtained, this study opens the door to the potential of doped MoO3 thin films to be used as optical limiters in the visible wavelength region.

Defect and interface/surface engineering synergistically modulated electron transfer and nonlinear absorption properties in MoX2 (X = Se, S, Te)@ZnO heterojunction.

Systematic interface and defect engineering strategies have been demonstrated to be an effective way to modulate the electron transfer and nonlinear absorption properties in semiconductor heterojunctions. However, the role played by defects and interfacial strain in electron transfer at the interface of the MoX2 (X = Se, S, Te)@ZnO heterojunction remains poorly understood. Herein, using the MoX2@ZnO heterojunction, we reveal that vacancies play a critical role in the interfacial electron transfer of heterojunctions. Specifically, we present the defect and interface engineering of the MoX2@ZnO heterojunction for controlled charge transfer and electron excitation-relaxation. The experimental characterization combined with first-principles calculations showed that the presence of defects promoted the transport of photogenerated carriers at the heterojunction interface, thereby inhibiting their rapid recombination. The DFT calculation confirmed that the electron band structure, density of states and charge density distribution in the system changed after the formation of Mo-O bonds. On the basis of defects and interfacial stress and the effective charge transfer, the MoX2@ZnO heterojunction exhibited excellent excitation and emission behaviors. The nonlinear optical regulation behavior of TMDs is expected to be realized with the help of the defects and interface/surface synergistically modulated effect of ZnO nanoparticles. The local strain generation on the MoX2@ZnO heterojunction boundary provides a new method for the design of new heterogeneous materials and will be of great significance to investigate the contact physical behavior and application of metals and two-dimensional (2D) semiconductors. This work provides some inspiration for the construction of heterojunctions with rich defects and surface/interface charge transfer channels to promote tunable electron transfer dynamics, thereby achieving a good nonlinear optical conversion efficiency and efficient charge separation in optoelectronic functional materials.

Application of Pr-MOFs as Saturable Absorbers in Ultrafast Photonics

As a newly synthesized metal-organic framework (MOF) material, Pr-MOFs have been theoretically predicted by researchers to have excellent optical response and nonlinear absorption properties. However, using Pr-MOFs for ultrafast photonics...

Enhancing saturable absorption in a Au-decorated MoS2/PEDOT:PSS nanocomposite through plasmon resonance and Pauli blocking.

We have effectively demonstrated a technique for substantial alteration of the nonlinear saturable absorption (SA) properties in nanocomposite films (NCF) composed of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) and molybdenum disulfide (MoS2) decorated with gold nanoparticles (AuNPs). This control is achieved by adjusting the AuNP concentration on the MoS2 surface and varying the input pulse energy of the laser. The simple drop-casting method is used to create the nanocomposite films (NCFs) on a glass substrate with different amounts of Au-decorated MoS2. The Kramers-Kronig equations are employed for determining the refractive index and extinction coefficient values of the resulting NCFs. Nonlinear investigations reveal that adding Au-decorated MoS2 to pure PEDOT:PSS alters its optical nonlinearity. Surface plasmon resonance and Pauli blocking have been observed in Au-decorated MoS2/PEDOT:PSS NCFs. This increases NCF's saturable absorption. An open aperture Z-scan method is utilized to study nonlinear optics, with excitation achieved using a nanosecond (ns) pulsed laser operating at a 532 nm wavelength. The findings reveal the noteworthy saturable absorption characteristics of the NCFs.

Q-switched fiber laser generation utilizing metal oxide-based saturable absorber in the region of 1.0 µm and 1.5 µm

In this study, we explored a saturable absorber (SA) using a metal oxide-biopolymer film, resulting in the generation of Q-switched fiber lasers at 1.0 µm and 1.5 µm wavelengths. A straightforward sonochemical technique was employed to synthesize a nickel oxide (NiO) film in cooperation with Chitosan as a host polymer. The fabricated NiO-Chitosan film exhibits nonlinear absorption properties with modulation depth of 32.20%, saturation intensity of 0.43 kW/cm2, and non-saturable loss of 7.80%. Upon integrating the NiO-Chitosan film into the cavities of Erbium-Doped Fiber Laser (EDFL) and Ytterbium-Doped Fiber Laser (YDFL), the emergence of stable self-starting Q-switched pulsed lasers were observed at 1040.86 nm and 1557.60 nm central wavelength, respectively. Notably, the shortest pulse widths of 0.73 µs and 2.44 µs were achieved, along with maximum repetition rates of 111.61 kHz and 61.73 kHz, respectively, at these wavelengths. Our investigation identifies an effective SA material with good nonlinear absorption properties for inducing Q-switching in the 1.0 µm and 1.5 µm regions. Significantly, the Chitosan properties, encompassing biocompatibility, non-toxicity, and high thermal resistance, combined with the uncomplicated NiO fabrication process and cost-effectiveness, hold promise for diverse applications.

2D Ti3AlC2 and Ti3C2 nanosheets: Excellent optical limiting materials for laser protection

MXenes have important research value in the field of photonics. In this work, Ti3C2 MXene was obtained by etching the Ti3AlC2 MAX phase with hydrofluoric acid, Ti3AlC2 and Ti3C2 nanosheets with a thickness of several nanometers were prepared by ultrasound-assisted liquid-phase exfoliation using anhydrous ethanol as the exfoliation solvent. The nonlinear absorption properties of the two nanosheets at 1064, 532 and 355 nm excitation wavelengths (infrared to ultraviolet band), especially the optical limiting behavior, were systematically investigated with the help of open aperture Z-scan technique. Interestingly, Ti3C2 MXene, obtained from Ti3AlC2 MAX by a simple hydrofluoric acid etching operation only, exhibits different nonlinear optical properties from Ti3AlC2 MAX under the same experimental conditions. Ti3AlC2 nanosheets exhibited excellent two-photon absorption behavior in the visible light band, while the two-photon absorption behavior of Ti3C2 nanosheets is better in the ultraviolet band. The excellent nonlinear absorption properties exhibited by Ti3AlC2 and Ti3C2 nanosheets demonstrate their advantages as OL materials with great potential for applications in laser protection.

VTe2: Broadband Saturable Absorber for Passively Q-Switched Lasers in the Near- and Mid-Infrared Regions.

In this study, we demonstrate the fabrication of a novel 2D transition metal dichalcogenide, VTe2, into a saturable absorber (SA) by using the liquid phase exfoliation method. Furthermore, the first-principles calculations were conducted to elucidate the electronic band structures and absorption spectrum. The nonlinear optical absorption properties of VTe2 at 1.0, 2.0, and 3.0 μm were measured using open-aperture Z-scan and P-scan methods, which showed saturation intensities and modulation depths of 95.57 GW/cm2 and 9.24%, 3.11 GW/cm2 and 7.26%, and 15.8 MW/cm2 and 17.1%, respectively. Furthermore, in the realm of practical implementation, the achievement of stable passively Q-switched (PQS) lasers employing SA composed of few-layered VTe2 nanosheets has manifested itself with broadband operating wavelengths from 1.0 to ∼3.0 μm. Specifically, PQS laser operations from near-infrared to mid-infrared with pulse durations of 195 and 563 ns for 1.0 and 2.0 μm solid-state lasers, respectively, and 749 ns for an Er3+-doped fluoride fiber laser at 3.0 μm were obtained. Our experimental results demonstrate that VTe2 is a potential broadband SA device for achieving PQS lasers. To the best of our knowledge, this is the first demonstration of using VTe2 as an SA in PQS lasers in the near- and mid-infrared regions, which highlights the potential of VTe2 for future research and applications in optoelectronic devices.

Nonlinear optical properties and ultrafast carrier dynamics of ultrathin ReSe2.

Rhenium diselenide (ReSe2) has shown great application potential in the field of optical devices because of its excellent optoelectronic properties. In this study, we systematically investigated the nonlinear optical absorption properties of mono- and bi-layer ReSe2 and the ultrafast carrier dynamics process in the ultraviolet to near-infrared spectral range as the essential foundational groundwork for harnessing the potential of ultrathin ReSe2-based optoelectronic devices. We found that ReSe2 has excellent nonlinear absorption performance and a low saturation absorption intensity that is better than that of many semiconductor materials. Meanwhile, pump-probe and transient absorption technology revealed the underlying dynamic mechanisms, including bandgap renormalization and Auger recombination. This study can broaden the horizons of material science and propel the development of different applications of ReSe2.

Study of the Nonlinear Optical Properties of Ag/CdTe Composites

CdTe films, Ag nanoparticles, and Ag/CdTe composites are successfully fabricated on substrates by means of the physical vapor deposition process. The morphological structure, crystal growth and bandgap of the samples are specifically characterized by scanning electron microscopy, X‐ray diffractometer, and UV–vis spectrophotometer. Picosecond (ps) Z‐scan technology is used to investigate the nonlinear optical (NLO) properties of the composites under 532 nm. The results indicate that all samples exhibit saturated absorption nonlinear absorption properties and self‐dispersion nonlinear refraction properties. In addition, Ag nanoparticles can improve the NLO properties of Ag/CdTe composites, and this improvement is more obvious with the increase of Ag power. The results show that the excellent properties of the Ag/CdTe composites are expected to make them an ideal material for use in the photoelectric field.

Role of Pauli blocking for enhancement of saturable absorption in MoS2/PEDOT:PSS nanocomposite films

We have effectively shown a technique for significantly altering the nonlinear saturable absorption (SA) properties of nanocomposite films (NCFs) based on poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) and molybdenum disulfide (MoS2) by regulating MoS2 concentration and input pulse energy of the laser. The NCFs are made using the straightforward drop-cast process on a glass substrate with varying quantities of MoS2. The produced NCFs’ refractive index (n) and extinction coefficient (k) values are determined using the Kramers–Kronig equations. Nonlinear studies show that the optical nonlinearity of pure PEDOT:PSS changes when mixed with MoS2. The Pauli blocking has been observed in MoS2/PEDOT:PSS NCFs. This leads to enhanced SA in NCF. The open-aperture Z-scan approach is used for the nonlinear optical research, and a nanosecond pulsed laser with a wavelength of 532 nm is used for the excitation. The findings obtained show the NCFs’ strong SA qualities.

Carbon nanomaterials as nonlinear optical modulators for pulsed laser generation at near-infrared region

In this study, carbon nanoparticles (CNPs) were experimentally investigated as novel saturable absorbers (SAs) capable of delivering strong ultrashort pulses in a passively Q-switched fiber laser. Carbon nanoparticles produced by candle burning and laser ablation can act as saturable absorbers (SAs). In addition, the nonlinear saturable absorption properties of the two synthetic CNPs in telecommunication region (1.5 μm) are investigated. Nonlinear optical measurements show that both SAs have good saturable absorption properties with average modulation depths of about ∼1 and 5 % at 1560 nm. These candle soot carbon nanoparticles (CSC-np) and laser ablation carbon nanoparticles (LAC-np) based SAs, can be used as a building blocker for the generating of stable Q-switched pulses in the near-infrared region. The shortest pulse duration measured with CSC-np and LAC-np are 5.62 and 3.87 μm, respectively. The pulse energy, peak power and SNR were also compared with both SA types at the highest pump power. The damage threshold and long-term stability of the CSC-cn SA and LAC-np were also explored. To the best of the author's knowledge, it is the first comparison of performance and long-term stability of EDFL based on two experimental techniques CSC-np and LAC-np based SAs. These results indicate that LAC-np SA provide have several advantages, including a high damage threshold, good saturable absorption, and optimum stability over a long time compared to CSC-np SA.