Saturable Absorption Performance Research Articles

Observation of terahertz nonlinear absorption activity in Al2O3

We investigate the terahertz (THz) nonlinear absorption characteristics in a thin Al2O3 crystal using nonlinear THz spectroscopy. A THz saturable absorption performance with a high modulation depth (27.5%) and a relatively low saturable intensity (6.99 µJ/cm2) of Al2O3 is revealed, covering the THz spectrum from 0.1 to 8 THz. The inevitable presence of oxygen vacancies and impurities in Al2O3 single crystal results in the existence of free electrons within the conduction band. The transmission enhancement can be described by the change of the mobility of electrons due to intervalley scattering induced by THz pulses, based on first-principles calculations. Therefore, Al2O3 crystals have promising application potential in mode-locked devices for directly delivering broadband ultrashort THz pulses.

Plasma etching promoting the saturable absorption of BiOI

Materials exhibiting exceptional saturable absorption performance and etching compatibility are significant in the context of advanced optical devices. Our study demonstrates that plasma etching can effectively promote the saturable absorption of BiOI nanosheets because of defect formation. Remarkably, the BiOI nanosheet subjected to the optimized H2/Ar-plasma treatment manifests a substantial nonlinear absorption coefficient (βeff) of (−5.5 ± 0.7) × 103 cm GW−1 under laser excitation at 800 nm, while the pristine BiOI sample exhibits no discernible nonlinear optical response. The βeff of plasma-treated BiOI samples is (−4.2 ± 0.9) × 103 cm GW−1 at 515 nm, surpassing that of the untreated counterpart by more than fourfold. A comprehensive structural and spectroscopic analysis indicates that oxygen vacancies serve to increase the density of in-gap states, thereby narrowing the bandgap of the BiOI. This reduced bandgap effectively facilitates the Pauli-blocking effect and, in turn, augments the saturable absorption properties of the samples. In contrast to oxygen vacancies, iodine vacancies make a negligible contribution to the performance enhancement of BiOI. Our result would provide a promising way to improve the nonlinear optical response of materials.

High-output ∼3 μ m MIR pulsed laser enabled by surface state regulation in PtTe2 optical switch

Mid-infrared (MIR) pulsed lasers operating in the ∼3 μm region play a crucial role in various applications, including molecular spectroscopy, ultrafast molecular imaging, and laser-assisted surgery. Despite recent advancements in MIR gain platforms, a notable technological challenge remains in the absence of an effective optical Q-switch. Here, a remarkable optical Q-switch in the 3 μm region based on a Dirac semimetal PtTe2 saturable absorber is realized. By modulating the surface state of PtTe2, the pulsed laser exhibited an increase in average power, escalating from 521 to 588 mW, accompanied by a significant decrease in pulse width from 368 to 187 ns. Nondegenerate pump–probe measurements showed that the recombination rate of the photocarrier in thinner PtTe2 nanoplates was effectively accelerated, primarily attributed to the substantial increase in surface state density, leading to better saturable absorption performance. As the thickness of the PtTe2 nanoplates decreases, the nonsaturable loss decreases from 12% to 3%, while the modulation depth increases from 6% to 12%. The enhanced ultrafast nonlinear absorption enables flexible modulation of saturation absorption parameters, which endows high-performance MIR pulsed laser generation.

Novel structure and excellent nonlinear optical performance nanocomposite derived from flower-like MOF grown on MoS2

Molybdenum disulfide (MoS2) is a nonlinear optical material with graphene-like structure. In order to further improve the nonlinear optical performance of MoS2 and expand the application fields of MoS2, we report a simple in-situ self-growth method to functionalize MoS2 nanosheets with metal-organic framework (MOF) for the first time to pursuit excellent reverse saturable absorption performance and optical limiting performance. Firstly, defective MoS2 nanosheets was obtained by chemical etching with H2O2 and cysteamine was inserted into the sulfur vacancies under ultrasound to obtain MoS2–NH2. Then 5,10,15,20-Tetra (4-carbomethoxyphenyl) porphyrin (TCPP) as MOF active growth sites were grafted on MoS2–NH2 by amido linkage to obtain MoS2-TCPP in mild conditions. Finally, flower-like porphyrin-based CuMOF was grown on MoS2-TCPP by solvothermal method to obtain MoS2-CuMOF with stable structure. The third order nonlinear optical performance of MoS2-CuMOF were studied by Z-scan technique. It was found that the third order nonlinear absorption coefficient of MoS2-CuMOF was significantly improved compared with MoS2. Under the same energy of laser irradiation, the third order nonlinear absorption coefficient of MoS2-CuMOF nanocomposite in solution was 6 × 10−10 m/W about 2.3 times of the pristine MoS2 (2.6 × 10−10 m/W). After blending the above materials with polymethyl methacrylate (PMMA) to prepare a solid device, the third order nonlinear absorption coefficient of MoS2-CuMOF/PMMA was 18 × 10−10 m/W about 3.6 times of the MoS2/PMMA (5 × 10−10 m/W). And MoS2-CuMOF/PMMA had better optical limiting ability than MoS2/PMMA. The significant improvement in the performance of the composites can be attributed to the energy transfer between MoS2 and CuMOF, and porphyrin aggregation was inhibited by PMMA after the preparation of devices. Energy transfer can be proved by fluorescence spectroscopy. This work not only provided an example for the covalent functionalization of MoS2, but also offered a new method for designing materials with excellent nonlinear optical performance.

Femtosecond laser ablation in liquid synthesis of iron-oxidation nanoparticles with saturable absorption performance.

"Naked" ferroferric-oxide nanoparticles (FONPs) synthesized by a femtosecond laser ablation on a bulk stainless steel in liquid were applied to the Nd: YVO4 laser to achieve passive Q-switched pulse laser output. Without the pollution of ligand, the inherent light characteristic of "naked" FONPs was unaffected. The analysis of the morphological characteristics, dominant chemical elements, and phase composition of the FONPs showed that they were mainly composed of Fe3O4, which was spherical with an average diameter of 40 nm. The electron transition and orbital splitting of the iron element's octahedral center position under the laser-driven were considered the primary mechanisms of saturable absorption of Fe3O4 nanoparticles.

CsPbBr3 Perovskite Nanocrystals for a Q-Switched Pulsed Fiber Laser in the C-Band Region.

All-inorganic perovskite nanocrystals have been widely reported as promising light-harvesting and light-emitting semiconductor nanomaterials. However, their nonlinear optical properties and laser applications have rarely been explored, especially for pulse laser modulation in the telecommunication C-band window. Herein, we experimentally demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) operation at the C-band region using perovskite CsPbBr3 nanocrystals as a saturable absorber (SA). The broadband linear optical absorption in the 300-2000 nm range and the nonlinear optical absorption at the C-band range of around 1560 nm were discovered and investigated in CsPbBr3 nanocrystals. The CsPbBr3-based SA exhibited good saturable absorption performance with a modulation depth and saturation intensity equivalent to 19.1% and 10.9 MW/cm2, respectively. By integrating the CsPbBr3 SA into an EDFL cavity, a passively Q-switched operation with a central wavelength of 1560 nm, a threshold pump power of 60 mW, and the shortest pulse duration of 5.96 μs was achieved. In addition, such a Q-switching operation exhibited long-term stability. Our results indicate that the CsPbBr3 perovskite nanocrystals can serve as an efficient candidate for constructing pulsed lasers in the C-band or even longer NIR wavelength region.

High-energy Q switched Yb-doped fiber laser based on a ternary layered structured Ti2AlC saturable absorber.

Ti2AlC is a kind of ternary layered structured ceramic metal compound, combining the advantages of both ceramic and metal. Herein, the saturable absorption performance of Ti2AlC at the 1-µm wave band is investigated. The Ti2AlC behaves with excellent saturable absorption, which has a modulation depth of 14.53% and a saturable intensity of 13.27 MW/cm2. An all-normal dispersion fiber laser based on the Ti2AlC saturable absorber (SA) is constructed. The repetition frequency of the Q switched pulses increased from 44 to 49 kHz as the pump power rose from 276 to 365 mW, and the corresponding pulse width decreased from 3.64 to 2.42 µs. The maximum output single Q switched pulse energy is as high as 169.8 nJ. Our experiments prove that the MAX phase Ti2AlC has potential as a low-cost, simple preparation, and broadband SA material. To the best of our knowledge, this is the first demonstration of Ti2AlC serving as a SA material achieving Q switched operation at the 1-µm wave band.

Saturable absorption performance of large area monolayer MoS2 coated planarized optical waveguide

The development of compact waveguide-based pulsed lasers has been of great interest in the past two decades. This is supported by the rapid development of two-dimensional (2D) materials saturable absorbers (SAs). In this paper, we integrate a large area monolayer molybdenum disulphide (MoS2) on a planarized silica optical waveguide and studied its performance as an SA. A single layer MoS2 film on polydimethylsiloxane substrate is mechanically transferred to the planarized optical waveguide. The single layer MoS2 can interact with the evanescent field of the waveguide core mode, thus achieving SA. The MoS2-coated waveguide is then integrated into an erbium-doped fibre laser cavity that operates in the telecommunication wavelength region. Q-switching is achieved with a repetition rate, pulse duration and maximum pulse energy of 22.5 kHz, 5.24 µs and 4.1 nJ, respectively at a pump power of 122.8 mW. The results show that 2D material thin films can be integrated onto a planarized optical waveguide to act as SAs. These findings show the potential of using 2D materials in developing compact, integrated waveguide pulsed laser sources.

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.

Optical and electrical properties of new NLO active ethynylated chalcone as solution-processed OLEDs material: Experimental and theoretical approaches

This present study investigated the contribution of new hybrid moieties of ethynylated (C≡C) and chalcone (–CO–CHCH-) units as nonlinear optically active and successfully applied to solution-processed OLEDs material. The simulated data from Density Functional Theory (DFT) indicates that 3-(pyren-1-yl)-1-((4-phenylethylyn)phenyl)-2-propen-1-one (MM-1a) reveals good polarizability properties of total first hyperpolarizability βtot at 842.32 × 10−30 esu associated with low HOMO-LUMO gap at 3.04 eV. The structure-property relationship also was highlighted using TD-DFT calculations for frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) maps and global chemical reactivity descriptors (GCRD). The photophysical behaviours of MM-1a presented emission maxima at 520 nm with large Stokes shifts at 95 nm where this emission shows fluoresce characters and intramolecular charge transfer (ICT) state. Remarkably, a response from the open and closed aperture Z-scan analysis reveals that MM-1a displays reverse saturable absorption (RSA) performance and self-defocusing effects under 532 nm continuous wave (CW) laser. Further, solution-processed OLED featuring single-layer of ITO/PEDOT:PSS/MM-1a/Au displayed electroluminescence effect by intense yellow emission obtained under direct current (DC) voltages supply. From the obtained result, the introduction of ethynyl as spacer in chalcone system facilitated intramolecular charge transfer and finely tuned the electronic properties to enhance NLO response and promising emissive layer for OLED applications.

Exciton-induced mid-infrared optical nonlinearity of wide bandgap hexagon boron nitride.

In this Letter, an exciton absorption assumption is made to explain the mid-infrared saturable absorption performance of the 2D h-BN nanosheet. The exciton binding energy of ∼0.4 eV corresponds to the light wavelength around 3 µm, matching well with the experimental results. Experimentally, the h-BN saturable absorber (SA) shows a modulation depth of 5.3% in the wavelength region of 3 µm. By employing the h-BN SA in an Er:Lu2O3 laser, laser pulses with a pulse duration of 252 ns are realized at a repetition rate of 169 kHz, corresponding to a pulse energy of 3.55 µJ and peak power of 14 W. The exciton absorption assumption will help obtain a better understanding of the nonlinear optical dynamics in 2D materials from a new perspective.

Two-Dimensional Gallium Sulfide as a Novel Saturable Absorber for Broadband Ultrafast Photonics Applications.

Two-dimensional (2D) gallium sulfide (GaS) offers a plethora of exceptional electrical and optical properties, allowing it to be used in a wide range of applications, including photodetectors, hydrogen generation, and nonlinear optical devices. In this paper, ultrathin 2D GaS nanosheets are synthesized using the liquid-phase exfoliation method, and the structure, morphology, and chemical composition of the as-prepared nanosheets are extensively investigated. After depositing 2D GaS nanosheets on side polished fibers, successful saturable absorbers (SAs) are fabricated for the first time. The realized modulation depths are 10 and 5.3% at 1 and 1.5 μm, respectively, indicating the wideband saturable absorption performance of the prepared SAs. By integrating GaS-SAs into three different wavelength-based fiber laser cavities, stable mode-locked pulses are achieved, having pulse durations of 46.22 ps (1 μm), 614 fs (1.5 μm), and 1.02 ps (2 μm), respectively. Additionally, different orders of harmonic mode-locked pulses with the highest repetition rate of 0.55 GHz (45th order) and Q-switched pulses with the shortest pulse duration of 2.2 μs are obtained in the telecommunication waveband. These findings suggest that 2D GaS has a lot of potential for broadband ultrafast photonics in nonlinear photonics devices.

Generation of rectangular pulses in ytterbium-doped fiber laser based on a SnSe2 saturable absorber

Based on an as-prepared high-quality tin diselenide-polyvinyl alcohol (SnSe2-PVA) saturable absorber (SA), the stable rectangular pulses operating at the dissipative soliton resonance (DSR) region were observed in a passively mode-locked ytterbium-doped fiber (YDF) laser at the center wavelength of 1062.3 nm. The laser characteristics versus the pump power were investigated experimentally. As the pump power increased, the wave-breaking-free DSR pulse width varied from 20.5 ns to 44.7 ns. At the pump power of 365 mW, the maximum pulse energy of the DSR pulse is 0.928 nJ, corresponding to a signal to noise ratio (SNR) up to 74 dB. The results demonstrate the excellent saturable absorption performance of SnSe2 in generating the DSR pulses in fiber lasers.

Broadband Nonlinear Photoresponse and Ultrafast Carrier Dynamics of 2D PdSe2

AbstractPalladium diselenide (PdSe2) exhibits considerable potential for application in broadband optoelectronic devices. In this work, the broadband nonlinear optical performance and ultrafast carrier dynamics from ultraviolet to near‐infrared of a trilayer PdSe2 are systematically studied. PdSe2 is found to achieve a giant saturable absorption performance. The modulation depth is 22.47% at 520 nm, whereas the nonsaturable loss and saturation intensity are only 3.83% and 15.47 GW cm−2, respectively, which are better than those of many 2D semiconductors. Based on these findings, a PdSe2‐based visible light thresholder is proposed, its function is to extract an undetectable pulse signal drowned in strong stochastic noise and thereby improve the signal‐to‐noise ratio. Pump–probe technique, along with first‐principles calculation and transient absorption spectra, reveals the intrinsic recombination mechanism, including Auger scattering and trap saturation. This work is expected to establish the foundation for the development of next‐generation PdSe2‐based devices in optoelectronics and visible light communication.

Nonlinear Optical Response of Gold Nanobipyramids for a Doubly Q-Switched Ho-Doped Laser at a Wavelength of 2.1 µm.

Gold nanobipyramids (Au-NBPs) were successfully fabricated using the seed-mediated growth method. The saturable absorption performance of the Au-NBPs at a 2-μm band wavelength was characterized. Using excellent-quality, mature Ho:YLF crystals, a doubly Q-switched (DQS) laser joining an acousto-optic modulator (AOM) with an Au-NBP saturable absorber (SA) was achieved. When the modulation rate of the AOM was 1 kHz, the shortest pulse width (54 ns) was attained, corresponding to the highest peak power (3.87 kW). This was compared with a singly Q-switched laser joining an AOM with an Au-NBP SA, whereby the maximum pulse width compression ratio was 15.2 and the highest peak power enhancement factor was 541.3. Our study has shown that Au-NBPs are a potential saturable absorption nanomaterial, and the DQS laser has the benefit of compressing the pulse width and increasing the peak power at a wavelength of 2.1 μm.

Single element material sulfur quantum dots nonlinear optics and ultrafast photonic applications

Single element low dimensional nanomaterials have been widely used in many electronic and optoelectronic application owing to their strong photo-material interactions and saturable absorption characteristics. In this work, we studied the saturable absorption properties of sulfur quantum dots (SQDs). The SQDs show an excellent saturable absorption performance with a nonlinear absorption coefficient of −5.89 × 10-2 cm/GW and a figure of merit of −10.2 × 10−14 esu cm. Furthermore, we demonstrated the first SQDs saturable absorber (SA) as a mode locker in a mode-locking erbium-doped fiber laser for the generation of ultrafast laser pulses (720 fs) with a center wavelength of 1530.6 nm and a corresponding single pulse energy up to 0.972 nJ. The experimental results open a new avenue for the use of SQDs in laser and photon applications.

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.

Fused polycyclic compounds: Synthesize, enhancing TPA cross-section by modifying torsional multiple ring

Abstract Four fused polycyclic compounds (DNBT, DNTB, DNPY, and DNNM) with different substituents were designed and synthesized to achieve excellent nonlinear optical materials. Broadband reverse saturation absorption performance based on TPA was carried out by Z-scan. Transient absorption spectrum showed that the different substituents can significantly regulate the ultrafast kinetic processes of their excited states. The relationship between excited states charge structure and nonlinear optical properties were studied by density functional theory (DFT) and sum over states (SOS) model. TPA of these compounds is modulated by local excitation in DBPy and TA fragments. Intra-molecular charge transfer weakens the TPA cross-section. These compounds are potential optical limiting (OL) materials in visible light range. The clear mechanism show that the nonlinear optical properties of organic materials can be improved purposefully through theoretical and experimental methods.

Synthesis and Characterization of Phthalocyanine Polymer Towards Nonlinear Optical Applications

In the present study, linear poly(methyl methacrylate161-co-phthalonitrile1.5) (P(MMA161-co-CPMA1.5)) polymer was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Then the P(MMA161-co-CPMA1.5) polymer followed by macrocyclization reaction to form poly(methyl methacrylate167-co-zinc phthalocyanine1.1) (P(MMA167-co-ZnPc1.1)) polymer. The P(MMA167-co-ZnPc1.1) polymer was characterized by fourier transform infrared, nuclear magnetic resonance, ultraviolet-visible absorption. The nonlinear optical properties of the P(MMA167-co-ZnPc1.1) polymer were investigated by using the Z-scan technique at 532 nm with 7 ns laser pulses. The results revealed that the P(MMA167-co-ZnPc1.1) polymer exhibited excellent reverse saturable absorption (RSA) performance.

Sodium deoxycholate surfactant selected large-diameter single-walled carbon nanotubes (~1.6 nm): Characterization and nonlinear optical properties

Abstract In the present work, we proposed a strategy to select the single-walled carbon nanotubes (SWCNTs) with a relatively large diameter (~1.6 nm) with a sodium deoxycholate (SDC) surfactant. Both the Raman spectrum and the transmission electron microscopy (TEM) image confirmed the successful sorting of the large diameter (~1.6 nm). In addition, the prepared large-diameter SWCNTs exhibited the wide absorption band, implying the possible wideband nonlinear optical properties. A conventional open-aperture Z-scan measurement was implemented to investigate typical saturable absorption performance at 1.3 and 1.9 μm. As a proof of the excellent nonlinear saturable absorption, passively Q-switched lasers were demonstrated with the prepared large-diameter SWCNTs based saturable absorber, producing the minimum pulse duration of 335 ns. Our work reversed that the saturable absorption of SWCNTs can extend to the Mid-IR regime by sort the proper diameter.