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CdSe, Cu2Se and CdSe:Cu2Se nanocrystal (NC) thin films were synthesized using vacuum deposition technique. The open aperture Z-scan measurements carried out using 7 ns pulses at 532 nm revealed that the CdSe and Cu2Se samples exhibited saturable absorption (SA) at 30 µJ. A nonlinear optical switching from saturable absorption (SA) to reverse saturable absorption (RSA) is observed by increasing the laser input intensity.

We firstly propose the integration of heterogeneous Tm:YAG and Ho:YAP crystals into a single bulk structure for a compact, diode-pumped passively Q-switched (PQS) Ho laser. Efficient 2129 nm laser, with maximum CW power of 6.67 W was obtained from the Tm:YAG/Ho:YAP gain medium, with slope efficiency of 38.3% and optical conversion efficiency of 27.4% by considering the incident diode power at 785 nm. Modulated by a Cr:ZnSe saturable absorber inside a hybrid cavity, characteristic self-pulsing of the integrated Ho laser can be suppressed for a stable PQS process, where average output power of 743 mW at 2053.3 nm was obtained with shortest pulse duration of 123 ns at 14.2 kHz. As the maximum thermal stress of 48.2 MPa is far below the fracture limits of each integrated section (~160 MPa), higher laser power can be expected. The results pave the way to explore the integration of other existing Tm-doped and Ho-doped hosts for an accessible 2.1 m source.

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.

Carbon nanocages with controllable nonlinear saturable absorber properties are synthesized at low carbonization temperature, and can be used for the generation of a Q-switching or mode-locking pulsed fiber laser.

Two-dimensional materials are among the most efficient optical materials for Q-switched pulse applications, rising to unprecedented heights. Although the exploration of 2D nanomaterials has attract...

Liquid-phase exfoliation can be developed for the large-scale production of two-dimensional materials for photonic applications. Although atomically thin 2D transition metal dichalcogenides (TMDs) ...

Funding Information: A.A.M. and A.G.N. thanks RFBR research project ? 20-32-90233 for support in experimental part of the work. D.V.K. thanks Russian Science Foundation grant No. 20-73-10256 for support in synthesis of aerosol SWCNT films. V.D. thanks the Russian Science Foundation (Grant No. 17-72-30006) for the support in characterization of pulse laser generation. Funding Information: A.A.M. and A.G.N. thanks RFBR research project № 20-32-90233 for support in experimental part of the work. D.V.K. thanks Russian Science Foundation grant No. 20-73-10256 for support in synthesis of aerosol SWCNT films. V.D. thanks the Russian Science Foundation (Grant No. 17-72-30006 ) for the support in characterization of pulse laser generation. Publisher Copyright: © 2021 Elsevier Ltd Single-walled carbon nanotubes (SWCNTs) are widely explored for the ultrashort pulse generation in the fiber lasers enabled by pronounced saturable absorption (SA) effect. Despite many remarkable results demonstrated in the area, degradation of the samples inside the laser cavity limits the widespread use of SWCNT-SA. In the present work, we investigate the degradation mechanism by measuring the temperature of the carbon nanotubes in an operating laser cavity in accordance with the Raman G-band position. We identify the process behind the sample degradation by comparing the burning temperature of the sample with results of thermogravimetric analysis. We apply this approach for the SWCNTs in polyvinyl alcohol polymer matrix and polymer-free SWCNT thin film and demonstrate that these samples undergo different degradation mechanism. Proposed technique provides a useful instrument for optimization of SWCNT-SA for desired ultrafast laser generation.

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm2, respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

We demonstrate a hybrid-structure fiber laser composed of single-mode fiber (SMF) and four-mode fiber (FMF), capable of delivering stable near-chirp-free soliton with the bandwidth of 75 pm. Ascribed to the spectral-domain intermodal interference, the SMF-FMF cavity serves not only as a ring resonator but also as an intrinsic spectral filter. The wavelength of the narrowband soliton is tunable within 10 nm by a polarization controller. Simulation results validate the experimental observations, revealing that the filtering effect simultaneously balances the self-phase modulation induced spectral broadening and saturable absorption induced temporal compression. The narrowband fiber laser is attractive for spectroscopy, quantum optics, and material processing, and offers a promising platform to study the evolution dynamics of few-mode solitons.

Van der Waals heterostructures composed of different two-dimensional films offer a unique platform for engineering and promoting photoelectric performances, which highly demands the understanding of photocarrier dynamics. Herein, large-scale vertically stacked heterostructures with MoS2 and ReSe2 monolayers are fabricated. Correspondingly, the carrier dynamics have been thoroughly investigated using different ultrafast spectroscopies, including Terahertz (THz) emission spectroscopy, time-resolved THz spectroscopy (TRTS), and near-infrared optical pump-probe spectroscopy (OPPS), providing complementary dynamic information for the out-of-plane charge separation and in-plane charge transport at different stages. The initial charge transfer (CT) within the first 170 fs, generating a transient directional current, is directly demonstrated by the THz emissions. Furthermore, the TRTS explicitly unveils an intermediate free-carrier relaxation pathway, featuring a pronounced augmentation of THz photoconductivity compared to the isolated ReSe2 layer, which likely contains the evolution from immigrant hot charged free carriers to bounded interlayer excitons (∼0.7 ps) and the surface defect trapping (∼13 ps). In addition, the OPPS reveals a distinct enhancement in the saturable absorption along with long-lived dynamics (∼365 ps), which originated from the CT and interlayer exciton recombination. Our work provides comprehensive insight into the photocarrier dynamics across the charge separation and will help with the development of optoelectronic devices based on ReSe2-MoS2 heterostructures.

This work demonstrates a simple and economical route of preparing molybdenum trioxide/polydimethylsiloxane composite saturable absorber (MoO3-SA) for ultrashort pulse generation. The average size of MoO3 used in this work was about 10 μm and conveniently prepared using standard bath sonication. The MoO3-SA was fabricated by depositing MoO3 composite on tapered microfiber structure of 10 μm waist diameter via spin coating technique. The modulation depth, saturation fluence and non-saturable loss of the fabricated MoO3-SA were measured to be 4.02%, 28.3 μJ/cm2 and 33.02%, respectively. The employment of the MoO3-SA in erbium-doped fiber laser was able to generate mode-locked pulses at a threshold pump power of 64.1 mW with a central wavelength of 1559.87 nm and an ultrashort pulse duration of 748 fs. Micrometer-sized materials are far simpler in preparation which relaxes tight requirements for SA fabrication compared to advanced nanomaterials.

We demonstrate a high-energy, passively Q-switched Er:YAG laser with a Co2+:MgAl2O4 saturable absorber. Pumped by an Er-doped fiber laser, the Er:YAG laser generates 1645-nm pulses with the maximum pulse energy of 656 $\mu \text{J}$ and the pulse duration of less than 200 ns at a high repetition rate of 2.285 kHz. The output laser beam remains high beam quality with the maximum output power of 1.5 W. The horizontal and vertical M2 factors are measured to be 1.22 and 1.32, respectively.

Single-walled carbon nanotube encapsulated in boron nitrite nanotube (SWCNT@BNNT) is a novel nanomaterial with a one-dimensional van der Waals (1D-vdW) heterostructure. In this paper, we demonstrated that the SWCNT@BNNT has an enhanced optical power tolerance compared to that of the pristine SWCNT while exhibiting an optical saturable absorption properties. Under optical power intensity of 13kW/cm2, the lifetime of the SWCNT@BNNT is found to be 2,270 times longer than SWCNT for 1% degradation in absorbance. A short-cavity mode-locked laser with a high repetition rate of 1 GHz has been realized using the SWCNT@BNNT as the saturable absorber. We have shown that the technique of fabricating nanomaterial with a 1D-vdW heterostructure can modify and enhance the optical properties of the encapsulated nanomaterials., 8 pages, 7 figures

We have experimentally demonstrated the mode-locked and Q-switched fibre lasers based on MXene Ti3C2Tx as a saturable absorber (SA). MXene Ti3C2Tx was obtained using selective etching and then embe...

Study of initial transmission effect on performance of saturable absorber material with Er+3 doped fiber laser was studied. Cr+4: YAG used as a saturable absorber (SA) in the study. Software computer program buildup in this study for numerical solving of rate equations model by Rung - Kutta –Fehlberg method. The study reported that the maximum optical bleaching, Threshold population inversion density are occurs at earlier buildup time of passive Q-switched, and the pulse reaches high power whenever SA characterized by low initial transmission. The study explains that related to the effect of SA initial transmission on the number density of photons feedback in resonator of laser system.

Functional materials displaying large ultrafast third-order optical nonlinearities across a wide spectral region and broad temporal domain are required for all-optical signal processing. Particularly desirable is nonlinear optical (NLO) activity at near-infrared (NIR) wavelengths with femtosecond pulses. Herein the first triply-fused porphyrin dimer (TFP)-functionalized single-walled carbon nanotube (SWCNT) nanohybrid was successfully constructed by covalently grafting TFPs onto SWCNT. The results of Z-scan techniques demonstrate that the newly obtained TFP-SWCNT nanohybrid was found with a strong NLO performance under both nanosecond and femtosecond irradiation. In the nanosecond regime, an enhancement in optical limiting (OL) of the TFP-SWCNT nanohybrid is seen at 532 nm when compared with the performance of porphyrin monomer-functionalized SWCNT nanohybrid Por-SWCNT. Under femtosecond irradiation, the TFP-SWCNT nanohybrid exhibits a particularly strong OL effect with a giant two-photon absorption (TPA) cross section value (ca. 15,500 GM) at 800 nm pulses that mainly stems from intense TPA of TFP, in sharp contrast to the Por-SWCNT nanohybrid which exhibits only saturable absorption under identical irradiation. These results demonstrate that the newly-developed TFP-SWCNT nanohybrid is a very promising OL candidate for practical applications across wide spectral and temporal domains, and that covalently functionalizing carbon-based materials with triply-fused chromophores may be a useful approach to engineering adaptable photonic devices with broad-ranging NLO activity.

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.

We have demonstrated the stable Q-switched Er-doped fluoride fiber laser with the help of the few-layered Ta2NiS5 in the mid-infrared spectral range. We fabricated the mid-infrared saturable absorber mirror (SAM) by depositing the layered Ta2NiS5 on a gold mirror. The layered Ta2NiS5 exhibited saturable absorption behavior with modulation depth 36% and saturation intensity 32.2 GW/cm2 at 2800 nm, respectively. With the Ta2NiS5-SAM, stable Q-switched pulses around 2.8 μm wavelength can be delivered with a pulse duration of 1.20 μs and a repetition rate of 102 kHz under an incident pump power of 860 mW from the ZBLAN fiber laser cavity. The experimental results confirm that Ta2NiS5 has great potentials as broadband saturable absorber in mid-infrared regions, paving the way for the application of low-dimensional ternary chalcogenide in broadband optoelectronic devices.

We introduce supercritical fluid (SCF) technology to epsilon-near-zero (ENZ) photonics for the first time and experimentally demonstrate the manipulation of the ENZ wavelength for the enhancement of linear and nonlinear optical absorption in ENZ indium tin oxide (ITO) nanolayer. Inspired by the SCF’s applications in repairing defects, reconnecting bonds, introducing dopants, and boosting the performance of microelectronic devices, here, this technique is used to exploit the influence of the electronic properties on optical characteristics. By reducing oxygen vacancies and electron scattering in the SCF oxidation process, the ENZ wavelength is shifted by 23.25 nm, the intrinsic loss is reduced by 20%, and the saturable absorption modulation depth is enhanced by > 30%. The proposed technique offers a time-saving low-temperature technique to optimize the linear and nonlinear absorption performance of plasmonics-based ENZ nanophotonic devices.

The structural, linear, and nonlinear optical (NLO) characteristics of solvent cast brilliant green (BG) dye-doped poly(vinyl alcohol) (PVA) composite films were investigated. The composites show strong linear absorption spectra at 635 nm in the visible region. The fluorescence emission wavelength shifted from 665 to 678 nm and the fluorescence anisotropy (r) was estimated. The energy transfer mechanism was explained by fluorescence lifetime decay curves. NLO properties, such as nonlinear refractive index (n2), two-photon absorption (β), and third-order nonlinear susceptibility χ(3), were studied using Z-scan technique with He–Ne laser at 633 nm. The influence of dye doping switched the nonlinear absorption from reverse saturable to saturable absorption and the obtained β, n2, and χ(3) are in the order of ~ 10–3 cm W−1, 10–8 cm2 W−1, and 10–6 esu, respectively, for all samples. The high fluorescence emission and NLO switching behavior show that the BG/PVA composites could be suitable for optoelectronic and photonic applications. The brilliant green (BG) dye-doped poly(vinyl alcohol) (PVA) polymer composite films were prepared using a solvent casting method. The refractive indexes of BG/PVA composites have been calculated from % transmittance and shows in the range between 1.23 and 1.26. The linear and nonlinear optical (NLO) properties of the composite films have been studied. Therefore, the BG–PVA composites could be useful for optoelectronic, photonic, and saturable absorber applications.

Passively Q-switched thulium doped fiber laser (TDFL) has been successfully demonstrated using gold nanoparticles (GNPs), which were embedded into polyvinyl alcohol as saturable absorber (SA). The stable self-starting Q-switched laser was generated to operate at 1 891 nm when a tiny piece of the prepared film was slot in between two fiber ferrules and incorporated into the laser cavity. The repetition rate can be adjusted from 48.54 kHz to 49.64 kHz while the pulse width decreased from 3.52 µs to 2.38 µs with the increase of 1 550 nm pump power from 840 mW to 930 mW. The corresponding pump power output power linearly increased from 3.62 mW to 6.3 mW with a slope efficiency of 2.53%. The maximum peak power and pulse energy were recorded at about 39 mW and 0.12 µJ, respectively at pump power of 930 mW. The Q-switching operation was caused by the surface plasmon resonance absorption of GNPs.

The Kerr nonlinear optical performance of silicon nanowire waveguides integrated with 2D layered graphene oxide (GO) films is theoretically studied and optimized based on experimentally measured linear and nonlinear optical parameters of the GO films. The strong mode overlap between the silicon nanowires and highly nonlinear GO films yields a significantly enhanced Kerr nonlinearity for the hybrid waveguides. A detailed analysis for the influence of waveguide geometry and GO film thickness on the propagation loss, nonlinear parameter, and nonlinear figure of merit (FOM) is performed. The results show that the effective nonlinear parameter and nonlinear FOM can be increased by up to 52 and 79 times relative to bare silicon nanowires, respectively. Self-phase modulation (SPM)-induced spectral broadening of optical pulses is used as a benchmark to evaluate the nonlinear performance, examining the tradeoff between enhancing Kerr nonlinearity and minimizing loss. By optimizing the device parameters to balance this, a high spectral broadening factor of 27.8 can be achieved, more than 6 times that achieved in previous experiments. Finally, the influence of pulse chirp, material anisotropy, and the interplay between saturable absorption and SPM is also discussed, together with the comparison between the spectral broadening after going through GO-coated and graphene-coated silicon waveguides. These results provide useful guidance for optimizing the Kerr nonlinear optical performance of silicon waveguides integrated with 2D layered GO films.

In this study, we have experimentally demonstrated the sodium carbonate (Na₂CO₃) thin-film as a saturable absorber (SA) for Q-switched laser generation in erbium-doped fiber laser (EDFL) cavity. Th...

Two-dimensional (2D) transition metal chalcogenides (TMCs) become more attractive upon addition of a third element owing to their unique structure and remarkable physical and chemical properties, which endow these materials with considerable potential for applications in nanoscale devices. In this work, a RexNb(1-x)S2-based saturable absorber (SA) device for ultrafast photonics applications is studied. The device is assembled by placing RexNb(1-x)S2 nanosheets with a thickness of 1-3 nm onto a microfiber to increase their compatibility with an all-fiber laser cavity. The prepared RexNb(1-x)S2-based device exhibits a modulation depth of 24.3%, a saturation intensity of 10.1 MW/cm2, and a nonsaturable loss of 28.5%. Furthermore, the RexNb(1-x)S2-based device is used to generate ultrashort pulses in an erbium-doped fiber (EDF) laser cavity. At a pump power of 260 mW, the EDF laser operates in a conventional soliton mode-locked region. The pulse width is 285 fs, and the repetition frequency is 61.993 MHz. In particular, the bound-state soliton mode-locking operation is successfully obtained in a pump power range of 300-900 mW. The bound-state pulses are formed by doubling identical solitons with a temporal interval of 0.8 ps. The output power is as high as 47.9 mW, and the repetition frequency is 123.61 MHz. These results indicate that the proposed RexNb(1-x)S2-based SAs have comparable properties to currently used 2D SAs and provide a basis for their application in the field of ultrafast photonics.

The influence of saturable absorber parameters on the operation regimes of a dumbbell-shaped thulium fibre laser is studied. As saturable absorbers, polymer films with nanotubes characterised by different transmission coefficients in the saturated and unsaturated states are used. The operation of lasers with absorbers of different configurations used to obtain stable Q-switching and mode-locking regimes in the spectral range 1930 – 1960 nm is demonstrated. The average output power in the single-pulse mode-locking regime is 3.5 mW at a pulse repetition rate of 8.4 MHz and a pulse duration of 1.08 ps.

New pulse dynamics, which generates time-stretched dissipative soliton, has been analyzed in theory and demonstrated in experiment. With introducing non-equilibrium saturable absorber (SA) into the laser cavity, the time-dependent loss of SA can balance the intracavity dispersion, while gain and nonlinearity assist to stabilize the pulse. The pulse envelop is in exact sech-shape and the duration can be stretched to sub-microsecond by the cavity dispersion. To verify the dynamics, a mode-locked Er-doped fiber laser (EDFL) is fabricated, in which a piece of Tm-doped fiber (TDF) serves as the non-equilibrium SA. The laser delivers stable nanosecond pulse and its temporal intensity is in exact sech 2 shape. The pulse duration is invariant with the pump power but determined by the cavity length. As large as 155nJ mode-locked pulse has been generated. Furthermore, such mode-locked pulse can serve as ideal pump source to optical parametric oscillators, and will have wide applications in optical communication, material processing and biomedicine technology.

We report a wavelength-tunable high-repetition-rate passively Q-switched fluoride fiber laser around $3~\mu \text{m}$ by using Ti3C2Tx MXene as saturable absorber (SA). The Ti3C2Tx MXene was synthesized by selectively etching aluminum layers in Ti3AlC2. The modulation depth, non-saturation loss and saturation fluence of the SA at 2866 nm were measured to be 43.10%, 25.16%, and 0.50 mJ /cm2, respectively. By introducing the Ti3C2Tx SA into a Ho3+/Pr3+ -codoped fluoride fiber, stable Q-switched pulses with a continuously tuning range of 30.8 nm (2868.4 nm-2899.2 nm) were achieved. The repetition rate was as high as 215.3 kHz with an output power of 142 mW at the wavelength of 2879.0 nm. Such compact mid-infrared Q-switched laser source with a high repetition rate is of great importance in various applications such as medicine, high-resolution photoacoustic microscopy, and remote sensing. Our work indicates that the Ti3C2Tx MXene is a promising broadband light modulator for pulsed laser sources around $3~\mu \text{m}$ .

We experimentally discussed the output characteristics of a passively mode-locked erbium-doped fiber laser using a single-mode fiber (SMF) structure as a saturable absorber (SA) based on nonlinear optic loop mirror (NOLM). The NOLM acting as an SA has properties of controllable pulse interval and pulse width. Four different types of NOLMs are experimentally discussed and the results show that fine adjustment to the coupler ratio together with optimization of the SMF length inside the NOLM can simultaneously implement high pulse energy and pulse internal tunability. The laser configuration provides a method to generate well-performing mode-locked lasing, and the investigations of the effects of changing some parameters of the laser also provide some help for the development of mode-locked fiber laser based on NOLM.

We demonstrate CuCrO2 (CCO) nanoparticle (NP)-polyimide (PI) composite film as a saturable absorber (SA) to regulate the output characteristics of passively Q-switched fiber laser at 1.55 μm. Based on the reverse saturable and saturable absorptions of the CCO NP-PI film, the passively Q-switched fiber laser expressed two stages with the increase of pump power for substantial performance enhancement. Reverse saturation absorption is observed to introduce appropriate cavity loss, which constructs effective pathways for promoting both the modulation depth and over threshold degree, as well as reducing the photon lifetime. In particular, our results realized the pulse duration and repetition rate compressing simultaneously for the first time. The second stage output laser exhibits a peak power of 1016 mW and a single pulse energy of 183 nJ, which are about 88 and 9 times higher than those of the first stage. Furthermore, the optical-optical conversion efficiency is up to 1270%. All of these can evidently demonstrate the importance of the appropriate cavity loss design for optimizing the Q-switched pulse laser output characteristics.

The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable, while it remains a great challenge. In this work, we demonstrate that electrochemical activation is a facile and convenient approach to modulating the broadband third-order nonlinear absorption of nanoporous tungsten oxide (WO3−x) thin film. The film does not exhibit optical nonlinearity at the initial state, while shows a distinct saturable absorption under an applied voltage of −2.5 V with the excitation of 515, 800, and 1,030 nm laser. The nonlinear absorption coefficient (βeff) is −766.38 ± 6.67 cm·GW−1 for 1,030 nm laser, −624.24 ± 17.15 cm·GW−1 for 800 nm laser, and −120.70 ± 11.49 cm·GW−1 for 515 nm laser, and the performance is competitive among inorganic saturable absorbers. The activation is accomplished in 2 min. The performance enhancement is ascribed to the formation of abundant in-gap defect states because of the reduction of the tungsten atoms, and a Pauli-blocking effect occurs during the excitation of in-gap defect states. The small feature size of WO3−x (∼ 12 nm) enables the effective and fast introduction and removal of the defects in porous film, and accordingly the fast and broadband modulation of optical nonlinearity. Our results suggest a controllable, effective, and convenient approach to tuning the nonlinear absorption of materials.

The ever-increasing space exploration enterprise calls for novel and high-quality radiation-resistant materials, among which nonlinear optical materials and devices are particularly scarce. Two-dimensional (2D) materials have shown promising potential, but the radiation effects on their nonlinear optical properties remain largely elusive. We previously fabricated 2D bismuthene for mode-locking sub-ns laser; herein, their space adaption was evaluated under a simulated space radiation environment. The as-synthesized thin layers of bismuthene exhibited strong third-order nonlinear optical responses extending into the near-infrared region. Remarkably, when exposed to 60Co γ-rays and electron irradiation, the bismuthene showed only slight degradation in saturable absorption behaviors that were critical for mode-locking in space. Ultrafast spectroscopy was applied to address the radiation effects and damage mechanisms that are difficult to understand by routine techniques. This work offers a new bottom-up approach for preparing 2D bismuthene, and the elucidation of its fundamental excited-state dynamics after radiation also provides a guideline to optimize the material for eventual space applications.

Metal nanomaterials have attracted increasing attention due to their outstanding nonlinear optical and photonic properties, making them as potential saturable absorber (SA) candidates for realizing ultrafast photonic devices. In this article, we demonstrate the generation of mode-locked dual-wavelength pulse trains in an Ag nanoplates (AgNPTs)-based Yb-doped all-fiber laser for the first time to the best of our knowledge. The AgNPTs are synthesized by seed-mediated growth and then integrated into a fiber ferrule by optical deposition, which serve as SA in the ring laser cavity. The plasmonic properties of such nanoplates are measured by absorption spectrophotometry and their nonlinear optical properties are characterized by Z-scan. The measured nonlinear saturable absorption of the AgNPTs-based SA is 6.4%. In our laser, the dual-wavelength synchronous mode-locking is achieved at the center wavelengths of 1031.92 and 1033.24 nm with 3-dB spectral bandwidth of 0.52 and 0.46 nm, respectively, where 293-ps pulse trains with a repetition rate of 11.43 MHz are obtained at the pump power of 350 mW. The results demonstrate that the solution-processed AgNPTs are promising SA candidates for achieving stable and low-cost pulsed laser sources which could be used for spectroscopy and ultrafast photonics.

An experimental investigation into the nonlinear optical properties of rhenium diselenide (ReSe2) was conducted at a wavelength of 1.9 μm using the open-aperture and closed-aperture Z-scan techniques for the nonlinear optical coefficient (β) and nonlinear refractive index (n2) of ReSe2, respectively. β and n2 measured at 1.9 μm were ~ − 11.3 × 103 cm/GW and ~ − 6.2 × 10–2 cm2/GW, respectively, which to the best of our knowledge, are the first reported measurements for ReSe2 in the 1.9-μm spectral region. The electronic band structures of both ReSe2 and its defective structures were also calculated via the Perdew–Becke–Erzenhof functional to better understand their absorption properties. A saturable absorber (SA) was subsequently fabricated to demonstrate the usefulness of ReSe2 for implementing a practical nonlinear optical device at 1.9 μm. The 1.9-μm SA exhibited a modulation depth of ~ 8% and saturation intensity of ~ 11.4 MW/cm2. The successful use of the ReSe2-based SA for mode-locking of a thulium–holmium (Tm–Ho) co-doped fiber ring cavity was achieved with output pulses of ~ 840 fs at 1927 nm. We believe that the mode-locking was achieved through a hybrid mechanism of saturable absorption and nonlinear polarization rotation.

In this study, titanium disulfide (TiS2) polyvinyl alcohol (PVA) film-type saturable absorber (SA) is synthesized with a modulation depth of 5.08% and a saturable intensity of 10.62 MW/cm2 by liquid-phase exfoliation and spin-coating methods. Since TiS2-based SA has a strong nonlinear saturable absorption property, two types of optical soliton were observed in a mode-locked Er-doped fiber laser. When the pump power was raised to 67.3 mW, a conventional mode-locked pulse train with a repetition rate of 1.716 MHz and a pulse width of 6.57 ps was generated, and the output spectrum centered at 1556.98 nm and 0.466 nm spectral width with obvious Kelly sidebands was obtained. Another type of mode-locked pulse train with the maximum output power of 3.92 mW and pulse energy of 2.28 nJ at the pump power of 517.2 mW was achieved when the polarization controllers were adjusted. Since TiS2-based SA has excellent nonlinear saturable absorption characteristics, broad applications in ultrafast photonic are expected.

We experimentally demonstrate generation of mode-locked pulses in dissipative soliton resonance (DSR) regime. The DSR pulses are obtained from a passively mode-locked figure-8 Er:Yb doped fiber laser operating in large net anomalous dispersion regime. The modelocked laser emission is based on a polarization-imbalanced nonlinear optical loop mirror (NOLM), acting as artificial saturable absorber. Stable square DSR pulses, obtained by carefully adjusting the NOLM properties, increase their duration from 2.47 ns to 46.52 ns as the pump power is increased from 0.68 to 6.31 W. With the maximum pump power launched, average output power of 73.95 mW with pulse energy of 53.39 nJ is achieved.

Antimonene, a new member of monoelemental two‐dimensional crystals composed of antimony atoms, was predicted to possess high stability, as well as outstanding electrical and optical properties. Here, we report on the experimental results of productive, high‐quality synthesis of antimonene quantum dots (AQDs) via liquid‐phase exfoliation. The obtained AQDs exhibited excellent nonlinear saturable absorption. The modulation depth and the saturable intensity were found to be around 3.9% and 10.02 GW/cm2, respectively. By using the AQDs saturable absorber in the 639 nm Pr:YLF laser, stable Q‐switching pulsed laser was realized. The maximum output power was 83 mW and the corresponding pulse width was 255 ns with a pulse repetition rate of 227 kHz. These results suggest that AQDs are a promising candidate for nonlinear optical applications.

We study the exfoliation of ultrathin ReS2 nanosheets from the prepared ReS2 powder and their application to Q-switched Er-doped fiber laser. XRD, Raman, and XPS spectra confirm the successful preparation of the layered ReS2. SEM images show that the obtained ReS2 sheets have lateral size below 200 nm. The thickness of the ReS2 nanosheets is smaller than 5 nm according to the AFM results. ReS2/PVA film is applied as a saturable absorber in an Er-doped Q-switched fiber laser, and a minimum pulse duration of 2.4 µs and an output power of 1.25 mW are obtained, indicating the potential application to Q-switched lasers.

By an improved nonlinear Schrodinger optical transmission equation, we theoretically study the pulse evolution dynamics in two-stage temporal compression by a graphene-silicon hybrid waveguide as a phase modulator. Graphene exhibits obvious saturable absorption (SA) but negligible linearly intensity-dependent absorption (IDA) (or two-photon absorption) when the optical intensity in graphene is below the threshold intensity of IDA of graphene. By the utilization of SA and the repression of IDA, for the temporally compressed pulse, the temporal shape can be achieved to be pedestal-free, and the temporal acceleration can be minimized. Meanwhile, the enhancement of linearly intensity-dependent refraction (or Kerr effect) can contribute to the decrement of the size of device and the input power of pulse. This model will be useful to develop graphene-based all-optical modulators in photonic integrated circuits.

A novel few-mode fiber (FMF) based saturable absorber (SA) that works on the principle of nonlinear multimode interference has been proposed. To optimize the FMF parameters for the fabrication of SA, which is a combination of FMF with two single mode fibers (SMFs), a detailed numerical simulation is performed. The developed SMF-FMF-SMF structure exhibits a modulation depth and saturation intensity of 30.6% and 11.01 MW $/$ cm2, respectively. By inserting the fabricated SA in an all-normal dispersion Ytterbium doped cavity, we have been able to generate a laser pulse duration of 300 fs with an average power/pulse energy of 2.4 mW/64.8 pJ and a repetition rate of 37 MHz as an output. Thus, the proposed SA helps in generating stable pulses from the laser with enhanced output characteristics. We envisage that the fabricated SA would play an indispensable role in the development of ultrafast fiber lasers.

Metallic 2D materials can be promising saturable absorbers for ultrashort pulsed laser production in the long wavelength regime. However, preparing and manipulating their 2D structures without layer stacking have been nontrivial. Using a combined experimental and theoretical approach, we demonstrate here that a metallic titanium carbide (Ti3C2Tx), the most popular MXene 2D material, can have excellent nonlinear saturable absorption properties even in a highly stacked state due to its intrinsically existing surface termination, and thus can produce mode-locked femtosecond pulsed lasers in the 1.9-μm infrared range. Density functional theory calculations reveal that the electronic and optical properties of Ti3C2Tx MXene can be well preserved against significant layer stacking. Indeed, it is experimentally shown that 1.914-μm femtosecond pulsed lasers with a duration of 897 fs are readily generated within a fiber cavity using hundreds-of-layer stacked Ti3C2Tx MXene saturable absorbers, not only being much easier to manufacture than mono- or few-layered ones, but also offering character-conserved tightly-assembled 2D materials for advanced performance. This work strongly suggests that as-obtained highly stacked Ti3C2Tx MXenes can serve as superb material platforms for versatile nanophotonic applications, paving the way toward cost-effective, high-performance photonic devices based on MXenes.

Topological insulator Sb2Te3 has the advantage of broadband saturable absorption from the visible to the infrared bands. Herein, the two-dimensional material Sb2Te3 saturable absorber (SA) of the topological insulator family was first applied experimentally in a wideband tunable passively Q-switched Yb-doped fiber laser. High-quality Sb2Te3 crystals were synthesized by the flux zone method. The Sb2Te3 SA with fewer layers was further prepared via a modified mechanical exfoliation procedure. Meanwhile, stable wavelength-tunable passive Q-switching pulse operation was obtained in a Yb-doped fiber ring cavity based on the Sb2Te3 SA, where the central wavelength can be continuously tuned from 1040.89 to 1092.85 nm. Results suggest that Sb2Te3 has wideband saturable absorption properties, and that the tunable pulse laser can provide a convenient and simple source for practical applications.

In this study, we demonstrate the generation of soliton mode-locked pulses from an erbium-doped fiber laser (EDFL) cavity configured with 8-Hydroxyquinolino cadmium chloride hydrate (8-HQCdCl2H2O) ...

Semiconductor saturable absorber mirrors (SESAMs) enable passive modelocking of several ultrafast solid-state lasers. Conventionally, SESAMs in the 1-µm wavelength range have employed InGaAs quantum wells (QWs) as absorbers. We demonstrate here a SESAM based on InAs/GaAs submonolayer quantum dots (SML QDs) capable of generating femtosecond pulses by passively modelocking a vertical-external-cavity surface-emitting laser (VECSEL). Structural measurements are carried out to verify the quality and composition of the QDs. Modelocking experiments with a VECSEL and the QD SESAM in a ring cavity configuration yield pulses as short as 185 fs at 1025 nm. Compared to a traditional QW absorber, SML QD SESAMs exhibit ~ 25% faster recovery times. This also translates to slower power degradation rates or higher damage thresholds in SML QD SESAMs.

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.

We have applied a new simplified combination of numerical methods for studying the time and three-dimensional space dependence of quasi-three-level Yb3+:Yttrium Aluminum Garnet (YAG) end-pumped lasers passively Q-switched by a Cr4+:YAG saturable absorber. We base our 3-D model on iterative, efficient, time- and space-dependent numerical propagation of the optical field through the laser cavity. The complex-valued laser field is coupled to the Yb3+:YAG and Cr4+:YAG media via complex optical permittivities, which are subsequently altered by gain/loss intensity saturation. The calculation is simplified using the radial symmetry of the system, with the cavity round-trip time as the smallest increment for updating the permittivities. We also include the effects of field diffraction in an intra-cavity air gap. For specified CW spatial pump conditions, self-consistent repetitively pulsed solutions for the laser field in a flat-flat or flat-convex mirror cavity are found with no ad hoc laser mode size or shape assumptions; these solutions are not Gaussian modes. We concentrate on compact lasers with multi-Watt average output power, operating at modest pulse energy (~1.0 mJ), high repetition rate (~5 kHz) and short pulse duration (~1.5 ns). Typical room-temperature pump-to-laser slope power efficiencies exceeding 50% are predicted, depending on laser pump and cavity loss parameters. Model results agree well with recently published experimental data.

We fabricate an oleic acid capped colloidal lead sulfide quantum dots (PbS QDs) by modified hot-injection method, and then drop them on the end of fiber connector to construct the fiber-based PbS QDs saturable absorber (SA). The modulation depth and saturation intensity of the PbS QDs SA are about 30% and 1.88 MW/cm2, respectively. The strong quantum confinement effect in PbS QDs enables wideband tunability. We get subpicosecond soliton pulses, wavelength-tunable between 1530 nm and 1560 nm, with stable mode-locking, by adjusting the orientations of the polarization controller. These results contribute to study the nonlinear optical properties of zero-dimensional nanomaterials and provide new opportunities for the applications of broadband photoelectronic devices.