Nonlinear Saturable Absorption Properties Research Articles

Nonlinear saturable absorption properties of indium selenide and its application for demonstrating a Yb-doped mode-locked fiber laser

Recently, two-dimensional materials have shown excellent nonlinear absorption properties and have practically promoted the development of ultrafast lasers. As one of the typical III-VI semiconductors, InSe has already been widely applied in designing photo-sensors and other optical devices due to its outstanding electrical transport, quantum physics and dramatic photo-response properties. However, the nonlinear absorption characteristics of InSe have not been experimentally investigated within ultrafast lasers so far. In our work, the nonlinear absorption properties of InSe were investigated. InSe-PVA film was successfully prepared and employed for achieving a mode-locked Yb-doped fiber laser. A stable mode-locked operation with a maximum output power of 16.3 mW and a minimum pulse width of 1.37 ns at a pulse repetition rate of 1.76 MHz was obtained, and the corresponding pulse energy was as high as 9.26 nJ. Our findings suggest that InSe may have wide potential ultrafast photonic applications due to its suitable bandgap value and excellent nonlinear saturable absorption characteristics.

Low‐Dimensional Saturable Absorbers in the Visible Spectral Region

AbstractVisible light has an important and unique value in research and practical applications, because of its perceptible characteristics by the human eye. Directly pumped bulk visible pulsed lasers are booming in recent years stimulated by the advances of blue laser diodes. As critical components, novel and favorable saturable absorbers in view of distinct nonlinear saturable absorption properties are desired, which can promote the development of ultrafast photonics in the visible range. Over the years, low dimensional materials with the advantages of ultrafast carrier recovery rate and distinct nonlinear saturable absorption have originated a class of innovative applications in photonics and optoelectronics, especially as saturable absorbers in the pulsed lasers. Here, the low dimensional saturable absorbers in the visible range are reviewed, including the fabrication, linear and nonlinear optical response, and applications in the pulsed visible lasers of low dimensional semiconductors and noble metal nanoparticles. The design criteria of the low dimensional saturable absorbers for generating laser pluse by Q‐switching and mode‐locking are proposed and discussed. Finally, some possible development tendency and directions of saturable absorbers for the visible pulsed lasers are proposed in this review by focusing on some potential strengths.

Nonlinear absorption properties of indium selenide and its application for demonstrating pulsed Er-doped fiber laser

Two-dimensional materials are now receiving continuously increasing attention due to their exceptional optical properties. Recently, it has been proved that indium selenide (InSe) is also an excellent photoelectric material, with wide applications in the field of photodetecters and so on. In our work, layered InSe was prepared through the liquid-phase exfoliation method, and the nonlinear saturable absorption properties of InSe were also experimentally investigated. In addition, InSe-polyvinyl alcohol film was successfully prepared and employed as an saturable absorber for demonstrating an Er-doped passive Q-switched mode-locked fiber laser for the first time. The largest Q-switched pulse energy was as high as 112.97 nJ and the narrowest mode-locked pulse duration was 2.96 ns at a repetition rate of 1.74 MHz. Our results fully indicate that InSe also has excellent nonlinear absorption properties in comparison with other commonly used 2D materials. Thus, the applications of InSe can be deeply investigated to promote the development of ultra-fast optics in the near future.

THz absorption spectrum employed for characterize the mixed Gallium selenide-Tin disulfide saturable absorber and its application for passively Q-switched solid state laser

Due to the ultra-short recovery time and the wider absorption range, graphene-like 2D material have been widely employed as saturable absorbers (SAs) in passively Q-switched and mode-locked lasers. Due to the low photon energy, noninvasive and high resolution, THz wave was widely used to characterize samples. In this paper, the nonlinear saturable absorption property and THz absorption spectrum of Gallium selenide/Tin disulfide (GaSe/SnS2) is reported. Passively Q-switched Nd:GdTaO4 laser with GaSe/SnS2 SA is demonstrated. The maximum output power of 551 mW under the pump power of 5 W. The minimum pulse width is 365 ns at the pulse repetition rate of 89 kHz. Our results indicate that GaSe/SnS2 nanosheets could be used in Q-switched lasers. The GaSe/SnS2 SA with good nonlinear absorption properties and easy fabricating process will promote the ultrafast photonics applications in solid state lasers.

Mesoporous Carbon Nanospheres as Broadband Saturable Absorbers for Pulsed Laser Generation

AbstractBroadband pulsed laser generation is demonstrated by using mesoporous carbon nanospheres (MCNs) as saturable absorbers (SAs). The MCNs are prepared by a “silica‐assisted” method, and then mixed with sodium carboxymethylcellulose (NaCMC) to form the MCNs film. The film not only shows strong absorption from visible to mid‐infrared spectral region, but also possesses the nonlinear saturable absorption properties. As the MCNs film is inserted into the laser cavity, a mode‐locked laser at 1 µm and Q‐switched lasers at 1.56 and 2 µm are realized, respectively. In addition, by depositing the MCNs onto tapered fiber as an SA, a mode‐locked fiber laser at 2 µm is also demonstrated. The results show that MCNs are promising SA material for broadband pulsed laser generation.

WS2-Clad Microfiber Saturable Absorber for High-Energy Rectangular Pulse Fiber Laser

Tungsten disulfide (WS2), which possesses broadband nonlinear saturable absorption property, displays promising applications in passively mode-locked lasers. Recent research works have demonstrated that WS2 shows much higher thermal conductivity than other transition metal dichalcogenides, which can withstand higher optical intensity and exhibit a higher damage threshold. However, the WS2-based high-energy fiber lasers have not been extensively studied. Here, a WS2-clad microfiber (WCM) saturable absorber (SA) is exploited by an effective transferring approach, which is precisely accomplished under optical microscope. The evanescent field interaction scheme has ability to further raise the optical damage threshold, as well as take full advantage of the nonlinear effect of WS2. Based on the WCM SA, high-energy rectangular pulses are achieved in an Er-doped fiber laser whose pulse duration and energy almost increase linearly with the enhancement of pump power. The maximum energy of single pulse in the cavity can reach 810 nJ under pump power of 800 mW. The experimental results open up venues to create new high-energy laser systems with rich functionalities and novel physical effects.

Passively Q-switched mid-infrared laser pulse generation with gold nanospheres as a saturable absorber.

High-quality gold (Au) nanospheres (Au-NPs) with a diameter of 52nm were prepared by the seeded growth method. The mid-infrared (MIR) nonlinear saturable absorption properties were measured by a balanced twin-detector measurement technique. With the as-prepared Au-NPs saturable absorber (SA), an efficient passively Q-switched laser was realized at 2.95μm for the first time, to the best of our knowledge. Under an absorbed pump power of 4.0W, a maximum output power of 268mW was obtained with the shortest pulse width of 734ns and repetition rate of 91kHz, corresponding to the pulse energy up to 2.95μJ. The results indicate that Au-NPs are promising candidates as SAs for MIR laser pulse generation.

Unexpected Broadband Optical Limiting Properties of Antimonene Quantum Dots

Antimonene has been found to possess excellent nonlinear refractive and saturable absorption properties recently. To further investigate its optical limiting properties, we prepared uniform antimonene quantum dots (AMQDs) via a facile ionic liquid-assisted exfoliation method. Thereafter the nonlinear absorption of the atomically thin AMQDs was studied using the open aperture Z-scan technique in the nanosecond laser pulse regime. Z-scan measurements indicate that the prepared AMQDs exhibited superior optical limiting properties at 532 nm and 1064 nm excitation, implying the antimonene hold potential for developing broadband nonlinear optical devices.

Broadband 1T-titanium selenide-based saturable absorbers for solid-state bulk lasers.

1T-titanium selenide (1T-TiSe2), a representative of 1T phase transition metal dichalcogenides (TMDs), exhibits semimetallic behaviour with a nearly zero bandgap structure, which makes it a promising photoelectric material. A high-quality multilayer 1T-TiSe2 saturable absorber (SA) is successfully fabricated by a combination of liquid phase exfoliation and the spin coating method. The broadband nonlinear saturable absorption properties of the prepared 1T-TiSe2 SA are investigated by using the open aperture (OA) Z-scan method. Passively Q-switched (PQS) all-solid-state lasers with different bulk crystals at the wavelengths of 1.0, 1.3, 2.0 and 2.8 μm are realised based on the 1T-TiSe2 SA. To the best of our knowledge, this is the first presentation of the application of a 1T-TiSe2 material to all-solid-state bulk lasers. The results indicate that 1T-TiSe2 could be an alternative broadband SA for solid-state pulsed lasers and exhibits promising potential applications in mode-locked ultrafast lasers.

Transition-metal dichalcogenides heterostructure saturable absorbers for ultrafast photonics.

In this Letter, high-quality WS2 film and MoS2 film were vertically stacked on the tip of a single-mode fiber in turns to form heterostructure (WS2-MoS2-WS2)-based saturable absorbers with all-fiber integrated features. Their nonlinear saturable absorption properties were remarkable, such as a large modulation depth (∼16.99%) and a small saturable intensity (6.23 MW·cm-2). Stable pulses at 1.55μm with duration as short as 296fs and average power as high as 25mW were obtained in an erbium-doped fiber laser system. The results demonstrate that the proposed heterostructures own remarkable nonlinear optical properties and offer a platform for adjusting nonlinear optical properties by stacking different transition-metal dichalcogenides or modifying the thickness of each layer, paving the way for engineering functional ultrafast photonics devices with desirable properties.

Passively Q-switched erbium-doped fiber laser based on SnS_2 saturable absorber

Layered metal dichalcogenides (LMDs) have been extensively employed as saturable absorbers (SAs) for demonstrating passively Q-switched or mode-locked lasers due to the advantages of wide absorption range and ultra-fast recovery time. In this paper, the nonlinear saturable absorption property of another IV-VI LMDs tin disulfide (SnS2) was investigated. SnS2-polyving alcohol (PVA) film was successfully prepared and employed as a SA for demonstrating an Er-doped passively Q-switched fiber laser. Under a pump power of 637 mW, the maximum average output power was 9.33 mW. The minimum pulse width was as narrow as 510 ns, which, to our knowledge, is the narrowest pulse width obtained within passively Q-switched Er-doped all-fiber ring-cavity lasers. The results indicate that film-type SnS2-PVA SA has excellent nonlinear absorption properties and outstanding performance in obtaining short-pulse passively Q-switched operation, which will promote the practical applications of SnS2 in the field of ultrafast photonics.

Passively Q-switched Nd:YVO_4 laser based on Fe_3O_4 nanoparticles saturable absorber

We report on a passively Q-switched Nd:YVO4 laser at 1064.34 nm by using the ferroferric-oxide (Fe3O4) nanoparticles (FONPs) saturable absorber (SA). It is corroborated that the FONPs SA exhibits a large nonlinear saturable absorption property with the modulation depth of 2.49% at the laser wavelength of 1 µm. By inserting the novel SA into a V-type Nd:YVO4 laser cavity, we obtain the shortest pulse duration of 53 ns with a repetition rate of 576.4 kHz. The corresponding average output power, single pulse energy, and peak power are 104 mW, 0.18 µJ, and 3.53 W, respectively. To the best of our knowledge, it is the first time to experimentally confirm the application of FONPs in a pulsed Nd:YVO4 solid state laser. The parameters of the pulse width, average output power, and peak power are superior to those in the reported pulsed fiber lasers with FONPs SA so far.

Filled Skutterudites for Broadband Saturable Absorbers

Filled skutterudites (FSs), which are known to be good thermoelectric materials, have been intensively investigated in the field of condensed matter physics in the past decades, due to their large variety of electronic and magnetic properties. However, to the best of the authors' knowledge, there has been no previous investigation of the optical properties of FSs. The nonlinear optical saturable absorption property of FSs is investigated in this work for the first time, and the results are reported here. More specifically, Co4Sb12 is chosen as a binary skutterudite system, and indium ions are added as a filling element to form a FS of In0.2Co4Sb12. The material properties are systematically investigated using a series of measurements. Density functional theory calculations of the electronic band structures of InCo4Sb12 and In0.25Co4Sb12 are conducted for better understanding of their energy band structures. It is also demonstrated that a broadband saturable absorber (SA) that can simultaneously operate at 1.5 and 1.9 µm can readily be implemented by depositing particles of In0.2Co4Sb12 onto fiber ferrules. The efficacy of the prepared SA is tested by incorporating the device into rare earth ion‐doped fiber ring cavities, to show its capability for both 1.5 and 1.9 µm operation.

Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies.

Q-switched fiber laser based on saturable absorption of ferroferric-oxide nanoparticles

We demonstrate that ferroferric-oxide (Fe3O4) nanoparticles exhibit nonlinear saturable absorption property at 1.55 μm, and fabricate two filmy saturable absorbers by embedding the nanoparticles into a polyvinyl alcohol (PVA) film or polyimide (PI) film separately. In the Fe3O4-PVA (Fe3O4-PI) Q-switched fiber laser, the pulse repetition rate increases from 8.5 kHz (5.5 kHz) to 28 kHz (49 kHz) and the pulse duration decreases from 23.5 μs (47 μs) to 6 μs (3.5 μs) by varying the pump power from 25 mW (23 mW) to 150 mW (650 mW). Experiment results indicate that PI-based saturable absorbers can afford larger powers than PVA-based saturable absorbers, which can be attributed to the higher fusion point of the PI film. The Fe3O4-PI saturable absorber exhibits features of high damage threshold, low cost, and good flexibility, which could be applied in fields of near-infrared pulse generation and frequency conversions.

Ultra-broadband Nonlinear Saturable Absorption for Two-dimensional Bi2TexSe3-x Nanosheets.

We report the ultra-broadband nonlinear optical (NLO) response of Bi2TexSe3−x nanosheets produced by a facile solvothermal method. Our result show that the extracted basic optical nonlinearity parameters of Bi2TexSe3−x nanosheets, αNL, Imχ(3), and FOM reach ~104 cm/GW, ~10−8 esu and ~10−13 esu cm, respectively, which are several orders of magnitude larger than those of bulk dielectrics. We further observed the excitation intensity dependence of the NLO absorption coefficient and the NLO response sensitivity. The mechanisms of those phenomena were proposed based on physical model. The wavelength dependence of the NLO response of Bi2TexSe3−x nanosheets was investigated, and we determined that the Bi2TexSe3−x nanosheets possess an ultra-broadband nonlinear saturable absorption property covering a range from the visible to the near-infrared band, with the NLO absorption insensitive to the excitation wavelength. This work provide fundamental and systematic insight into the NLO response of Bi2TexSe3−x nanosheets and support their application in photonic devices in the future.

WS2 as a saturable absorber for Q-switched 2 micron lasers.

We prepared WS2 nanosheets by using the thermal decomposition method and demonstrated for the first time its nonlinear saturable absorption property at around 2 μm. With the as-prepared WS2 nanosheets as saturable absorber (SA), a passively Q-switched Tm:LuAG laser was realized successfully, and 660 ns laser pulses with an average output power of 1.08 W and pulse peak power of 26 W at a repetition rate of 63 kHz were obtained for an incident pump power of 7 W. Our experimental results definitely demonstrate that WS2 could be a kind of promising SA for solid-state 2 μm lasers.

Erbium-doped fiber laser passively mode locked with few-layer WSe2/MoSe2 nanosheets.

Few-layer transition-metal dichalcogenide WSe2/MoSe2 nanosheets are fabricated by a liquid exfoliation technique using sodium deoxycholate bile salt as surfactant, and their nonlinear optical properties are investigated based on a balanced twin-detector measurement scheme. It is demonstrated that both types of nanosheets exhibit nonlinear saturable absorption properties at the wavelength of 1.55 μm. By depositing the nanosheets on side polished fiber (SPF) or mixing the nanosheets with polyvinyl alcohol (PVA) solution, SPF-WSe2 saturable absorber (SA), SPF-MoSe2 SA, PVA-WSe2 SA, and PVA-MoSe2 SA are successfully fabricated and further tested in erbium-doped fiber lasers. The SPF-based SA is capable of operating at the high pump regime without damage, and a train of 3252.65 MHz harmonically mode-locked pulses are obtained based on the SPF-WSe2 SA. Soliton mode locking operations are also achieved in the fiber laser separately with other three types of SAs, confirming that the WSe2 and MoSe2 nanosheets could act as cost-effective high-power SAs for ultrafast optics.

Nonlinear Saturable Absorption of Liquid-Exfoliated Molybdenum/Tungsten Ditelluride Nanosheets.

Molybdenum disulfide (MoS2 ) and tungsten disulfide (WS2 ), two representative transition metal dichalcogenide materials, have captured tremendous interest for their unique electronic, optical, and chemical properties. Compared with MoS2 and WS2 , molybdenum ditelluride (MoTe2 ) and tungsten ditelluride (WTe2 ) possess similar lattice structures while having smaller bandgaps (less than 1 eV), which is particularly interesting for applications in the near-infrared wavelength regime. Here, few-layer MoTe2 /WTe2 nanosheets are fabricated by a liquid exfoliation method using sodium deoxycholate bile salt as surfactant, and the nonlinear optical properties of the nanosheets are investigated. The results demonstrate that MoTe2 /WTe2 nanosheets exhibit nonlinear saturable absorption property at 1.55 μm. Soliton mode-locking operations are realized separately in erbium-doped fiber lasers utilizing two types of MoTe2 /WTe2 -based saturable absorbers, one of which is prepared by depositing the nanosheets on side polished fibers, while the other is fabricated by mixing the nanosheets with polyvinyl alcohol and then evaporating them on substrates. Numerous applications may benefit from the nonlinear saturable absorption features of MoTe2 /WTe2 nanosheets, such as visible/near-infrared pulsed laser, materials processing, optical sensors, and modulators.

WS₂ saturable absorber for dissipative soliton mode locking at 1.06 and 1.55 µm.

Transition-metal dichalcogenides, such as tungsten disulfide (WS2) and molybdenium disulfide (MoS2), are highly anisotropic layered materials and have attracted growing interest from basic research to practical applications due to their exotic physical property that may complement graphene and other semiconductor materials. WS2 nanosheets are found to exhibit broadband nonlinear saturable absorption property, and saturable absorbers (SAs) are fabricated by depositing WS2 nanosheets on side-polished fibers. Attributing to the weak evanescent field and long interaction length, the WS2 nanosheets are not exposed to large optical intensity, which allows the SA to work at the high-power regime. The SAs are used to mode lock erbium- and ytterbium-doped fiber lasers with normal dispersion, producing trains of dissipative soliton at 1.55 and 1.06 µm respectively. Simulations show that the bandgap of WS2 nanosheets decreases from 1.18 to 0.02 and 0.65 eV by introducing W and S defects respectively, which may contribute to the broadband saturable absorption property of the WS2.