Bismuthene quantum dots based optical modulator for MIR lasers at 2 μm

doi:10.1016/j.optmat.2020.109830

Optical Materials

Volume 102, April 2020, 109830

https://doi.org/10.1016/j.optmat.2020.109830 Get rights and content

Highlights

•
Bismuthene quantum dots (BiQDs) were fabricated by LPE method.
•
Nonlinear optical properties were investigated by OA Z-scan technique at 2 μm.
•
BiQDs had a large modulation depth of 15.4% with a low saturated intensity.
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PQS Tm:YLF laser at 2 μm with BiQDs-SA was demonstrated for the first time.

Abstract

The uniformly sized two-dimensional (2D) bismuthene quantum dots (BiQDs) were fabricated through the liquid-phase exfoliation (LPE) route and characterized comprehensively. By transferring the BiQDs onto a quartz substrate, BiQDs saturable absorber (SA) was prepared and applied in a Tm:YLF bulk laser. To get the best output performance of passive Q-switching (PQS) laser with BiQDs-SA, three output couplers with different transmittance were applied in laser implementation. The stable solid-state 2 μm laser was obtained, generating a maximum peak power of 8.1 W and shortest pulse width of 440 ns with the T = 5% output coupler. To the best of our knowledge, it is the first demonstration of BiQDs-SA for Q-switching operation around 2 μm, implying that the BiQDs-SA can be considered as a promising optical modulator for the mid-infrared (MIR) pulses producing.

Introduction

In recent decades, the pulsed lasers in the mid-infrared (MIR) region, especially around 2 μm, have drawn a plenty of attention due to the potential application prospects in numerous fields (such as medicine treatment, materials processing, free-space communication, and detection) [[1], [2], [3], [4]]. Additionally, the pulsed laser emitting the radiation around 2 μm is an effective approach of driving MIR optical parametric oscillators (OPOs) [2]. Basically, Q-switching is usually employed to generate pulsed laser via active or passive techniques. Up to date, extensive Q-switching operations in thus MIR regime have been demonstrated in terms of solid-state and fiber lasers. Among them, the thulium (Tm³⁺) ion is extremely attractive for emitting lasers in this region because of its wavelength emission at ~2 μm (³F₄ → ³H₆ transition). Therefore, Q-switched all-solid-state 2 μm lasers based on Tm-doped gain medium have been reported [[5], [6], [7]]. Compared with the complicated and bulky active Q-switching technique, passive Q-switching (PQS) technique is one more efficient means to obtain pulsed lasers, possessing some obvious advantages for instance compact, easily-operated and low-cost [8].

For the PQS operation, the most critical component is the saturable absorber (SA). For the last few decades, numerous novel SAs have been utilized in lasers operating around 2 μm wavelength, including carbon group materials like graphene [9], single-walled carbon nanotubes (SWCNTs) [10], and other layered two-dimensional (2D) nanomaterials for instance transition metal chalcogenides (TMDs) [11], black phosphorus (BP) [12], and topological insulators (TIs) [13]. Although the 2D materials have the advantages of being readily available, the amorphous morphology and hundreds-nanometers sizes usually lead to poor uniformity [[11], [12], [13]], which makes the pulse unstable. In addition to the 2D materials, quasi zero-dimension quantum dot (QD) with size of several nanometers exhibits excellent optoelectronic properties due to the quantum confinement effect and size-edge effect [14]. So far, researchers have fabricated carbon and MoS₂ QDs and employed them in photovoltaic devices [15], optoelectronics [16], and biological analysis [17,18]. The impressive results stimulated researchers to make more effort to explore QDs family members.

On the other hand, the Group-VA monolayers arouse much interest due to their broadband absorption property, which caused by wide range of band gaps from 0.36 to 2.62 eV. As the most concerned Group-VA 2D material, black phosphorus (BP) has been indicated to possess excellent nonlinear optical (NLO) properties and employed as SA in bulk laser generation [13]. Recently, Xu et al. synthesized BP quantum dots (BPQDs) and investigated their NLO properties [19]. However, the development of BP-based applications was limited by the inherent instability and susceptibility to oxidation in ambient condition [[20], [21], [22]]. Therefore, researchers not only focus on solving the issues of oxidation and long-term stability [23,24], but also continuously develop new Group-VA 2D materials with excellent optoelectronic property and good chemical stability [25]. Unlike BP, another Group-VA material, bismuth (Bi), is typical semimetal in a layered bulk state of nature [26], which possesses higher chemical stability than BP in normal condition. Based on first-principle calculations [[26], [27], [28]], it is also theoretically predicted to possess enhanced stability and unique properties. In this case, with considering the high scalability, Bi has attracted more attention among monoelemental 2D nanomaterials. Inspired by the unique feature of graphene and TMDs QDs, as well as the novel chemical and physical properties of bismuth materials, we synthesized high quality BiQDs for the NLO research.

In this work, uniform-sized BiQDs (approximately 4 nm) were prepared by the liquid-phase exfoliation (LPE) route. The NLO properties of BiQDs were investigated by the Z-scan technique. Owing to the saturable absorption feature, the BiQDs were successfully applied in 2 μm solid-state pulse laser as an optical modulator. A passive Q-switching (PQS) Tm:YLF laser was presented with employing BiQDs as the SAs for the first time. The stable PQS laser pulse with the minimum pulse width of 440 ns at the repetition rate of 93.6 kHz are realized with T = 5% OC, corresponding to the single-pulse energy of 3.6 μJ and the peak power of 8.1 W. The demonstration of BiQDs-SA based PQS laser operating around 2 μm region may promote the development of high-quality 2D monoelemental QDs in optical modulation field. In addition, it is also very meaningful for broadening the research path of 2 μm solid-state lasers.

Section snippets

Synthetic methods

Firstly, the original Bi powder was dissolved in N-methyl pyrrolidone (NMP) solution with a concentration of 5 mg/mL. Then the mixed solution was bath sonicated for 48 h with applying a power of 400 W. The work temperature was kept at 5 C by the built-in cooling water system during the whole process. Subsequently, the above mixture was filtrated through a porous anodized aluminum oxide (AAO) membrane, whose pore diameter is 100 nm, to eliminate large-sized Bi particles and then filtered again

Characterization and discussion

The morphological and structural characterizations of as-prepared BiQDs were shown in Fig. 1. TEM and HRTEM were utilized to observe the morphology of BiQDs. From the TEM images in Fig. 1(a), the average diameter of as-prepared BiQDs was counted as 3.8 ± 0.6 nm (Fig. 1(d)). The HRTEM images of BiQDs show lattice spacing of 0.21 nm (shown in Fig. 1(b)) and 0.32 nm (shown in Fig. 1(c)), corresponding to the (110) and (012) planes of the Bi crystal, respectively. The topographic morphology of

Conclusions

In summary, BiQDs was successfully fabricated and employed in Q-switched Tm:YLF laser operating at 2 μm. The obtained minimum pulse width was 440 ns at a repetition rate of 94 kHz with an OC of 5% transmittance. A maximum single-pulse energy of 4.5 μJ and a maximum peak power of 8.1 W were delivered from the realized BiQDs-SA based Tm:YLF laser with OCs of T = 3% and 5%, respectively. The laser experimental results indicate the huge potentiality of BiQDs-SA acting as a new type of optical

CRediT authorship contribution statement

Han Pan: Investigation, Methodology, Writing - original draft. Weichun Huang: Investigation, Resources. Hongwei Chu: Conceptualization, Supervision, Writing - review & editing. Ying Li: Formal analysis, Validation. Shengzhi Zhao: Formal analysis. Guiqiu Li: Formal analysis. Han Zhang: Resources, Validation. Dechun Li: Conceptualization, Supervision, Writing - review & editing, Funding acquisition, Project administration.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (NSFC) (61575109, 21872084); Fundamental Research Fund of Shandong University (2018TB044); Natural Science Foundation of Shandong Province (ZR2018MF033).

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¹: These authors contributed equally to this work.

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Bismuthene quantum dots based optical modulator for MIR lasers at 2 μm

Highlights

Abstract

Introduction

Section snippets

Synthetic methods

Characterization and discussion

Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgements

Opt. Mater.

J. Alloys Compd.

Optic Laser. Technol.

Industrial applications of laser micromachining

Optic Express

High average power 2 μm generation using an intracavity PPMgLN optical parametric oscillator

Opt. Lett.

Mid-Infrared Coherent Sources and Applications

Modulated and continuous-wave operations of low power thulium (Tm:YAP) laser in tissue welding

J. Biomed. Optic.

Kilo-hertz-level Q-switched laser characteristics of a Tm,Y:CaF2 crystal

Opt. Mater. Express

Silicon-nanoparticle-based broadband optical modulators for solid-state lasers

Opt. Lett.

Efficient, broadly tunable, laser-pumped Tm:YAG and Tm:YSGG cw lasers

Opt. Lett.

Ho:SSO solid-state saturable-absorber Q-switch for pulsed Ho:YAG laser resonantly pumped by a Tm:YLF laser

Optic Laser. Technol.

Graphene on SiC as a Q-switcher for a 2 μm laser

Opt. Lett.

Passive Q-switching and Q-switched mode-locking operations of 2 μm Tm:CLNGG laser with MoS2 saturable absorber mirror

Photon. Res.

2 μm passively Q-switched laser based on black phosphorus

Opt. Mater. Express

High-quality 2-μm Q-switched pulsed solid-state lasers using spin-coating-coreduction approach synthesized Bi2Te3 topological insulators

Photon. Res.

The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons

Nat. Mater.

Kilo-hertz-level Q-switched laser characteristics of a Tm,Y:CaF₂ crystal

Passive Q-switching and Q-switched mode-locking operations of 2 μm Tm:CLNGG laser with MoS₂ saturable absorber mirror

High-quality 2-μm Q-switched pulsed solid-state lasers using spin-coating-coreduction approach synthesized Bi₂Te₃ topological insulators