Q-switched mode-locked Nd:GGG waveguide laser with tin disulfide as saturable absorber
Introduction
Since the discovery of graphene in 2004, two-dimensional (2D) materials have rapidly become the research hot points in the world [1]. The unique and excellent properties of 2D materials in optics and electronics provided unprecedented technological application possibilities in the nonlinear optics, optoelectronics, and electronics [2,3]. As a prime category of emerging 2D materials, transition-metal dichalcogenides (TMDs) has attached much scientific interests for its distinct optical properties, exhibiting a bright developing prospect in photonics [4], chemical sensing [5], catalysis [6] and many other application fields. Particularly, with intriguing nonlinear saturable absorption, TMDs have been widely used in the generation of pulsed lasers as efficient saturable absorbers (SAs) [[7], [8], [9], [10]]. Tin disulfide (SnS2), as a kind of newly-developed TMDs, possesses a sizeable bandgap [11] as well as an ideal absorbance in near-infrared region [12], indicating bright potential as effective SAs.
With dimensions of micrometer or sub-micrometric scales, optical waveguides could confine the propagation of light within extremely small volumes, thus the optical intensities could achieve a much higher level with respect to the bulks [13,14]. Based on these features, waveguides receive a broad variety of applications in many areas. For example, waveguides have exhibited a great developing prospect in medical ultrasonography, radar, and augment reality [15,16]. In quantum photonics, waveguides play a crucial role of the light guidance and on-chip quantum elements [17,18]. In laser technology, by altering surface refractive index of gain materials, waveguide lasers have been implemented with on-chip integration towards miniature and compact laser sources [[19], [20], [21], [22], [23], [24], [25], [26], [27]]. The Q-switched as well as mode-locked (i.e., Q-switched mode-locked, QML or continuous-wave mode-locked, CWML) laser operations both have been achieved in varieties of laser gain media based on the waveguide platform and nanomaterial SAs [[28], [29], [30], [31], [32]]. Nowadays, mode-locked waveguide lasers have caught growing research interest to the relatively great stability and high repetition rate, for which they possess a great application potential in ultrafast nonlinear spectroscopy, precision metrology and high-speed optical communication [[33], [34], [35]]. In recent years, it has achieved repetition rate up to 1.5, 5.9, 6.5, and 8.8 GHz for different QML lasers [28,[36], [37], [38], [39]] as well as 6.5, 11, 15.2, and 21.25 GHz for diverse CWML lasers [[40], [41], [42], [43]]. As a widely-used laser crystal, Nd:GGG possesses outstanding optical advantages such as high slope efficiency and low propagation losses [44,45].
In this work, we report on a 1-μm QML with a few-layer SnS2 as SA. The system is based on a ridge Nd:GGG waveguide produced by C ion implantation and femtosecond laser ablation. As the first successful attempt for applying Nd:GGG waveguides in pulsed laser operations as well as SnS2 film in waveguide lasers, it achieved a fundamental repetition rate as high as 17.9 GHz and the output power of Q-switched envelopes is 115 mW on average. The mode-locked lasing performances have also been investigated in details.
Section snippets
Properties of SnS2 saturable absorber
The high-quality few-layer SnS2 SA, which was synthesized by chemical vapor deposition (CVD), was customized from 6 Carbon Technology Co., Ltd. (Shenzhen, China). Fig. 1a indicates a good linear optical absorption of the as-synthesized SnS2 sample in visible to near-infrared region. The absorption decreases as wavelength increases, possessing a threshold photon energy lower than 0.83 eV. These absorption properties illustrate a great potential for the SnS2 film as a broadband SA. An atomic
Results and discussion
Based on the monolithic Nd:GGG cladding waveguide, we have achieved a 1-μm mode-locked pulse laser operation, which is modulated by a CVD-grown SnS2 sample as the SA. Fig. 4 shows the performances of the pulses modulated by SnS2 sample. The linear fit in Fig. 4a indicates a 60-mW threshold pump power while the maximum power output is 115 mW and the corresponding slope efficiency is ~12.5%. The inset illustrates a near-field intensity image of the output laser. With pump power is 484 mW, a
Conclusions
In summary, based on the nonlinear optical properties of SnS2 we investigated, a 1-μm Q-switched mode-locked laser operation was achieved. The laser was modulated by a few-layer SnS2 saturable absorber and integrated in a Nd:GGG waveguide system. The fundamental repetition rate of the laser has reached 17.9 GHz with relatively low lasing threshold and high peak power, exhibiting bright prospects of SnS2 SAs as well as Nd:GGG waveguides in future ultrafast optical applications.
CRediT authorship contribution statement
Xuejian Dong: Formal analysis, Writing - original draft. Ziqi Li: Formal analysis, Writing - original draft. Chi Pang: Formal analysis, Writing - original draft. Ningning Dong: Writing - original draft. Hailing Jiang: Formal analysis, Writing - original draft. Jun Wang: Writing - original draft, Formal analysis. Feng Chen: Writing - original draft, Formal analysis.
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.
Acknowledgments
This work was supported by National Natural Science Foundation of China (No. 61775120, 61875213) and STCSM Excellent Academic Leader of Shanghai (No. 17XD1403900).
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