# Diode-Pumped Solid-State Q-Switched Laser with Rhenium Diselenide as Saturable Absorber
## 1 Introduction  
Few-layer materials are of great importance to researches and applications due to their unique optical and electronic characteristics. Current researches on few-layer materials are principally focused on graphene, insulating hexagonal boron nitride (hBN), topological insulators (TIs), black phosphorus (BP), and transition metal dichalcogenides (TMDs) [1; 2; 3; 4; 5; 6]. Among these materials, TMDs are a large family, which exhibits a variety of photo-electric properties and offers a wide range of applications in broad research fields [5; 6]. TMDs include some metals, various semiconductors, as well as superconductors. Over years of development, studies of TMDs have mainly concentrated on MoS2, MoSe2, WS2, and WSe2[7; 8; 9]. They have a changed characteristic (such as electronic structure, band gap) with their different layer thickness, owing to interlayer interactions and the variations of screening. While some TMDs have different transformation characteristics when the structure is changed from bulk to single or few-layer. Reports show that both SnS2 and SnSe2 (one type of TMDs) are layer-independent on in-plane lattice parameters, interlayer distances, and binding energies [10; 11]. In addition, the ReSe2 class also has different transformation characteristics with the change of the number of layers. ReSe2, a new member of semiconductor TMDs, owns the distorted 1T structure, compared with the typical 2H-shaped MoS2 class of TMDs [12]. In their in-plane, Re atoms arrange in linked Re4 \"diamond\" shapes along the b [010] direction. These Re4 'diamonds' are coplanar and arecoupled with one another to form a one-dimensional clustering pattern of 'diamond chains' [13]. Its distorted 1T structure results in the weaker interlayer coupling action [12; 13; 14; 15; 16; 17]. Further, \(\text{ReSe}_{2}\) behaves as electronically and vibrationally decoupled monolayers [15; 16]. The weaker interlayer coupling action makes \(\text{ReSe}_{2}\) weak-layered dependence. Due to the distorted 1T structure, \(\text{ReSe}_{2}\) has a low-symmetry lattice characteristic that is similar to \(\text{ReS}_{2}\) and BP [18]. In different directions of the in-plane structure of \(\text{ReSe}_{2}\), there are significant differences in properties, including phonon behavior, magnetic characteristics, transport properties, and so on [19]. Therefore, this material has a larger variation in physical, chemical, optical, and electrical properties, and it has great potential in applications [20; 21; 22; 23; 24; 25; 26]. With the rapid development of the material applications, one of the significant applications of the few-layer TMDs are to be used as SA. Such as MoS\({}_{2}\) have been widely studied in the field of fiber laser and all-solid-state laser [27; 28]. Recently, \(\text{SnS}_{2}\) and \(\text{SnSe}_{2}\) are successfully applied to pulse lasers acting as saturable absorber (SA) in fiber laser and in waveguide laser, respectively [29; 30]. \(\text{ReSe}_{2}\), as a specific TMDs, is able to work as a SA. Because of the weak-layered dependent feature, it is not necessary to strictly control the thickness of \(\text{ReSe}_{2}\) for many applications, which greatly simplifies the preparation requirements [17]. There is a report about a Q-switched fiber laser with \(\text{ReSe}_{2}\) SA, whose shortest pulse width was 4.98 \(\upmu\)s and highest repetition rate was 16.64 kHz [31]. However, based on \(\text{ReSe}_{2}\) SA, the all-solid-state laser performances have not been reported. In this paper, we firstly demonstrated a passively Q-switched Nd:YVO\({}_{4}\) laser incorporating \(\text{ReSe}_{2}\) as SA in an all-solid-state laser. The \(\text{ReSe}_{2}\) with a few-layer structure was prepared by the ultrasonic exfoliation technique. A series of measurements were used to characterize the properties of \(\text{ReSe}_{2}\) sample. The saturation intensity was about 6.37 MW/cm\({}^{2}\), the non-saturable absorbance equaled to 16.84%, and the modulation depth was fitted to be 1.89%.