# Diode-Pumped Solid-State Q-Switched Laser with Rhenium Diselenide as Saturable Absorber
## 3 The Passively Q-Switched Experiment  
The passively Q-switched Nd:YVO\({}_{4}\) experiment was pumped by a fiber coupled diode laser. Its central wavelength, core diameter and numerical aperture were 808 nm, 200 \(\upmu\)m and 0.22, respectively. An 1:1 optics coupling system focused the pump laser into a commercialized Nd:YVO\({}_{4}\) bulk crystal stabilized by a water-cooling system to remove heat. The linear type resonator had two mirrors, M1 and M2, of which M1 was the input mirror with radius of 100 mm and M2 was the output mirror with transmission of 5%. The cavity length was about 30 mm. After acquiring the continuous wave (CW) laser, the ReSe\({}_{2}\) SA was inserted in the resonator. Owing to the effect of ReSe\({}_{2}\) SA, the passively Q-switched laser was then obtained.  
Figure 4a shows the average output power properties for CW and Q-switched laser. The CW laser obtained the maximum average output power of 284 mW and it had a slope efficiency of 36.72%. For the Q-switched laser, the threshold of absorbed pump power was 227 mW, and the pulse laser had an average output power of 17 mW. When the absorbed pump power was increased to 837 mW, the maximum average output power was 125 mW. The average output power was linear with the absorbed pump power, and the slope efficiency was 17.27%. As illustrated in the Figure 4b, the measured beam profile was close to the TEM\({}_{00}\) mode, and the spot size is as shown. The laser spectrum, as shown in Figure 4c, is centered at 1064.4 nm, with a full width at half maximum of 0.68 nm (The spectrometer had a sampling resolution of 0.24 nm).  
At the absorbed pump power of 227 mW, the passively Q-switched laser was established with a pulse width of 1.16 \(\upmu\)s and repetition rate of 42.08 kHz. As the absorbed pump power increased, Figure 5a presents the behaviors of the pulse width and the pulse repetition rate. The experiment acquired the shortest pulse width of 682 ns and the highest repetition rate of 84.16 kHz. The corresponding pulse energy and peak power are shown in Figure 5b. Under the absorbed pump power of 837 mW, the Q-switched laser was calculated to be a pulse energy of 1.49 \(\upmu\)J and a pulse peak power of 2.18 W. Figure 6 shows the corresponding pulse form. For these measurements, we used a power meter (Ophir 30(150)A-BB-18, Jerusalem, Israel), optical spectrum analyzer (Ocean Optics HR4000, Largo, FL, USA), fast photodiode (EOT ET-3000A, Traverse, MI, USA), and digital oscilloscope (Tektronix MD03104, Beaverton, OR, USA).  
Figure 3: Nonlinear saturable absorption curve of the few-layer ReSe\({}_{2}\) SA.  
Figure 4: (**a**) Average output power properties for CW and Q-switched laser, (**b**) two-dimensional (2D) image of Q-switched output beam spatial profile, and (**c**) the laser spectrum at the maximum output power for Q-switching.  
Figure 5: (**a**) The variation of the pulse width and repetition rate, and (**b**) the variation of the pulse energy and peak power.  
Figure 6: The pulse profile of the Q-switched laser.  
Table 1 summarized the various Q-switched lasers that were used the diverse TMDs as SA in all-solid-state devices, with Nd-ion-doped gain medium and emitting wavelength at near 1064 nm. When compared with results, based on ReSe\({}_{2}\) SA, our works obtained the comparable laser performances. Table 1 concludes that ReSe\({}_{2}\) has the capacity to act as SA for all-solid-state pulse laser experiments. More importantly, the weaker interlayer coupling properties greatly reduced the preparation requirements of few-layer materials. Further optimizing the material, better results are expected to be achieved.