Fig. 1. (a) Synthesis scheme of bulk crystals by CVT with dual-temperature zones. Photographs and atomic models of the formation of 2H ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$. Photographs and atomic models of layer-structure bulks of (b) 2H ${\mathrm{WSe}}_2$ and (c) Td ${\mathrm{WTe}}_2$. TEM and SEAD characterizations of few-layer nanosheets of (d) ${\mathrm{WSe}}_2$, (e) ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and (f) ${\mathrm{WTe}}_2$. Corresponding full EDS scanning of (g) ${\mathrm{WSe}}_2$, (h) ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and (i) ${\mathrm{WTe}}_2$. AFM images and thickness measurements of typical nanosheets of (j) ${\mathrm{WSe}}_2$, (k) ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and (l) ${\mathrm{WTe}}_2$.

Fig. 2. (a) Raman spectra of few-layer ${\mathrm{WSe}}_2$, ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and ${\mathrm{WTe}}_2$ nanosheets. (b) Comparison of recorded transmittance spectra and corresponding fitted lines. (c) The refractive index of ${\mathrm{WSe}}_2$, ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and ${\mathrm{WTe}}_2$ based on the relationship of Kramers–Kronig.

Fig. 3. (a) Determination of the Tauc optical gap. The spectral dependence of $\sqrt{\alpha \hslash \omega }$ on $\hslash \omega$. (b) The open-aperture Z-scan results of ${\mathrm{WSe}}_2$, ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$, and ${\mathrm{WTe}}_2$ nanoflakes.

Fig. 4. Experimental setup of the LD pumped passively $Q$-switched laser.

Fig. 5. (a) Output power with increasing incident pump powers. (b) Variations of pulse repetition rates and pulse duration with increasing pump powers. (c) Typical temporal pulse trains of $Q$-switched lasers. (d) Single pulse traces.

Fig. 6. Optical spectrum of a ${\mathrm{WSe}}_{1.4}{\mathrm{Te}}_{0.6}$$Q$-switched laser.

Table 1. Results of Z-scan Measurements at 1070 nm

Table 2. Parameters of WSexTe2−x Saturable Absorbers Based Q-switched Lasers