By using the LPE technique, a high-quality TaSe2 thin film was successfully fabricated on a gold-coated silicon substrate mirror. First, 20 mg commercial powder of TaSe2 and 10 ml mixture of N-methylpyrrolidone (NMP) and Ethanol were mixed in a centrifuge tube, then centrifuge tube was sonicated in an ultrasonic machine for 0.5 h with a power of 600 W. Next, the TaSe2 dispersions were centrifuged at 3500 rmp for 15 min and the supernatant was collected. Last, the processed TaSe2 dispersion was dropped on gold-plated silicon mirror and spin-coated on a spin-coating machine, then dried in a drying cabinet at temperature of 70 °C and the reflective TaSe2 SAM was successfully prepared. To identify the chemical element composition of the TaSe2 powder, Energy-dispersive X-ray spectroscopy was used, the element map showed a homogeneous distribution of Ta and Se elements, and the atomic number ratio of Ta and Se elements was about 1:2, as shown in Fig. 1(a). The Raman scattering spectrum of TaSe2 nanosheets was characterized by a Raman spectroscopy. Fig. 1(b) shows the Raman peak of TaSe2 nanosheets was at 238.6 cm−1, which accord with previously reported work [26]. To characterize the morphology and the thickness of as-prepared TaSe2 nanosheets, atomic force microscopy (AFM) was taken. Fig. 2(a) shows the 2D AFM image of TaSe2 nanosheets, Fig. 2(b) shows the profiles of TaSe2 nanosheets, it can be clearly observed that the dimension of TaSe2 nanosheets was about two hundred nanometers, and the average thickness of TaSe2 flakes was in a range of 5 nm to 17.5 nm, which was estimated to be 8–27 layers ( ∼ 0.64 nm of each layer spacing [26]). The nonlinear optical absorption of reflective TaSe2 SAM was investigated by the open-aperture Z-scan method. The laser source is a home-made pulsed PPMgLN-OPO with a pulse width of ∼ 100 ns and a repetition rate of 30 kHz, operating at ∼ 2.8 μ m. The diameter of the beam was focused by a CaF2 lens to be ∼ 150 μ m. The measured results, as shown in Fig. 3(a), indicates the as-fabricated TaSe2 SAM has stronger saturated absorption behavior. The experiment dates, as shown in Fig. 3(b), were fitted by the following formula [29]: (1) 𝑅 ( 𝐼 ) = 1 − 𝛥 𝑅 ⋅ 𝑒 𝑥 𝑝 ( − 𝐼 𝐼 𝑠 𝑎 𝑡 ) − 𝑅 𝑛 𝑠 where R(I), 𝛥 R, I, I 𝑠 𝑎 𝑡 and R 𝑛 𝑠 represent the reflectivity, the modulation depth, the incident intensity, the saturable intensity, and the total non-saturable loss, respectively. The calculated modulation depth, the total non-saturable loss, and the saturation intensity were 5.3%, 2.2% and 0.3 MW/cm2, respectively. The damage threshold of the reflective TaSe2 SAM was measured by the twin-detector technology at 1.06 μ m. According to the measured result, the laser-induced damage threshold was estimated to be ∼ 12 MW/cm2, which was about 25 times as much as that of SESAMs [30], and about 40 times as much as its saturation intensity.

By using the LPE technique, a high-quality TaSe2 thin film was successfully fabricated on a gold-coated silicon substrate mirror. First, 20 mg commercial powder of TaSe2 and 10 ml mixture of N-methylpyrrolidone (NMP) and Ethanol were mixed in a centrifuge tube, then centrifuge tube was sonicated in an ultrasonic machine for 0.5 h with a power of 600 W. Next, the TaSe2 dispersions were centrifuged at 3500 rmp for 15 min and the supernatant was collected. Last, the processed TaSe2 dispersion was dropped on gold-plated silicon mirror and spin-coated on a spin-coating machine, then dried in a drying cabinet at temperature of 70 °C and the reflective TaSe2 SAM was successfully prepared. To identify the chemical element composition of the TaSe2 powder, Energy-dispersive X-ray spectroscopy was used, the element map showed a homogeneous distribution of Ta and Se elements, and the atomic number ratio of Ta and Se elements was about 1:2, as shown in Fig. 1(a). The Raman scattering spectrum of TaSe2 nanosheets was characterized by a Raman spectroscopy. Fig. 1(b) shows the Raman peak of TaSe2 nanosheets was at 238.6 cm−1, which accord with previously reported work [26]. To characterize the morphology and the thickness of as-prepared TaSe2 nanosheets, atomic force microscopy (AFM) was taken. Fig. 2(a) shows the 2D AFM image of TaSe2 nanosheets, Fig. 2(b) shows the profiles of TaSe2 nanosheets, it can be clearly observed that the dimension of TaSe2 nanosheets was about two hundred nanometers, and the average thickness of TaSe2 flakes was in a range of 5 nm to 17.5 nm, which was estimated to be 8–27 layers ( ∼ 0.64 nm of each layer spacing [26]). The nonlinear optical absorption of reflective TaSe2 SAM was investigated by the open-aperture Z-scan method. The laser source is a home-made pulsed PPMgLN-OPO with a pulse width of ∼ 100 ns and a repetition rate of 30 kHz, operating at ∼ 2.8 μ m. The diameter of the beam was focused by a CaF2 lens to be ∼ 150 μ m. The measured results, as shown in Fig. 3(a), indicates the as-fabricated TaSe2 SAM has stronger saturated absorption behavior. The experiment dates, as shown in Fig. 3(b), were fitted by the following formula [29]: (1) 𝑅 ( 𝐼 ) = 1 − 𝛥 𝑅 ⋅ 𝑒 𝑥 𝑝 ( − 𝐼 𝐼 𝑠 𝑎 𝑡 ) − 𝑅 𝑛 𝑠 where R(I), 𝛥 R, I, I 𝑠 𝑎 𝑡 and R 𝑛 𝑠 represent the reflectivity, the modulation depth, the incident intensity, the saturable intensity, and the total non-saturable loss, respectively. The calculated modulation depth, the total non-saturable loss, and the saturation intensity were 5.3%, 2.2% and 0.3 MW/cm2, respectively. The damage threshold of the reflective TaSe2 SAM was measured by the twin-detector technology at 1.06 μ m. According to the measured result, the laser-induced damage threshold was estimated to be ∼ 12 MW/cm2, which was about 25 times as much as that of SESAMs [30], and about 40 times as much as its saturation intensity.