Results and Discussions To evaluate the amplification ability of the amplification system under different seed laser repetition frequencies, the seed source is operated at repetition frequencies of 24.46 MHz, 4.89 MHz, 2.038 MHz, 1.019 MHz, 500 kHz, 200 kHz, 99.4 kHz, 49 kHz, and 25 kHz, and the output power is obtained as a function of the pump power (Fig. 7 and Table 1). Once the seed light passes through the isolator and the beam expansion system, the single pulse energy injected into the slab is 19.6 nJ. In the single-end pumped case, when the repetition frequency of the seed source is 24.46 MHz, the output power is 228 W, the single-pulse energy is 9.3 μJ, the optical-optical conversion efficiency is 20.2%, and the beam quality (M2) values in the guided and non-guided directions are 1.4 and 4.6, respectively. In order to measure the amplification system, we change the repetition frequency of the seed laser under the condition that the pulse width of the seed laser is 11.7 ps and the single pulse energy of the seed laser is fixed at 19.6 nJ.When the repetition frequency of the seed source is 49.8 kHz, a laser output power of 31.6 W is obtained with the single-pulse energy of 0.63 mJ. When the repetition frequency of the seed source is 25 kHz, a laser output power of 24.2 W is obtained with the single-pulse energy of 0.97 mJ and the peak power of 82.9 MW. The magnification factor is up to 4.9×104. Experimental results show that this amplifier can suppress the amplification of the spontaneous emission (ASE) effect and can effectively increase the magnification, thereby improving the output power and conversion efficiency. Moreover, the method of improving the output and suppressing the ASE is further analyzed based on the theoretical calculations. Experimental results reveal that the system has a strong amplification ability.
High-energy, high-peak power, picosecond pulse lasers have broad application prospects in laser science research and industrial processing. The configuration of a master oscillator power amplifier (MOPA) is commonly used to obtain a high output power. In this case, a low-power oscillator with the desired characteristics is used as the seeder, whose radiation is injected into an amplifier to scale the output power or pulse energy, while other properties remain mostly unchanged. The planar waveguide can provide high seed light injection powers and high pumping power densities. Therefore, the planar waveguide lasers are a potential laser technology for obtaining picosecond pulse laser with high energy and high peak power.
A Nd∶YAG planar waveguide picosecond laser amplifier is designed. The seed is a fiber picosecond laser, which is amplified by a compactness amplifier with a Nd∶YAG planar waveguide as the gain medium to obtain a picosecond laser output. The small signal gain coefficient and power distributions at different positions within the planar waveguide are calculated using related theories. Finally, based on the results of theoretical calculations, a picosecond laser amplifier is designed and built, and the experiment is completed under different seed laser repetition frequencies.
In this study, a back end-pumped Nd∶YAG planar waveguide picosecond laser amplifier is designed. The fiber laser provides a picosecond seed source with a tunable repetition frequency, and the pumping source operates in the continuous mode. Based on the results, when the seed light repetition frequency is 24.46 MHz, the pulse width is 11.7 ps, the injection power is 0.48 W, the output power is 228 W, the single-pulse energy is 9.3 μJ, and the optical-optical conversion efficiency reaches 20.2%. Moreover, the beam quality values in the guided and non-guided directions are 1.4 and 4.6, respectively. In contrast, when the repetition frequency of the seed laser is reduced to 25 kHz, the average output power is 24.2 W, the single-pulse energy is increased to 0.97 mJ, and the single-pulse energy magnification factor is 4.9×104, indicating that the amplification system has a strong amplifying ability. The methods to further improve the optical-optical conversion efficiency and suppress ASE are analyzed based on the theoretical calculations. To the best of our knowledge, this is the first report on a planar waveguide picosecond laser amplifier.
