Objective At present,distributed Bragg reflector (DBR), distributed feedback (DFB) laser, or external cavity diode laser (ECDL) is usually used to realize a tunable single-frequency laser output in 1.3 μm. However, the output power of these diode lasers is as low as several mW. Some studies used a 1.3-μm laser for an effective selective atom stimulation; hence, a higher output power of the lasers was needed. This work presents an injection-locked Nd∶YVO₄ ring laser that can effectively improve the power of a CW single-frequency 1342-nm laser with wavelength tuning. The amplified 1342-nm laser retains most of the spectral characteristics of the seed laser. This injection-locked Nd∶YVO₄ ring laser has the advantages of high gain and high beam quality and is very easy to realize. As a consequence of the high power, the doubling frequency of 1342 nm (671-nm red light) and the quadruple frequency (336-nm UV light) can be obtained more easily for some other works.

Methods An injection-locked Nd∶YVO₄ ring laser was studied herein. Three modules were considered, namely the seed laser, the laser amplifier, and the Pound-Drever-Hall (PDH) frequency locking system. The seed laser provides the injection source. While the PDH system is being unlocked, the seed laser is reflected away from the cavity because it does not match the resonant conditions of the power cavity. Conversely, while the PDH system is locked, the seed light can be injected into the amplifier cavity and effectively amplified. In this work, a seed laser with output power of the order of mW, good beam quality, and good stability was used. After the injection-locked amplification, the laser retained the spectral characteristics of the seed light, including the single longitudinal mode and the adjustable wavelength. Meanwhile, the laser energy and the beam quality were improved. In this study, a tunable 1.0 W CW single-frequency 1342-mm laser was used as the seed light, and an 8-type ring resonator was used as the amplifier cavity. The injection-locked Nd∶YVO₄ ring laser was realized, based on the frequency locking technology of the PDH. The seed laser was amplified by the amplifier cavity, and the output power was significantly increased.

Results and Discussions A 1.3-μm seed laser is successfully injected into the amplifier cavity, and an effective laser amplification with the PDH frequency locked is realized (Fig. 2). At the same time, the frequency characteristics of the 1342-nm output laser are measured by an F-P scanning interferometer. The 1342-nm laser is operated at a single frequency. The spectral line-width is approximately 240 MHz (Fig. 3). We inject 1.0 W of seed light into the amplifier cavity and perform experiments on the input coupling mirror with different transmittances. We achieve a good experimental result with 7% transmittance of the coupling mirror (Table 1). We also perform an optimization experiment of the laser output power with different seed light powers using 7% transmittance of the input mirror. With the increase of the seed light power, the amplified laser power gradually increases, and the frequency locking becomes more stable. The total amplified output power of the 1342-nm laser reaches 8.3 W, when the power of the seed laser is 1 W. Therefore, increasing the seed light power seems to be an effective method of increasing the amplification efficiency and stability (Fig. 4). The maximum output power is 8.3 W with the 35-W pump laser (Fig. 5). Following the increase of the pump power (>35 W), the amplified laser output power decreases with the pump power because of the noise in the laser system. We also investigate the laser tunability. The tuning range is 1342.05--1342.25 nm when the power of the seed laser is 1 W, with 4.8 W as the highest output power. The tuning range of the output laser is 1342.09--1342.21 nm, which is smaller than 4.8 W (Fig. 6), when the power of the seed laser is 1.0 W, with 7.8 W as the highest output power. The experiment result demonstrates that the tuning range of the amplified laser decreases with the increase of the output laser. Increasing the energy of the injected seed laser is likely to be an effective method of increasing the tuning range. The innovative result obtained in this work is the demonstration of an easy and effective method of constructing a tunable CW single-frequency 1342-nm injection-locked Nd∶YVO₄ ring laser with the maximum power output of 8.3 W. Some experiment results are also presented in this paper.

Conclusions An injection-locked Nd∶YVO₄ring laser is studied herein. The influence of the amplification parameters, including the different transmittances of the input mirrors and the different powers of the injected seed light of the injection-locked ring laser, is analyzed. The maximum output power of the CW single-frequency 1342-nm laser is 8.3 W, which is obtained with the 8-type ring cavity at the power of the seed laser of 1.0 W. Characteristics such as high power, high beam quality, and continuous wavelength tunability are observed. The structure of the amplifier cavity will be optimized in subsequent experiments. We expect to acquire a wider tuning range with higher power and more stability of the CW single-frequency 1342-nm laser by increasing the frequency locking accuracy, reducing the system noise, and improving the seed light power.