Objective  The single-frequency lasers operating at 1.3 µm have been extensively investigated in a variety of fields, including quantum optics and fiber optical communication. A noteworthy example is the single-frequency tunable continuous-wave 671 nm laser based on frequency doubling of 1 342 nm laser, which is near the D-line atomic transitions (670.97 nm) of lithium vapor. Consequently, it finds important applications in the field of atomic physics related to lithium atoms, such as optical cooling, lithium atom interferometer, and lithium isotope separation. In applications like the lithium atom interferometer, a higher output power of the laser can yeild improved results. At present, the output power of single-frequency continuous-wave 1 342 nm diode lasers is as low as several miliwatts, necessitating application by Raman laser amplifiers and solid-state laser amplifiers. Therefore, the entire system becomes large and heavy. This paper introduces an injection-locked single-frequency tunable 1 342 nm Nd:YVO₄ laser with high output power. The injection-locked laser offers the advantages of a small size and high gain, making it suitable for special demands.

  Methods  In this paper, an injection-locked 1 342 nm continuous-wave single-frequency tunable Nd:YVO₄ laser is developed. The system employs an end-pumped Nd:YVO₄ ring laser as the slave laser, with a distributed feedback laser (DFB) as the seed laser. The seed laser is coupled into the Nd:YVO₄ ring laser through output mirror (Fig.1). To achieve cavity length locking, a lock-in (LI) module is employed. The LI module detects laser intensity through a photoelectric detector and provides feedback control by adjusting the voltage on the piezoelectric transducer (PZT). The Nd:YVO₄ ring laser operates bidirectionally under free operation. When the PZT on the cavity mirror is adjusted to match the cavity length with the wavelength of the injected seed laser, the laser can operate unidirectionally, resulting in a single-frequency continuous-wave 1 342 nm laser. The laser's tuning capability is achieved by changing the wavelength of the seed laser.

  Results and Discussions   The measured output laser power in free operation is 13.9 W as recorded by power meter (Fig.2). In this state, the influence of the seed power on the injection locking of the ring laser is obtained (Fig.3). An output power of 13.9 W for the injection-locked laser is achieved with an input seed laser power of 20.69 mW. Under this condition, the tuning range of the laser is measured by a wave-meter, and a tuning range from 1 341.677 4 nm to 1 341.802 5 nm is achieved (Fig.4). Simultaneously, the laser line-width is studied using an F-P scanning interferometer (Fig.5). The laser operates in a single frequency with a line-width of approximately 41 MHz. The line-width of the output laser is enhanced compared to the seed laser, a result attributed to low seed power and the reverse-running laser mode in the cavity. The beam quality factors M² of the injection-locked 1 342 nm laser are determined to be M_x^2 = 1.3 in the x direction and M_y^2 = 1.23 in the y direction using a laser beam analyzer (Fig.6). The power fluctuations (RMS) at the 13.9 W of the laser are measured and the stability is better than ± 0.5% (Fig.7).

  Conclusions  A high-power tunable single-frequency 1 342 nm Nd:YVO₄ laser based on LI injection-locked technology was successfully designed. The output power of injection-locked 1 342 nm laser reached 13.9 W, with a DFB seed laser power of 20 mW. The tunning range of the laser system was analyzed using a wave-meter, and the measured tuning range spanned from 1 341.677 4 nm to 1 341.802 5 nm. Various characteristics, including beam quality, laser line-width, power stability were comprehensively measured. To achieve the better stability and lower system noise, the methods of employing a seed laser with higher power and implementing methods such as reducing vibration and enclosed the structures have been identified as effective.