Seed-injection-locked Narrow-linewidth， Low-noise Single-frequency Nd∶YVO₄ Laser

Single-frequency continuous-wave lasers are critically important for advanced applications in quantum information science， high-precision metrology， and lidar systems. These applications demand laser sources that combine a narrow linewidth， low amplitude and frequency noise， and high temporal coherence. A significant challenge in the field is scaling the output power of such lasers while simultaneously preserving their superior spectral purity and high stability. Conventional techniques for achieving single-frequency operation often face limitations in power scaling due to thermal effects and nonlinearities.This research demonstrates a high-power， single-frequency Nd∶YVO₄ laser system utilizing the seed injection-locking technique. A stable， narrow-linewidth fiber laser operating at 1 064 nm serves as the master oscillator. The slave laser is configured as an “8”-shaped ring resonator， which is pumped by an 888 nm diode laser. A composite Nd∶YVO₄ crystal is used as the gain medium to mitigate thermal lensing effects. Active frequency stabilization is implemented using the Pound-Drever-Hall （PDH） method. An error signal， derived from the cavity transmission， feeds back to a piezoelectric transducer to control the slave cavity length， thus locking it to the seed laser frequency.Under optimal injection-locking conditions and at a pump power of 38.12 W， the laser delivers a maximum output power of 13.5 W in a single longitudinal mode. The linewidth of the amplified output is measured to be 7.0 kHz. This represents only a minor broadening compared to the 5.6 kHz linewidth of the original seed laser. The system exhibits excellent power stability， with a root-mean-square power instability of less than 0.18% over a continuous 60-minute period. Furthermore， the frequency stability is significantly enhanced through injection locking. The long-term wavelength drift is reduced to 132.4 MHz， a substantial improvement over the 300 MHz drift observed for the free-running seed laser. A detailed frequency noise characterization reveals effective suppression of noise at low Fourier frequencies （1~100 Hz） in the locked state compared to the free-running slave laser. A slight increase in noise is observed at higher frequency offsets， which is attributed to residual mechanical vibrations from the locking actuator. These results confirm that the seed injection-locking technique successfully amplifies the optical power while maintaining the spectral characteristics of the seed. Crucially， this high stability is achieved without the need for active frequency stabilization of the seed laser itself. This work contributes by achieving a compelling combination of high power （13.5 W）， narrow linewidth （7.0 kHz）， and high stability at the important 1 064 nm wavelength. A key finding is that this high stability is accomplished without requiring active stabilization of the seed laser itself. The results robustly demonstrate that the seed injection-locking technique is a highly effective method for amplifying optical power while simultaneously preserving and even enhancing the frequency stability and spectral characteristics of the original seed source.In conclusion， this research successfully realizes a high-power， narrow-linewidth， low-noise single-frequency Nd∶YVO₄ laser. The system exhibits outstanding power and frequency stability， making it suitable for demanding applications. The approach provides a viable and practical pathway for developing high-performance single-frequency lasers. Future work will focus on refining the feedback control system to achieve even lower frequency noise. Additionally， the integration of intracavity nonlinear frequency conversion techniques， such as second harmonic generation， could be implemented to produce high-power， single-frequency radiation at other strategically important wavelengths， further expanding the utility of this laser architecture.