Continuous-wave single-frequency 589 nm yellow laser generated from sum frequency of single-block non-planar ring cavity laser in periodically poled KTiOPO₄ crystal

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO₄ crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 μm by an achromatic lens. The sum-frequency generation takes place in a 1 mm×2 mm×20 mm phase-matched type-I periodically poled KTiOPO₄ crystal with a matching temperature of 55℃ and polarization period of 12.35 μm The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M² = 1: 14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO₄ temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D_2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.