阐述了一种基于单块周期极化铌酸锂晶体级联三倍频实现440 nm蓝光输出的实验方案。根据周期极化铌酸锂晶体的Sellmeier方程以及倍频与和频的相位匹配条件，在一块周期极化铌酸锂晶体上设计了两段不同的极化周期，使其在同一工作温度下能分别实现倍频与和频，在先后经过倍频与和频后，实现级联三倍频输出。实验采用Nd:YAG产生的1319 nm光作为基频光，重频400 Hz，脉宽110 ns，横向和纵向光束质量因子分别为1.81和2.65。耦合进周期极化铌酸锂晶体后，出射光中检测到660 nm的红光和440 nm的蓝光。通过调整工作温度和入射基频光功率，得到2.4 mW的最大蓝光输出，此时工作温度55.5 ℃，基频光功率530 mW。实验结果验证了单块晶体实现级联三倍频440 nm蓝光输出的可行性。

A 440 nm solid-state blue laser produced by a periodically poled lithium niobate (PPLN) crystal based on cascaded third-harmonic generation (THG) is introduced. According to Sellmeier equation and phase-matching conditions of second-harmonic generation (SHG) and sum-frequency generation (SFG), two different poling periods of PPLN were designed to realize SHG and SFG at the same working temperature, and then the cascaded THG can be realized through SHG and SFG. The fundamental laser was produced by Nd:YAG, and had a 110 ns pulse width at 400 Hz pulse repetition rate with a measured beam quality of M2x=1.81 and M2y=2.65. It was coupled in PPLN and the 660 nm and 440 nm laser were detected after it passed through the crystal. The maximum output power of 440 nm laser was 2.4 mW where the working temperature was 55.5 ℃，and the power of 1319 nm laser was 530 mW. It is proved that a cascaded THG 440 nm blue laser can be realized by this method and it can realize a high power and high efficiency blue laser after optimization.