A method and system for generating femtosecond (fs) ultraviolet (UV) laser pulses enables stabile, robust, and optically efficient generation of third harmonic fs laser pulses using periodically-poled quasi-phase-matched crystals (PPQPMC) having different numbers of periodically poled crystalline layers that enable a long conversion length without back-conversion and without a special phase-matching direction. The fs UV laser may have a high conversion efficiency and may be suitable for high power operation.用於產生飛秒(fs)紫外線(UV)雷射脈衝之方法及系統使用週期性極化準相位匹配晶體(PPQPMC)允許三次諧波fs雷射脈衝之穩定、穩健及光學有效的產生，該等週期性極化準相位匹配晶體具有不同數目之週期性極化結晶層，該等週期性極化結晶層在無反向轉換且無特殊相位匹配方向的情況下允許長轉換長度。fs UV雷射可具有高轉換效率，且可適合於高功率操作。
