An ultraviolet laser at 228 nm with adjustable repetition rate and narrow pulse width
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摘要:
紫外激光器是研究紫外共振拉曼光谱的重要工具，拉曼信号可以通过共振拉曼效应得到增强，从而降低拉曼测量的探测极限。本文研究了一种输出波长为228 nm的窄脉宽全固态紫外激光器。首先，以Nd:YVO4作为增益介质，采用电光调Q腔倒空技术，实现了纳秒量级914 nm基频光输出。然后，经过偏硼酸锂(LBO)晶体产生二次谐波，最终经偏硼酸钡(BBO)晶体获得四次谐波228 nm紫外激光。在此基础上，进一步研究了不同重复频率时基频光和倍频光功率的变化规律，优化了紫外激光器的输出效率。实验结果表明：当总抽运功率为30 W时，在10 kHz重复频率下，可获得最高平均功率为84 mW的228 nm紫外激光输出。228 nm激光在5~25 kHz重复频率范围内连续可调，脉冲宽度保持在2.8~2.9 ns，能够满足紫外光谱检测技术领域的应用需求。
Abstract:Ultraviolet lasers play an important role in the study of ultraviolet resonance Raman spectroscopy. The Raman signals can be enhanced by the resonant Raman effect, thereby reducing the detection limit of Raman measurement. We focus on the study of a narrow-pulse all-solid-state ultraviolet laser with an output wavelength of 228 nm. The Nd:YVO4 is used as the gain medium and the electro-optic Q-switched cavity dumped technique is applied to achieve a fundamental frequency output of 914 nm in pulse width of several nanoseconds. Then, the second-harmonic light is generated by LiB3O5(LBO), and the fourth-harmonic 228 nm UV laser is obtained by beta-barium-borate (BBO) crystal. On this basis, further research has been conducted on the variation of fundamental and second harmonic laser power at different repetition rates. Due to the low gain of Nd:YVO4 at 914 nm, the average power of the laser is saturated and decreases with increased repetition rate. The output efficiency of UV laser is optimized by adjusting the focus lens. At the pump power of 30 W and the repetition frequency of 10 kHz, a 228 nm UV laser output with the highest average power of 84 mW is obtained. The UV laser is continuously adjustable within the range of 5−25 kHz repetition frequency and the pulse width is maintained at 2.8 to 2.9 ns, which meets the application requirements in the field of UV spectroscopy detection technology.
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Key words:
- 228 nm laser /
- ultraviolet laser /
- cavity dumped laser /
- second harmonic
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图 4 不同腔长时，晶体内基模半径随抽运功率的变化
Figure 4. Fundamental mode radius in crystals varying with pump power when the cavity length is different
图 6 914 nm激光的平均功率与脉冲能量随脉冲重复频率的变化情况
Figure 6. Average output power and pulse energy varying with pulse repetition rate for 914-nm laser
图 7 457 nm激光的平均功率与脉冲能量随脉冲重复频率的变化情况
Figure 7. Average output power and the pulse energy varying with pulse repetition rate for 457-nm laser
图 9 228 nm激光平均功率与脉宽随脉冲重复频率的变化情况
Figure 9. Average output power and pulse width varying with repetition rate of 228-nm laser
图 11 288 nm输出脉冲序列和脉宽。(a)、(b)分别为10 kHz时的脉冲序列和脉宽；(c)、(d)分别为18 kHz时的脉冲序列和脉宽
Figure 11. Pulse sequence and pulse width of 228-nm laser. (a) Pulse sequence and (b) pulse width at 10 kHz; (c) pulse sequence and (d) pulse width at 18 kHz
图 12 紫外激光光斑强度分布图。(a)二维空间强度分布；(b)三维空间强度分布；(c)水平方向强度分布；(d)竖直方向强度分布
Figure 12. Spot intensity distribution diagrams of ultra-violet laser. (a) Two-dimensional spatial intensity distribution; (b) three-dimensional spatial intensity distribution; (c) horizontal intensity distribution; (d) vertical intensity distribution
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