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摘要:
紫外 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，提高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 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 。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 的输出效率。当总抽运功率为30W时，在10kHz重复频率下，获得最高平均功率为84 mW的228 nm紫外 输出。228 nm 在5 kHz~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 resonant Raman effect enhance Raman signals and reduces the detection limit of Raman measurement. This paper focuses on the study of an all-solid-state deep-ultraviolet laser with an output wavelength of 228 nm. The laser uses Nd:YVO4as a gain medium and electro-optic q-switched cavity dumping technique to achieve a fundamental frequency output of 914 nm in pulse widths of several nanoseconds. Then, the second-harmonic generation is achieved by LiB3O5(LBO), and the fourth-harmonic 228 nm UV laser is obtained by beta-barium-borate (BBO). The variation of fundamental and second harmonic laser power at different repetition rates is investigate. The average power of Nd:YVO4is saturated and decreases with increased repetition rate due to the low gain at 914 nm. The output efficiency of UV laser is optimized by adjusting the focus lens. At the pump power of 30 W, the highest average power of a 228nm UV laser is 84 mW at 10 kHz. The repetition rate of UV laser is continuously adjustable within the range of 5 kHz−25 kHz, 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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图 4不同腔长时，晶体内基模半径随抽运功率的变化
Figure 4.Variation of the the fundamental mode radius in crystals with different cavity length and pump power
图 6914nm 的平均功率与脉冲能量
Figure 6.Average output power and peak power at different repetition rate for 914nm laser
图 7457nm 的平均功率与脉冲能量
Figure 7.Average output power and the peak power at different repetition rate for 457nm laser
图 9228 nm 平均功率与脉宽随频率的变化
Figure 9.Average output power and pulse width of 228 nm laser at different repetition rate
图 11288 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.Oscilloscope traces of pulse trains and pulse width of 228 nm laser：(a), (b) Pulse trains and pulse width at 10 kHz respectively; (c), (d) Pulse trains and pulse width at 18 kHz respectively
图 12紫外 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 diagram 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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