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全固态高功率深紫外激光器具有光子能量高、脉冲宽度短和空间分辨率优异等优点, 在科学研究和先进制造等领域展现出重要的应用价值. 本文基于自主研发的全固态Nd:YVO4皮秒MOPA激光放大器(平均功率140 W、重复频率800 kHz、脉冲宽度8.33 ps), 开展了LBO和β-BBO晶体Ⅰ类相位匹配的腔外二倍频与四倍频研究. 双光子吸收是限制深紫外光功率进一步提升的关键因素, 通过研究高功率双波长激光在β-BBO晶体的透过率和温升, 发现高功率深紫外光在β-BBO晶体中存在较强的双光子吸收, 引发的热效应导致相位失配, 严重影响频率转换效率和输出稳定性. 为了进一步提高深紫外功率, 本文采用大尺寸光斑泵浦(光斑尺寸1.5 mm×1 mm) β-BBO晶体方案, 在泵浦峰值功率密度<1.11 GW/cm2的条件下, 有效地抑制了双光子吸收效应引起的热梯度, 实现了平均功率11 W的四倍频深紫外光输出, 单脉冲能量为13.75 μJ. 经过8 h运行, 功率抖动的均方根小于0.96%(@ 8 W). 该光源有望在超快精密加工和高次谐波产生等领域发挥重要作用.
Deep ultraviolet (DUV) picosecond lasers, operating in a 200–280 nm wavelength range, possess significant advantages, such as high photon energy and high resolution. These attributes make them highly promising for applications like semiconductor detection, ensuring the production of high-quality, defect-free semiconductor devices, as well as for advanced scientific research and industrial processing. High-power DUV picosecond lasers are typically generated via nonlinear frequency conversion of infrared lasers based on master oscillator power amplifier (MOPA) configurations. Among various DUV laser technologies, systems based on β-BBO crystals are particularly valuable due to their simple design and cost-effectiveness. However, the linear two-photon absorption, as well as the formation of dynamic color centers in BBO, are significant limitations for high-power, high-repetition-rate UV radiation, leading to thermal effects. Hence, it is important to carefully study the performance characteristics of BBO for high-power, high-repetition-rate pulse generation in the UV at 266 nm. This study presents a high-power, all-solid-state DUV picosecond laser developed using a 1064 nm Nd:YVO4 MOPA amplification architecture. In this experimental setup, a 50 mW, 7.8 ps, 20 MHz all-fiber SESAM mode-locked laser is used as a seed source, achieving 140 W in amplified output power 8.33 ps in pulse duration at 1064 nm via MOPA. In the nonlinear frequency conversion process, the amplified laser pulses are initially focused onto an LBO crystal for secondary harmonic generation (SHG). Precise temperature control of the LBO crystal can generate a 532 nm output with 73 W in power and 6.93 ps in pulse duration, while achieving 52.64% in conversion efficiency. Two-photon absorption is a key factor limiting the further enhancement of deep ultraviolet (DUV) laser power. By investigating the transmittance and temperature rise of a high-power dual-wavelength laser in a β-BBO crystal, the results indicate that strong two-photon absorption occurs under high-power DUV irradiation. This absorption induces significant thermal effects, resulting in a temperature gradient within the crystal and leading to phase mismatch, which severely affects frequency conversion efficiency and output stability. To solve this problem and further increase the DUV output power, a large-spot pumping scheme (spot size: 1.5 mm × 1 mm) is adopted in this work. Under a pump peak power density of less than 1.11 GW/cm2, the thermal gradient caused by two-photon absorption is effectively suppressed, achieving maximum fourth-harmonic output power of 11 W. The corresponding single-pulse energy reaches 13.75 μJ. The root mean square (RMS) jitter, measured in an 8-hour period, is less than 0.96%. This all-solid-state DUV laser demonstrates excellent performance characteristics, including high average power, stability, resolution, and peak power, making it a strong candidate for applications requiring efficient and high-precision processing or detection. By further increasing the pump power and optimizing the temperature control system, the output power of the laser can be significantly enhanced, thereby broadening its applicability and competitiveness in high-end fields such as semiconductor manufacturing, advanced research, and industrial processing. -
Keywords:
- deep ultraviolet /
- picosecond laser /
- β-BBO /
- fourth-harmonic generation
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图 1 全固态深紫外皮秒激光器实验装置图. AOM, 声光调制器; Pre-Amp, 光纤预放大模块; HWP, 半波片; PBS, 偏振分光棱镜; TFP, 薄膜偏振片; DM, 双色镜
Fig. 1. All-solid-state DUV picosecond lasers experimental setup. AOM, acoustic optical modulator; Pre-Amp, fiber pre-amplification module; HWP, half-wave plate; PBS, polarizing beam splitter prisms; TFP, thin-film polarizer; DM, dichroic mirror.
图 2 近红外光光束特性 (a) 近场光斑及M2; (b) 自相关曲线; (c) 重复频率; (d) 输出光谱
Fig. 2. Beam characteristics of Near-infrared laser: (a) Near-field spot and M2; (b) autocorrelation curve; (c) repetition rate; (d) output spectrum.
图 3 绿光光束特性 (a) 绿光功率随近红外光功率变化曲线; (b) 自相关曲线及重复频率; (c) 近场光斑及M2; (d) 输出光谱
Fig. 3. Beam characteristics of green laser: (a) Green laser power changes with Near-infrared laser power; (b) autocorrelation curve and repetition rate; (c) near-field spot and M2; (d) output spectrum.
图 4 不同激光功率注入下的透过率与β-BBO晶体温度 (a) 绿光; (b) 深紫外光
Fig. 4. Transmission and temperature of β-BBO crystal under different laser power injection: (a) Green laser; (b) DUV.
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