摘要
近些年,法国Amplitude公司提出了"吉赫兹(GHz)革命"的口号,主要指发展重复频率在GHz量级的超短脉冲激光光源,并将其应用于工业加工、精密测量和生物成像等方面。深紫外激光器具有波长短、分辨率高、光子能量高的特点,因而在芯片缺陷检测、光电子能谱实验等方面具有重要应用,但目前已有的深紫外激光器的重复频率主要集中在千赫兹(kHz)和兆赫兹(MHz)量级,在GHz重复频率方面的研究极少,这大大限制了深紫外激光器在上述方面的应用。因此,针对上述研究现状,对高重复频率超短脉冲激光器的产生及频率变换技术的发展趋势展开研究。首先,详细介绍了近红外(NIR)波段GHz重复频率激光光源的发展现状;归纳总结了近二十年来国内外深紫外激光光源的研究进展——主要集中于四倍频(266 nm和258 nm)、五倍频(213 nm和206 nm)以及193 nm,指出了GHz重复频率深紫外脉冲激光领域的空白。接着,对GHz近红外激光和GHz深紫外激光各自的难点、相互之间的关系进行了探讨。最后,在对高重复频率深紫外激光器未来发展进行展望的同时也指出了其发展过程中亟需解决的问题。
Significance Ultrafast lasers with pulse durations on the orders of picosecond and femtosecond are widely used in various fields,such as supercontinuum generation,photoelectron microscopy,and material micromachining.The traditional high-power ultrafast lasers with repetition rates of kHz-MHz exhibit a large heat-affected zone during material micromachining,leading to unpleasant damage to the materials.The emergence of pulse lasers with~GHz repetition rate can effectively solve this problem.Combining the very high repetition rate of~GHz and novel burst mode processing technique,the GHz"burst-mode"femtosecond lasers have been used to ablate the target materials before the residual heat deposited by previous pulses diffuses away from the processing region,which can not only improve the ablation efficiency,but also ensure excellent processing quality.Due to its short wavelength,high resolution,and high photon energy,deep ultraviolet(DUV)lasers are widely used in chip defect detection and photoelectron spectroscopy experiments.In order to obtain DUV lasers with high beam quality,high coherence and high repetition rate,near-infrared all-solid-state lasers are usually used as the fundamental drivers to DUV lasers through the nonlinear optical crystals-based multi-stage frequency conversion technique.Due to the high peak powers and high wavelength conversion efficiencies of the near-infrared pulsed lasers with repetition rates of kHz and MHz,it is easy to obtain high-power DUV lasers for lasers with those repetition rates.At present,the repetition rates of industrial high-power ultraviolet lasers are usually in kHz and MHz range.There are very few research results on DUV lasers with~GHz repetition rate,which greatly limits the application potential of DUV lasers in the above aspects.In recent years,various methods have been proposed to achieve DUV laser pulses with repetition rates of~GHz.However,these methods still face a series of challenges.Therefore,it is necessary to summarize recent development tendency of technology of high repetition rate ultrashort laser pulse generation and frequency conversion.Progress There are many methods for producing GHz bursts of laser pulses.Femtosecond pulses at multi-GHz repetition rates can be obtained directly from the oscillators with harmonic mode-locking technique,semiconductor saturable absorber mirror and Kerr lens based passive mode-locking techniques.Typical pulse repetition rates of pulse trains generated by mode-locked fiber oscillators are in the range from tens up to hundreds of MHz.The GHz pulses can be obtained through repetition rate multiplication techniques.In this study,we briefly illustrate their pros and cons and review their recent developments.The emergence of multi-stage amplification systems has increased the average power of~GHz femtosecond pulses in the near-infrared band to the order of hundreds of watts(Table 1).There are many methods for producing DUV lasers.For the method of nonlinear crystal frequency conversion,the research of 266/258 nm DUV nanosecond lasers(Table 3),picosecond lasers(Table 4)and femtosecond lasers(Table 5),as well as 213/206 nm(Table 6)and 193 nm DUV lasers(Table 7)in the past two decades are summarized.Nowadays,the average powers of high power 355 nm ultraviolet lasers have reached hundreds of watts,and the market is relatively mature.Although commercialization of DUV lasers with wavelength below300 nm is still not mature,the current 266 nm laser developed in the laboratory can achieve an output average power of 50.1 W,which is about to enter the order of 100 W,and has passed the stability test for more than 5000 hours of continuous operation.For high power GHz repetition rate near-infrared femtosecond pulse lasers,the difficulty lies in the generation of GHz seed.For GHz repetition rate amplifier,it is relatively easy to obtain higher average powers due to low single pulse energy and low peak power.For GHz repetition rate DUV femtosecond pulse laser source,the difficulty is not in the generation of the fundamental frequency laser,but in the low peak power of the fundamental frequency laser and the thin nonlinear medium used,which leads to low nonlinear frequency conversion efficiency,and it is difficult to obtain GHz femtosecond pulse laser in the DUV band(Fig.6).Conclusion and Prospect In recent years,the French company Amplitude has put forward the idea of"GHz Revolution",which mainly refers to the development of ultra-short pulse laser sources with pulse repetition rate in GHz.The emergence of multi-stage amplification systems has increased the average power of GHz femtosecond pulses in the near-infrared band to the order of hundreds of watts,which successfully solves the problem of the GHz pulse in industrial processing.Therefore,the development of high-power near-infrared band GHz repetition rate pulse lasers is relatively mature at present.Coupled with the continuous improvement of nonlinear frequency conversion technology,DUV laser repetition rate has entered the GHz.Although the industrialization and commercialization of DUV laser techniques still face some problems,such as easily damaged crystal coating,low wavelength conversion efficiency of DUV lasers,and long-term unstable operation of high-power DUV lasers,these problems have been gradually solved in practice.With the further maturity of frequency conversion and power amplification techniques,perhaps kilowatt-level DUV lasers will appear in the next 5-10 years,all of which will certainly make a breakthrough in the secondary laser source based on ultraviolet laser and DUV laser.
作者
郑佳琪
丛振华
刘兆军
王上
赵智刚
Zheng Jiaqi;Cong Zhenhua;Liu Zhaojun;Wang Shang;Zhao Zhigang(School of Information Science and Engineering,Shandong University,Qingdao,Shandong 266237,China;Shandong Provincial Key Laboratory of Laser Technologies and Applications,Qingdao,Shandong 266237,China;State Key Laboratory of Quantum Optics and Quantum Optics Devices,Shanxi University,Taiyuan,Shanxi 030006,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第12期120-140,共21页
Chinese Journal of Lasers
基金
国家自然科学基金(118041292)
教育部联合基金(6141A02022413,6141A02022421)
山东省重点研发计划(2019JMRH0111)
山东省自然科学基金面上项目(ZR2020MF114)
山东大学杰出中青年学者计划
山东大学齐鲁青年学者计划
山西大学量子光学与光量子器件国家重点实验室开放课题(KF202007)。
