2μm单纵模全固态脉冲激光技术研究进展(封面文章·特邀)

Advances in 2μm single-longitudinal-mode all-solid-state pulsed lasers(cover paper·invited)

2μm激光属于人眼安全波段,具有高大气透过率和水吸收特性,能覆盖CO_(2)等温室气体的吸收峰,因此在大气环境监测、光通信、激光雷达、材料加工、医疗手术等领域有广泛应用。其中,单纵模运转的全固态2μm脉冲激光器以其高稳定性、窄线宽和优良的光束质量等优势,可作为多普勒测风、相干差分吸收等激光雷达应用的优质光源,在工业、国防和科研等领域具有重要意义。目前,实现2μm激光输出的主要方法有光参量技术和直接泵浦法。相比光参量技术,直接泵浦法更具高效率、可调节性和集成性等优点,已成为2μm全固态激光的主流方式。文中总结了常用的2μm固体激光增益介质,分析了空间结构振荡器单纵模选择的原理和特点,综述了2μm单纵模全固态脉冲激光的研究进展,并对不同结构激光器的输出特性进行了比较,最后对2μm单纵模全固态脉冲激光的发展前景进行了展望。

Significance The 2µm single-longitudinal-mode(SLM)all-solid-state pulsed laser has attracted much attention for its applications in lidar,gas monitoring,laser medicine,material processing and scientific research,owing to its high stability,narrow spectral linewidth and other advantages.For instance,the 2µm SLM laser features high atmospheric transmittance and eye-safety,making it an ideal emission source for Doppler wind lidar.Moreover,the 2µm laser covers the absorption peaks of various gases such as H_(2)O,CO_(2) and CH_(4),enabling it to be used as the emitter of differential absorption lidar for atmospheric greenhouse gas monitoring.By combining the 2µm laser with other sensors,a comprehensive atmospheric environment monitoring system can also be established.In the field of material processing,the 2µm laser can interact with many materials,greatly simplifying the processing steps.Furthermore,the 2µm laser has diverse applications in medical surgery,such as tissue cutting,stone crushing and eye surgery.Through the characteristics of its working wavelength,the 2µm laser can achieve precise tissue treatment,while reducing the damage to the surrounding tissue,offering a safer and more effective option for medical surgery.The 2µm SLM all-solid-state pulsed laser also plays a vital role in the field of military defense.The 2µm laser output can be obtained by using nonlinear frequency conversion or directly pumping gain medium doped with Tm^(3+)or Ho3+.However,the linewidth of the 2µm laser output generated by nonlinear frequency conversion is relatively wide,so it is extremely difficult to achieve SLM laser output.In contrast,compared with the nonlinear frequency conversion technique using 1µm lasers as the pump source of optical parametric oscillators,Tm^(3+)or Ho3+doped Q-switched lasers typically involve using a special resonator design or introducing mode selection elements,which have more compact structure and higher stability in achieving a 2µm SLM pulsed laser.With the significant development of laser technologies such as laser pump technology,single longitudinal mode selection technology,and high energy laser pulse technology,the 2µm SLM all-solid-state pulsed laser is developing towards smaller size,better performance,and more stable output performance.In recent years,researchers at home and abroad have designed and fabricated various 2µm SLM all-solid-state pulsed lasers.According to the specific application scenario,the most suitable SLM selection scheme is chosen,and researchers have obtained 2µm SLM pulsed lasers with different characteristics and successfully applied them to several fields.However,there are still some technical challenges to be overcome in the development of the current 2µm SLM all-solid-state pulsed laser technology.In this paper,the common 2µm single-mode all-solid-state pulsed laser technologies with the ring cavity,twisted-mode cavity,volume Bragg grating and injection-seeded method are analyzed and summarized.Progress This paper reviews the research progress of 2µm SLM all-solid-state pulsed laser technology,in conjunction with its applications across various fields.It introduces the working principles and characteristics of SLM selection techniques such as the ring cavity,twisted-mode cavity,volume Bragg grating,and injectionseeded method.The laser output characteristics of different structures,including central wavelength,output energy,pulse width,full width at half maximum(FWHM)of the spectrum,pulse repetition rate,and beam quality factor,are summarized based on different SLM selection techniques.The results indicate that the 2µm SLM allsolid-state pulsed laser has made significant strides in single pulse energy,spectral line width,and stability.It can achieve high-energy SLM laser output with a line width on the order of MHz and pulse repetition frequency on the order of kHz.However,the output pulse width remains wide(on the order of nanoseconds),the structure is complex,and the thermal effect is pronounced.Finally,the paper analyzes the current technical bottlenecks,provides corresponding solutions,and prospects the future development of 2µm SLM all-solid-state pulse lasers.Conclusions and Prospects Driven by the escalating demand for practical applications,2µm SLM all-solidstate pulsed lasers are evolving rapidly towards miniaturization,enhanced stability,high efficiency,narrow spectral linewidth,and substantial output energy.Future development trends are expected to focus on further advancements in output performance and the exploration of innovative methods for realizing 2µm SLM all-solidstate pulsed lasers.Moreover,with the progression of laser technologies such as longitudinal-mode selection,pulse width compression,and thermal management,coupled with the continuous exploration of new gain media and laser structures,the comprehensive performance of 2µm SLM all-solid-state pulse lasers is anticipated to be further improved to cater to diverse application requirements.