摘要
8~12μm长波红外波段激光位于大气传输窗口并覆盖诸多气体分子的吸收带,在大气探测、光电对抗等领域具有重要的应用。目前,通过粒子数反转激光器直接辐射以及非线性频率变换间接辐射是实现8~12μm长波红外激光输出的主要方式。其中,基于非线性光学晶体频率转换的长波红外激光器具有结构紧凑、波长选择灵活、功率拓展性强等优势,近年来得到了快速发展和广泛应用。本文对二阶非线性频率变换的光学晶体、工作原理,以及获得长波红外激光的研究进展进行综述,并对基于受激拉曼散射的三阶非线性频率变换获得长波红外的方法进行了介绍和展望。
Significance The 8-12μm longwave infrared(LWIR)laser,which is within the atmospheric transmission window and the eyesafe range and demonstrates a higher transmittance in atmospheric media(Fig.1),has critical applications in various fields,such as directed infrared countermeasures,environmental monitoring,lidar,and surgery.For example,the laser in this LWIR band plays an important role in environmental monitoring and differential absorption lidar because this band covers the fundamental absorption bands of many gas molecules,such as H2O,CO_(2),NH3,and O3.In terms of medical treatment,the 8-12μm LWIR laser,with a large absorption coefficient and a shallow penetration depth in water and other components of biological tissues,serves as a unique and effective tool in biological tissue treatment.In addition,highenergy 8-12μm LWIR lasers are in high demand in the field of defense.At present,approaches to 8-12μm LWIR laser mainly include direct radiation from gain media represented by carbon dioxide(CO_(2))lasers and semiconductor quantum cascade lasers(QCLs)and nonlinear optical techniques represented by secondorder nonlinear frequency conversion.CO_(2) lasers have been one of the most mature coherent radiation sources for the LWIR band since the invention of the first CO_(2) laser in 1964.However,their output wavelengths are limited to the spectral lines of 9.2-9.8μm and 10.1-11μm.In addition,since CO_(2) lasers usually need to be supported by a large cooling system,the overall size of the device is huge,which greatly limits the application range of CO_(2) lasers.QCLs feature a broad emission spectrum(3.5-160µm)with a relatively narrow linewidth and favorable wavelength tunability.However,due to the limited depth of their quantum wells,QCLs offer low efficiency in the 8-12µm band and consequently fail to achieve highpower and highpulse energy operation.Besides,they are difficult to design and entail a relatively high manufacturing cost.Although 8-12μm LWIR lasing has already been achieved with gas and semiconductor as gain media,no mature method of LWIR lasing by directly pumping crystalline gain media is obtained so far due to the restriction of the intrinsic emission spectra of the currently available crystals.As the most mature and most widely used method,nonlinear frequency conversion is an effective approach to 8-12μm lasing.Notably,solidstate lasers based on secondorder nonlinear frequency conversion techniques break through the predicament that crystalline gain media cannot directly achieve LWIR lasing.Furthermore,compared with CO_(2) lasers and QCLs,allsolidstate lasers based on nonlinear frequency conversion techniques have the characteristics of excellent wavelength tunability and power scalability.The diversities of the available pump parameters(wavelength,width,energy,power,etc.)and emerging nonlinear optical crystals provide LWIR lasers based on nonlinear frequency conversion with a broader development space towards but not limited to ultrashort pulse width,high repetition rate,wide wavelength tuning range,high energy,and high power.This paper reviews the working mechanisms and research progress of LWIR lasers based on secondorder nonlinear frequency conversion to provide a reference for the personnel engaged in the research and development of lasers.Progress Specifically,the working principles and characteristics of the secondorder nonlinear frequency conversion techniques,including optical parametric generation(OPG),optical parametric oscillation(OPO),difference frequency generation(DFG),and optical parametric amplification(OPA),are described(Fig.3).Subsequently,the physical and nonlinear optical properties,including nonlinear coefficient,transparency range,thermal conductivity,and damage threshold,of commonly used nonlinear crystals,such as ZnGeP2,BaGa4Se7,CdSe,GaSe,LiGaS2,orientationpatterned GaAs,and orientationpatterned GaP,are summarized(Table 1).Then,the detailed properties of different crystals and the output characteristics of the corresponding LWIR laser based on the crystals are analyzed.The research progress analysis shows that LWIR lasers based on secondorder nonlinear frequency conversion have achieved femtosecond,picosecond,and nanosecond output in pulse width and repetition rates ranging from several hertz to megahertz.However,due to the low inherent quantum conversion efficiency of nonlinear frequency conversion towards the LWIR band(pumped by 1-3μm near-and midinfrared lasers),the output energy of the LWIR lasers is mainly at the microjoule and millijoule levels at present(Fig.10).Finally,the opportunities and challenges for LWIR lasers based on secondorder frequency conversion techniques are discussed,and the potential method of LWIR lasing via Raman conversion based on the thirdorder nonlinear effect and its prospect are presented.Conclusions and Prospects Crystalline LWIR lasers based on secondorder nonlinear frequency conversion techniques have made outstanding achievements in ultrashort pulse width,high repetition rate,wide wavelength tuning range,and high peak power.The improvement of crystal growth technique,the emergence of new types of nonlinear optical crystals,and the development of currently available crystals with higher optical quality and larger volume crystals pave the way for the further improvement of the power and conversion efficiencies of LWIR lasers.In addition to the above reviewed secondorder nonlinear frequency conversion techniques,diamond Raman lasers(based on the thirdorder nonlinear optical effect)with an extremely wide spectral transmission range and an extremely high thermal conductivity are considered a promising way of wavelength conversion from shortwave to longwave.
作者
白振旭
高嘉
赵臣
颜秉政
齐瑶瑶
丁洁
王雨雷
吕志伟
Bai Zhenxu;Gao Jia;Zhao Chen;Yan Bingzheng;Qi Yaoyao;Ding Jie;Wang Yulei;LüZhiwei(Center for Advanced Laser Technology,Hebei University of Technology,Tianjin 300401,China;Hebei Key Laboratory of Advanced Laser Technology and Equipment,Tianjin 300401,China;Science and Technology on ElectroOptical Information Security Control Laboratory,Tianjin 300308,China)
出处
《光学学报》
EI
CAS
CSCD
北大核心
2023年第3期142-155,共14页
Acta Optica Sinica
基金
国家自然科学基金重大科研仪器研制项目(61927815)
中国科学院功能晶体与激光技术重点实验室开放课题(FCLT202004)
量子光学与光量子器件国家重点实验室开放课题(KF202201)
河北工业大学基本科研业务费资助(JB‑KYTD2201)。
