摘要
基于非线性光学频率变换技术的可调谐中红外激光器在光电对抗、气体检测、生物医学等应用领域有着重要价值。近红外激光,尤其是1μm激光直接泵浦的可调谐中红外激光器具有结构紧凑、调谐范围宽、稳定性高的优势。从非线性光学频率变换技术的核心器件——非线性晶体出发,综述新型非氧化型晶体在可调谐中红外激光产生中的应用现状,介绍了不同晶体的光学特性及实现中红外产生的方法。针对可调谐中红外激光源的调谐范围、单脉冲能量、重复频率等关键参数,分析了不同晶体的中红外产生性能及其适用的中红外产生方法。最后对近红外激光器泵浦的可调谐中红外激光器进行了展望。
Tunable mid-infrared lasers based on nonlinear optical frequency conversion play a vital role in application fields including environment monitoring,remote sensing and biomedical diagnosis.The longterm development of near-infrared laser technology has led to a high degree of commercialization of nearinfrared pumped lasers.The utilized of the commercial near-infrared laser as the pump source is easy to realize miniaturization,high power and high stability operation of the tunable mid-infrared laser.Nonlinear optical crystal,which is the core component of the tunable mid-infrared laser,determines the output characteristics of the mid-infrared laser source.Suffering from multi-phonon absorption,the tunable output band of traditional oxide crystals is limited to below 4μm.On the other hand,the most commonly used ZnGeP_(2) has strong two-photon absorption at 1.06μm.High-quality mid-infrared crystal pumped by nearinfrared laser have remained of great interest in recent years.In this paper,we reviewed the application of the newly developed non-oxide crystals in mid-infrared laser generating.BaGa4Se7 and BaGa_(4)S_(7) have wide transparency range,high laser damage threshold and nonlinear coefficient.Using a low repetition frequency pump source,the tunable output range covers the entire mid-infrared band,and the output energy achieves mJ-level even in the long wave infrared band.Under a pump repetition rate of hundreds of Hz,the average output power in the mid-wave infrared band reaches 1 W.However,due to the low thermal conductivity of these two crystals and the near-infrared absorption,there is no report on the near-infrared laser pumped source with repetition rate of kHz-level and average output power of W-level.Subsequent research mainly focused on the improvement of pump and crystal cooling conditions.LiGaSe_(2) and LiGaS_(2) crystals are suitable for near-infrared ultrashort pulse pumping to produce mid-infrared lasers due to their large band gap.In particular,LiGaS_(2) crystal has high laser damage threshold and thermal conductivity.At present,there have been many reports about the generation of mid-infrared laser with repetition frequency of kHz or even MHz.The femtosecond laser source based on LiGaS_(2) crystal has been applied to the research of vibration sum-frequency spectrum detection,biomolecular fingerprint spectrum recognition,etc.However,due to the small geometric size of LiGaSe_(2) and LiGaS_(2) crystals in the existing reports,their output powers under nanosecond laser pumping are relatively low.In addition,LiGaSe_(2) and LiGaS_(2) crystals have an obvious absorption peak near 8μm.The transmittance above 8μm decreases rapidly,so it is not suitable for the generation of long-wave infrared lasers.The improvement of crystal synthesis and growth process will help to play the potential of LiGaS_(2) crystal in broadband tuning and high-power laser generation.LiInS2 and LiInSe_(2) are newly developed crystal with high band gap.The laser damage threshold of LiInS2 crystal and LiInSe2 crystal is relatively low,so the existing reports mostly based on picosecond/femtosecond laser system.Under nanosecond laser pumping,it is difficult to achieve mJ-level,high energy mid-infrared laser generation.The current research is mainly focused on broadband tunable mid-infrared laser generation.Although the current output average power is low,LiInS_(2) and LiInSe_(2) crystals have high thermal conductivity and low thermo-optical coefficient,so these crystals have the potential to be used in the generation of high repetition rate and high average power mid-infrared lasers.At present,the main bottleneck lies in the synthesis and growth process of large size and high-quality crystals.CdSiP_(2) crystals have high thermal conductivity,nonlinear coefficient and band gap,and the cutoff wavelength in the short-wave direction is relatively short.Using a near-infrared laser pump source,the output energy reaches mJ-level under low repetition rate operation.The output average power exceed 100 mW with repetition frequency of several MHzs.High efficiency 6~7μm generation with 1064 nm laser pumping can be achieved under non-critical phase matching condition.The output band can be expanded to 2~8μm by combining pump wavelength tuning and angle tuning.CdSiP_(2) also has great potential in the on-chip application.However,the laser induced damage threshold of CdSiP_(2) crystal is low,and the transmittance above at 8μm decreases rapidly,which limits its application in high power and long-wave infrared laser generation.Quasi-phase-matched crystals represent a new research direction of mid-infrared nonlinear optical crystal materials.Quasi-phase matching technology can utilize the maximum nonlinear coefficient and avoid walk-off effect,so tunable mid-infrared source based on quasi-phase-matched crystals have the advantages of high conversion efficiency and can realize mid-infrared output in the whole transparency band.Orientation-patterned gallium phosphide(OP-GaP)has high nonlinear efficient and thermal conductivity.It has great application potential in high power and high efficiency middle infrared laser generation.However,the synthesis of high-quality single crystals with large aperture and high uniformity are difficult.The improvement of material growth technology will significantly improve the output power of existing mid-infrared lasers based on quasi-phase-matched crystal materials.The further research will focus on:1)improvement of the crystal quality,especially the size and the uniformity of the crystal;2)improvement of the output characteristics of the near-infrared pump laser;3)development of the new nonlinear optical crystals.
作者
陈锴
徐德刚
贺奕焮
钟凯
李吉宁
王与烨
姚建铨
CHEN Kai;XU Degang;HE Yixin;ZHONG Kai;LI Jining;WANG Yuye;YAO Jianquan(School of Precision Instrument and Optoelectronics Engineering,Tianjin University,Tianjin 300072,China;Key Laboratory of Optoelectronics Information Technology of Ministry of Education,Tianjin University,Tianjin 300072,China;Key Laboratory of Micro Opto-electro Mechanical System Technology(Ministry of Education),Tianjin University,Tianjin 300072,China;Beijing Institute of Electronic System Engineering,Beijing 100854,China)
出处
《光子学报》
EI
CAS
CSCD
北大核心
2023年第9期1-28,共28页
Acta Photonica Sinica
基金
国家自然科学基金(Nos.U22A20123,62175182,62275193,U22A20353)。
关键词
中红外激光器
非线性光学频率变换
光学参量放大
光学参量振荡
差频产生
Mid-infrared laser
Nonlinear optical frequency conversion
Optical parametric amplification
Optical parametric oscillation
Difference frequency generation
