Research progress of all-solid-state intra-cavity vortex beam generation in visible laser (invited)
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摘要: 涡旋光由于携带轨道角动量信息,在天文学、光学操控、显微成像、传感、量子科学和光通信等领域有着广泛的应用前景。特别地,针对可见光波段涡旋激光,在水下通信领域,涡旋光束可以显著提高通信容量。此外,在可见激光高分辨成像领域,涡旋光束可大幅度提高成像分辨率。目前,可见光波段涡旋光主要通过无源法和有源法产生。相比腔外转换的无源法,有源法在转换效率、光束质量(模式纯度)以及功率提升方面均具有显著优势。该综述重点阐述激光腔内直接产生可见光波段涡旋光的产生技术,具体包括离轴泵浦法、环形泵浦法、腔内球差法等技术手段。综述了可见光波段涡旋固态激光的腔内产生技术,分别从基于非线性频率变换的可见光涡旋激光产生技术、基于分立元器件的LD直接泵浦可见光全固态涡旋激光产生技术、基于光纤介质的LD直接泵浦可见光全固态涡旋激光产生技术方面进行介绍。最后对其未来发展进行分析和展望。Abstract:
Significance In recent years, visible vortex laser carrying orbital angular momentum (OAM) has been widely used in the fields of astronomy, optical manipulation, microscopic imaging, sensing, quantum science and optical communication. Especially for the underwater communication or the super-resolution imaging, further optimizing the output of vortex beams in the visible range is of great significance in enhancing imaging resolution and communication capacity. This not only holds importance in scientific research but also holds vast potential for wide-ranging applications in real-life scenarios, paving the way for advancements in high-resolution imaging, high-speed communication, and other fields. Progress Visible vortex beams can be generated through both extra-cavity and intracavity conversion methods. This study focuses on the intracavity conversion approach to obtain visible vortex beams. With the development of the vortex lasers operating at 1 μm, nonlinear frequency doubling has become a common technique for generating visible vortex beams. By utilizing techniques such as intracavity thermal lens effect, etched point defects, and design of a hemispherical resonator cavity, combined with frequency doubling method, visible vortex beams can be generated without the need for additional components. Alternatively, an extra-cavity mode converter can be used to generate vortex beams, which is then combined with frequency doubling method to produce visible vortex beams. Compared to nonlinear frequency conversion techniques, direct pumping the visible laser crystals to obtain visible vortex beams in the visible range can improve conversion efficiency. For the LD pumped Pr3+ doped all-solid-state laser, visible vortex beams can be generated through intracavity mode conversion techniques such as off-axis pumping, annular light pumping, spherical aberration mode selection. Visible vortex fiber lasers offer advantages of compact structure and high conversion efficiency. They mainly utilize techniques such as fiber core misalignment fusion splicing or specially designed mode selectors to generate visible vortex lasers. Conclusions and Prospects Currently, visible vortex solid-state lasers are mainly achieved by combining near-infrared vortex beams with frequency doubling or by utilizing LD direct pumped Pr3+-doped crystals combined with intracavity vortex beam conversion technology. The former approach typically requires the insertion of laser crystals and frequency doubling crystals inside the cavity, leading to a complex system structure and lower optical-to-optical conversion efficiency. In the future, visible vortex solid-state lasers have great potential for development in terms of tunability, multi-wavelength operation, high power, and single longitudinal mode characteristics. Achieving multi-wavelength visible vortex beam output and generating ultra-short pulse vortex beams (such as picosecond and femtosecond vortex beams) are among the directions for further advancement. Furthermore, if visible vortex solid-state lasers can be extended to the realm of spatiotemporal mode locking, it will inject new vitality into the development of vortex beams. -
Key words:
- visible light /
- vortex laser /
- active method /
- solid-state laser
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图 2 直接产生涡旋光的激光源。(a)基于热透镜效应产生涡旋光的倍频激光器[37];(b)~(c)基于点缺陷镜技术的Nd:GdVO4内腔倍频激光器[38-39];(d)基于半球形谐振腔的Nd:YVO4内腔倍频激光器[40]
Figure 2. Laser source that directly generates vortex beam. (a) Frequency doubled laser generating vortex laser based on thermal lens effect[37]; (b)-(c) Nd:GdVO4 intra-cavity frequency doubling laser based on point defect mirror technology[38-39]; (d) Nd:YVO4 intra-cavity frequency doubling laser based on hemispherical resonator[40]
图 3 基于腔外螺旋相位板调制元件结合倍频输出可见涡旋光的实验装置。 (a)基于LBO倍频晶体的涡旋绿光激光器[46];(b)基于Ba(NO3)2拉曼晶体的可见涡旋拉曼激光器[49]
Figure 3. An experimental device for output visible vortex beam based on an external cavity helical phase plate modulation element combined with frequency doubling. (a) Vortex green laser based on LBO frequency doubled crystal[46]; (b) Visible vortex Raman laser based on Ba(NO3)2 Raman crystal[49]
图 7 离轴泵浦技术产生的可见涡旋光激光装置。(a)离轴泵浦结构的手性可控涡旋光激光器[61];(b)离轴泵浦结构的腔内倍频Pr:YLF激光器装置及基频和紫外高阶结构光场[61];(c)离轴倍频Pr:YLF涡旋晶格激光器[63]
Figure 7. Visible vortex laser generation based on off-axis pumping technology. (a) Chiral controllable vortex laser with off-axis pumping structure[61]; (b) Intracavity frequency doubling Pr:YLF laser and ultraviolet high order structured light field based on off-axis pumping structure[61]; (c) Off-axis frequency doubling Pr:YLF vortex lattice laser[63]
图 13 基于光纤错位熔接技术的光纤涡旋光激光器。(a)可见光波长全光纤激光器及纤芯位移光纤耦合原理图[86];(b)红-绿脉冲涡旋光纤激光器[82]
Figure 13. Fiber vortex laser based on the core-shifted fiber coupling method. (a) Schematic of the visible all-fiber laser and the principle of core-shifted fiber coupling method[86]; (b) Red-green pulse vortex fiber laser[82]
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