Advanced Laser Technology
2020, 49(12): 20201076.
doi: 10.3788/IRLA20201076
With the highest thermal conductivity, low thermal expansion coefficient, high chemical inertness, and excellent optical properties among known materials, diamond can meet the application requirements of many extreme conditions in the fields of mechanics, optics, and materials, etc. In recent years, with the improvement of the chemical vapor deposition preparation technology, the optical quality of synthetic diamond has been rapidly improved, which leads to the optical grade diamond crystals excellent power improvement, coherence enhancement, and frequency conversion ability due to their excellent Raman and Brillouin characteristics. Meanwhile, diamond lasers overcome the thermal effect in the particle number inversion laser based on the traditional gain media, and the difficulty to consider both the wavelength and power. The research progress of high-power diamond laser technology was summarized, and the development trend and application of diamond lasers were prospected.
2020, 49(12): 20201077.
doi: 10.3788/IRLA20201077
Vertical-cavity surface-emitting lasers (VCSELs) have important applications in the short-distance optical interconnection attributed to their advantages, such as low cost, low threshold current, high modulation bandwidth and low power consumption. With the development of big-data and supercomputer technology, the performance demand of short-distance optical interconnection is increasing quickly, which also proposes a challenge for high-speed 850 nm VCSEL. In this paper, the latest development of high-speed 850 nm VCSEL technology was reviewed from the aspects of bandwidth-limited factors and new modulation methods, and the growing trend of this technology is prospected and summarized.
2020, 49(12): 20201052.
doi: 10.3788/IRLA20201052
Due to its unique structure and low coherence, random lasers are widely used in fields such as speckle-free imaging, sensing, and light therapy. The feedback mechanism of random lasers is light scattering introduced by disordered media. High threshold and non-directionality are its main disadvantages. In order to solve these problems, researchers used the one-dimensional confinement of optical fibers to obtain random fiber lasers with a low threshold and a certain directionality. In the past ten years, the development of random lasers has experienced a process from incoherent feedback to coherent feedback, from complete disorder to controllable output parameters. A large number of studies have tried to explain the physical nature of random lasers using quantum theory, chaotic laser theory, and numerical analysis. The origin and development history of random lasers and random fiber lasers were reviewed, the classification and related principles of random lasers were introduced, the methods of controlling random laser output parameters were summarized, the recent typical applications of random lasers were demonstrated, fiber random lasers feedback types and gain mechanisms were analyzed, and finally the future of random lasers development was prospected.
2020, 49(12): 20201069.
doi: 10.3788/IRLA20201069
Compared with traditional ~100 MHz femtosecond lasers, the mode spacing is larger of GHz femtosecond lasers so that each comb can simply be resolved. Furthermore, the less dense of longitudinal modes results in higher average power. Therefore, it has more important application value in many research fields, such as comb-resolvabled spectroscopy, direct optical frequency comb spectroscopy, optical arbitrary waveform generation and astronomical spectrograph calibration. In this review, the generation schemes of GHz femtosecond pulses and the corresponding technical challenges of GHz-repetition-rate all-solid-state femtosecond lasers pumped by laser diode were introduced in detail firsly. Secondly, the international research progresses of all-solid-state GHz femtosecond lasers based on SESAM passively mode-locking and Kerr-lens mode-locking were summarized. Finally, the application value and research object of our group in all-solid-state GHz-repetition-rate femtosecond lasers were forcasted based on our preliminary research results.
2020, 49(12): 20201066.
doi: 10.3788/IRLA20201066
Chaotic laser has been widely applied in the fields of secure optical communication, random number generation, chaotic lidar, chaotic optical time domain reflector and distributed optical fiber sensing due to its characteristics of wide-spectrum, noise-like, low-coherence and so on. Photonic integrated chaotic semiconductor laser is a kind of chaotic laser which is small in size, stable and low-cost. The progress of photonic integrated chaotic semiconductor laser and its main applications in recent ten years were reviewed. Firstly, the photonic integrated methods of chaotic semiconductor laser were introduced. Then, the classification of photonic integrated chaotic semiconductor lasers was demonstrated. According to the perturbation mode, the external cavity structures including straight cavity, multiple-cavity, ring cavity, two-dimensional cavity and mutual injection were discussed. The advantages and characteristics of these devices were compared. Furthermore, the applications of photonic integrated chaotic semiconductor lasers in optical time domain reflectometer, secure optical communication and random number generation were introduced. Finally, the key integration techniques, time delay signature and intermittent chaos in photonic integrated chaotic laser were discussed.
2020, 49(12): 20201074.
doi: 10.3788/IRLA20201074
In the process of laser driven inertial confinement fusion, the inhomogeneity of light field with different spatial frequencies will cause the hydrodynamic instability, imprinting and laser plasma instability in implosion. These instabilities will eventually affect the compression ratio of implosion, thus affecting the ignition. In order to control the focal spot nonuniformity and suppress instabilities, beam smoothing technology was proposed to control the beam target coupling process through light field control. Beam smoothing can be divided into spatial smoothing and temporal smoothing. Spatial smoothing can reduce the low-frequency inhomogeneity by controlling the wavefront shape. Temporal smoothing reduces the speckle in the focal spot by controlling the coherence of the laser beam, and then reduces the medium and high frequency inhomogeneity. With the increasing demand for laser-plasmas instability suppression at higher laser power density, some new beam smoothing methods have emerged. The application of beam smoothing technology in large laser facilities was introduced, and the currently proposed beam smoothing technologies were summarized and analyzed.
2020, 49(12): 20201058.
doi: 10.3788/IRLA20201058
The time jitter of a femtosecond laser is the short-term deviation of the optical pulse position relative to its ideal equally spaced pulse position. Femtosecond lasers emit uniformly spaced ultrashort pulse train. The quantum-noise-limited timing jitter can be as low as few tens of attoseconds in millisecond time scale. This unique property and its advanced applications constitute a new branch of ultrafast research, "Attosecond precision ultrafast photonics". In this paper, the recent advances in femtosecond laser timing jitter research, high-precision timing jitter characterization methods, and the ultralow timing jitter that can be achieved by different kinds of femtosecond laser sources were reviewed. Finally, the application of low-jitter femtosecond lasers in the fields of synchronization of large-scale scientific instruments, high-speed analog-to-digital conversion, absolute ranging technology and coherent beam combination are introduced.
2020, 49(12): 20201073.
doi: 10.3788/IRLA20201073
The measurement accuracy of laser precision measurement is mainly limited by optical field noise and various technical noises. After the de-coupling technical noises, quantum noise becomes the main factor limiting the measurement accuracy. Based on the intensity noise characteristics of solid-state single-frequency lasers, the main sources of intensity noise and their influence on the power noise spectrum were described, and three kinds of intensity noise suppression techniques, including traditional DC feedback control, optical AC coupled feedback control and quantum squeezer, were reviewed in this paper. By reviewing the development history of relevant technologies, the current development level and future development trend of intensity noise suppression technology were summarized-the noise suppression scheme combining three technologies is an important approach to solve high sensitivity detection.
2020, 49(12): 20201051.
doi: 10.3788/IRLA20201051
Mid-infrared laser sources with broad instantaneous-bandwidth are critical for many applications, including infrared micro-spectroscopy, environmental monitoring, medical diagnosis, and ultra-short pulse generation. In this article, the output spectrum bandwidth from synchronously pumped optical parametric oscillator (SPOPO) was focused on and a scheme, chirped-pulse optical parametric oscillator (CPOPO) was proposed to achieve broadband output beyond the limitation of pump pulse width. The CPOPO with self-phase modulation (SPM) or chirped quasi-phase matching (CQPM) were studied and achieved through period-poled lithium niobate (PPLN) based SPOPO. The outputs covered 2.9-3.9 μm (~27 THz) with power up to 92 mW and 2.9-5.0 μm (~44 THz) with 64 mw, respectively.
2020, 49(12): 20201056.
doi: 10.3788/IRLA20201056
2 µm, 3-5 µm and 8-12 µm infrared lasers are located in the atmospheric transmission window, which have broad applications in laser medicine, laser imaging, environmental monitoring, lidar, chemical remote sensing and infrared countermeasure. Based on the optical nonlinear frequency conversion technology and nonlinear optical crystals, it has obvious advantages in achieving middle-long-wave infrared solid lasers, such as compact and simple structure, wide tunable wavelength range and high output power. Using ZnGeP2 crystal with 2 µm Ho single-doped solid laser as pump especially has an outstanding performance in middle-long-wave infrared field. In the aspect of average output power, it has reached the level of 102 W@3-5 µm, 12.6 W@8.2 µm and 3.5 W@9.8 µm. Moreover, they all have a beam quality factor M2 less than 3 and the corresponding optical-to-optical conversion efficiency of 3-5 µm is about 60%. This paper reviewed the research progress of 2 µm Ho single-doped solid laser and application of ZnGeP2 on middle-long-wave infrared in detail.
2020, 49(12): 20201061.
doi: 10.3788/IRLA20201061
Orbital angular momentum (OAM) vortex beam has a phase singularity with a twisted wave-front, whose complex amplitude comprises the helical term exp (ilθ). OAM vortex beam has been widely used in optical manipulation, imaging, optical communication, sensing and so on. Ultra-short pulse OAM vortex beams have the advantages of both vortex beams and ultra-short pulses, and can be applied to chiral material processing, long distance transmission, strong field physics and nonlinear frequency conversion. Direct generation of ultra-short OAM vortex beams has the advantages of compact and simple system and good beam quality. The research progress on direct generation of ultra-short OAM vortex beams was summarized. At present, the pulse width of the ultra-short OAM vortex beam generated by the active method is still limited to a few hundred femtoseconds. How to obtain the pulsed vortex beam output within 100 femtoseconds or even with a few cycles through the direct output method will be an important future development direction.
2020, 49(12): 20201080.
doi: 10.3788/IRLA20201080
Diode pumped alkali metal vapor laser (DPAL) combines the technical characteristics of both diode laser and gas laser, with the advantages of high quantum efficiency, large excited emission cross section, small refractive index perturbation, convenient thermal management and rich output wavelength, which can achieve high efficiency, high power and high beam quality near infrared laser output, and has important applications in industrial manufacturing, military, medical and scientific research fields. For closed static DPAL, under the condition of high power pump, the working gas temperature in the steam pool increases, and the thermal effect is serious, resulting in the decline of DPAL performance. The circulating flow DPAL uses gas flow to take away waste heat, which can significantly alleviate the thermal effect of working gas, so as to achieve high-power laser output. At present, it has become the mainstream technical route to achieve high power laser output. In this paper, the principles and current development of the flowing-gas circulation DPAL are outlined, the obstacles and solutions of high power scaling of DPAL are analysed, and prospects for the future development of high-power alkali metal lasers.
2020, 49(12): 20201075.
doi: 10.3788/IRLA20201075
The 2-4 μm band is a very important infrared atmospheric window. Lasers operating in this band have a wide range of applications in gas detection, medical application and industrial processing. The low-dimensional structure of antiminide semiconductor materials has the unique advantage of narrow forbidden band, direct transition luminescence, and is an ideal material system for realizing mid-infrared semiconductor lasers. In recent years, research on antimonide semiconductor lasers at home and abroad has made important progress, achieving wavelength expansion of quantum well luminescence, room temperature continuous lasing of high-power single chip and laser bars, and continuous room temperature continuous operation of multi-band single-mode lasers. Due to the complex composition of the low-dimensional materials of the antimonide and the special interface passivation properties, the epitaxial materials and process preparation techniques are difficult. Based on the basic principle of antimonide semiconductor lasers, this paper reviewed the research status at home and abroad, introduced the design scheme of the low-dimensional structure lasers antimonide materials, and the main progress of key preparation techniques, and analyzed the performance optimization, focused on research and development direction of such lasers in the future.
2020, 49(12): 20201053.
doi: 10.3788/IRLA20201053
Spectral beam combining (SBC) uses dispersive elements or dichroic elements to make multi-channel lasers of different wavelengths overlap in the near-field and far-field at the same time, so as to combine the laser beam with single aperture output. It is one of the technical approaches to achieve high power and high beam quality laser output, which has attracted great attention of researchers. Especially in the past decade, with the continuous improvement of the performance of grating and other combining components, the spectral beam combining laser output with high power and high beam quality has played an important role in industry, national defense and other fields, and has a wide application prospect. The research progress of SBC was reviewed for the two typical laser working medias of semiconductor laser and fiber laser. The current mainstream scheme and research status of high power SBC at home and abroad were summarized. In addition, combined with our research works on SBC, the development trend of SBC in recent years were shown, and the future development prospect of SBC technology was forecasted.
2020, 49(12): 20201062.
doi: 10.3788/IRLA20201062
Fluoroaluminate, fluoroindate and fluorozirconate glass samples were prepared by using melt-quenching method, their abilities of resistance to deliquescence were studied by water treatment experiment, proving that the fluoroaluminate glass had better stability than the others. Thus Ho3+/Pr3+ codoped fluoroaluminate glasses with different concentrations were fabricated, the properties of spectral transmittance were measured, showing a high transmittance and wide transmission window. Under the pump of an 1150 nm Raman laser, the emission spectra were obtained for analyzing the emitting mechanism. 2 Ho3+/0.2 Pr3+ codoped fluoroaluminate glass preform were fabricated by suction method and fiber by rod-in-tube method. Using the cutback method, the loss of the fiber at 793 nm was 1.8 dB/m. By using the 1150 nm Raman laser as pump source, a 2.865 μm lasing with output power as high as 207 mW were detected in an 8.6 cm-long fluoroaluminate glass fiber, its slope efficiency was 11.4%. The above research results show that fluoroaluminate glass fiber is a gain medium material that can be used to develop stable mid-infrared fiber lasers.
2020, 49(12): 20201054.
doi: 10.3788/IRLA20201054
Multi-gigahertz optical pulse trains generated from mode-locked semiconductor lasers are promising for a number of applications in many areas. For most of these applications, a fixed and stable pulse repetition frequency is necessary. Since the repetition frequency of such lasers is primarily determined by the effective refractive index of the laser waveguide and the laser cavity length, uncertainties during device fabrication as well as cleaving process may bring deviations to the repetition frequency. To gain better knowledge of how working conditions of such lasers effect their repetition frequency and thus compensate the above-mentioned deviations, a novel 2 µm InGaSb/AlGaAsSb single quantum well (SQW) mode-locked laser (MLL) was presented in this work. It has a two-section configuration (gain section and saturable absorber section separated by an electrical isolation region) and stable mode locking was achieved in this laser under a variety of bias conditions up to 60 ℃. Repetition frequency variations of this mode-locked laser with bias condition (gain section current Ig, absorber section voltage Va) and working temperature (T) were systematically recorded, and the mechanisms behind these variations were analyzed. It is believed that this work enables us to have a better understanding of passively mode-locked semiconductor lasers and is of interest to better meet the application-required frequencies.
2020, 49(12): 20201070.
doi: 10.3788/IRLA20201070
A 320 nm ultraviolet laser with Pr:YLF crystal was pumped by different wavelength blue laser diode was designed and double end pumping mode was adopted. The structure of the laser is V-folded cavity. A 444 nm blue laser diode with pump power of 3 W and a 469 nm blue laser diode with pump power of 1.4 W was used as pump source. The Pr:YLF crystal has a length of 12 mm and a doping concentration of 0.3%. The phase-matched LBO crystal was used as frequency doubling crystal. By optimizing the resonator parameters, when the incident pump power is 5700 mW, the maximum output power of 320 nm ultraviolet continuous laser with 1005 mW is output, and the optical conversion efficiency is about 17.6%.
