Simultaneous all-solid-state multi-wavelength lasers——a promising pump source for generating highly coherent terahertz waves

A diode-end-pumped Nd：YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M^2 of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino-methyl-stilbazolium tosylate （DAST） crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate （LBO） crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M^2 of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.

Dual-wavelength distributed Bragg reflector semiconductor laser based on a composite resonant cavity

We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector （DBR） composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing （QWI） technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.

An all-solid-state high power quasi-continuous-wave tunable dual-wavelength Ti：sapphire laser system using birefringence filter

This paper describes a tunable dual-wavelength Ti：sapphire laser system with quasi-continuous-wave and high-power outputs. In the design of the laser, it adopts a frequency-doubled Nd：YAG laser as the pumping source, and the birefringence filter as the tuning element. Tunable dual-wavelength outputs with one wavelength range from 700 nm to 756.5 nm, another from 830 nm to 900mn have been demonstrated. With a pump power of 23 W at 532 nm, a repetition rate of 7 kHz and a pulse width of 47.6 ns, an output power of 5.1 W at 744.8 nm and 860.9 nm with a pulse width of 13.2 ns and a line width of 3 nm has been obtained, it indicates an optical-to-optical conversion efficiency of 22.2%.

Multi-wavelength laser active coherent combination

A seed laser oscillating at different frequencies is proved to have the potential to mitigate the stimulated Brillouin scattering（SBS） effect in a fiber amplifier,which may increase the emission power of a coherent beam combination（CBC） system greatly.In this study,a basic mathematical model describing the multi-wavelength CBC is proposed on the fundamentals of CBC.A useful method for estimating the combination effect and analysing the feasibility and the validity of the multi-wavelength coherent combination is provided.In the numerical analysis,accordant results with four-wavelength four-channel CBC experiments are obtained.Through calculations of some examples with certain spectra,the unanticipated excellent combination effect with a few frequencies involved is explained,and the dependence of the combination effect on the variance of the amplifier chain length and the channel number is clarified.

Terahertz Generation Using Implanted InGaAs Photomixers and Multi-wavelength Quantum Dot Lasers

We report on a study of terahertz(THz) generation using implanted In Ga As photomixers and multi-wavelength quantum dot lasers. We carry out In Ga As materials growth, optical characterization, device design and fabrication, and photomixing experiments. This approach is capable of generating a comb of electromagnetic radiation from microwave to terahertz. For shortening photomixer carrier lifetime, we employ proton implantation into an epitaxial layer of lattice matched In Ga As grown on InP. Under a 1.55 μm multimode In GaAs/In GaAsP quantum dot laser excitation, a frequency comb with a constant frequency spacing of 50 GHz generated on the photomixer is measured, which corresponds to the beats of the laser longitudinal modes. The measurement is performed with a Fourier transform infrared spectrometer. This approach affords a convenient method to achieve a broadband multi-peak coherent THz source.

Numerical Study of the Threshold Intensity Dependence on Wavelength in Laser Spark Ignition of Molecular Hydrogen Combustion

A numerical investigation of laser wavelength dependence on the threshold intensity of spark ignition in molecular hydrogen over a wide pressure range is presented. A modified electron cascade model (Gamal et al., 1993) is applied under the experimental conditions that carried out by Phuoc (2000) to determine the threshold intensity dependence on gas pressure for spark ignition in hydrogen combustion using two laser wavelengths namely;1064 nm and 532 nm. The model involves the solution of the time dependent Boltzmann equation for the electron energy distribution function (EEDF) and a set of rate equations that describe the change of the formed excited molecules population. The model takes into account most of the physical processes that expected to occur in the interaction region. The results showed good agreement between the calculated thresholds for spark ignition and those measured ones for both wavelengths, where the threshold intensities corresponding to the short wavelength (532 nm) are found to be higher than those calculated for the longer one (1064 nm). This result indicates the depletion of the high density of low energy electrons generated through multi-photon ionization at the short wavelength via electron diffusion and vibrational excitation. The study of the EEDF and its parameters (viz, the temporal evolution of: the electron density, ionization rate electron mean energy, …) revealed the important role played by each physical process to the spark ignition as a function of both laser wavelength and gas pressure. More over the study of the time variation of the EEDF explains the characteristics of the ignited spark at the two wavelengths for the tested pressure values.

Tunable Multi Wavelength by Pulse Signal Modulation in Laser Pumping of EDFA

This report is aimed to present the result of experimental setup of the erbium-doped fiber amplifier (EDFA) with modulated pulse signal by laser pumping at wavelength 980 nm. The amplified spontaneous emission (ASE) from EDFA has multi wavelength and the spacing of wavelength can be controlled by controlling the pulse width of laser pumping. The result in this experiment shows that the feasibility of using EDFA system can generate the multi wavelength of all of C-Band spectrum. The pulse signal, for modulated laser pumping, is observed ranging from 10 to 100 Hz and the wavelength spacing can be tuned from 14.7 nm to 14.9 nm.

Base Width Variations and its Effects on Frequency Response of Double Hetero-structure Long Wavelength Transistor Laser

In this paper we investigate the effects of base width variation on performance of long wavelength transistor laser. In our structure with increasing the base width, the cut off frequency increases until 367 nm with 24.5 GHz and then abruptly fall. In 100 nm base width, we have 17.5 GHz cut off frequency, and overall ac performances become optimized, although, other parameters like optical losses and threshold current density are not optimized.

Multi-wavelength continuous-wave Nd:YVO4 self-Raman laser under in-band pumping

Multi-wavelength continuous-wave self-Raman laser with an a-cut composite YVO4/Nd:YVO4/YVO4 crystal pumped by an 879-nm wavelength-locked laser diode is demonstrated for the first time.Multi-wavelength Raman lasers at 1168.4,1176,1178.7,and 1201.6 nm are achieved by the first Stokes shift of the multi-wavelength fundamental lasers at 1064,1066.7,1073.6,1084,and 1085.6 nm with two Raman shifts of 890 and 816 cm^-1.A maximum Raman output power of 2.56 W is achieved through the use of a 20-mm-long composite crystal,with a corresponding optical conversion efficiency of 9.8%.The polarization directions of different fundamental and Raman lasers are investigated and found to be orthogonalπandσpolarizations.These orthogonally polarized multi-wavelength lasers with small wavelength separation pave the way to the development of a potential laser source for application in spectral analysis,laser radar and THz generation.

Triple Wavelength and 810 nm Diode Lasers for Hair Removal: A Clinical and in Silico Comparative Study on Indian Skin

In laser hair removal treatments on dark skin, the high concentration of melanin in the skin competes with the melanin in the hair. During standard laser procedures, with wavelengths of 755 nm or 810 nm, a high level of laser light absorption by melanin in the skin is observed. Therefore, to avoid side effects, lower fluence values are used, which further reduces hair-removal efficacy. To improve results, 810 nm diode lasers operating in dynamic mode, with high frequency and multiple passes, are typically used. The aim of this study is to compare the efficacy and safety of triple-wavelength diode lasers (810 nm, 940 nm, 1060 nm) with that of 810 nm diode lasers on Indian patients. A side-by-side comparison was performed using a triple-wavelength diode laser in stamping mode on one side, and an 810 nm diode laser in dynamic mode on the other. Three subjects with skin type IV on the Fitzpatrick scale participated in the study. Efficacy was assessed through hair counting using clinical photographs, taken before and after the treatments, and the Global Aesthetic Improvement Scale (GAIS). Additionally, comparisons related to epidermal heating and thermal damage to the hair follicle were conducted through mathematical 3D simulations using COMSOL Multiphysics® software. Side effects were also evaluated. A superior end point was observed with triple wavelength compared to the 810 nm diode laser. Hair counting showed a 27% greater hair reduction with triple wavelength. No adverse effects were observed. Thermal simulations revealed 29% higher thermal damage with the triple-wavelength laser compared to the 810 nm diode laser. To conclude, on darker skin types, the triple-wavelength diode laser has been shown to be more effective at removing hair, compared to the 810 nm diode laser, while also being a safe procedure.

Diode-pumped Kerr-lens mode-locked Ti: sapphire laser with broad wavelength tunability

We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.

Dual-wavelength dissipative soliton operation of an erbium-doped fibre laser using a nonlinear polarization rotation technique

We report on the generation of dual-wavelength dissipative solitons in a passively mode-locked fibre laser with a net normal dispersion using the nonlinear polarization rotation （NPR） technique. Taking the intrinsic advantage of the intracavity birefringence-induced spectral filtering effect in the NPR-based ring laser cavity, the dual-wavelength dissipative solitons are obtained. In addition, the wavelength separation and the lasing location of the dual-wavelength solitons can be flexibly tuned by changing the orientation of the polarization controller.

基于变步长扫描策略的FBG高速解调

现有的FBG高速解调方法都各有优缺点,其中扫描式光谱分析系统通用性好、成本较低,在速度和精度上的表现较为均衡。针对扫描激光器型光纤布拉格光栅波长解调仪在实际应用中调谐次数多、扫描耗时久等问题,设计了一种变步长扫描策略,使用较少的波长调谐次数实现光谱局部峰值的检出。实验表明,在通道内只有单个光栅的情况下,使用变步长扫描策略需要扫描的点数降低了至少90%,扫描耗时减少了90%,解调速度提高至10倍。在上位机对传输的局部光谱数据进行高斯拟合解调,并对变步长扫描策略进行信噪比仿真实验测试,仿真证明变步长扫描策略适用于信噪比高于9.23 dB的情况且对后续解调的精度和平均误差几乎没有影响,具有一定的应用价值。

双波长激光联合生物陶瓷材料iRoot SP辅助磨牙根管治疗效果分析

目的:探讨双波长激光联合生物陶瓷材料iRoot SP辅助磨牙根管治疗的效果。方法:选择2020年1月—2023年6月收治的104例磨牙根管治疗患者,按照随机数字表法分为对照组与试验组,每组52例。对照组采用iRoot SP糊剂进行根管充填,试验组以双波长激光(Nd:YAG和Er:YAG)联合iRoot SP糊剂进行治疗。比较2组总有效率、疼痛程度及并发症,观察治疗前、治疗后6周及12周的血清白细胞介素6(IL-6)、白细胞介素17(IL-17)、肿瘤坏死因子α(TNF-α)、出血指数(bleeding index,BI)、牙周探诊深度(depth of periodontal probing,PD)和临床附着水平(clinical attachment level,CAL)。采用SPSS 22.0软件包对数据进行统计学分析。结果:试验组总有效率显著高于对照组,根管填充后疼痛程度显著低于对照组(P<0.05);试验组治疗后6、12周的IL-6、IL-17、TNF-α、BI、PD和CAL显著低于对照组(P<0.05)。结论:双波长激光联合生物陶瓷材料iRoot SP辅助磨牙根管治疗效果较为理想,有利于减轻牙周炎症和疼痛程度。

激光除漆频率对LIBS准确性影响研究

验证激光诱导击穿光谱(Laser-Induced Breakdown Spectroscopy,LIBS)技术在千赫兹级激光条件下检测准确性对LIBS技术应用于大区域、高效率激光除漆过程监测具有重要意义。本文采用高频(kHz级)1064nm红外脉冲光纤激光器清洗飞机蒙皮漆层,结合能谱仪测试结果及原子光谱数据库数据,研究千赫兹激光对LIBS光谱谱峰波长和峰值强度的影响,并验证LIBS技术在千赫兹级激光除漆过程中的准确性。结果表明千赫兹谱峰较赫兹谱峰波长位置向蓝光区域偏移,偏移量不大于0.18nm。380nm~425nm范围内的谱峰完全消失,425nm~550nm范围内的谱峰信噪比下降。能谱仪测试结果与赫兹级LIBS光谱协同验证了千赫兹级激光条件下LIBS技术检测效果的准确性。表明在大区域、高效率飞机蒙皮激光除漆过程中,LIBS技术可用于除漆过程监测。本研究可为千赫兹级激光除漆过程LIBS监测提供参考。

基于VisuShrink小波阈值变换的甲烷检测降噪技术

在利用可调谐半导体激光吸收光谱技术探测甲烷气体泄漏时,复杂的环境光干扰会降低浓度检测信号的信噪比使波形失真。为了抑制噪声,增强电信号与浓度值的线性相关度,提出一种以VisuShrink方法改善小波阈值函数的小波阈值去噪算法。该算法针对小波阈值去噪算法的软硬度不能平衡信号,存在失真的问题,利用统计方法对阈值进行计算,弱化间断点阈值跳变影响。通过仿真计算对比未加噪声前的信号与滤波后的信号,提出算法的信噪比为28.405 30,优于四阶巴特沃斯滤波器。VisuShrink方法在SNR和NCC参数上性能远优于巴特沃斯滤波器,与软阈值函数相近,在MSE均方误差分析上远小于软阈值精度,与巴特沃斯相近,具有较好的平滑特性。实际搭建检测平台对多个浓度样本采样进行多次采样,采用VisuShrink方法设计的滤波器将系统误差精度从4.14%提升至2.472%,算法可有效用于甲烷检测系统提高光谱数据的平滑性和准确性。

用于SS-OCT的扫频光源控制系统研制

针对SS-OCT系统中对扫频光源多路同步驱动的控制需求,研制了一种基于FPGA作为主控单元的扫频光源控制系统。系统采用Xilinx公司XC7A100T芯片进行主控模块的设计,采用5个带缓冲反馈的增强型Howland电流源集成的方式进行激光器驱动模块设计,采用ADN8834芯片控制TEC的方式进行激光器温控模块设计,采用上位机软件进行人机交互。最后通过波长输出自动测试实验制作“波长-电流”查询表;通过调用“波长-电流”查询表进行自动连续线性输出实验,系统展现出在激光器全波长范围内具备1 nm控制精度和任意波长范围具备0.01 nm控制精度的控制效果,在SS-OCT的扫频光源集成控制领域具有借鉴意义。

1470 nm半导体激光治疗仪对犬前列腺切除术的有效性研究

目的评估1470 nm半导体激光治疗仪(简称:科瑞达治疗仪)对犬前列腺切除术的有效性。方法选取成年雄性Beagle犬28只,随机分为3组,即假手术组3只、试验组15只和同类对照组10只;其中试验组又分为120 W/50 W、150 W/50 W、160 W/50 W的汽化切割/凝固止血3个小组;同类对照组又分为120 W/50 W、150 W/50 W的汽化切割/凝固止血2个小组;每小组各5只。试验组和同类对照组均在电切镜下经膀胱颈入口行犬前列腺切除术。术中观察产品的操作适配性和有效性;术后观察犬的一般体征,以及在术前、术后即刻、3 d、7 d、28 d时取血测定血液生化和血液学指标;分别在术后1 h、4周时,行超声和电切镜下观察尿道前列腺部情况,并取前列腺组织进行HE染色分析术后1 h的凝固层厚度和4周尿道上皮修复情况。结果术中,试验品和同类对照品进行犬前列腺切除术的操作性能良好,具有较好的汽化切割和凝固止血性能;术后对犬的一般体征、血液学和血液生化指标均未见明显影响;且超声显示术后即刻均可见尿道扩张,尿道上皮回声略有增强;4周时,可见前列腺组织实质为略低回声,内部为均匀分布细小点状回声,包膜呈线状高回声,与假手术组一致。测量分析显示,试验组和同类对照组汽化切割前列腺组织重量约为0.91~1.33 g,切除比例达17.11%~20.27%;且随汽化切割功率的增加,激光发射时间逐渐减少,而汽化切割速度和效能均有所增加;但试验组与同类对照组比较均未见明显差异(P>0.05)。电切镜下可见试验组和同类对照组在术后1 h时前列腺尿道部创面呈烧灼样改变,创面和正常尿路上皮分界明显;4周时,前列腺部尿路上皮已修复平整,周围正常尿路上皮分界较模糊。同样,病理观察也显示,术后1 h时试验组和同类对照组均可见前列腺尿道口损伤明显,创面表面有少量碳化和凝固性坏死,少量炎性细胞聚集,凝固层厚度约在0.4 mm左右;术后4周时,假手术组前列腺尿道部形态未见异常,试验组和同类对照组均可见新生上皮基本覆盖创面,厚度较均匀,无凝固性坏死组织附在创面上,周围仍有轻度炎性反应,成纤维细胞增生明显,周围前列腺可见间质和上皮细胞增生,部分可见鳞状化发生;前列腺包膜完好,周围神经血管形态未见异常。结论科瑞达治疗仪对Beagle犬前列腺切除术是有效的,具有较好的汽化切割和凝固止血性能,且术后的各项生理指标较假手术组无显著差异。

633 nm热稳频He-Ne激光真空波长校准研究

633 nm热稳频He-Ne激光是激光干涉测量技术中应用最广泛的波长标准光源。633 nm激光波长是几何量计量中最重要的溯源路径。该文分析了633 nm热稳频He-Ne激光的频率特性,并以此为依据详细探讨了633 nm热稳频He-Ne激光器真空波长的校准内容和校准方法。在激光平均波长测量和波长不确定度评定中均考虑了波长复现性产生的影响,给出了校准数据处理方法和不确定度评定示例。结果显示,在633 nm热稳频He-Ne激光真空波长校准中,考虑复现性的影响是必要的。