利用自相位延迟方法测量单块腔反馈半导体外腔激光器的线宽

提出了采用单块折叠法布里-珀罗(F-P)腔作为外腔反馈元件实现窄线宽半导体激光器,采用单块腔的光学反馈来锁定外腔激光器,使用自相位延迟法测量该窄线宽激光器的线宽。实验结果表明,激光器线宽小于35kHz。实验还观测到由于单块腔耦合面上各耦合点的几何量和物理量误差不一样,随着折叠面兼输入输出耦合面上的耦合点的变化,外腔激光器的线宽发生改变。     

激光线宽对单次通过PPMgO:LN晶体倍频效率的影响

通过单次穿过PPMgO:LN晶体产生了2.06 W的780 nm可调谐的连续倍频光. 采用1560 nm的分布反馈式(DFB)半导体激光器、光栅外腔半导体激光器(ECDL)和分布反馈式掺铒光纤激光器(DFB-EDFL)分别作为掺铒光纤放大器(EDFA)的注入光源, 所用的EDFA具有保持窄线宽的功能, 因此可以忽略它对基波线宽的展宽. 研究了激光线宽对单次通过PPMgO:LN 晶体的倍频效率的影响. 控制三台激光器各自注入EDFA的功率一致, 同时也保持EDFA 的输出功率. 在基波功率为12.42 W 时, 使用DFB半导体激光器注入EDFA时得到了1.36 W的780 nm倍频光输出, 转换效率为11.0%; 使用ECDL作为种子源时得到了1.78 W 的780 nm倍频光输出, 转换效率为14.3%; 使用DFB-EDFL作为种子源时得到了2.06 W的780 nm倍频光输出, 转换效率为16.6%. 测得三台种子激光器的线宽分别为1.2 MHz (DFB), 200 kHz (ECDL)和600 Hz (DFB-EDFL). 线宽越窄, 倍频效率越高, 实验结果与理论分析一致.     

电光晶体调谐的外腔反馈半导体激光器

报道一种用电光晶体实现快速调谐和凋制激光频率的方法.在Littrow型外腔反馈半导体激光中插入LiNbO3晶体,利用LiNbO3晶体的电光效应,通过改变晶体电压来调节激光器的有效腔长,可以对激光频率进行快速的调谐和调制.采用该方法,自制外腔反馈半导体激光器的调谐频率可达到2 kHz,它的调谐范围为350 MHz,激光频率调谐系数约为1.06 MHz/V,用饱和吸收光谱观测频率调谐的效果.快速激光频率调制可以应用在稳频技术上,将外腔反馈半导体激光器调制在5～100 kHz频率下,均获得了87Rb原子D2线的饱和吸收光谱的色散信号,并实现了激光频率在饱和吸收峰上的长期稳定.     

A 1550-nm linearly tunable CW single-mode external cavity diode laser based on a single-cavity all-dielectric thin-film Fabry–Pérot filter

A 1550-nm linearly tunable CW single-mode external cavity diode laser (ECDL) based on a single-cavity all-dielectric thin-film Fabry–Pérot filter (s-AFPF) is proposed and realized in this paper. Its internal optical components as well as their operation mechanisms are introduced first, and then its longitudinal mode output characteristic is theoretically analyzed. Afterwards, we set up the experimental platform for the output characteristic measurement of this tunable ECDL; under different experimental conditions, we execute accurate and real-time measurements for the output central wavelength, output optical power, output longitudinal mode distribution, and the line-width of the tunable ECDL in its tuning process. By summing up the optimal experimental condition from the measured data, we obtain the optimal tunable relevant parameters ECDL of the tunable ECDL has a linear mode-hop-free wavelength tuning region of 1547.203 nm-1552.426 nm, a stable output optical power in the range of 40 μW-50 μW, and a stable output longitudinal mode distribution of a single longitudinal mode with a line-width in the range of 100 MHz-150 MHz. This tunable ECDL can be used in environmental gas monitoring, atomic and molecular laser spectroscopy research, precise measurements, and so on.     

Frequency-stabilized high-power violet laser diode with an ytterbium hollow-cathode lamp

We have demonstrated in an ytterbium laser cooling and trapping experiment a high-power violet extendedcavity diode laser (ECDL) stabilized to the Yb resonant transition at 398.9 nm in an Yb hollow-cathode lamp. A frequency-dispersion signal, which we obtained by applying a modulation-free dichroic-atomic-vapor laser lock technique, allowed us to stabilize the violet ECDL at a frequency stability below 1 MHz at 1-s average time and a useful output power of 15 mW.     

光栅外腔半导体激光器GHz射频调制特性研究

研究了光栅外腔半导体激光器(ECDL)对射频频率调制的响应特性,分析了射频频率调制时光栅外腔对半导体激光器的边带信号的影响.实验中测量了GHz射频频率调制的.ECDL输出的边带信号随射频信号功率、注入电流、光栅外腔长度的变化情况.证实了当射频调制频率等于光栅外腔自由光谱区的整数倍时,ECDL输出的边带信号可在一定程度上得到增强.     

Widely tunable diffraction limited 1000 mW external cavity diode laser in Littman/Metcalf configuration for cavity ring-down spectroscopy

We report on recent progress on external cavity diode lasers (ECDL) using a new concept of a Littman/Metcalf configuration. Within this concept one facet of the diode laser chip is used for coupling to a high quality Littman/Metcalf resonator whereas the other side of the diode laser chip emits the output beam. The alignment of the external resonator is independent from the alignment of the output beam and there is no need for any compromise in the alignment. This results in an improved behavior of the external resonator with the benefit of a drastic increase in power and single mode tuning.We investigated this light source for high resolution spectroscopy in the field of cw-cavity ring-down spectroscopy (CRDS). The monitoring of environmental and medical gases from vehicles or human breath requires a suitable radiation source in the mid-infrared (MIR) between 3 and 5 μm that is frequency stable and can be widely tuned. Since this wavelength cannot be reached via direct emitting room temperature semiconductor lasers, additional techniques like difference frequency generation (DFG) are essential. Tunable difference frequency generation relies on high power, small linewidth, fast tunable, robust laser diode sources with excellent beam quality.With our new compact, alignment-insensitive and robust ECDL concept, we achieved an output power of 1000 mW and an almost Gaussian shaped beam quality (M²<1.2). The coupling efficiency for optical waveguides as well as single mode fibers exceeds 70%. The wavelength is widely tunable within the tuning range of 20 nm via remote control. This laser system operates longitudinally in single mode with a mode-hop free tuning range of more than 150 GHz without current compensation and a side-mode-suppression better than 50 dB. This concept is currently realized within the wavelength regime between 750 and 1080 nm.Our high powered Littman/Metcalf laser system was part of a MIR-light source which utilizes DFG in periodically poled lithium niobate (PPLN) crystals. At the wavelength of 3.3 μm we were able to achieve a high-resolution absorption spectrum of water with four different isotoplogues of H₂O components. This application clearly demonstrates the suitability of this laser for high-precision measurements. PACS 07.57.Ty; 42.55.Px; 42.62.Fi     

243 nm稳频窄线宽半导体激光器

243 nm是氢原子1S-2S能级跃迁光谱波长. 本文利用Pound-Drever-Hall稳频技术将972 nm光栅反馈外腔半导体激光稳定在一个高精细度低膨胀系数的超稳法布里-珀罗腔上, 通过锥形放大器放大和腔内两次共振增强倍频得到243 nm激光, 最终实现用于探测氢原子1S-2S双光子跃迁的243 nm窄线宽激光.     

基于自制超稳定F-P腔压窄632.8nm外腔半导体激光线宽的实验研究

窄线宽激光由于其具有单色性好、稳定度高、相干长度长等优点,广泛应用于光电检测领域,包括相干通信、精密测量、光学频率标准、吸收光谱计量以及光与物质相互作用研究等。目前频率稳定的氦氖激光器线宽可以达到MHz量级,分布反馈式（DFB）光纤激光器线宽可达kHz量级,DFB半导体激光器线宽可以达到MHz量级,然而光栅反馈半导体激光器可以实现百kHz量级线宽的输出。为了进一步压窄各类激光器线宽,需要通过反馈控制技术来锁定激光到某一频率参考。该研究将自行设计的超稳腔作为频率参考,实现了632.8 nm外腔半导体激光器（ECDL）线宽的有效压窄。本窄线宽激光产生系统的研制包括超稳腔设计、光路设计、ECDL频率控制以及系统集成。超稳腔采用两镜法布里-珀罗腔（F-P腔）结构,腔体是膨胀系数约为10-6 K-1的微晶玻璃,腔镜为一对反射率达99.988 5%(±0.003 5%）的平面镜和凹面镜。为进一步减小外界环境对F-P腔腔长的影响,需要对腔体进行温度控制,本系统采用四片总功率为96 W的半导体制冷片以及水冷散热设计。同时为了降低声音和空气流动对腔模频率的影响,将F-P腔置于真空度为10-5 torr的真空室中;另外为了有效隔振,腔体与真空室用硅橡胶材料隔离。该系统采用的ECDL为德国Toptica公司的DL pro系列激光器,其具有压电陶瓷（PZT）和电流调制两个频率控制端,响应带宽分别为1 kHz和100 MHz。激光器的频率控制采用了Pound-Drever-Hall （PDH）锁频技术,18 MHz的调制频率加载到激光器的电流调制端,通过对F-P腔的反射信号进行解调获得误差信号,通过两路反馈控制,实现了近1 MHz的锁定带宽。通过对系统的不断优化,最后将自由运转状态下约300 kHz的激光线宽压窄到了10 kHz量级,并且系统运行稳定,连续12小时锁定的频率漂移量约为30 MHz。该研究研制的632.8 nm窄线宽激光源不仅可以应用到吸收光谱计量领域,同时也可以在光学面型精密测量领域发挥重要作用。     

Laser frequency locking based on Rydberg electromagnetically induced transparency

We present a laser frequency locking to Rydberg transition with electromagnetically induced transparency(EIT)spectra in a room-temperature cesium vapor cell. Cesium levels 6S_(1/2), 6P_(3/2), and the n D_(5/2) state, compose a cascade three-level system, where a coupling laser drives Rydberg transition, and probe laser detects the EIT signal. The error signal, obtained by demodulating the EIT signal, is used to lock the coupling laser frequency to Rydberg transition. The laser frequency fluctuation, ~0.7 MHz, is obtained after locking on, with the minimum Allan variance to be 8.9 × 10~(-11).This kind of locking method can be used to stabilize the laser frequency to the excited transition.     

Broadband amplitude-modulated laser source with high output power for FM/cw lidar transmitter

We are building a long-range FM/cw nonscanning imaging lidar breadboard. This lidar system achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique, implemented by an amplitude modulated mid-IR diode laser transmitter with a linear frequency modulation (LFM) of the subcarrier. Firstly, various schemes of light beam modulation are analyzed. Secondly, we put forward a laser modulation scheme whose core was formed by a 1.55 μm electro-absorption modulated laser diode (EML) and an erbium-doped optical fiber amplifier (EDFA), then a corresponding experimental system architecture and components for light beam modulation and detection are established. Finally, a corresponding experiment of laser beam modulation is completed for the first time. In our experiment, the EML amplitude is modulated by a 200 MHz to 800 MHz LFM signal, whose amplitude value is 2.05 V. The average output power of the modulated laser obtained in the experiment is 10 W, peak power is 16.4 W, and the average modulation depth is 78%. The results of tests predict that this laser modulation scheme is likely to improve the imaging range of the FM/cw lidar.     

激光光源线宽对外差探测性能的影响

本文根据统计理论分析了激光线宽对外差探测结果的影响, 并讨论了激光线宽对杨氏干涉条纹对比度的影响. 本文基于解析结果做了数值仿真, 所得结果表明激光线宽增加时, 外差探测方式仍可以检测到中频信号, 但在线宽较大时, 受噪声影响无法准确地提取到中频频率. 为验证理论分析结果, 使用线宽为1 MHz的激光光源进行了8.1 km外场实验, 实验结果与数值分析结论一致, 即不会因为线宽增加而无法检测到中频信号. 文中所得结论对于外差探测光源的选择有重要指导意义, 因此根据测量目标的特性和测量要求, 可按照文中结论评估光源的线宽指标.     

A 657-nm narrow bandwidth interference filter-stabilized diode laser

We present a 657-nm external cavity diode laser (ECDL) system,where the output frequency is stabilized by a narrow-band high transmission interference filter.This novel diode laser system emits laser with an instantaneous linewidth of 7 kHz and a broadened linewidth of 432 kHz.     

铷原子饱和吸收光谱与偏振光谱对780nm半导体激光器稳频的比较

将激光频率锁定于合适的参考频率,可以有效地抑制激光器的频率起伏。本文采用铷原子D2线超精细跃迁线的饱和吸收光谱和偏振光谱分别获得鉴频曲线,通过电子伺服系统将频率校正信号负反馈到780 nm光栅外腔反馈半导体激光器外腔的压电陶瓷上的方法对激光器进行稳频。介绍了两种方法的基本原理和实验方案。与激光器自由运转300s时激光器典型的频率起伏约6.6 MHz相比,采用饱和吸收光谱和偏振光谱进行稳频,运转300 s时激光器典型的残余频率起伏分别约为1.5 MHz和0.6 MHz。分析表明,饱和吸收光谱稳频采用了相敏检波技术,需要对激光器进行频率调制,带来了额外的频率噪声,而偏振光谱稳频则是一种完全无频率调制的稳频方案。     

Two Step Deceleration of Cesium Atomic Beam by Frequency Modulated Diode Lasers

Two step white light slowing of a cesium atomic beam was demonstrated by using two kinds of frequency modulated diode lasers. In addition to a frequency modulated free-running diode laser used for the first step of wide range deceleration, a frequency modulated external cavity diode laser (ECDL) with narrower and sharper spectrum was used for the second step deceleration. It was shown that the number of slowed atoms was increased more than twofold by the two step deceleration which kept narrow velocity width of 27 m/s, which is smaller than that by only the single step deceleration.     

Diode-laser-based ultraviolet absorption sensor for nitric oxide

An all-solid-state continuous-wave laser system for ultraviolet absorption measurements of the nitric oxide (NO) molecule has been developed and demonstrated. The single-mode, tunable output of a 10-mW, 395-nm external-cavity diode laser (ECDL) is sum-frequency-mixed with the output of a 115-mW, frequency-doubled, diode-pumped Nd:YAG laser in a beta-barium-borate crystal to produce 40 nW of tunable radiation at 226.8 nm. The wavelength of the 395-nm ECDL is then scanned over NO absorption lines to produce fully resolved absorption spectra. Initial results from mixtures of NO in nitrogen in a room-temperature gas cell are discussed. The estimated NO detection limit of the system for a demonstrated absorption sensitivity of 2×10^-3 is 0.2 ppm per meter of path length for 300 K gas. The estimated accuracy of the measurements is ±10%. Received: 25 February 2002 / Revised version: 31 May 2002 / Published online: 8 August 2002     

Grating-Stabilized External Cavity Diode Lasers for Raman Spectroscopy—A Review

Abstract: Conventional Raman techniques require a continuous-wave laser with stabilized wavelength, narrow line width, and sufficient output power. Due to their miniature size and low cost, diode lasers are good choice as light sources for Raman spectroscopy, especially when compact and portable instruments are needed. However, a solitary multimode diode laser has certain drawbacks that limit its use for Raman application. To circumvent these drawbacks, an external cavity can be coupled to the active gain medium of the diode to enhance the laser performance. A grating-based external cavity allows the laser to operate in a single longitudinal mode with greatly reduced line width and stabilized wavelength. This article examines the fundamentals of semiconductor lasers to show the necessity of operating diode lasers in an external cavity for Raman applications. Two feedback grating-based external cavity diode laser (ECDL) designs, viz. Littrow and Littman-Metcalf configurations, are explained. Historic and recent progress in the development of ECDL devices is reported. An updated summary of ECDL-equipped Raman systems applied to fields such as in vivo biomedical studies and in situ process/quality control is provided. Topics on mode-hop-free continuous scanning, wavelength stabilization, and dealing with ambient conditions are discussed.     

Stable Narrow Linewidth 689nm Diode Laser for the Second Stage Cooling and Trapping of Strontium Atoms

We report stable narrow linewidth laser systems based on self-developed Littman configuration external cavity diode lasers （ECDLs）. The frequency of the ECDL is stabilized to a high fineness ultralow-expansion glass reference cavity with the Pound-Drever-Hall technique. By heterodyne beating of two identical systems, we conclude that the linewidth 4.3× 10^-14 at an averaging measurement time. of each ECDL is reduced to lower than 150 Hz and its frequency stability reaches time of 1 s, the averaged long-term frequency drift is less than 0.2 Hz/s over 30 h     

Stabilization and Shift of Frequency in an External Cavity Diode Laser with Solenoid-Assisted Saturated Absorption

A simple method to realize both stabilization and shift of the frequency in an external cavity diode laser （ECDL） is reported. Due to the Zeeman effect, the saturated absorption spectrum of Rb atoms in a magnetic field is shifted. This shift can be used to detune the frequency of the ECDL, which is locked to the saturated absorption spectrum. The frequency shift amount can be controlled by changing the magnetic field for a specific polarization state of the laser beam. The advantages of this tunable frequency lock include low laser power requirement, without additional power loss, cheapness, and so on.     

EFFECTS OF PUMP SOURCE ON SPECTRA OF OPTICALLY PUMPED SUB-MILLIMETER WAVE LASER

The output power intensity of optically pumped sub-millimeter wave laser(OPSMMWL) increased with increasing of power intensity of pump source, till to its maximum; and decreased with increasing of the frequency off-set of pump source, if frequency off-set reached or exceeded its Raman threshold, no SMMWL could be obtained; the infrared pumping laser with collision broadening was considered in our computing model, which made our theoretical calculations agreed with the practical. Spectra of CO₂-9R(16) pumped NH₃ 90.4 μm laser was used to be a practical case. Supported by Natural Science Foundation of Guangdong Province, P.R.China(04300458)