A magnetically polarized He-Ne laser

The performance of an internal mirror He-Ne laser that has a fraction of its capillary immersed in a strong transverse magnetic field will be described. The field is produced by permanent magnets which are built into the laser's housing. The laser produces a light output which has less than 0.1% of its power in the modes polarized orthogonal to the magnetic field. The attainment of such a high degree of polarization requires that the magnetic field be oriented relative to naturally occuring anisotropies of the laser cavity. Misalignment not only lowers the degree of polarization, but also decreases the laser's output.     

Polarization properties of internal mirror He-Ne lasers in a strong transverse magnetic field

The polarization behaviour of an internal mirror He-Ne laser at 6328 Å in a strong transverse magnetic field is shown to be severely affected by the presence of a small phase anisotropy in the laser cavity. Experimental observations of the polarization properties of small, general purpose lasers are found to be in good agreement with the predictions of a simple model, which starts from the assumption that the laser mirrors are slightly birefringent.     

激光陀螺本征模偏振态与磁敏感特性的理论研究

环境磁场的干扰是影响激光陀螺精度的重要因素之一. 为了减小二频机械抖动激光陀螺的磁敏感性, 推导了环形腔的琼斯矩阵, 其中考虑了非共面角、增益介质、腔损耗、腔镜反射各向异性和应力双折射, 采用矩阵本征问题求解的摄动理论分析了环形腔的偏振态和磁敏感特性. 研究表明, 为了减小激光陀螺的磁敏感性, 应减小非共面角和腔损耗, 增大腔镜的反射各向异性. 腔镜应力双折射究竟会增大还是减小磁敏感性与应力作用主轴、受应力腔镜的位置有关, 此外它还会引起顺时针和逆时针模式之间的偏振非互易性. 磁敏感性与腔失谐近似成线性关系, 导致激光陀螺工作于增益峰值时磁敏感性并非最小. 这些结果对减小二频机械抖动激光陀螺的磁敏感性具有较好的指导意义. 关键词： 激光陀螺 磁敏感性 椭圆度 琼斯矩阵     

Polarization properties of a single-mode gas laser in transverse magnetic fields

The effect of transversally applied magnetic fields on the polarization behavior of a single-mode gas laser is theoretically investigated, stressing the importance of the additivity of respective contributions influencing the time evolution of polarization parameters. By adding a new element to the existing theory, namely the contribution of magnetic-field-free regions in the active medium, and by considering the relatively large effects that small cavity anisotropies can cause, several apparent discrepancies between experiments and existing theory are resolved.     

Unidirectional Single-Mode 532-nm Nd:YAG Laser Using Intracavity Frequency Doubling in Nonplanar Ring Geometry

Intracavity frequency doubling of a single-mode Nd:YAG laser using a nonplanar ring cavity is demonstrated. The nonplanar ring cavity consists of a Brewster-angled Nd: YAG crystal placed in a magnetic field, a KTP crystal, and two spherical mirrors. In this design the Nd:YAG crystal acts as both a nonreciprocal polarization rotator and a partial polarizer, and the nonplanar portion of the ring cavity, which is formed by a relative twist angle between the Brewster-angled end surfaces of the crystal, serves as a reciprocal polarization rotator. Eigenpolarization theory for the cavity configuration is presented and a suitable value of the relative twist angle for unidirectional operation is estimated. A single-mode output power of 22 mW at 532 nm is obtained with a 1.2-W diode laser at 809 nm and a laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems.     

Coupling of polarization and spatial degrees of freedom of highly divergent emission in broad-area square vertical-cavity surface-emitting lasers

The polarization of highly divergent modes of broad-area square vertical-cavity surface-emitting lasers is shown to be only marginally affected by material anisotropies but determined by an interplay of the polarization properties of the Bragg cavity mirrors and of the transverse boundary conditions. This leads to a locking of the polarization direction to the boundaries and its indeterminacy for wave vectors oriented along the diagonal. We point out a non-Poissonian character of nearest-neighbor frequency spacing distribution and the impossibility of single-wave number solutions.     

Coherence and polarization properties of electromagnetic laser modes

A recently formulated mode representation of stochastic electromagnetic fields, based on a unified theory of coherence and polarization is applied to determine the transverse laser resonator modes in any rotationally symmetric cavity. It is found that the electromagnetic modes can be expressed in a simple way in terms of the classic Fox-Li modes of the monochromatic scalar theory; and that, if there is no degeneracy, each mode is completely spatially coherent and its degree of polarization is the same at each point of the cavity mirror.     

Optical resonators with inhomogeneous mirrors

It is shown that the possibility of changing a laser light beam intensity distribution exists when the output mirror transmittance depends on the transverse plane coordinates. Methods of manufacture of inhomogeneously transmitting laser mirrors with constant phase of the reflected beam over the whole surface are described. Two examples of application of such systems are considered: one for obtaining a laser beam with constant intensity distribution in the transverse plane, the other for single-segment energy extraction from high-order transverse modes. The total laser output power is shown to be almost the same as for use of a homogeneous output mirror.     

Mode profiles in resonators with a near 90° roof-top mirror

The transverse modes of a laser resonator comprising a near 90° roof-top mirror and a feedback mirror are studied theoretically. We relate this configuration to an almost plane roof-top resonator and apply the Fox and Li technique to compute the lowest-order symmetric and antisymmetric modes. The effects of perturbations to the vertex angle of the roof-top mirror, misalignments of the feedback mirror and curved feedback mirrors are examined.     

衰减全反射磁镜偏频激光陀螺的理论分析

通过分析常规磁镜在红光波长下制造激光陀螺技术不可行的原因，提出了一种新型的磁镜偏频激光陀螺结构，其核心是利用全内反射结构和掺杂YIG薄膜的横向克尔磁光效应作为偏频技术去克服闭锁的衰减全反向磁镜。     

Zeeman双频激光器频率分裂与纵模间隔变动一致性分析

激光谐振腔内相位各向异性会引起频率分裂,两分裂模的频差大小由表现出的相位延迟所决定.对于腔内相位延迟较小的He-Ne激光器,两分裂模很接近,处于烧孔重叠区,存在模式竞争而不能同时振荡,形成隐频率分裂.同时,使得激光器两正交偏振方向上的相邻级纵模产生固定的变动量,其大小等于隐频率分裂量的2倍.如果沿激光偏振方向施加横向磁场,Ne原子谱线发生横向Zeeman分裂,增益原子分成两群,分别为平行于磁场和垂直于磁场方向偏振的光提供增益,大大减弱模竞争,使得激光器的两分裂模可同时振荡并测得频差.在谐振腔内放入倾斜的石英晶体片或半波片,由两种方法分别测量频率分裂量并进行比较.实验表明两种方法测量的结果均与理论计算相符,平均相对偏差不超过1%.据此可以准确得到Zeeman双频激光器的频差大小,并为半波片测量提供了新方法.     

Amplitude-squeezed emission from a transverse single-mode vertical-cavity surface-emitting laser with weakly anticorrelated polarization modes

We discuss the polarization-resolved intensity noise characteristics of a transverse single-mode vertical-cavity surface-emitting laser (VCSEL). Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yield only an imperfect anticorrelation between the strong and the weak orthogonally polarized fundamental modes. Yet the total emission shows amplitude squeezing of 0.4 dB below the shot-noise level. Unlike for transverse two-mode emission, a perfect anticorrelation between the two polarization modes is not necessary for generation of amplitude-squeezed emission in a transverse single-mode VCSEL, in agreement with theoretical predictions.     

Frequency-locking and single-mode operation of a CW dye ring laser near the atomic lines of a gas discharge

Assuming lens action by the gas discharge we can theoretically substantiate the features of a CW dye ring laser locked near an atomic transition; features such as the dependence of the laser bandwidth and the frequency separation from the atomic transition on the spacing of the curved mirrors and the occurrence of an asymmetric profile for the laser output. The values experimentally obtained for the 588.2 nm absorption line in a neon discharge show good agreement with those predicted by theory. In the strong-locking regime bistable, unidirectional, single-mode operation occurs. This behaviour could be utilized to obtain sharp frequency marks in the tuning range of a CW dye ring laser.     

Enhanced excess noise in laser cavities with tilted mirrors

Enhancement of the transverse excess-noise factor is theoretically predicted in optical laser cavities with tilted end mirrors and nonuniform transverse loss. In particular, it is shown that in a loss-guided laser close to the plane-plane geometric instability boundary the excess-noise factor that is induced by mirror tilting may largely exceed that predicted for the aligned cavity. This excess noise is related to beam walk-off induced by mirror tilting, which makes possible transient amplification of noise in the transverse plane.     

Optical studies of spin precession in magnetic two-dimensional electron gases

Magnetic two-dimensional electron gases are studied using time-resolved Kerr and Faraday rotation spectroscopy in the Voigt geometry. The data directly reveal both electron and Mn spin precession in modest transverse fields. Scattering by Mn ions dominates the electron spin relaxation processes in these materials, and prevents the electron gas from acquiring a long-lived spin polarization as observed in non-magnetic structures. Nonetheless, a persistent Mn spin polarization occurs which creates a oscillating magnetic field within the electron gas for hundreds of picoseconds.     

Transverse-electric and transverse-magnetic beam modes beyond the paraxial approximation

Transverse-electric and transverse-magnetic beam modes are considered based on a theory in which complex dipole sources and sinks are oriented along the beam axis; the theory is similar to one that was previously presented for transverse dipoles. The field in the region of the waist is explored. Modes with such polarization have been reported from a wide range of laser types.     

The influence of collective effects on quantum fluctuations of laser radiation

Quantum fluctuations in a laser with two different relaxation times are considered, i.e., transverse (polarization relaxation) and longitudinal (population relaxation) in the case in which the cavity transmission band half-width is much smaller than the transverse width and much larger than the longitudinal one. The lasing frequency detuning from the transition frequency of a two-level system is assumed to be arbitrary in this case, and it is necessary to take into account the contribution of two-particle correlators into the dispersion and laser linewidth. The results are considered as applied to a semiconductor laser.     

猫眼腔激光器的横模变换与频率分裂

为了产生多种激光横模,以前的系统相对比较复杂,而且一般只能产生基横模和低阶横模,很难产生高阶横模,同时也很难观察到模竞争中一个频率抑制另一个频率的变化过程。基于猫眼谐振腔激光器和频率分裂技术,提出了一种新型的激光原理综合实验系统。该系统利用猫眼逆向器作为He-Ne激光器的一个腔镜,通过调节猫眼逆向器中两镜片间距可输出包括基横模、低阶横模、高阶横模在内的十余种典型横模,并可完成纵模、偏振、出光带宽等多种激光基本特性的实验。同时在基横模状态下,利用谐振腔内加入的石英晶体片可实现激光频率分裂及其频差调节。在此基础上又可实现完整的模竞争过程的观察。     

Spectroscopic measurements of the evanescent wave polarization state

We applied optogalvanic spectroscopy to observe Zeeman effect in the evanescent wave in Ar gas with the help of a single-mode diode laser. The use of an homogenous external magnetic field enabled us to observe different π and σ Zeeman split lines contribution. We studied two orthogonal directions of external magnetic field and two orthogonal polarizations of the incident wave with respect to the plane of incidence. The analysis of relative line strengths leads to the determination of the polarization state of the evanescent wave.     

Heating by Optical Absorption and Cooling of High Power Laser Mirrors

In high power laser system, laser mirror is the core and the most sensitive optical component, which influences the increase of laser power and the quality of laser. Absorption of light at mirrors causes wavefront distortions through the thermal deformations of substrates. The analytical solutions of the two-dimensional transient thermal theory of high power laser mirrors are developed, copious graphical results in our case are presented, and the predicted results are compared with those of the experiment.