Influence of optical confinement and excitonic absorption on strong coupling in a bulk GaN microcavity grown on silicon

We report the optical study of a lambda-thick GaN microcavity grown by molecular beam epitaxy on a silicon substrate. Angle-resolved reflectivity measurements evidence the strong coupling regime at room temperature on the half cavity (without the top mirror), but at low temperature, the high excitonic absorption quenches the optical cavity mode at the excitonic energies. On the whole microcavity, the improved quality factor leads to the observation of the polariton emission whatever the temperature. No bottleneck is observed at 70 K even at low pumping power and large negative detuning. The impact of the optical confinement and the excitonic absorption, studied through reflectivity measurements are accurately reproduced by the transfer-matrix formalism. The optimization of the design in this structure leads to a large Rabi splitting (52 meV) at room temperature.     

医用高功率CTH:YAG脉冲激光器的研究

为了提高Cr,Tm,Ho∶YAG激光器的输出功率对CTH∶YAG准三能级能量转移特性进行了分析,优化了谐振腔的腔长及腔镜的曲率半径,采用了高漫反射陶瓷聚光腔.结果表明,有效抽运光谱带的反射率高达95％,在冷却水温为19 ℃,抽运能量为159 J时,获得最大单脉冲输出能量5.11 J,斜率效率5.6%.     

Design of Long-Wavelength Vertical-Cavity Surface-Emitting Lasers with Resonant Optical Pumping

An optically pumped long-wavelength vertical-cavity surface-emitting laser (VCSEL) with resonant optical pumping has been proposed. The proposed structure enables the dual-resonance of pump light (1300 nm band) and output light (1550 nm band) at the same time. It is shown that high pumping efficiency of ∼99% can be obtained by adjusting the top mirror reflectivity and the cavity length. This dual-resonance VCSEL (DR-VCSEL) may have great advantages of high efficiency pumping, low power consumption and can be fabricated by using conventional VCSEL fabrication techniques with reasonable fabrication tolerances.     

任意球面元件的超高反射率测量方法

为了实现任意球面元件的超高反射率测量,提出直腔和折叠腔两种光腔结构,以实现0,10,15和30等不同角度下球面元件的超高反射率测量。详细分析了这两种测量方式,根据光束传输变换公式,推导了任意球面元件在测量中引入的衰荡光腔物理腔长的变化,得到了实验测量中腔长调节指导。并根据光腔衰荡法原理,推导了球面元件在超高反射率测量中的通用数学表达式,对测量公式进行了讨论,分析结果扩展了光腔衰荡法在元件超高反射率测量的使用范围。     

Proposal for loss reduction and output enhancement of silicon Raman laser using bi-directional pumping scheme

Based on a novel loss analysis, we numerically demonstrate that bi-directional pumping scheme is an effective technique to achieve loss reduction and maximum output power enhancement in silicon Raman laser. We then investigate the influence of cavity end-facet reflectivity under the bi-directional pumping scheme. Low end-facet reflectivity cavity simultaneously maximizes the output power and enhancement effect of bi-directional pumping, resulting in a fully optimized peak Stokes output.     

Doppler optomechanics of a photonic crystal

A laser beam directed at a mirror attached onto a flexible mount adds friction to its mechanical motion by the Doppler effect. For a normal mirror the efficiency of this radiative Doppler friction is very weak and practically masked by laser shot noise. We find that it can become very efficient using a photonic crystal mirror near its photonic band gaps. As an example, a Bragg mirror used at the long wavelength edge of its band stop can be efficiently optically cooled using the Doppler friction. The opposite effect opens new routes for optical pumping of mechanical systems: a laser pointing at a Bragg mirror and tuned at its short wavelength edge induces amplification of the vibrational excitation of the mirror leading eventually to its self-oscillation. These new effects rely on the strong dependency of a photonic crystal reflectivity on the wavelength.     

Mollow triplet under incoherent pumping

A counterpart of the Mollow triplet (luminescence line shape of a two-level system under coherent excitation) is obtained for the case of incoherent excitation in a cavity. The system acquires coherence through the strong-coupling between the cavity and the emitter. Analytical expressions, in excellent agreement with numerical results, pinpoint analogies and differences between the conventional resonance fluorescence spectrum and its cavity QED analogue under incoherent excitation. Most notably, the satellites broaden and split sublinearly with increasing incoherent pumping.     

用光腔衰荡技术测量镜片的反射率

 根据光腔衰荡光谱技术原理,建立了测量镜片反射率的实验装置。利用该装置测定了一对反射率相等的高反射腔镜,反射率测试结果为（99.925±0.001）%;以22.5°将直腔变为折叠腔,测得的反射率为（99.992±0.003）％。重复测定反射镜样品的反射率,精度达到10^－5。该测量装置可用于超低损耗薄膜高反射镜反射率的精确测量。轻微移动探测器位置,对腔镜的测试结果影响不大。     

高光谱分辨率激光雷达鉴频器的设计与分析

提出了利用Fabry-Perot干涉仪的反射场实现高光谱分辨率激光雷达精细探测大气光学参量的新方法和思路.设计了高光谱分辨率的分光系统,并分析了干涉仪反射场的光谱透过特征曲线.结合高光谱激光雷达探测信号特征,讨论分析了谱分离比和瑞利信号透过率随反射率和腔长的变化曲线,同时结合误差传递公式,建立了仿真分析模型,讨论了回波光束发散角和入射角变化对激光雷达探测结果的影响.结果表明,所提出的Fabry-Perot干涉仪反射场可以实现高光谱分辨率激光雷达探测系统的精细分光,同时探测结果误差随回波光束发散角变化不敏感,控制发散角在10 mrad以内,入射角在1.5 mrad以内时,可以实现气溶胶光学参数廓线的高精度探测.     

Observation of polarization switching: D1 line of sodium in a Fabry-Perot

We report observation of the complete polarization switching sequence for a gas of atoms with a J = $\text{1}\text{2}$ to J = $\text{1}\text{2}$ transition, exposed to resonant or near resonant, linearly polarized laser excitation in an optical cavity. The sequence is from linearly polarized cavity output at low input power to predominantly circularly polarized output at intermediate power and back to linearly polarized output at high input power. The switching is abrupt, exhibits hysteresis and, when hyperfine optical pumping effects are minimized, is phenomenologically in accord with predictions from theory.     

A broadband ytterbium-doped tunable fiber laser for <Superscript>3</Superscript>He optical pumping at 1083 nm

Large amounts of hyperpolarized ³He gas with high nuclear polarization rates are required for use in neutron spin filters or nuclear magnetic resonance imaging of human lung. Very high efficiency can be obtained by metastability exchange optical pumping using multimode lasers to excite the ^[ 2 _]3S-^[ 2 _]3P transition at 1083 nm. Broadband ytterbium-doped tunable fiber lasers have been designed for that particular application. Different options for the architecture of the fiber oscillator are presented and compared. Emphasis is given to a linear cavity configuration that includes a high reflectivity fiber mirror and a low reflectivity tunable fiber Bragg grating. Optical measurements are performed to finely characterize the spectral behavior of the lasers. Atomic response is also quantitatively probed to assess the optimal design of the oscillator for optical pumping. Multimode operation matching the 2 GHz Doppler-broadened helium resonance line and tunability over more than 200 GHz are demonstrated. Boosting the output of this fiber laser with a Yb-doped fiber power amplifier, all-fiber devices are built to provide robust, high-power turnkey sources at 1083 nm for improved production of laser polarized ³He. PACS 42.60.-v; 42.55.Wd; 32.80.Bx     

光纤光栅对FBG-ECL静态特性的影响

光纤光栅外腔半导体激光器(FBG-ECL)在未来光通信系统占有着越来越重要的地位。根据FBG-ECL的等效腔模型,讨论了光纤光栅反射率、带宽对FBG-ECL的输出功率,阈值特性、边模抑制比等静态特性的影响。指出了存在最佳光纤光栅峰值反射率,不仅使得FBG-ECL具有更高的输出功率,而且可以获得极好的边模抑制比。最后根据实测在不同反射率下外腔激光器的激射光谱,发现理论分析结果和实验数据是吻合的。     

分布反馈光纤激光器阵列中外腔反馈特性研究

以半导体激光器中的复合腔模型和实测的分布反馈光纤激光器的外腔端面反射率为基础,对不同反射率条件下分布反馈光纤激光器的输出功率进行了仿真,同时搭建了二基元分布反馈光纤激光器阵列实验平台,对仿真结果进行了验证.仿真与实验结果表明:外腔反馈光重新注入分布反馈光纤激光器会增加激光器的输出功率,降低了阵列的输出功率平坦性.并且外腔端面反射率越大,这种平坦性降低的效果越明显.在构建分布反馈光纤激光器阵列时,应考虑外腔反馈对阵列输出功率平坦性造成的影响,尽量选择外腔端面反射率较小的激光器进行组阵.     

光腔衰荡法数据截取对时间常数测量精度的影响分析

光腔衰荡方法是目前测量光学元件超高反射率(反射率>99.9%)的唯一方法。介绍了一种对光腔衰荡法中激光信号强度与时间关系的优化提取方法。设计了基于光腔衰荡法的光学元件超高反射比的测试系统,通过对采集的光腔衰荡曲线数据进行分段指数拟合,将光腔衰荡曲线数据分为5段,对每段指数拟合结果对应的R² (R-square)和RMSE(root mean squared error)值进行对比分析,计算每段指数拟合的衰荡时间。实验结果表明:截取光腔衰荡曲线数据40%～60%部分拟合得到的结果最接近真实值,求得对应的腔镜的反射率为99.988 977%。最后通过与腔镜的自身反射率进行比较,表明该种数据拟合方法能有效地测量腔镜的反射率,并能减小实验数据本身带来的误差。     

Improvement of the operation parameters for a Cr:LiSAF ultrashort-pulsed laser

The optimization of the pumping power that is focused on a gain medium inside an optical cavity is fundamental for increasing the efficiency of the power transferred inside a crystal, in this way increasing the output power of the laser. Nevertheless, in the case of pumping with a highly astigmatic laser diode, an undesirable form of the beam is focused on the cavity and the process to improve the cross section and sizes of the beam produce a notable reduction in the effective pump power ultimately focused in the crystal. The cavity design improvements for a Cr:LiSAF laser pumped with a 200 um × 1 um laser diode emission is presented for three different configurations, Z, V, and ring. The pump power is introduced in the cavity through a simple optical array, coupling more than 83% of the laser-diode power. The design requirements for the resonant cavity are reviewed in order to improve the coupling between the fundamental mode of the cavity and the cross-section form of the pumping beam. The stability limits of the cavities and Kerr sensitivity region are presented.     

A compact high efficient diode-double-passing-pumped mid-IR Tm:YLF laser at room temperature

A new compact high efficient diode-double-passing-pumped Tm:YLF laser at room temperature is presented. Using a crystal of 3 mm × 3 mm × 12 mm 4% doping Tm:YLF and double-end-double-passing pumping cavity structure without complex optical splitter pumping system, 5.6 W CW 1907.6 nm laser is obtained at 26.2 W 792 nm pumping laser. The slope efficiency is as high as 37.8% and the spectrum width is 2 nm. The relationship between cavity length and output laser is also analyzed. Experiments verify that the highest energy and convertion efficiency can be reached by optimizing the oscillator cavity length. Finally, we used this Tm:YLF laser to pump Ho:YAG crystal at room temperature and achieved 1.65 W 2.1 μm output laser with slope efficiency 67%.     

Excitation-induced absorption and luminescence at the GaSe exciton

Transmission changes induced by extremely high optical excitation at or below the fundamental direct exciton level of GaSe in the parallel geometry (light propagating parallel to the c-axis) are reported. A double-beam technique is used. The data show that no gain develops up to the highest pumping levels attainable. Careful luminescence measurements, taken concurrently, indicate that the observation of stimulated emission in such geometry, often reported in the literature, is a spurious effect. Optical amplification is possible in the transverse geometry, and is accompanied by the disappearance of discrete exciton levels, including the ground state. A continuous distribution is rather observed, which tails deep into the forbidden energy gap. The possibility of a final plasma state is discussed.     

CO2的腔增强吸收与高灵敏吸收光谱研究

腔增强吸收光谱(CEAS)是在衰荡吸收光谱的基础上发展起来的一种新型的直接吸收光谱技术.文章报道了用中心输出波长为1.573μm的窄线宽连续可调谐半导体激光器(DFB封装)作光源,用两块高反射率平凹透镜(在1.573μm附近,凹面反射率R～99.4%,曲率半径r～1 m)组成对称共焦腔作吸收池的腔增强吸收光谱系统.采用扫描腔长的方法改变谐振腔的模式,当激光器的输出频率与谐振腔的某一腔模之间满足共振匹配关系时,激光被耦合到谐振腔内,用探测器接收透过谐振腔的光信号,同时用波长计精确测量激光器的输出波长.在33.5 cm长的吸收池内测量了吸收强度为1.816×10-23cm-1·(molecule·cm-2)-1的二氧化碳分子的弱吸收谱线,探测灵敏度达到了6.78×10-7 cm-1.实验结果表明,腔增强吸收光谱具有灵敏度高,装置简单,易于操作等优点.     

基于垂直谐振腔结构的半导体光放大器理论分析

由新型垂直腔半导体光放大器（VCSOAs）器件结构出发,在反射模式和透射模式两种 情况下,计算了VCSOAs的分布布拉格反射堆（DBR）反射率、单程增益与增益、带宽的关系 ,其中DBR反射率的增大伴随着增益的上升,但也伴随着带宽的减小.通过引入增益-带宽 积的概念,以均衡增益与带宽.计算中表明:10 dB以上增益,50 GHz以上带宽可以实现. 计算结果与文献实验相吻合,对优化VCSOAs的结构设计和性能有所裨益.