超高Q值mm级晶体回音壁微腔加工

回音壁微腔具有超高Q值和极小的模式体积,在微波光子系统、非线性光学和量子光学等领域中具有广阔的应用前景。通过分析mm级氟化镁(MgF₂)晶体回音壁微腔的损耗因素,确认了影响回音壁微腔品质因数的主要指标为材料等级和表面粗糙度。设计了mm级MgF₂晶体回音壁微腔的结构形式,使用DUV级MgF₂晶体,如果回音壁微腔表面粗糙度小于0.7 nm,则MgF₂晶体回音壁微腔的极限损耗理论计算值为4.781×10^-11,对应的极限Q值为2.09×10¹⁰。通过对MgF₂晶体回音壁微腔进行粗成型、精密车削、精密抛光,实现了高品质因数的微腔制造。测试结果表明,回音壁微腔的表面粗糙度Ra值为0.669 nm、微观形貌PV值为6.767 nm、品质因数为2.054×10⁹@1 550 nm。     

超高Q值光学微腔光谱信号采集系统设计与分析

针对超高品质因子Q值光学微腔实验系统的光谱数据采集难题,设计了一款针对光学微腔的光谱信号采集系统。对光谱信号采集系统进行了基本功能验证,证明了系统的稳定性和实用性;分别测试了基于电弧放电法制备的光纤微球腔与基于超精密抛光法制备的氧化硅晶体微盘腔。采集了光纤微球腔和氧化硅晶体微盘腔的透射谱,并对其模式谱线进行追踪。结果表明：光纤微球腔的Q值达到2.26×10⁶,氧化硅晶体微盘腔的Q值达到10⁹;采集系统具有很好的消噪功能,模式谱线能长时间保持稳定。针对超高Q值光学微腔开发的光谱信号采集系统具有很高的可靠性,可用于微腔光子学系统以及后续微腔传感应用开发。     

非线性一维光子晶体波导光双稳

利用非线性折射率系数较大且非线性时间响应较快的CdS_xSe_1-x玻璃为材料,设计并制备了非线性一维光子晶体波导光双稳器件,该器件的折射率空间分布呈正弦形式。实验测得双稳开关的阈值功率密度为1.60×10⁵W/cm²,开关时间为63ps。采用时域有限差分方法讨论了光子晶体带隙随入射光强变化而移动的情况,随着入射光功率密度的增加,光子晶体的带隙中心向短波方向移动。同时计算了该器件的双稳特性,理论计算得到双稳开关的阈值功率密度为1.40×10⁵W/cm²,开关时间约为50ps。获得了理论与实验基本一致的结果。     

钴离子注入对二氧化钛晶体的结构和光学性能的影响

采用离子注入法制备了钴离子掺杂的金红石相TiO₂样品;离子注入能量、注量分别为40 keV(1×10¹⁶cm^-2),80 keV(5×10¹⁵,1×10¹⁶,5×10¹⁶,1×10¹⁷cm^-2),120 keV(1×10¹⁶cm^-2). 通过XRD,XPS和UV-Vis等手段对掺杂前后样品的结构和光学性能进行了表征,分析了掺杂元素在金红石TiO₂中的存在形式. XRD测试表明随着注入能量的增加晶体的损伤程度增加. UV-Vis测试表明掺杂后所有样品在可见光区的吸收增强; 并且随着注量的增加,注量为5×10¹⁵cm^-2到5×10¹⁶cm^-2范围内注入样品的光学带隙逐渐变小. 关键词： 钴 二氧化钛 离子注入 掺杂     

一种新型高透射率高品质因子光子晶体耦合腔波导结构

提出了一种在二维三角晶格光子晶体线缺陷波导中放置椭圆空气孔的耦合腔波导结构。基于平面波展开法,利用MPB对线缺陷波导的能带结构进行了计算并给出能带图。基于时域有限差分法（FDTD）,利用MEEP对椭圆空气孔在波导中的排列方式、数量、尺寸进行优化设计,并对频率位于微腔共振频率处的光波在耦合腔波导结构中的品质因子和传输特性进行研究与比较,给出了电场分布图。仿真结果表明,当椭圆空气孔的长轴方向纵向排列时,相应的微腔共振频率在光子禁带内可获得90%以上的透射率,对应的品质因子Q可达10⁴量级;选择合适的参数,获得的Q可高达10⁷量级,对应共振频率的透射率仍在60%以上。     

ZBLAN玻璃中Pr3+掺杂离子3P0和1D2能级的发光特性和寿命

对ZBLAN氟锆酸盐玻璃中Pr³⁺掺杂离子³P₀和¹D₂能级的寿命和发光特性进行了较详细的光谱学研究。首先测量了两种掺杂浓度(质量分数分别为1×10^-3,5×10^-3)的Pr³⁺:ZBLAN玻璃的吸收光谱,然后运用时间分辨激光光谱技术测量了³P₀和¹D₂能级在激光单光子共振激发下的荧光发射谱和能级寿命。将不同荧光发射谱带的强度和文献报道的Judd Ofelt理论计算辐射跃迁几率数值做了比较分析,证明了文献中理论计算结果的可靠性。由于浓度猝灭效应,在相同的激发条件下,掺杂浓度为1×10^-3样品的荧光发射强度明显大于5×10^-3样品的荧光发射强度。但是从我们的测量结果看,掺杂浓度对³P₀和¹D₂ 的能级寿命值无显著影响。掺杂浓度为1×10^-3时,Pr³⁺离子³P₀和¹D₂能级的寿命值分别为46,322μ_s。     

应用于铯原子喷泉钟的二维磁光阱研制

理论模拟研究了二维磁光阱原子束流量与饱和蒸汽压、冷却光强、激光失谐量的关系, 构建了二维磁光阱(2D-MOT)装置, 实验上实现了大流量的慢速原子束, 其测量值为2.1× 10⁹/s.利用荧光法测量了各实验参数与流量的关系, 测量结果与数值模拟结果符合较好. 关键词： 2D-MOT 流量 慢速原子束 铯原子喷泉钟     

氩气微腔放电中特性参数的数值模拟研究

本文采用二维自洽完全流体模型,针对阳极为通孔的高气压微腔放电结构,研究了微腔放电的参数特性.数值计算得到了氩气压强为100 Torr,放电稳态时的电势分布、电子数密度分布和电子温度分布等重要参数.模拟结果表明放电区存在显著的阴极鞘层结构,电子数密度的峰值达到10²⁰ m^-3,电子温度的量级为几个eV至十几eV,该结论与实验结果相一致.数值模拟合理的解释了微腔放电的基本原理. 关键词： 微腔放电 等离子体模拟 流体模型     

太赫兹波段介质微腔光学特性研究

采用匀胶法制备了厚度在微米量级的 Si/[TiO₂/Al₂O₃]²TiO₂和Si/[TiO₂/MgO]²/TiO₂ 多层介质膜反射镜. 采用太赫兹(THz)时域透射光谱系统获得了多层膜的时域透射谱. 用传输矩阵法模拟了Si/[TiO₂/Al₂O₃]²TiO₂ 和Si/[TiO₂/MgO]²/TiO₂两种分布式布拉格反射镜 (DBR)的反射相移和相位穿透深度等光学特性. 设计了两种结构为 DBR/LT-GaAs/DBR的对称THz光学微腔结构并模拟了腔结构的辐射光谱. 结果表明:通过引入谐振腔, 两种DBR组成的微腔器件在谐振波长处的强度分别提高了19和14倍. 其中Si/[TiO₂/Al₂O₃]²TiO₂/LT-GaAs (12 μm)/ [TiO₂/Al₂O₃]²TiO₂腔的辐射光谱存在两个峰, 分别位于208和248 μm, 并分析了出现两个谐振峰的原因. 探讨了通过引入介质谐振腔实现对THz源的辐射特性进行调控的可行性. 关键词： 分布式布拉格反射镜 光子晶体 穿透深度 太赫兹微腔     

CFETR磁体系统的中子学计算及活化分析

用蒙特卡洛中子输运程序(MCNPX)对中国聚变工程实验CFETR超导磁体进行中子学输运计算,利用欧洲活化计算程序FISPACT对其进行活化计算分析,针对计算结果重点分析了磁体系统的中子学剂量分布以及活化情况。计算结果表明,中子能量通量最大处出现在聚变堆内侧线圈处,为3.97×10¹⁴ MeV•m^–2,在该条件下超导线圈可以满足设计要求。停机后磁体组件的活度为3.33×10¹⁰Bq•kg^–1,停机10年后下降2个数量级达到6.14×10⁸Bq•kg^–1。研究结果验证了所使用的CFETR 3维模型满足初步设计条件。     

A terahertz photonic crystal cavity with high Q-factors

A terahertz 1D photonic crystal cavity with very high Q-factor is demonstrated. The cavity consists of two parallel distributed Bragg mirrors and one air layer between them as defect layer. By increasing the length of the defect layer, the cavity has a very narrow transmission bandwidth of 30 MHz at resonant frequency of 336 GHz, i.e., a high Q over 1.1 × 10⁴ is achieved. Furthermore, an optically controllable THz switch is demonstrated by light irradiating on one of the middle silicon wafer in the cavity. And the power of optical beam needed for the switch is remarkably reduced to 0.16 W/cm², which is nearly 50 times smaller than that for a THz switch using a single silicon wafer.     

Frequency-agile,rapid scanning spectroscopy: absorption sensitivity of 2 × 10−12 cm−1 Hz−1/2 with a tunable diode laser

We present ultrasensitive measurements of molecular absorption using frequency-agile rapid scanning, cavity ring-down spectroscopy with an external-cavity diode laser. A microwave source that drives an electro-optic phase modulator with a bandwidth of 20 GHz generates pairs of sidebands on the probe laser. The optical cavity provides for high sensitivity and filters the carrier and all but a single, selected sideband. Absorption spectra were acquired by stepping the tunable sideband from mode-to-mode of the ring-down cavity at a rate that was limited only by the cavity decay time. This approach allows for scanning rates of 8 kHz per cavity resonance, a minimum detectable absorption coefficient of 1.7 × 10^?11 cm^?1 after only 20 ms of averaging, and a noise-equivalent absorption coefficient of 1.7 × 10^?12 cm^?1 Hz^?1/2. By comparison with cavity-enhanced laser absorption spectrometers reported in the literature, the present system is, to the best of our knowledge, among the most sensitive and has by far the highest spectrum scanning rate.     

Mode-by-mode optical feedback: cavity ringdown spectroscopy

We describe a new continuous wave cavity ringdown spectroscopy (cw-CRDS) approach using an extended cavity diode laser (ECDL) optically self-locked to a high finesse cavity including an intracavity glass plate under the Brewster angle. Low noise, mode-by-mode absorption spectra are recorded at a high acquisition rate (laser frequency scan greater than 400 GHz/s) and covering four orders of magnitude in absorption coefficient. Sampling spectra with the fixed high finesse cavity frequency comb provides high precision frequency markers. An original scheme for the laser beam shut-down, based on signal shape analysis and the diode laser injection current control, is presented. This scheme avoids any supplementary switching device. To retrieve ringdown processing at a kilohertz rate several exponential decay fit algorithms are compared. Performances of this new scheme are demonstrated with the observation of very weak lines of the oxygen B-band around 680 nm. Atmospheric spectra of isolated lines averaged for less than 10 s show a baseline noise of 5×10^-10 cm^-1 and a single point minimum detectable absorption loss over a one-second measurement interval of 2×10^-10 cm/ is obtained. PACS 07.88.+y; 42.55.Px; 42.62.Fi     

Simple vibration-insensitive cavity for laser stabilization at the 10−16 level

We present the design and realization of two reference cavities for ultra-stable lasers addressing narrow transitions in mixed-species (¹¹⁵In⁺ / ¹⁷²Yb⁺) Coulomb crystals. With a simple set-up, we achieve a fractional frequency instability close to the thermal noise limit of a 12-cm-long cavity, reaching σ _y  = 4.7 × 10^?16 at 10 s with a linear drift of 53 mHz/s. We discuss the individual instability contributions and show that in a set-up with a lower thermal noise floor and vibration sensitivity, an instability of 1 × 10^?16 can be reached. To achieve this, we implement a vibration-insensitive design for a 30-cm-long cavity mounted horizontally and conduct first tests that show a sensitivity of 1.8 × 10^?11 ms^?2 to vertical accelerations. This is about a factor of 20 less than the value observed for the short cavity. Mechanical tolerances and ways to further reduce the sensitivity are discussed.     

Cavity-enhanced optical feedback-assisted photo-acoustic spectroscopy with a 10.4 μm external cavity quantum cascade laser

An ultra-sensitive photo-acoustic spectrometer using a 10.4 μm broadly tunable mid-IR external cavity quantum cascade laser (EC-QCL) coupled with optical feedback to an optical power buildup cavity with high reflectivity mirrors was developed and tested. A laser optical power buildup factor of 181 was achieved, which corresponds to an intra-cavity power of 9.6 W at a wavelength of 10.4 μm. With a photo-acoustic resonance cell placed inside the cavity this resulted in the noise-equivalent absorption coefficient of 1.9 × 10^?10 cm^?1 Hz^?1/2, and a normalized noise-equivalent absorption of 1.1 × 10^?11 cm^?1 W Hz^?1/2. A novel photo-acoustic signal normalization technique makes the photo-acoustic spectrometer’s response immune to changes and drifts in the EC-QCL excitation power, EC-QCL to cavity coupling efficiency and cavity mirrors aging and contamination. An automatic lock of the EC-QCL to the cavity and optical feedback phase optimization permitted long wavelength scans within the entire EC-QCL spectral tuning range.     

Quantum-noise-limited cavity ring-down spectroscopy

We demonstrate a heterodyne-detected cavity ring-down spectroscopy (CRDS) method that allows for a noise-equivalent absorption coefficient of 6 × 10^?14 cm^?1 Hz^?1/2, the lowest which has been reported in a CRDS measurement. It is shown that heterodyne-detected CRDS also reaches the quantum noise limit at reasonable optical powers. In addition to offering ultra-high sensitivity, this technique provides high frequency agility over a range of 2 THz in the near-infrared, which allows entire absorption bands to be recorded in minutes. As a demonstration experiment, high resolution spectra of a near-infrared carbon dioxide band have been recorded.     

CH3I: Isotope shift for 129I in the v6 band

The isotope shift in the v₆ band of CH₃I has been measured with high resolution for the radioisotope ¹²⁹I (half-life = 1.6 × 10⁷ y) with respect to the stable ¹²⁷I, using tunable diode laser spectroscopy. The average shift obtained from 30 transitions, free from interference in the ^RQ(J, 3) and ^RQ(J, 4) branches, amounted to (-0.0135 ± 0.0006) cm^-1. The abundance ratio ¹²⁹I/¹²⁷I in the gas mixture was determined spectroscopically on ^RQ(16, 3) and found to be (0.032 ± 0.003), as compared to a mass-spectrometric analysis of (0.030 ± 0.001). The self and air broadening coefficients measured on ^RR(6, 0) of CH₃¹²⁷I were (32 ± 3) MHz Torr^-1 and (10.4 ± 1.5) MHz Torr^-1 respectively. The line strengths for ^RQ(16, 3) were found to be (2.0 ± 0.2) × 10^-21 cm^-1 mol^-1 cm² for both CH₃¹²⁷I and CH₃¹²⁹I.     

Time resolved simultaneous detection of 14NO and 15NO via mid-infrared cavity leak-out spectroscopy

We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near λ?=?5 μm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R?=?99.988 %), we observed a noise-equivalent absorption coefficient of 3?×?10^?10 cm^?1Hz^?1/2. This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for ¹⁴NO and 40 ppt for ¹⁵NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The δ¹⁵N value was obtained with a precision of ±1.2‰ in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of ¹⁵NO as a tracer molecule for endogenous biomedical processes.     

Double beta decay of 100Mo

Two-neutrino double beta decay of ¹⁰⁰Mo with half-life T _1/2=[7.2±0.9(stat)± 1.8(syst)]×10¹⁸ yr was detected using a liquid argon ionization chamber. With a C.L. of 68% (90%), the bounds on neutrinoless decay and decay with majoron emission were found to be 8.4(4.9)×10²¹ and 4.1(3.2)×10²⁰ yr, respectively. An analysis of all available results provides the average “world” value T _1/2=(8.0±0.7)×10¹⁸ yr for the two-neutrino decay of ¹⁰⁰Mo, and the corresponding nuclear matrix element is M _GT=0.118±0.005.     

Induced emission from a sodium Rydberg atom in a microwave cavity

Results are presented from an experiment on the observation of an induced microwave transition 37P-37S in sodium Rydberg atoms under the action of 30 thermal photons in a microwave cavity. The measured value of the transition rate (4±1.5)×10⁴ s⁻¹ agrees with the calculated value. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 413–416 (25 March 1999)