Excitation cross sections for odd triplet levels of LaII in e-La collisions

The method of extended crossing beams with the recording of an optical signal from an intersection region is used to study the excitation of a singly charged lanthanum ion. The process in question is accomplished in a single collision event between a lanthanum atom and an electron, i.e., as an excitation process with simultaneous single ionization. Excitation cross sections for 105 spectral lines arising upon transitions from odd triplet levels of LaII are measured. Also recorded are 16 optical excitation functions for 85 lines. The results obtained are used to calculate the cross sections for excitation of the energy levels and the contribution of cascade transitions to their population.     

Optical amplification using raman transitions between spin-singlet and spin-triplet states of a pair of coupled in-GaAs quantum dots

We report the observation of steady-state optical amplification in Raman transitions between the lowest-energy spin states of a single quantum-dot molecule. Absorption and resonance fluorescence experiments demonstrate that the entangled two-electron singlet and triplet states have electric-dipole coupling to a common optically excited state. Fast spin relaxation ensures optical gain on the triplet transition when the singlet transition is driven resonantly. By embedding the quantum-dot molecule in a cavity of modest quality factor, a solid-state single-emitter laser can be realized.     

腔场耦合的二能级原子荧光谱

过光与物质相互作用的主方程计算了强场激励的二能级原子与单模腔耦合的稳态荧光谱。在腔场的强耦合作用下,三峰Mollow谱的每个成分都分裂为多重的,这种现象由腔场使原子修饰态能级漂移而导致的,荧光谱的具体结构则依赖于驱动场的拉比频率和原子-腔的耦合系数。     

Determination of relative triplet sublevel populating rates during optical pumping using ODMR

A method is introduced, based on optical detection of triplet state magnetic resonance (ODMR), to determine the relative populating rates of photoexcited triplet state sublevels during optical pumping. Phosphorescence transients induced by microwave rapid passage during optical pumping are analyzed globally utilizing kinetic parameters obtained from separate microwave-induced delayed phosphorescence measurements to obtain relative sublevel populating rates. Results are unaffected by phosphorescence from triplet populations that do not yield an ODMR response. The method is applied to the triplet state of the indole chromophore in various environments to reveal the effects of local interactions on the pattern of intersystem crossing. Enhanced spin--orbit coupling effects are attributed to interactions that reduce the planar symmetry of the indole chromophore.     

Spectroscope studies of YAlO_3: (Lu~(3 )Nd~(3 ))

An increase of the Nd~(3 ) doping concentration and an enhancement of the laser induced fluorescence in the single crystal of YAlO_3: (Lu~(3 ), Nd~(3 )) have been observed and are attributed to the size compensation effect. The low temperature (4.2K) fluorescence spectra indicate that the structure of the sharp lines arising from the radiative transitions of Nd~(3 ) ions is not changed by the existence of Lu~(3 ) ions, but the emission lines are inhomogeneously more broadened. Besides, it has been observed that the fluorescence due to the radiative transition from the Stark's sublevel R_2 of the metastable level ~4F_(3/2) to the sublevels Y_1 of the manifold ~4I_(11/2) decreases with decreasing temperature and the fluorescence arising from the transitions R_1→Y_1 is relatively increased. The experimental fact is qualitatively interpreted.     

Fluorescence from doubly driven four-level atoms

The unusually narrow features in the fluorescence from ⁸⁵Rb driven by two laser fields L1 and L2, reported in [1], are explained on the basis of a four-level density matrix calculation. The L2 laser enables atom transfer to the fluorescing levels connected by the strong L1 laser. In turn the L1 laser causes the Autler-Townes splitting of the upper levels connected by L2 laser. These two effects are shown to maximise fluorescence within a narrow spectral range of the scanned L2 laser due to velocity selection of atoms from co-propagating and counter propagating L1 and L2 lasers. The analysis reveals the existence of narrow spectral features from a collection of atoms at room temperature even in the absence of induced coherences between the levels.Received: 2 July 2004, Published online: 21 September 2004PACS: 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift - 32.80.Bx Level crossing and optical pumping     

On the possibility of polarizing atoms and nuclei by pulsed electromagnetic fields without using ultra-low temperatures

A method is proposed for fast and deep polarization of the system of hyperfine sublevels of the ground state of an atom having an optical excited state by means of two-component microwave pulses. The pulse of the bichromatic optical field that induces the transitions between the ground state and excited state of the atom is supposed to provide coherence among the hyperfine sublevels of the atomic ground state via the effect of coherent population trapping. The subsequent resonance microwave pulses create the polarization of equally populated ground state sublevels of the atom. The proposed polarization technique may be used for designing the new schemes of quantum computers, for the pulse transformation in optical experiments when light passes through a resonant medium containing rear-earth ions, as well as for producing polarized nuclear targets.     

Spin polarization induced by optical and microwave resonance radiation in a Si vacancy in SiC: A promising subject for the spectroscopy of single defects

Depending on the temperature, crystal polytype, and crystal position, two opposite schemes have been observed for the optical alignment of the populations of spin sublevels in the ground state of a Si vacancy in SiC upon irradiation with unpolarized light at frequencies of zero-phonon lines. A giant change by a factor of 2–3 has been found in the luminescence intensity of zero-phonon lines in zero magnetic field upon absorption of microwave radiation with energy equal to the fine-structure splitting of spin sublevels of the vacancy ground state, which opens up possibilities for magnetic resonance detection at a single vacancy.     

Wide-Range Spectral Diffusion in Single Mg-Tetraazaporphyrin Molecules in a Polymer Matrix at Cryogenic Temperatures

Zero-phonon spectral lines of single Mg-tetraazaporphyrin molecules in a polymer matrix and their spectral trails are recorded using cryogenic fluorescence nanoscopy at a temperature of 6 K. Spectral diffusion (stochastic jumps of zero-phonon lines) in an anomalously wide spectral range up to several tens of inverse centimeters is revealed. The structure of the vibronic band in the fluorescence excitation spectrum of single molecules, including both a narrow zero-phonon line and a broad phonon sideband, is directly observed.     

“Unusual” lines observed in low-frequency cw ENDOR of photoexcited triplet state molecules: the primary donor triplet in photosynthetic reaction centers as an example

The origin of frequently observed “negative” (opposite phase) ENDOR lines in the low-frequency region of triplet state ENDOR spectra is explained in terms of microwave hole burning and RF modulation phenomena. From this, a new method of detecting burnt side holes in EPR spectra is derived which is based on cw ENDOR instrumentation. The method uses the modulation satellites that are induced by a longitudinal RF field component and appear around any EPR line, including burnt holes (“negative” lines). The longitudinal RF field was generated by a coil oriented parallel to the external field, but a longitudinal component of the RF field also exists in most conventional ENDOR spectrometers because of slight misalignments of the ENDOR coil generating the transversal RF field. The lines it induces in the low-frequency part of ENDOR spectra are generally considered as artifacts. It is shown, however, that RF induced modulation satellites provide valuable information concerning the lines distant from the spectral position in the EPR spectrum chosen for ENDOR observation. This allows one to record the pattern of side holes burnt by microwave saturation through forbidden transitions that carries information about ENDOR frequencies comparable to what can be extracted from ESEEM experiments. Such comparability is demonstrated for examples of nitrogen ENDOR of photoexcited triplet states of the primary donor in photosynthetic reaction centers and related compounds.     

Effects of spontaneously generated coherence on resonance fluorescence in a microwave-driven four-level atomic system

We investigate the spectrum of the resonance fluorescence from a coherent driven four-level atomic system. We observe interesting features such as controllable triple narrow peaks. The number, widths and heights of the emission peaks can be controlled by tuning the Rabi frequencies of the laser fields and the microwave field. We attribute these features to the effects of Spontaneously Generated Coherence between the close-lying levels in the dressed state picture. We also explain the observed spectrum with the transition properties of the dressed states generated by the coupling of the two laser fields and the microwave field.     

Magnetic-field dependent optically detected ESR in the photoexcited triplet states of bridged Zr(IV) metallocenes

We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples of the bridged Zr(IV) metallocenes, Me₂Si<(Cp₂)ZrCl₂ ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me₂C<(Cp₂)ZrCl₂ (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously the intensities of all three lines. The ODMR line intensities increase in proportion toB ⁿ, wheren<1. This field dependence is weaker than the expected proportionalB ² dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes.     

Trace Moisture Measurement with 5. 2 mu m Quantum Cascade Laser Based Continuous-Wave Cavity Ring-Down SpectroscopyEI北大核心CSCD

Trace moisture concentration in high-purity gases is an important parameter in semiconductor manufacturing because many manufacturing processes are sensitive to moisture even on the level of parts per billion by volume (ppbv). Detection of trace moisture in mid-infrared spectral region is beneficial due to more abundant and stronger spectral lines in this region. Recently, Quantum cascade lasers (QCLs) with high output power, narrow line-width, and high reliability have been developing rapidly and have become promising light sources for sensitive spectroscopic measurements. By employing a 5. 2 mu m external-cavity tunable quantum cascade laser, a continuous-wave cavity ring-down spectroscopy (CRDS) experimental setup is established and applied to detect trace moisture in high-purity nitrogen gas. In the experiment, the CRDS signal is averaged to improve the detection sensitivity, and the optimal averaging number is determined by Allan variance calculation to be 602. For trace moisture detection, the absorption cross-section of H2O in the spectral range between 1 905 and 1 925 cm(-1) is simulated according to the HITRAN database and the optimal detection spectral line is chosen. Detected at 1 918 cm(-1) absorption line at 296 K temperature and 1 atm pressure, the measured moisture concentration is in good agreement with the nominal value, and the minimum detectable moisture concentration of 24. 8 ppbv is achieved when cavity mirrors with reflectance of 99.93% are used. The experimental results show that mid-infrared cavity ring-down spectroscopy technique has great potential in a wide variety of applications, such as industrial production control, environmental monitoring and health diagnosis, etc.     

RADIATION OF DRESSED EXCITONS IN THE SEMICONDUCTOR MICROCAVITY

In this paper, we introduced the dressed exciton model of the semiconductor micro-cavity device. In the semiconductor micro cavity of vertical-cavity surface-emission device, the excitons first coupled with the cavity through an intra-electromagnetic field and formed the dressed excitons. Then these dressed excitons decayed into the vacuum cavity optical mode, as a multi-particle process. Through the quantum electrodynamics method, the dipole emission density and system energy decayed equation were obtained. And it was predicted that the excitons decay into a very narrow mode when the exciton-cavity coupling becomes strong enough.     

非旋波耦合条件下微波控制的光学双稳与多稳

研究了在非旋波耦合条件下微波场建立的原子相干对光学双稳与多稳的控制.通过改变微波场的初始相位,可以有效地控制双稳与多稳的存在与否、迟滞环宽度和阈值强度的高低.旋波和非旋波耦合在物理上可视为双色激发,耦合的能级分裂成无穷多个子能级,原来的裸态跃迁变成无穷多个不同频率的跃迁.这些跃迁的相干叠加决定了介质的非线性吸收与色散,相干叠加的结果取决于微波场的相位. 关键词： 原子相干 非旋波耦合 光学双稳与多稳 相位控制     

5.2μm量子级联激光器光腔衰荡光谱技术的痕量水汽检测

高纯气体中水汽含量是半导体工业生产中的一个重要参数,气体中残余水汽含量即使是ppbv量级也会对产品质量产生影响。气体在中红外区域具有更丰富的特征谱线,在该区域对水汽含量进行检测十分必要。宽调谐范围、高输出功率和窄线宽量子级联激光器的快速发展,推动了该区域红外光谱检测技术的发展。首次在中红外波段,采用5.2μm可调谐量子级联激光器,基于连续光腔衰荡光谱技术建立了痕量水汽的检测装置,并开展了痕量水汽检测实验。通过阿伦方差分析系统噪声水平,确定了光腔衰荡信号最优平均次数为602次。根据HITRAN数据库,模拟实验条件下1 905~1 925cm~(-1)范围内水汽的吸收截面,选取最佳的检测谱线位置。在常压和室温下,对1 918cm~(-1)附近的水汽吸收光谱进行测量,测定高纯氮气中的痕量水汽浓度,检测结果与标称值一致。在腔镜反射率为99.93%时水汽的检测灵敏度达到24.8ppbv。分析结果表明,中红外高灵敏痕量气体检测技术在工业监测、环境检测以及医学诊断等领域具有很好的应用前景。     

Microwave spectroscopy of cold rubidium atoms

The effect of microwave radiation on the resonance fluorescence of a cloud of cold ⁸⁵Rb atoms in a magnetooptical trap is studied. The radiation frequency was tuned near the hyperfine splitting frequency of rubidium atoms in the 5S ground state. The microwave field induced magnetic dipole transitions between the magnetic sublevels of the 5S (F=2) and 5S (F=3) states, resulting in a change in the fluorescence signal. The resonance fluorescence spectra were recorded by tuning the microwave radiation frequency. The observed spectra were found to be substantially dependent on the transition under study and the frequency of a repump laser used in the cooling scheme.     

光梳主动滤波放大实现锶原子光钟二级冷却光源

提出一种结合注入锁定技术的主动滤波放大方法,将光梳直接注入锁定至光栅外腔半导体激光器,产生窄线宽激光光源,该光源可以用于锶原子光钟二级冷却.实验中,将中心波长为689 nm,带宽为10 nm的光梳种子光源注入689 nm光栅式外腔半导体激光器,通过半导体增益光谱与半导体光栅外腔,从飞秒光梳的多个纵模梳齿中挑选出一个纵模模式来进行增益放大,再通过模式竞争,实现单纵模连续光输出;同时,光梳的重复频率锁定在线宽为赫兹量级的698 nm超稳激光光源上,因此,注入锁定后输出的窄线宽激光也继承了超稳激光光源的光谱特性.利用得到的输出功率为12 mW的689 nm窄线宽激光光源实现了88Sr原子光钟的二级冷却过程,最终获得温度为3μK,原子数约为5×10~6的冷原子团.该方法可拓展至原子光钟其他光源的获得,从而实现原子光钟的集成化和小型化.     

Optical pumping in a L-system by parametric luminescence light

We examine the optical pumping effect in an ensemble of three-level atoms with a Λ configuration of the energy sublevels excited by parametric luminescence light in the squeezed state. We derive quantum kinetic equations that describe the evolution of the density matrix of atoms irradiated by low-intensity squeezed light with a finite-width spectrum. In particular, we show that because of the quantum statistical properties of the squeezed light there can be a redistribution of atoms among the lower energy sublevels, despite the equality of the intensities of the spectral components of the light that resonantly excites optical transitions in the Λ-system. The relation of the optical pumping effect to the correlation and spatial-temporal spectral properties of squeezed light is discussed in detail. Finally, we show that the effects are closely linked to the finiteness of the width of the squeezed-light spectrum. Zh. éksp. Teor. Fiz. 112, 137–162 (July 1997)     

充氖夫兰克-赫兹管的发射光谱研究

用光栅光谱仪测量了夫兰克-赫兹实验中Ne原子的发射光谱.光谱分析表明,橙黄色的发射光包含多条谱线,已标定的谱线都是Ne原子从第二激发态的各个子能级跃迁到第一激发态的对应能级所产生的.