【作者】 王彦华；

【导师】 王军民；

【作者基本信息】 山西大学 ， 光学， 2007， 博士

【摘要】 量子光学主要研究原子同光场的相互作用，它借助光对原子、离子等客体的量子态进行制备、探测和控制，其中电磁感应透明、电磁感应吸收等相干光谱和激光冷却与俘获原子是实现量子态操控的重要基础。光作用于原子后的相干量子效应可以使原子处于相消或相长干涉的量子叠加态上，并通过光谱的方法来研究其中的量子现象。而通过激光冷却与俘获技术几乎消除了粒子的宏观热运动，则可以制备并影响控制冷原子系综的量子态甚至单个的原子。本文的工作从新实验室光学平台的安装开始并逐步完善基础建设，完成了光栅外腔反馈半导体激光器的设计制作，并利用不同的稳频方案实现了频率稳定，随后利用自制半导体激光器从实验上研究了铯原子相干光谱以及铯原子在磁光阱及近共振光学晶格中的冷却与俘获。研究室温下气室中铯原子在近共振光场中的电磁感应透明，电磁感应吸收相干光谱，虽然这些方法可以提高光谱的精度，突破多普勒频移的影响，但同原子速度平方有关的二阶多普勒效应并没有改善，而通过激光冷却的方法得到几十μK的原子样品，不仅可以产生高精度光谱，而且极大地改善了原子无规热运动对光与原子相互作用形成的干扰，成为研究量子现象的基础平台。本文主要内容有以下几部分：1)分析激光二极管工作原理，结合下一步实验的要求，设计、制作、调试了多台采用Littrow结构的光栅外腔反馈半导体激光器，并使其稳定工作在铯原子D₂线频率附近可连续调谐约2GHz。2)由铯原子饱和吸收光谱和F-P腔作提供频率参考，采用调制或无调制的多种方法对半导体激光器进行了频率锁定。稳频后的频率起伏小于1MHz，可以满足实验的需要。3)两台半导体激光器分别提供耦合光和探测光，对铯原子D₂线的两个循环跃迁6²S_1／2F_g=3→6²P_3／2F_e=2和6²S_1／2F_g=4→6²P_3／2F_e=5构成的简并二能级系统分别进行研究，得到了电磁感应透明和电磁感应吸收的相干光谱，研究了耦合光的失谐和强度的变化对光谱的影响，同时基于量子相干基本理论和气室中原子的速度选择机制分析了形成光谱的物理机制。4)以三能级原子为模型，基于dressed理论，通过探测光的吸收谱和耦合光随探测光扫频而表现的吸收变化研究了铯原子气室中的A-T分裂以及亚多普勒吸收。5)在利用饱和吸收技术实现了冷却光相对于原子跃迁线的负失谐锁定，并通过双次通过声光调制器的频移技术对负失谐进行自动控制的基础上，采用三束光往返对射的方案构建气室磁光阱系统，实现了对¹³³Cs原子的冷却和俘获。磁光阱可俘获原子约10⁷个，等效温度约30-50μK。同时改进并完善了Pascal程序控制的时序控制系统，通过外围执行元件包括压控振荡器、声光调制器、射频开关、磁场电流开关对冷却光光场强度、光场失谐、磁场及探测光场等实现自动时序控制。6)由计算机控制实验中的光场和磁场，构建了吸收法测量原子数以及飞行时间荧光法、短程飞行时间吸收法测量冷原子等效温度的系统。并利用测量到的冷原子基本参数如冷原子云大小、冷原子数、冷原子温度优化磁光阱、偏振梯度冷却及光学晶格装载过程中的光场、磁场参数。7)在磁光阱冷却与俘获的基础上，实现了的亚多普勒冷却，借助短程飞行时间吸收信号研究了molasses冷却各个参数对冷原子温度的影响。8)建立了由四束线偏振光构成的3D近共振光学晶格系统，并成功实现了磁光阱冷却的冷原子到光学晶格的装载，在国内率先实现了铯原子的三维近共振光学晶格。铯原子在晶格中的等效温度约10μK，寿命大于70ms。同时以温度的测量为工具对光学晶格中Sisyphus冷却机制进行了实验和理论研究。更多还原

【Abstract】 Quantum optics focus on the interaction of atoms and light, in the domain the light can be used to prepare and control the quantum state of atoms or ions. Based on the atomic coherence, many quantum effects have been found. The information of the coherent process between pump and probe light fields and the atomic medium can be obtained via the probe absorption spectra. The electromagnetically induced transparency （EIT） and electromagnetically induced absorption （EIA） have become tools to prepare the quantum state in atomic vapour cell. In addition, laser cooling and trapping of neutral atoms could distinctly avoid the thermodynamic phenomena and processes and make the quantum effects emerge.The works in this thesis beginning with the basical lab configuration, step by step, we developed several homemade grating-external cavity diode lasers （ECDL） and realized the frequency stabilization. Then, with the homemade ECDLs, EIT and EIA coherent spectra have been experimentally investigated. But precision of these coherence spectra is also limited by the Doppler effect. By virtue of the laser cooling and trapping, we can prepare the atomic sample with a temperature of sub mK, in which the Doppler effect can be greatly inhibited. With the development of technologies of cold atoms, preparing and controlling of atomic quantum state shuld be realized. In this thesis main works are as followings:1) Based on the original ECDL configuration, we improve the design and assemble several ECDL systems. They all can be used to driver the transition of Cesium D2 line, with a frequency tunable range of approxinatly 2GHz.2) With the frequency reference of Cesium saturated absorption spectrum （SAS） or Fabry-Perot cavity and the modulation or modulation-free locking scheme, our homemade ECDL can be stabilized by a feedback loop, the frequency fluctuation is less than 1MHz in 50 seconds.3) Based on the degenerated two-level Cesium system 6²S_1/2F_g=3→6²P_3/2F_e=2 or 6²S_1/2F_g=4→6²P_3/2F_e=5, the EIT and EIA have been investigated via pump-probe spectra.The effect of the intensity and detuning of different coupling laser on EIT and EIA were also demonstrated in experiments. Within the Doppler background, optical pumping among Zeeman sublevels and the speed selection mechanism dominate the spectra.4) With a detuning-fixed intense coupling laser and a frequency scanning probe beam, three-level laser-driven atomic system can be described with the dressed atom picture. The Autler-Townes doublet is experimentally investigated in the doppler-broaded cesium vapor cell. In a Atype three-level system, sub-Doppler spectra have been observed via the probe absorption. And a novel spectra followed by probe scanning is realized by detecting the transmission of the coupling laser. The effects of coupling laser intensity on the splitting and linewidth of the Autler-Townes doublet are experimentally investigated.5) With red-detuning offset locking of cooling & trapping laser, the detuning of cooling laser can be convientialy controllable. By means of double-passed acoustic-optical-frequency shifting system,three pairs of circularly polarized cooling beams intersect at the center of ultrahigh vacuum chamber, vapor cell magneto-optical trap （VCMOT） is realized. About 107 cesium atoms with temperature of 30-50μK are prepared. With developing and improving the programmable controlling system, some external performance part such as voltage controlled oscillator （VCO）, acoustic-optical modulator （AOM）, radio frequency switch and Magnetic coil circuit switch can be controlled following a programmed time sequence. So the laser intensity, laser detuning and magnetic fields can be controlled.6) After the MOT is released, the cold atoms drop in gravitational field and expand freely with its initial velocity distribution. With the computer controlling of laser and magnetic fields, we setup the system for the fluorescence or absorption detection. So we can measure the number of cold atoms by probe absorption, and derived the temperature of cold atoms from traditional fluorescence time of flight （TOF） spectra or short distance TOF absorption spectra. By virtue of these results, we optimized the MOT, optical molasses and optical lattices parameters.7) Following the MOT, the further sub-Dopplerσ⁺-σ^- cooling stage are realized, the 3D optical molasses are domonstrated. Employing the short distance TOF spectra as a tools, we investigatd the optical molasses cooling.8) A four beams lin⊥lin 3D near resonace optical lattices （NROL） are constructed in the lab. We also successful transfer the atoms from MOT to optical molasses, at last to optical lattice stage. The intensity and detuning effects of lattice beams have been experimentally investiageted. Finally, atoms trapped in the optical lattice with thetemperature of 10μK have a life time about 70ms.更多还原