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光与原子之间的相互作用, 导致了许多有趣的现象, 如电磁感应透明 [1-2]、相干布居俘获 [3]、四波混频(four-wave mixing, FWM)[4-5]、无布居数反转光放大[6]等, 这些非线性过程诱发的原子相干效应极大地增强了介质的非线性极化率, 并在实际中得以广泛的应用. 特别是近年来, 人们在碱金属原子气体中, 通过参量FWM非线性过程, 产生紫外波段、红外乃至太赫兹波段的相干光源备受关注, 在自由空间的水下通信、量子信息处理、遥感、激光雷达等领域有广泛的应用前景[7-9]. Akulshin等[7]基于钠原子23Na 3S1/2-3P3/2-4D5/2-4P3/2-4S1/2-3P3/2能级系统, 实现了2.21 μm 相干红外光的输出. Lam等[8]基于铷原子85Rb 5S1/2-5P3/2-10D5/2-11P3/2-5S1/2菱形能级系统, 实现了311 nm相干准直紫外光的输出, 同时伴有3.28 THz 波的产生. 基于铯原子133Cs 6S1/2-6P3/2-11D5/2-12P3/2-6S1/2菱形能级系统, 实现了335 nm相干准直紫外光的输出, 也伴有其他多个跃迁通道的相干蓝紫光和THz 波的产生[9]. 更多的理论、实验研究是基于铷原子5S1/2-5P3/2-5D5/2-6P3/2-5S1/2能级系统, 实现了420 nm相干蓝光和5.5 μm红外光的产生[10-15], 通过优化实验参数[16-20]和建立光学腔[21-22]来增强相干420 nm蓝光的输出功率, 探究了种子光注入与自种子注入对相干蓝光的影响[23]. 也有为数不多的研究工作是基于铯原子133Cs 6S1/2-6P3/2-6D5/2(6D3/2)-7P3/2(7P1/2)-6S1/2菱形能级系统, 实现了455, 459, 861 nm相干光场的输出, 研究了种子光注入和自种子注入对相干光场产生的影响, 深化了通过参量FWM过程产生相干光场物理机制的理解, 拓展了其潜在的应用前景[24-26].
尽管本文所选取的铯原子菱形能级6S1/2 (F = 4)→6P3/2 (F' = 5)→6D5/2 (F'' = 6)→7P3/2 (F' = 5)→6S1/2 (F = 4) 是一个循环跃迁系统, 但由于原子之间的相互碰撞及麦克斯韦-玻尔兹曼分布, 必然有部分原子处于基态6S1/2 (F = 3)的超精细子能级, 从而制约了相干455 nm蓝光的输出. 类似于利用磁光阱技术冷却、俘获中性碱金属原子, 增加了一束894 nm的反抽运光将部分原子抽运回基态6S1/2 (F = 4)的超精细子能级, 实验证明可进一步增加相干蓝光的输出.
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图1为与实验相关的133Cs原子能级图, 为了在优化的实验条件下通过FWM过程频率上转换产生相干、准直蓝光, 选择了菱形6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)→7P3/2(F' = 5)→6S1/2(F = 4) 循环跃迁能级系统. 图2为实验装置示意图. 波长为852 nm的光栅外腔反馈半导体激光器(ECDL)作为一抽运光, 通过饱和吸收光谱(图2中未画出)将其频率调谐到铯原子6S1/2(F = 4)→6P3/2(F' = 5)共振跃迁线上; 波长为917 nm的ECDL作为另一抽运光, 工作于6P3/2→6D5/2跃迁线之间. 两抽运光束均为椭圆光斑 , 约2 mm × 3 mm. 在FWM实验中, 通常需要满足以下两个条件.
图 1 与实验相关的133Cs原子能级图
Figure 1. Energy levels of 133Cs involved in the 6S1/2-6D5/2 two-colour excitation and parametric FWM processes.
图 2 反抽运光增强相干455 nm蓝光的实验装置示意图(PBS, 立方偏振棱镜; HWP, 半波片; QWP, 四分之一波片; DM, 双色镜; M, 平面反射镜; Cs cell, 铯原子气室; Filter, 蓝光滤色片; PD, 光电探测器; PMT, 光电倍增管; Spectrometer, 光纤光谱仪)
Figure 2. Schematic of experimental setup for coherent 455 nm blue light enhancement via repumping laser (PBS, polarizing beam splitter; HWP, half wave plate; QWP, quarter wave plate; DM, dichroic mirror; M, mirror; Cs cell, cesium vapor cell; Filter, 455 nm blue filter; PD, photo diode; PMT, photomultiplier tube; Spectrometer, optical fiber spectrometer).
相位匹配条件:
$ ∆{\boldsymbol{k}} = {\boldsymbol{k}}_{852\; {\rm{nm}} }+ {\boldsymbol{k}}_{917\; {\rm{nm}} }- {\boldsymbol{k}}_{15.1\; {\text{μm}} }- {\boldsymbol{k}}_{455\; {\rm{nm}} }= 0_{ \text{, } } $ 式中,
$ {\boldsymbol k}_{i} $ 为参与FWM过程中的各光场的波矢,$ {k}_{i}=2\mathrm{\pi }/{\lambda }_{i}={\omega }_{i}n\left({\omega }_{i}\right)/c $ ,$ {\lambda }_{i} $ 为光波长,$ {\omega }_{i} $ 为角频率,$ n\left({\omega }_{i}\right) $ 为折射率,$ c $ 为真空中的光速, i = 852 nm, 917 nm, 15.1 μm, 455 nm.能量守恒条件:
$ {\omega }_{852\mathrm{ }\mathrm{n}\mathrm{m}}+{\omega }_{917\mathrm{ }\mathrm{n}\mathrm{m}}={\omega }_{15.1\mathrm{ }\text{μm}}+{\omega }_{455\mathrm{ }\mathrm{n}\mathrm{m}}. $ 为了使更多的原子参与FWM过程, 实验上让两抽运光束通过双色镜(DM)在一温度可控的铯原子气室(Cs cell 1: 长50 mm, 直径25 mm)中同向共线重合, 可满足上述条件: (1)式表明, 新产生的光场具有强烈的方向性; 从(2)式可知, 通过改变抽运光的频率, 使产生的相干蓝光在一定范围内频率可调.
铯原子在两抽运光的共同激励下, 由初态6S1/2(F = 4)布居到激发态6D5/2, 然后经中间激发态7P3/2级联辐射回到初态, 在这一参量FWM过程中, 辐射出15.1 μm (由于实验条件限制未探测)和455 nm的相干光场. 通过滤色片, 将产生的455 nm蓝光从两抽运光场中分离出来. 之后, 再通过半波片(HWP)和立方偏振棱镜(PBS)将455 nm蓝光分为两束, 一束到光电倍增管(PMT)探测, 另一束送到光纤光谱仪(fiber spectrometer: 380 nm—900 nm)进行分析. 探测器PMT距离Cs cell 1 的末端光学窗口约为 50 cm, 尽可能减小各向同性的455 nm荧光光子沿轴向进入探测器产生的影响. 为了便于研究抽运光偏振组合对相干蓝光的影响, 在DM前加各自波长的四分之一波片(QWP)对其偏振进行控制; 为了探究917 nm抽运光频率对相干蓝光的影响, 将两抽运激光各分出一部分激光, 在另一个铯原子气室(Cs cell 2)中反向共线重合, 在光电探测器(PD)处获得激发态6P3/2→6D5/2超精细能级之间跃迁的窄线宽光学双共振吸收光谱(OODR)[27-28], 其作为频率参考, 与PMT处的相干蓝光信号同时送入数字示波器存储记录. 在上述实验装置的基础上, 增加了一束波长为894 nm的激光作为反抽运光, 便于光路布置, 其通过DM与两抽运光束在Cs Cell 1 中反向重合. 反抽运光的光斑直径约为5 mm, 其频率调谐到6S1/2(F = 3)→6P1/2的跃迁线上, 从而将更多的原子布居到基态6S1/2(F = 4)超精细能级上, 进一步增加了相干455 nm蓝光的输出.
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当抽运光@852 nm的频率调谐到铯原子6S1/2(F = 4)→6P3/2(F' = 5)超精细跃迁线, 抽运光@917 nm的频率通过OODR光谱调谐到6P3/2(F' = 5)→6D5/2(F'' = 6)超精细跃迁线, 铯原子气室温度控制到约70 ℃时, 便可获得一束相干的455 nm蓝光. 图3为光谱仪记录到的相干蓝光信号, 插图为其通过二维光栅(50线/mm)的衍射图像, 说明其具有很好的相干性.
图 3 光谱仪探测到的相干455 nm蓝光信号, 插图为其通过二维光栅的衍射图像
Figure 3. Coherent 455 nm blue light observed by an optical fiber spectrometer, and the inset shows the interference pattern of the 455 nm blue beam through a diffraction grating with the 50 mm–1 lines.
相干455 nm蓝光信号强度对两抽运光场的偏振状态非常敏感, 如图4所示. 当两抽运光场为同方向的圆偏振光时, 原子倾向于布居到最大的塞曼子能级上, 级联激发原子由基态6S1/2(F = 4)经中间激发态6P3/2到激发态6D5/2效率最高, 故产生的相干蓝光信号最强; 反之, 当两抽运光场为相反的圆偏振时, 激发效率最低, 相干蓝光信号几乎探测不到; 两抽运光场为相互平行、或垂直的线偏振光时, 相干蓝光信号强度介于中间. 同时, 从图4可以看出, 在抽运光@917 nm频率近共振于6P3/2→6D5/2跃迁线处约200 MHz的范围, 均可实现相干455 nm蓝光的产生.
图 4 不同抽运光场偏振组合下, 相干455 nm蓝光信号随抽运光@917 nm频率失谐的变化. 抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)跃迁线, 抽运光@917 nm频率在6P3/2→6D5/ 2跃迁线之间扫描. 最上方黑色曲线为6P3/2→6D5/ 2跃迁的OODR光谱, 其作为频率参考; 其他曲线为来自光电倍增管PMT的相干455 nm蓝光信号
Figure 4. Profiles of the 455 nm coherent blue light at different combinations of the two pump lasers’ polarizations. The pump laser @852 nm is resonant on the 6S1/2(F = 4)→ 6P3/2(F' = 5) transition, while the pump laser @917 nm is scanned over the 6P3/2→6D5/2 transition. The upper curve represents the OODR spectrum between the 6P3/2→6D5/2 hyperfine transition as a frequency reference, and other curves are the 455 nm coherent blue light signals from the PMT.
实验上虽然已选择了菱形6S1/2(F = 4)→ 6P3/2(F' = 5)→6D5/2(F'' = 6)→7P3/2(F' = 5)→ 6S1/2(F = 4)的循环跃迁能级系统来优化相干蓝光产生的条件, 但由于气室中的原子服从麦克斯韦-玻尔兹曼分布, 以及原子之间、原子与气室内壁的碰撞, 必然有部分原子处于基态6S1/2(F = 3)的超精细子能级, 限制了相干蓝光的进一步产生. 在前述实验的基础上, 增加了一束894 nm反抽运光, 其频率扫描通过铯原子6S1/2(F = 3)→6P1/2超精细跃迁线, 功率约为5.8 mW. 此时, 两抽运激光频率共振于6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)超精细跃迁线, 功率分别约为31 mW和41 mW, 实验结果如图5所示. 图5上方黑色曲线为铯原子6S1/2(F = 3)→6P1/2跃迁时的饱和吸收光谱, 下方为反抽运光存在时在PMT上探测到的相干455 nm蓝光增强的信号, 并将其归一化(在其他实验参数完全一样, 仅反抽运光存在与否时相干蓝光强度的比值), 即信号背景为“1”代表反抽运光不存在时, 相干蓝光信号的相对强度. 从图5可看出, 当894 nm反抽运光频率扫描到6S1/2(F = 3)→6P1/2(F' = 3, F' = 4)共振位置时, 将更多的原子光抽运回菱形能级系统的初态6S1/2(F = 4), 显著增强了相干455 nm蓝光的输出, 高达4倍之多, 且增强的两个蓝光信号位置之间的频率间隔为1.167 GHz, 即激发态6P1/2超精细分裂的频率间隔, 见图1.
图 5 归一化的相干455 nm蓝光增强信号随894 nm反抽运光频率失谐的变化. 两抽运光852 nm和917 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)循环跃迁线, 894 nm反抽运光零失谐位置为6S1/2(F = 3)→6P1/2(F' = 4)超精细跃迁线. 图中上方黑色曲线为6S1/2(F = 3)→6P1/2跃迁的饱和吸收谱, 其作为频率参考
Figure 5. Normalized coherent 455 nm blue light intensity as a function of frequency detuning of repumping laser @894 nm from the 6S1/2(F = 3)→6P1/2(F' = 4) transition. The 852 nm and 917 nm pump lasers are resonant on the 6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6) transitions, respectively. The upper curve represents the SAS signal between the 6S1/2(F = 3)→6P1/2 transition as a frequency reference.
基于图5的实验结果, 后续实验中将894 nm反抽运光的频率调谐共振于6S1/2(F = 3)→6P1/2(F' = 4)的共振跃迁线上, 其功率约为5.8 mW, 系统地探究其对455 nm相干蓝光产生的影响. 图6(a)为反抽运光@894 nm存在与否时, 相干455 nm蓝光信号强弱的对比, 其中抽运光@852 nm的频率调谐到铯原子6S1/2(F = 4)→6P3/2(F' = 5)共振位置, 抽运光@917 nm的频率在6P3/2→6D5/2超精细跃迁线附近扫描, 铯原子气室温度控制到约70 ℃. 可以看出在相干蓝光信号最强的位置处, 反抽运光可将蓝光信号增强1.8倍. 图6(b)为归一化的相干蓝光信号强度随894 nm反抽运光功率的变化. 当反抽运光功率小于 3.0 mW时, 相干蓝光近乎呈线性增强, 随后趋于饱和.
图 6 (a) 894 nm反抽运光存在与否时, 相干455 nm蓝光强度的对比(抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)跃迁线, 抽运光@917 nm频率在6P3/2→6D5/ 2跃迁线之间扫描); (b) 归一化的相干455 nm蓝光强度随894 nm反抽运光功率的变化
Figure 6. (a) Comparison of coherent 455 nm blue light intensity versus the frequency detuning of pump laser @917 nm between the presence or absence of repuming laser @894 nm, when the pump laser @852 nm laser is resonant on the 6S1/2(F = 4)→6P3/2(F' = 5) transition; (b) normalized coherent 455 nm blue light intensity dependence of the power of repumping laser @894 nm.
相干准直455 nm蓝光强度除了受抽运光的偏振状态、频率失谐、反抽运光功率和频率失谐的影响之外, 还受抽运光功率以及铯原子气室温度的影响. 图7展示了反抽运光存在与否时, 相干蓝光信号强度随铯原子气室温度、抽运光功率变化的对比情况. 所用抽运激光器的运转情况与图6一致, 其他实验参数如下: 可用的抽运光@852 nm和抽运光@917 nm在Cs cell 1前的最大功率分别约为31 mW和41 mW; 反抽运光@894 nm在Cs cell 1前的功率固定约为5.8 mW, 实验中通过遮挡反抽运光来测量相关数据. 在固定两抽运光功率为最大值, 相干455 nm蓝光强度随铯原子气室温度的增加呈先上升后下降的趋势, 如图7(a)所示. 随着Cs cell 1温度的升高, 其内铯原子的数密度也相应增大, 频率上转换产生的相干蓝光强度必然增强直到最大; 随着气室温度的进一步升高, 有限的两抽运光功率随着穿透原子介质的深度增大而显著衰减, 以及原子介质的自吸收效应逐渐增强, 产生的相干蓝光又被原子介质吸收, 故最终输出的蓝光强度呈下降趋势. 在现有实验参数下, 输出的相干蓝光最强时, 优化的气室温度约为70 ℃, 对应的气室中铯原子数密度约为2.1 × 1012 cm–3.
图 7 反抽运光存在与否时, 相干455 nm蓝光强度随铯原子气室温度(a)、抽运光@852 nm功率 (b)、抽运光@917 nm功率(c)的变化. 抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)超精细跃迁线, 抽运光@917 nm频率在6P3/2→6D5/2跃迁线之间扫描. 反抽运光@894 nm频率共振于6S1/2(F = 3)→6P1/2(F' = 4)超精细跃迁线
Figure 7. Comparisons of coherent 455 nm blue light intensity versus the temperature of the Cs vapor cell (a), power of pump laser @852 nm (b), and power of pump laser @917 nm (c) between the presence or absence of 894 nm repumping laser: The pump laser @852 nm is resonant on the 6S1/2(F = 4)→6P3/2(F' = 5) transition, while the pump laser @917 nm is scanned over the 6P3/2→6D5/2 transition, and the repumping laser @894 nm is resonant on the 6S1/2(F = 3)→6P1/2(F' = 4) transition, respectively.
在优化的原子气室温度(约70 ℃)下, 固定其中一个抽运光功率为最大值, 测量相干455 nm 蓝光信号强度随另一抽运光功率的变化, 如图7(b)和图7(c)所示. 当抽运光@852 nm功率大于21 mW时, 相干蓝光信号强度随其功率呈明显的线性增长, 如图7(b)所示. 由图1所知, 激发态6D5/2上原子布居数在很大的程度上取决于抽运光@852 nm的强度, 只有当其大于某一值时, 才可能导致6D5/2-7P3/2形成布居数反转, 受激辐射产生15.1 μm的激光, 即FWM的第3个光场, 进而相干产生455 nm蓝光. 当固定抽运光@852 nm功率为最大值时, 显然中间态6P3/2上应有足够的原子布居, 因此抽运光@917 nm功率即便较弱时, 也观察到了相干455 nm蓝光的辐射, 如图7(c)所示. 在抽运光@917 nm功率小于15 mW时, 相干蓝光呈急剧上升, 直到最大值, 随后又呈缓慢下降的趋势: 一定强度的抽运光@852 nm, 只能将有限数目的原子由初态6S1/2(F = 4)布居到中间态6P3/2, 即便抽运光@917 nm功率再强, 产生的相干蓝光也依然有限, 且相对过强的抽运光@917 nm会导致铯原子相关能级的频移, 故蓝光强度又呈略微下降的趋势. 当开启反抽运光@894 nm时, 由于其频率共振于6S1/2(F = 3)→6P1/2(F' = 4)的超精细跃迁线, 有助于将更多的原子抽运到基态6S1/2(F = 4)超精细子能级, 从而显著增强了相干455 nm蓝光, 如图7所示.
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基于铯原子6S1/2(F = 4)→6P3/2(F' = 5)→ 6D5/2(F'' = 6)→7P3/2(F' = 5)→6S1/2(F = 4) 菱形能级系统, 在两抽运激光共同作用下将原子布居到激发态6D5/2, 通过参量FWM过程产生了455 nm的相干、准直蓝光. 详细测量、分析了相干蓝光信号强度随抽运光偏振、功率、以及原子气室温度的变化趋势. 尤其是增加了一束反抽运光, 将更多的原子由基态6S1/2(F = 3)抽运回初态6S1/2(F = 4)超精细子能级, 在各实验参数变化情况下, 实验证明均可有效增加相干455 nm蓝光的输出. 这一技术也适用于其他种类碱金属原子方面的实验, 特别是对于一些基于非循环跃迁线的菱形能级实验系统, 反抽运光增强相干激光的产生可能更有效, 在水下自由空间光通信领域有重要的应用价值.
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基于铯原子菱形能级6S1/2 (F = 4)→6P3/2 (F' = 5)→6D5/2 (F'' = 6)→7P3/2 (F' = 5)→6S1/2 (F = 4)系统, 在波长为852 nm (6S1/2→6P3/2)和917 nm (6P3/2→6D5/2)两红外抽运激光共同激励下, 通过四波混频过程频率上转换产生了波长为455 nm (7P3/2→6S1/2)的相干、准直蓝光. 实验上详细研究了抽运光偏振组合、功率、铯原子气室温度对蓝光强度的影响. 在此基础上, 通过增加了一束波长为894 nm (6S1/2 (F = 3)→6P1/2 (F' = 3, 4))的反抽运激光, 将更多的原子抽运回基态6S1/2 (F = 4)超精细能级, 显著增加了相干蓝光功率的输出, 在水下自由空间光通信领域等有一定的应用价值.We demonstrate the generation of coherent and collimated blue light (CBL) based on cesium (Cs) 6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)→7P3/2(F' = 5)→6S1/2(F = 4) diamond-type atomic system in a heated vapor cell. Two infrared pumping lasers with wavelengths at 852 nm (6S1/2→6P3/2) and 917 nm (6P3/2→6D5/2), provide step-wise excitation to the 6D5/2 excited state, and induce strong two-photon coherence between the 6S1/2 state and 6D5/2 state. The atoms undergo a double cascade accompanied with the amplified spontaneous emission at 15.1 μm via the 7P3/2 intermediate excited state, and produce a beam of 455 nm (7P3/2→6S1/2) CBL with highly spatiotemporal coherence through a parametric four-wave mixing process. We investigate the influence of experimental parameters such as polarization combination of the two pumping lasers, and their power, and the temperature of Cs vapor cell on the CBL. Especially, we add a beam of 894 nm laser operating at the 6S1/2(F = 3) →6P1/2 transition as repumping laser, which can pump atoms back to the 6S1/2(F = 4) state from the 6S1/2(F = 3) state, thus significantly improving the power of CBL. This technique of the CBL enhancement via optical pumping is also useful for the other alkali metal atoms.
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Keywords:
- four-wave mixing /
- nonlinear optics /
- frequency conversion /
- optical pumping
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图 1 与实验相关的133Cs原子能级图
Fig. 1. Energy levels of 133Cs involved in the 6S1/2-6D5/2 two-colour excitation and parametric FWM processes.
图 2 反抽运光增强相干455 nm蓝光的实验装置示意图(PBS, 立方偏振棱镜; HWP, 半波片; QWP, 四分之一波片; DM, 双色镜; M, 平面反射镜; Cs cell, 铯原子气室; Filter, 蓝光滤色片; PD, 光电探测器; PMT, 光电倍增管; Spectrometer, 光纤光谱仪)
Fig. 2. Schematic of experimental setup for coherent 455 nm blue light enhancement via repumping laser (PBS, polarizing beam splitter; HWP, half wave plate; QWP, quarter wave plate; DM, dichroic mirror; M, mirror; Cs cell, cesium vapor cell; Filter, 455 nm blue filter; PD, photo diode; PMT, photomultiplier tube; Spectrometer, optical fiber spectrometer).
图 3 光谱仪探测到的相干455 nm蓝光信号, 插图为其通过二维光栅的衍射图像
Fig. 3. Coherent 455 nm blue light observed by an optical fiber spectrometer, and the inset shows the interference pattern of the 455 nm blue beam through a diffraction grating with the 50 mm–1 lines.
图 4 不同抽运光场偏振组合下, 相干455 nm蓝光信号随抽运光@917 nm频率失谐的变化. 抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)跃迁线, 抽运光@917 nm频率在6P3/2→6D5/ 2跃迁线之间扫描. 最上方黑色曲线为6P3/2→6D5/ 2跃迁的OODR光谱, 其作为频率参考; 其他曲线为来自光电倍增管PMT的相干455 nm蓝光信号
Fig. 4. Profiles of the 455 nm coherent blue light at different combinations of the two pump lasers’ polarizations. The pump laser @852 nm is resonant on the 6S1/2(F = 4)→ 6P3/2(F' = 5) transition, while the pump laser @917 nm is scanned over the 6P3/2→6D5/2 transition. The upper curve represents the OODR spectrum between the 6P3/2→6D5/2 hyperfine transition as a frequency reference, and other curves are the 455 nm coherent blue light signals from the PMT.
图 5 归一化的相干455 nm蓝光增强信号随894 nm反抽运光频率失谐的变化. 两抽运光852 nm和917 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6)循环跃迁线, 894 nm反抽运光零失谐位置为6S1/2(F = 3)→6P1/2(F' = 4)超精细跃迁线. 图中上方黑色曲线为6S1/2(F = 3)→6P1/2跃迁的饱和吸收谱, 其作为频率参考
Fig. 5. Normalized coherent 455 nm blue light intensity as a function of frequency detuning of repumping laser @894 nm from the 6S1/2(F = 3)→6P1/2(F' = 4) transition. The 852 nm and 917 nm pump lasers are resonant on the 6S1/2(F = 4)→6P3/2(F' = 5)→6D5/2(F'' = 6) transitions, respectively. The upper curve represents the SAS signal between the 6S1/2(F = 3)→6P1/2 transition as a frequency reference.
图 6 (a) 894 nm反抽运光存在与否时, 相干455 nm蓝光强度的对比(抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)跃迁线, 抽运光@917 nm频率在6P3/2→6D5/ 2跃迁线之间扫描); (b) 归一化的相干455 nm蓝光强度随894 nm反抽运光功率的变化
Fig. 6. (a) Comparison of coherent 455 nm blue light intensity versus the frequency detuning of pump laser @917 nm between the presence or absence of repuming laser @894 nm, when the pump laser @852 nm laser is resonant on the 6S1/2(F = 4)→6P3/2(F' = 5) transition; (b) normalized coherent 455 nm blue light intensity dependence of the power of repumping laser @894 nm.
图 7 反抽运光存在与否时, 相干455 nm蓝光强度随铯原子气室温度(a)、抽运光@852 nm功率 (b)、抽运光@917 nm功率(c)的变化. 抽运光@852 nm频率共振于6S1/2(F = 4)→6P3/2(F' = 5)超精细跃迁线, 抽运光@917 nm频率在6P3/2→6D5/2跃迁线之间扫描. 反抽运光@894 nm频率共振于6S1/2(F = 3)→6P1/2(F' = 4)超精细跃迁线
Fig. 7. Comparisons of coherent 455 nm blue light intensity versus the temperature of the Cs vapor cell (a), power of pump laser @852 nm (b), and power of pump laser @917 nm (c) between the presence or absence of 894 nm repumping laser: The pump laser @852 nm is resonant on the 6S1/2(F = 4)→6P3/2(F' = 5) transition, while the pump laser @917 nm is scanned over the 6P3/2→6D5/2 transition, and the repumping laser @894 nm is resonant on the 6S1/2(F = 3)→6P1/2(F' = 4) transition, respectively.
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[1] Mohapatra A K, Jackson T R, Adams C S 2007 Phys. Rev. Lett. 98 113003
Google Scholar
[2] Yang B D, Gao J, Zhang T C, Wang J M 2011 Phys. Rev. A 83 013818
Google Scholar
[3] Vanier J 2005 Appl. Phys. B 81 421
Google Scholar
[4] Akulshin A M, Perrella C, Truong G W, McLean R J, Luiten A 2012 J. Phys. B: At. Mol. Opt. Phys. 45 245503
Google Scholar
[5] 冯啸天, 袁春华, 陈丽清, 陈洁菲, 张可烨, 张卫平 2018 物理学报 67 164204
Google Scholar
Feng X T, Yuan C H, Chen L Q, Chen J F, Zhang K Y, Zhang W P 2018 Acta Phys. Sin. 67 164204
Google Scholar
[6] Scully M O, Fleischhauer M 1994 Science 263 337
Google Scholar
[7] Akulshin A M, Bustos F P, Budker D 2018 Opt. Lett. 43 5279
Google Scholar
[8] Lam M, Pal S B, Vogt T, Gross C, Kiffner M, Li W H 2019 Opt. Lett. 44 2931
Google Scholar
[9] Gai B D, Hu S, Chu J Z, Wang P Y, Cai X L, Guo J W 2021 OSA Continuum. 4 2410
Google Scholar
[10] Zibrov A S, Lukin M D, Hollberg L, Scully M O 2002 2002 Phys. Rev. A 65 051801(R
Google Scholar
[11] Meijer T, White J D, Smeets B, Jeppesen M, Scholten R E 2006 Opt. Lett. 31 1002
Google Scholar
[12] Akulshin A M, McLean R J, Sidorov A I, Hannaford P 2009 Opt. Express 17 22861
Google Scholar
[13] Kienlen M B, Holte N T, Dassonville H A, et al. 2013 Am. J. Phys. 81 442
Google Scholar
[14] Akulshin A M, Budker D, McLean R J 2014 Opt. Lett. 39 845
Google Scholar
[15] Sebbag Y, Barash Y, Levy U 2019 Opt. Lett. 44 971
Google Scholar
[16] Vernier A, Franke-Arnold S, Riis E, Arnold A S 2010 Opt. Express 18 17020
Google Scholar
[17] Akulshin A M, Orel A A, McLean R J 2012 J. Phys. B: At. Mol. Opt. Phys. 45 015401
Google Scholar
[18] Cao R, Gai B D, Yang J, et al. 2015 Chin. Opt. Lett. 13 121903
Google Scholar
[19] Prajapati N, Akulshin A M, Novikova I 2018 J. Opt. Soc. Am. B 35 1133
Google Scholar
[20] Moreno M P, Almeida A A C, Vianna S S 2019 Phys. Rev. A 99 043410
Google Scholar
[21] Offer R F, Conway J W C, Riis E, Franke-Arnold S, Arnold A S 2016 Opt. Lett. 41 2177
Google Scholar
[22] Yuan J P, Liu H, Wang L R, Xiao L T, Jia S T 2021 Opt. Express 29 4858
Google Scholar
[23] Akulshin A M, Budker D, Mclean R J 2017 J. Opt. Soc. Am. B 34 1016
Google Scholar
[24] Schultz J T, Abend S, Döring D, Debs J E, Altin P A, White J D, Robins N P, Close J D 2009 Opt. Lett. 34 2321
Google Scholar
[25] Zhang Y Y, Wu J Z, He Y Y, Zhang Y, Hu Y D, Zhang J X, Zhu S Y 2020 Opt. Express 28 17723
Google Scholar
[26] Wu J Z, Xu Y H, Dong R G, Zhang J X 2021 Opt. Lett. 46 3119
Google Scholar
[27] Yang B D, Liang Q B, He J, Zhang T C, Wang J M 2010 Phys. Rev. A 81 043803
Google Scholar
[28] Yang B D, Zhang J F, Wang J M 2019 Chin. Opt. Lett. 17 093001
Google Scholar
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