We report high-precision measurements on the thallium fluoride $\tilde{J}$ $=$ 1 hyperfine manifold of the$ B^{3}{1}(v =$ 0) state. This state is of special interest because it is central to an optical cycling scheme that is envisioned to play an important role in enhancing the sensitivity of the CeNTREX nuclear Schiff-moment experiment presently under construction. The measurements are made by monitoring the fluorescence induced by narrow-band laser excitation of a cryogenic molecular beam. We use a multipass arrangement of the laser beam to enhance fluorescence. When viewed with a camera, we can spatially resolve images from adjacent passes that approach the molecules from opposing directions. These images yield a sensitive visual method to identify the central frequency of a transition. Coupling these line-center determinations with frequency calibration from an acousto-optic modulator has allowed a more precise determination of the $\tilde{J}=$ 1 manifold of hyperfine level splittings. We observe Stark shifts of the $\tilde{J}=$ 1 levels and infer a permanent electric dipole moment of 2.28(7) D and -doublet splittings for the $F_{1\thinspace }=$ 1/2 and $F_{1\thinspace }=$ 3/2 manifolds of 14.4(9) MHz and 17.4(11) MHz, respectively. INTRODUCTION The thallium fluoride (TlF) $X^{1}\Sigma^{\mathrm{+\thinspace }}$state has been previously used to make precision tests of parity- and time-reversal symmetry violations [1-3]. The high mass of Tl and the high polarizability of the molecule make TlF ideal for measuring the Schiff moment of the Tl nucleus [4]. The TlF $B^{3}\Pi _{1\thinspace }(v_{e}_{\thinspace }=$ 0) $\leftarrow \quad X^{1}\Sigma^{+\thinspace }(v_{g\thinspace }=$ 0) transition has been proposed [5] as a candidate for optical cycling and laser cooling; such techniques could be effective for enhancing the sensitivity of symmetry violation measurements [6-8]. Here,$ v{g}$ and $v_{e\thinspace }$are the ground and excited state vibrational quantum number. Laser cooling and cycling as a means to enhance symmetry violation measurements has been proposed in other diatomic molecules such as BaF [9], RaF [10], and YbF [11-12] as well as polyatomic molecules like BaOH and YbOH [13-14]. The TlF $B^{3}\Pi_{1\thinspace }$state has resolved hyperfine (HF) structure. The HF interaction produces mixing of states with different rotational quantum numbers, $J$. This mixing can spoil the usual rotational selection rules and lead to branching to additional ground rotational levels, thus compromising optical cycling. Therefore, in order to achieve optical cycling, it is critical to understand the rotational and HF structure of the excited states and their effects on rotational branching. In earlier work, the $X $state HF and rotational energies were determined by high-resolution microwave spectroscopy [15] and the rovibrational energies of the $B^{3}\Pi_{1\thinspace }$state were determined by low-resolution spectroscopy with a pulsed UV laser [16]. Recently, high-resolution laser spectroscopy of the $B^{3}\Pi _{1\thinspace }(v_{e}_{\thinspace }=$ 0) …

中文翻译：

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氟化thB3Π1态的分子偶极矩和超精细和Λ-双分裂的测量

我们报告了氟化fluoride的高精度测量 $\widetilde{Ĵ}$ $=$ $ B ^ {3}的1个超精细流形{1}（v = $ 0）状态。该状态特别令人关注，因为它对于光学循环方案至关重要，该方案可在增强目前正在建设的CeNTREX核席夫矩实验的灵敏度中发挥重要作用。通过监测由低温分子束的窄带激光激发引起的荧光来进行测量。我们使用激光束的多通道布置来增强荧光。当使用相机查看时，我们可以在空间上解析来自相邻方向的图像，这些方向从相反的方向接近分子。这些图像产生了一种灵敏的视觉方法来识别过渡的中心频率。将这些线心确定与声光调制器的频率校准相结合，可以更精确地确定$\widetilde{Ĵ}=$1个超细级裂口。我们观察到$\widetilde{Ĵ}=$1级，并推论$ F_ {1 \ thinspace} = $ 1/2和$ F_ {1 \ thinspace} = $ 3/2的流形14.4（ 9）MHz和17.4（11）MHz。简介氟化th（TIF）$ X ^ {1} \ Sigma ^ {\ mathrm {+ \ thinspace}} $状态以前曾用于对奇偶校验和时间反转对称性违规进行精确测试[1-3]。T1的高质量和分子的高极化率使T1F成为测量T1核席夫矩的理想工具[4]。Tlf $ B ^ {3} \ Pi _ {1 \ thinspace}（v_ {e} _ {\ thinspace} = $ 0）$ \ leftarrow \ quad X ^ {1} \ Sigma ^ {+ \ thinspace}（v_ {g \ thinspace} = $0）已经提出过渡[5]作为光学循环和激光冷却的候选；这样的技术可以有效地提高对称性违规测量的灵敏度[6-8]。在此，$ v {g} $和$ v_ {e \ thinspace} $是基态和激发态振动量子数。在其他双原子分子（例如BaF [9]，RaF [10]和YbF [11-12]）以及多原子分子（例如BaOH和YbOH [13-]中，已经提出了激光冷却和循环作为增强对称性违反测量的一种手段）。 14]。TIF $ B ^ {3} \ Pi_ {1 \ thinspace} $状态已解析超精细（HF）结构。HF相互作用产生具有不同旋转量子数的状态的混合，$Ĵ$。这种混合会破坏通常的旋转选择规则，并导致分支到附加的地面旋转级别，从而损害光学循环。因此，为了实现光学循环，了解激发态的旋转和HF结构及其对旋转分支的影响至关重要。在较早的工作中，$ X $状态的HF和旋转能通过高分辨率微波光谱法确定[15]，而$ B ^ {3} \ Pi_ {1 \ thinspace} $状态的旋转振动能量由低能级确定。脉冲紫外激光的高分辨率光谱[16]。最近，$ B ^ {3} \ Pi _ {1 \ thinspace}（v_ {e} _ {{thinspace} = $ 0）的高分辨率激光光谱仪…