Direct laser cooling molecule is useful way to obtain the accurate molecular spectroscopy. However, most of the reported direct laser cooling schemes are only involved the molecules with a singlet or doublet ground state because the one with a triplet ground state is more complex, especially when the first-excited state is not suitable for the pseudo-closed loop transition. Using NH as the prototype of the simplest heteronuclear molecule with a triplet ground state, we focus on constructing the direct laser cooling scheme with a pseudo-closed loop triplet-triplet transition including intervening electronic states. The potential energy curves and transition dipole moments are calculated for the X³Σ^-, a¹Δ, b¹Σ⁺, and A³Π states by using the multireference configuration interaction including spin-orbit coupling with the aug-cc-pV5Z basis sets. The rotational and vibrational energy levels of each electronic state are obtained by solving the Schrödinger equation of nuclear motion with the obtained potential energy curves. A two-color laser cooling scheme is established based on the ³Π₁→X³Σ^- transition because the highly diagonal Franck-Condon factors make the transition suitable for constructing the pseudo-closed loop transition. The radiative lifetimes, the Doppler temperature, and the recoil temperature are calculated to access the cooling effect of the optical scheme. The results demonstrate that the ³Π₁→X³Σ^- transition is much superior to the other transitions and the intervening a¹Δ and b¹Σ⁺ will not significantly impact the pseudo-closed loop transition of the laser cooling scheme. The accumulate FCF reach 0.99996 implies that about 25000 scattering photons are available before leaking, which can cool the NH molecule to the Doppler temperature of 20.2 μK.

直接激光冷却分子是获得精确分子光谱的有用方法。但是，大多数报道的直接激光冷却方案仅涉及具有单重态或双重态基态的分子，因为具有三重态基态的分子更复杂，尤其是当第一激发态不适合拟闭环时。过渡。使用NH作为具有三重态基态的最简单异核分子的原型，我们专注于构建具有包括电子态的伪闭环三重态-三重态跃迁的直接激光冷却方案。势能曲线和跃迁偶极矩计算为X ³ Σ ^- ，一个¹ Δ，B ¹ Σ ⁺，并且通过使用多参考配置交互（包括与aug-cc-pV5Z基集的自旋轨道耦合）来表示A ³。通过用获得的势能曲线求解核运动的薛定er方程，可以获得每个电子态的旋转能级和振动能级。基于A双色激光器冷却方案建立³ Π ₁ →X ³ Σ ^-因为高度对角线弗兰克- Condon因子使过渡适于构建伪闭环过渡的过渡。计算辐射寿命，多普勒温度和反冲温度以获取光学方案的冷却效果。结果表明³Π ₁ →X ³ Σ ^-过渡大大优于其他的过渡和中间一个¹ Δ和b ¹ Σ ⁺不会显著影响激光冷却方案的伪闭环过渡。累积的FCF达到0.99996意味着在泄漏之前大约有25000个散射光子可用，这可以将NH分子冷却到20.2μK的多普勒温度。