Molecular amplified spontaneous emission in the far-infrared region

到目前为止，NO的8Sσ态是弱预离解态，在任何光谱区域都没有观察到荧光，而在27μm和14μm附近观察到了两个主要的ASE系统。从探测器在25μm以上的低量子效率来看，27μm波段的发射强度至少比14μm波段强两个数量级。27μm波段27μm附近的光谱系统被指定为8sσ^2Σ^+(ν=0)→7pσ^2Σ^+(ν=0)跃迁。观察到的转动结构符合R分支。相应的P分支位于28μm以上。向下跃迁到较低的pσ里德堡基团，如6.6m处的8Sσ→6pσ，是检测不到的。同时指出，在6Sσ→态中，不存在具有σn=2的Δpσ跃迁。无法检测到约23.5μm的8Sσ→7Pπ^2Π系统。这可能是由于8Sσ态的S~d混合导致了8Sσ→7Pπ和7dσ→7Pπ跃迁偶极子的相消干涉所致。类似的强度降低…当n=4、5和6时，发现了更多的nsσ→(n-1)pπ体系。未观察到从7pσ(ν=0)→7Sσ(ν=0到19μm附近的级联体系。14μm附近的系统归属于8sμ=0)σ(ν=0)→6f(ν=0)跃迁。这是首次发现nsσ→N‘finter-Rydberg酶违反ΔL=±1选择规则。跃迁力矩是由dσ特征和8sσ混合而成的。我们的分析表明，这些峰值属于P分支，其中6f态的量子数ι(轨道角动量在旋转轴上的投影)为+3。这与我们之前的4f(v=0)→SσE^2Σ^+(ν=0)ASE通道只对ι=+3开放的研究是一致的。当6f(ν=0，L=+3)能级由A^2Σ^+(ν=0直接填充时，ASE光谱被分配给6f THz5dμ跃迁的8→m附近的能带所主导。目前的观测表明，ASE分子可以用作σ区的准相干脉冲光源。当较高的(n[大于或等于]9)里德堡成员被激发时，激光制备的能级和相邻能级之间的能量差变得更小，潜在地产生更长的ASE波长。例如，10sσ^2Σ^+(ν=0)态和9pσ^2Σ^+(ν=0)态之间的能量差为~165 cm^-1，相当于60μm(约等于5.0太赫兹)。尽管连续调谐是不可行的，但分子的共生结构为我们提供了比原子发射更广泛的波长选择。较少

The 8sσ state of NO is weakly predissociative and no fluorescence has been reported at any spectral regions so far, whereas two major ASE systems were observed around 27 μm and 14 μm. Judging from the low quantum efficiency of the detector above 25 μm, the emission intensities of the 27 μm band is evaluated to be at least two orders of magnitude stronger than the 14 μm band.The 27 μm bandThe band system around 27 μm is assigned to the 8sσ ^2Σ^+(ν=0)→7pσ ^2Σ^+(ν=0) transition. The observed rotational structure accords with the R branch. The corresponding P branch is located above 28 μm. The transition down to the lower pσ Rydberg members such as 8sσ→6pσ at 6.6 μm is not detectable. The absence of the sσ→pσ transitions with Δn=2 has been also pointed out for the 6sσ state. The 8sσ→7pπ ^2Π system around 23.5 μm is undetectable. This may be caused by s 〜 d mixing in the 8sσ state, leading to destructive interference of the 8sσ→7pπ and 7dσ→7pπ transition dipoles. A similar intensity reducti … More on of the nsσ→(n-1)pπ ASE systems was found for n=4,5 and 6. Cascade ASE from 7pσ (ν=0)→7sσ (ν=0) around 19 μm was not observed.The 14 μm bandThe band system around 14 μm is assigned to the 8sσ(ν=0)→6f(ν=0) transition. This is the first observation of the nsσ→n'finter-Rydberg ASE which violates the Δl=±1 selection rule. The transition moment is derived from the mixing of dσ character with 8sσ. Our analyses revealed that the peaks belong to the P branch where the quantum number ι (projection of the orbital angular momentum l onto the rotational axis) in the 6f state is +3. This assignment is in good accordance with our previous investigation in which the 4f(v=0)→sσ E^2Σ^+ (ν=0) ASE channel was open only for ι=+3. When the 6f(ν=0,L=+3) levels are directly populated from A^2Σ^+(ν=0), the ASE spectra were dominated by the band around 8 μm assigned to the 6f→5dσ transition.The current observation implies that molecular ASE may be used as quasi-coherent pulsed light source in THz regions. As the higher (n【greater than or equal】9) Rydberg members are excited, the energy differences between the laser-prepared and the adjacent levels become smaller, potentially yielding longer ASE wavelengths. For instance, the energy difference between 10sσ ^2Σ^+(ν=0) and 9pσ ^2Σ^+(ν=0) states is〜165 cm^<-1>, corresponding to 60 μm (【approximately equal】 5.0 THz). Although continuous tuning is not feasible, robivational structures of molecules provide us with much wider choices of wavelength than atomic emissions. Less