Nonlinear Laser Spectroscopy of vibrationally excited molecules using a high-finesse cavity

在第一年，外腔半导体激光器的光谱的1.65妈妈区域。这一年制造了精细度为300的光腔吸收池。共振辐射在腔内形成驻波，驻波波腹处的辐射功率比入射功率提高了150倍，这使得饱和光谱的实现变得容易。利用伺服回路，激光频率总是锁定在腔的谐振频率。在甲烷的泛音带上记录了饱和光谱。它的谱线宽度约为0.5MHz，比多普勒限宽290MHz小得多，因此在多普勒限宽谱中，某些重叠谱线可以清晰分辨。本文还建立了一个具有斯塔克电极的光腔吸收池，用于研究甲烷的斯塔克效应。由Stark位移的振幅确定的振动诱导永久偶极矩的大小与Coriolis子能级有明显的依赖关系，首次观察到这种依赖关系，并作了理论分析.利用该吸收池对乙炔的弱结合带进行了吸收光谱研究。由于辐射在腔中被多次反射，因此有效地增强了吸收长度。这种吸收池的吸收强度比单程吸收池的吸收强度大1000倍。腔的精细度被确定为1400，然而，这远小于从反射镜的反射率预期的10000。这种退化的主要原因可能是由于镜面上的斑点。钛蓝宝石激光器的频率与光腔共振不够稳定，无法观察到饱和光谱。

In the first year, an external-cavity semiconductor laser was constructed for spectroscopy of the 1.65-mum region. This year an optical-cavity absorption cell having a finesse of 300 was made. Resonant radiation forms a standing wave in the cavity, and the radiation power at the antinode of the standing wave is enhanced by 150 times larger than tha incident power, which makes it easy to perform saturation spectroscopy. With a servo loop, laser frequency is always locked at the resonant frequency of the cavity. Saturation spectrum has been recorded on the overtone band of methane. Its spectral Iinewidth is about 0.5 MHz, which is much smaller than Doppler width of 290 MHz, hoence some lines overlapped in Doppler-limited spectroscopy are cleary resolved. Another opical-cavity absorption cell having a pair of Stark electrodes has been built to study Stark effects of methane. The magnitude of the vibrationally-induced permanent dipole moment detarmined from easurements of the Stark shift shows a clear dependence on the Coriolis sublevels.This dependence is observed for the first time, and a theoretical anlysis has been made.An optical-cavity absorption cell was built using a pair of mirrors having a reflectivity of 99.97% around 790 nm. Using this cell, absorption spectroscopy of a weak combination band of acetylene was carried out. Because radiation is reflected many times in the cavity, an absorption length is effectively enhanced. Absorption strength in this cell is a thousand times larger than that in a single-pass absorption cell. A finesse of cavity is determined to be 1400, which is, however, far less than 10000 expected from the reflectivity of the mirrors. The main reason of this degrading is probably due to spots on the mirror surface. Frequency of a titanium-sapphire laser and the optical cavity resonance is not stable enough to observe saturation spectrum.