High Resolution and High Sensitivity Laser Spectroscopy Using Non-Classical Light

我们已经开发了高分辨率和高灵敏度的新的激光光谱学方法，其原理与迄今开发的任何其他方法都有很大的不同。在目前的方法中，利用了自由振荡半导体激光器的特性，即非常稳定的输出功率(幅度)和导致谱线展宽的大频率(相位)噪声。所使用的现象是基于原子与这样的激光场的非线性相互作用。研究发现，这种激光场比单色激光场具有更大的自由度，从而携带了更多待研究的原子和分子的信息。提出和研究的第一种方法可以用一个简单的系统来实现，在该系统中，向样品施加半导体激光光束，并检测透射光强度的时间变化。对探测到的强度起伏进行了频谱分析，发现功率谱同时包括高分辨原子光谱，如塞曼光谱和基态和激发态的超精细光谱，它们的频率范围从100 kHz到1 GHz以上。这里提出的第二种类型是同位素选择光谱学，它使我们能够从混合气体样品中观察到特定同位素的吸收光谱。当激光频率通过各种同位素的吸收线扫描时，通过检测特定同位素的塞曼频率分量来进行同位素选择。上述激光光谱学方法对于特定情况下的原子特别有用。作为这样的原子，我们首次研究了超流氦中的中性原子，以及固体表面附近的气体原子。

We have developed new methods of laser spectroscopy with high resolution and high sensitivity, the principles of which are considerably different from any other methods developed so far. In present methods, the characteristics of a free-running diode laser is used, i.e.very stable output power (amplitude) and large frequency (phase) noise causing the broadening of the spectral line. The phenomena used are based on the nonlinear interaction of atoms with such a laser field. It was found that such a laser field has more degree of freedom than a monochromatic laser field, so that it carries more information of atoms and molecules to be studied. The first method proposed and studied can be realized by a simple system, where a diode laser beam is applied to the sample and the temporal variation of the transmitted light intensity is detected. Frequency-analyzing the detected intensity fluctuation, we have found that the power spectrum includes simultaneously high resolution atomic spectra, such as the Zeeman and hyperfine spectra in both the ground and excited states, which are in a very wide frequency range from 100 kHz to more than 1 GHz. The second type proposed here is the isotope-selective spectroscopy, which enables us to observe the absorption spectra of a particular isotope from the mixed gaseous sample. The isotope selection is made by detecting a Zeeman frequency component of a particular isotope, as the laser frequency is scanned through the absorption lines of of various isotopes. Above methods of laser spectroscopy is useful particularly for the atoms in a particular circumstances. As such atoms, we have made the first studies on the neutral atoms in a superfluid helium, and also on the gaseous atoms existing in the vicinity of the surface of solids.