Study on high density and monochromatic atomic beam by ultra-high speed frequency modulation laser

一般来说，原子束是由一小部分热生成的气体从一个小孔径喷发而产生的。然而，这种方法有一个缺点，即由于原子源处于热平衡状态，速度分布较宽。因此，热原子束的这一特性在用作功能性束流，如材料表面探针和高能束流源时是一个问题。本课题的目的是利用高速调制半导体激光器实现单色原子束。传统的激光器有许多窄谱，称为横向模式，而不是一个单一的广谱，需要由激光控制原子运动。因此，我们开发了一种超高速调频半导体激光器，其振荡频率变化快于原子自然寿命的倒数。对高频电流调制技术和频移反馈技术进行了应用和比较。这些激光源通过照射原子束来控制原子速度。原子速度分布是通过绘制原子扫过另一个单模激光器频率的发光强度得到的。验证了热原子束在激光照射下速度分布的变化。通过改变超高速调频激光器的中心频率和谱宽，速度分布随激光器参数的变化而变化。换句话说，多普勒频移对应于激光频率的原子速度减小。结果，实现了高密度单色原子源。

In general, atomic beam is generated by eruption of a small part of thermally generated gas from a small aperture. However, this method has a drawback that the velocity distribution is broad because the atomic source is in thermal equilibrium. Thus, this feature of the thermal atomic beam is a problem when used as a functional beam such as a probe of material surface and an energetic beam source. The purpose of this project is to realize a monochromatic atomic beam by using a high-speed modulation semiconductor laser.Conventional lasers have many narrow spectra called transverse mode, which are not a single broad spectrum required for atomic motion control by the laser light. Therefore, we developed an ultra-high speed frequency modulation semiconductor laser, of which the oscillation frequency varies faster than the reciprocal of the natural lifetime of the atom. High frequency current modulation and frequency-shifted feedback techniques are applied and compared.These laser sources were applied to control the atomic velocity by irradiating to an atomic beam. The atomic velocity distribution was obtained by plotting luminescence intensity from the atoms sweeping the frequency of an another single mode laser. It was verified that the velocity distribution of the thermal atomic beam changes by the laser irradiation. By changing the center frequency and the spectral width of the ultra-high speed frequency modulation laser, the velocity distribution, the distribution change followed the change of the laser parameter. In other words, the velocity of the atoms which Doppler shift corresponds to the laser frequency decreased. As a result, a high density and monochromatic atomic source was achieved.