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产生的气体从一个小孔中喷出而产生的。然而，这种方法有一个缺点，即速度分布是广泛的，因为原子源是在热平衡。因此，热原子束的这个特征在用作功能束（诸如材料表面的探针和高能束源）时是一个问题。本项目的目的是利用高速调制半导体激光器实现单色原子束，常规激光器具有许多被称为横模的窄光谱，这些窄光谱不是激光控制原子运动所需的单一宽光谱。因此，我们研制了一种超高速调频半导体激光器，其振荡频率的变化快于原子自然寿命的倒数。比较了高频电流调制和频移反馈两种激光光源，并将其应用于原子束的速度控制。原子速度分布是通过绘制原子的发光强度扫描另一个单模激光的频率而获得的。验证了热原子束的速度分布在激光照射下发生变化。通过改变超高速调频激光器的中心频率和谱宽，得到了超高速激光器的速度分布，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的速度减小。结果，实现了高密度和单色的原子源。

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.