monochromatic atomic beam
Generation of monochromatic beam of cesium atoms using semiconductor laser
we are developing a nano-fabrication method by controlling atomic motion based on laser light -atom interaction. Since the thermally generated atomic beam is broadened according to the Maxwell-Boltzmann distribution, the broadening should be narrowed. Thus we are trying to develop a technique to generate a monochromatic atomic beam for nano-fabrication using a laser cooling method.
In order to slow down atomic beam velocity, a white light cooling is a very simple method, which requires broadband laser source. Frequency modulated semiconductor lasers are very attractive because the spectrum can be easily broadened by a frequency modulation of the injection current. However, when the modulation depth is increased to increase the spectral width for compensating the Doppler broadened atomic beam, the spectral rise at the edge becomes broader resulting wider atomic velocity distribution. We proposed a two step deceleration method using two kinds of frequency modulated semiconductor laser sources to solve this problem.
Figure 1 shows a schematic for generation of monochromatic atomic beam we are developing. The upper and lower figures show distributions of the atomic beam and spectra of the laser for deceleration of the atomic beam, respectively. In a first step, the thermally generated atomic beam (①) are cooled by using a laser beam that has spectrum shown by ②. The resulting atomic velocity distribution will be presented by a curve ③. As a second step, a laser beam indicated by ④ whose spectrum is narrower than that of ② can make the atomic beam monochromatic as shown by ⑤.
In the experiment, a cesium atomic beam with narrower velocity distribution was obtained by the two step deceleration than ordinal single step deceleration.
1. T. Yoneyama and S. Sato, Two Step Deceleration of Cesium Atomic Beam by Frequency Modulated Diode Lasers, Optical Review, 12 (2005) 456. link
2. T. Hirayama and S. Sato, Velocity Control of Cesium Atomic Beam using Two Frequency-modulated External-cavity Diode Lasers, Jpn. J. Appl. Phys., 45, 8910 (2006). link
3. T. Hirayama, Y. Kozawa, T. Nakamura and S. Sato, Generation of a cylindrically symmetric, polarized laser beam with narrow linewidth and fine tunability, Opt. Express, 14, 12839 (2006). http://www.opticsexpress.org/abstract.cfm?id=121400