Investigations On Radiation With Millihertz Linewidth Based On Four Wave Mixing Scheme

Quantum frequency standard (also named as atomic clock) is one of the most important fields in precision spectroscopy and metrology. The achievements of quantum frequency standard have important applications to check the funda-mental theories, to observe new phenomena etc. for fundamental research; and also have promising applications foreground to establish new time standard and GPS etc. for social activities. The microwave atomic clock doesn't meet the in-creasing demand of scientific research and national activities, though it has been widely used. Optical atomic clock is regarded as outstanding candidate in com-parison to microwave atomic clock because of its high spectral resolution, and therefore the potential stability and accuracy. Hence, it has been world widely studied. However, most schemes for optical atomic clock are focused on the opti-cal transition profiles of absorption peaks, which demanding narrow line-width laser source. At present, the narrowest line-width of lasers is about 0.2 Hz. Hence, it is impossible to use such a laser to measure a narrower transition in atoms such as Sr, Yb. Our work, which using broad line-width laser sources to generate a much narrower one, is a proposal to overcome this difficulty.Under the supervision of Prof. HUANG and Prof. MA, in this research a new ultra-narrow radiation scheme and farther, a new optical clock scheme using Four Wave Mixing based on neutral atoms trapped in an optical lattice is theoretically investigated. This scheme mainly has 2 advantages:1. In the process of four wave mixing, each loop is closed in phase. The three frequency components of incident fields (with HMFW-1 Hz, HMFW: Half Maximum Full Width) can be obtained or can be locked (which can't be obtained from comb laser) from one comb laser, with their wave vectors being arranged in same direction, thus, the phase matching condition is easily satisfied.2. Since all wave-vectors for each laser are in same direction, then the recoil effect and other effects such as atoms heated by lasers, are sufficient small, empowering enough time to probe signals.In our work, the results show: a. the total AC Stark shift not equals 0:1. the AC Stark shift is helpful to enhance the intensity of four wave mixing signal; 2. the signal intensity can be at the level of 1 pW/mm2 with HMFW -10 mHz, once 105 atoms can be trapped in 1 mm3 volume. b. the total AC Stark shift vanishes:1. the radiation can be obtained at the level of 1 pW/mm2 with HMFW-10 mHz, if 106 atoms are trapped in 1 mm3 volume.2. the influence of incident fields interacting with non-resonant levels is sufficiently small (light shift (?) 1 mHz, line-width broaden: much smaller) to be safely ignored. This result can be suggested for optical clock experiment.Our results are expected to provide a new approach to experiments on real-izing ultra-narrow line-width radiations as well as optical clocks.