Efficient Stimulated Slowing Of MgF Diatomic Molecules In Bichromatic Beams

Laser cooling of molecules is one of the hottest topics in the field of atomic and molecular optics. Recently people generally achieve the laser cooling using the method of Doppler slowing and cooling, but some problems, such as the compensation of the Doppler shift, have not been solved successfully. This paper proposed a new scheme for the laser cooling of molecules theoretically, which used the bichromtic force exerted on the molecules in the bichromatic beams to make the molecular beam slow efficiently. Then in the experiment we invented a new technique to lock the frequency of laser in the long term, by which we successfully controlled long-term frequency deviation of the dye laser to 2MHz.Theoretically we should solve the problem of compensation of the Doppler shift, we proposed a scheme using bichromatic force to slow the molecules, which is suitable to the small molecules whose Frank-Condon factors are mostly diagonalizable, such as MgF and SrF. This method needs two laser beams whose frequencies are almost the same and some repumping beams. Compared with the laser cooling with radiative force this scheme is simplified, because the need of compensation of the Doppler shift is eliminated, which is meaningful. This paper introduced the physical image of the production of the bichromatic force and the Optical Bloch Equations (OBEs) of the molecules in the bichromtic beams has been derived. We also attained the numerical solving of the OBEs by using programming language. In the end we have done the Monte-Carlo simulation of the bichromic slowing of MgF molecular beam, which showed the properties of the bichromatic slower.In the experiment of laser cooling of molecules, some laser beams with long-term stability are needed. Due to the special wavelength of the cooling laser and the requirement of frequency tuning, we proposed a new technique of frequency locking which combined the PDH locking and the scanning transfer cavity. This technique is applied on the dye laser successfully for the first time and achieved a dye laser beam with narrow linewidth and high long-term stability, which provided a good laser for the laser cooling of MgF molecules. In the experiment we built a system of data acquirement and designed a Labview program, with which we realized the frequency locking in the long term successfully.