Frequency Doubling With PPKTP Crystal At The Fundamental Wave Of 795nm (Rubidium D₁ Transition)

The development of cold atoms and cold molecular physics allow people to deeply understand the quantum properties of the interaction of light with matter. When the photons serve as the carrier of quantum information and atomic as quantum information storage medium, transfer of quantum states between light and atoms (quantum interface) has been paid more attention. In recent years, a new scheme, which use of the electromagnetic induced transparency (EIT) medium to store the quantum states of light field, is one of the important researches in quantum information science. To generate entangled light beams with the frequency doubling matched to the atomic absorption line or optical communication window is important in the quantum information science. Because Rb atoms with aΛ-type level structure of the system is a very good EIT media, developing non-classical light field whose frequency can be matching Rb atoms will be an important research contents. Firstly, we should obtain 397.5nm light by frequency doubling. Then we will get a 795nm squeezed states by using parametric down-conversion, and 795 entangled light. Lastly, we will carry out the research of storing quantum states in cold atomic ensemble of Rb.This paper demonstrates the experimental study of 795nm laser frequency doubling with periodically poled KTP crystal. We fires derived from Maxwell equations the three-wave coupled wave equation and the formula of the second harmonic process theory to analyze each parameter of the SHG efficiency in the formula multiplier efficiency, and introduced the quasi-phase matching. Pump source is composed by a 795nm grating feedback laser diode and tapered amplifier, resulting in a nearly continuous 400mW of 795nm single-frequency laser, and the output power of more than 100mW is obtained after shaping through a fiber. Firstly, we measured the relationship between efficiency of frequency doubling versus crystal temperature in the case of laser single passing through the crystal and got the effective work of the crystal temperature between 58℃to 60℃Then we gained nearly 14mW of 397.5nm laser by using resonant frequency doubling of a standing wave cavity nearly total of the heart, which had two concave mirror and radius of curvature are 30mm, and the frequency efficiency is 13% when the cavity length was 59.2mm and the crystal temperature was 55.9℃.Also, locking the cavity length through the sideband locking technology to obtain a more stable than 10mW output frequency light.We use Ti:Sapphire laser which has high-power,narrow linewidth,good spatial mode and low noise as the pump source to improve the experimental setup. We describe the Ti:Sapphire laser and preliminary results. At last, we comparative analysis of the experimental results by resonant frequency doubling of the two pump source, and propose a further improvement scheme.