Abstract
In this thesis, the progress for creation of dilute gas rubidium Bose-Einstein condensation in the National Tsing Hua University is described. The experimental apparatus features a single MOT, a MOPA laser system, an ultrahigh vacuum system, and a 3-coils Ioffe-Prichard (IP) magnetic trap. The procedure adopted here to lead us to the BEC transition is that we collect atoms from background vapor by a dark-SPOT, CMOT and polarization gradient cooling is employed, and then load the trapped atoms into a magnetic trap and evaporate the trapped atoms. The procedure is discussed step by step in this thesis. Chapter 1 describes the main components of the experiment. First, it outlines the laser system consisting of five diode lasers and gives an introduction to their purposes. Second, the ultrahigh vacuum system in this experiment is described . It consists of a single pyrex cell, an ion guage, rubidium getters, titanium sublimation pump, and an ion pump. With this vacuum system, the pressure within the vapor cell is about 10^-11 torr. Third, the imaging system is described. The behavior of saturation of absorption imaging is discussed, too. Furthermore, the specifications of magnetic coils and experimental timing control are also summarized in this chapter. In Chapter 2 the dark-SPOT employed to collect atoms from background vapor is described. Some questions about dark-SPOT in section 2.1 are answered in order to introduce the behavior of dark-SPOT. To measure the number of atoms, we use two methods, fluorescence detecting method and optical pumping method. Besides, the measurement of lifetime is done by a nondestructive method. Chapter 3 describes the way we further compress the MOT. It also gives an brief explanation for the purpose of CMOT. The remainder of this chapter is employed to introduce the implementation of polarization gradient cooling and time of flight (TOF) technique. Chapter 4 introduces the theory of magnetic trapping, magnetic field, and potential transformation of the 3-coil IP trap. It also describes the process of magnetic loading and adiabatic compression. In order to control the current flowing through coils, we use MOSFETs to control power supplies. The wiring diagram of coils and current controller are shown in this chapter, too. Chapter 5 introduces the principal of evaporative cooling in a magnetic potential. The RF source and antenna are also described in this chapter. Finally the latest result of evaporative cooling is shown.