| The wave nature of physical particle is a major discovery in the field of physics. Matter wave theory was first put forward by the French physicist de Broglie who believed that "ordinary" matter also has wave-particle duality. As de Broglie described, the meaningfulness of matter wave is that when we describe the nature of the matter particles we cannot simply consider the matter particle as individual particle, but rather as a combination of wave and particle. Similar to a coherent light field in classical optics, matter waves also have coherence property, and we can study the first-order coherence of matter waves through the interference effects of physical particles. Advances in atom cooling popularizes the study of matter wave’s coherence from the micro to the macro areas, such as the occurrence of the new state of matter, Bose-Einstein condensation (BEC), which greatly improved Bose gas’coherence length, so that physicists could produce high-contrast matter wave interference patterns in the experiment directly with the two BECs. The atomic gas above the critical temperature is generally considered to be a thermal gas, since the coherence length is very short, it is difficult to study the first-order coherence by directly overlapping two atom clouds to produce interference patterns. In this thesis, the first-order spatial coherence of ultracold Bose gas above the critical temperature is studied by use of phase modulation effect of a one-dimensional optical lattice on the 87Rb atomic gas in magnetic trap.The main works are as follows:1. A1064 nm laser is used to form ID optical lattice with which we have studied the first-order spatial coherence of ultracold Bose gas above the critical temperature in static-magnetic trap. First of all, the interference patterns of the thermal gas after applying a pulsed ID optical lattice are calculated theoretically. Second, the interference patterns of ultracold atomic gas above the critical temperature is also obtained from experimental absorption images. At last, by comparing the visibility of interference patterns obtained from theory and experiment, the properties of first-order spatial coherence are figured out. We find that when the temperature of ultracold atomic gas is very close to the critical temperature, the first-order spatial coherence of atomic gas is better than the thermal gas, and increasing the temperature above a sufficiently high temperature, the coherence of the ultracold atomic gas is the same as thermal gas’, which is determined by de Broglie wavelength.2. Using a balanced bi-polarimeter dispersion-like curve generated from polarization spectroscopy as frequency-discriminating signal, we have realized the frequency stabilization of a diode laser. Without the need of frequency modulation, the laser locked by using polarization spectroscopy will have a higher frequency stability than the laser locked by using traditional saturated absorption spectroscopy. The frequency of a semiconductor laser is locked to a balanced bi-polarimeter dispersion-like signal, which corresponds to the hyperfine component of 87Rb atoms 5 2S1/2 F=2â†'62P3/2 F’=3. After locking the laser, the frequency fluctuation is measured to be less than 0.46 MHz within 60 seconds, which is greatly improved comparing with about 2.6 MHz frequency fluctuation in the condition of free-running. The locked laser will be used for cooling 87Rb atoms in our upgraded... |
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