Abstract
Abstract In order to realize Bose－Einstein Condensation（BEC）of Rb87 atoms, we build a 500-mW high power laser as the trapping laser in this BEC experiment by utilizing injection-locking technology. In this master-oscillator-power-amplification （MOPA）work, we use the former trapping laser, a Hitachi HL7851G low-power diode laser, as the master laser and a modified SDL8630 diode laser as the optical amplifier. As a result, the optical amplifier provides more than ten times as much output power as the former trapping laser （master laser） did. Furthermore, it reserves the properties of the former trapping laser in terms of single mode and narrow linewidth： 18 plus or minus 1.4MHz for the optical amplifier and 16MHz for the master laser. In addition, both of the master laser and the optical amplifier oscillate at the same frequency, which is proven by the simultaneous emission of two fluorescence tracks at a certain wavelengthλA inside a Rb vapor cell. In this experiment, we observed that the output power of the optical amplifier periodically oscillate with the increasing driving currents of the master laser and of the optical amplifier separately. The peak-to-peak fluctuations of the output power are up to 137mW, which is nearly thirty percent of the maximum output power of 500mW. We show that this phenomenon is caused by the spectrally periodically oscillating transmission of the optical amplifier, which is indeed of an Fabry－Perot Resonator. Therefore, the output power of the high-power trapping laser can be adjusted and stabilized by tuning the driving current of the optical amplifier back and forth. Besides, a list of optimum operating condition for the MOPA system is given. According to the transition theory of a two-level atom, the number of the captured atoms in a magneto-optical trap is proportional to the output power of the trapping laser. Thus, we expect the high-power trapping laser to capture more than ten times as many cold Rb87 atoms as the previous low-power trapping laser did. This will increase the density of the cold Rb87 atoms in the trap to reach the critical condition for the transition into BEC. In the future BEC experiment, we suggest that a dual-wavelength MOPA system be manufactured in which two master lasers of different frequencies are injected into one single optical amplifier. Such a dual-wavelength MOPA trapping laser will cool and capture two species of atoms simultaneously, which helps the realization of two BECs at a time.