Generation Of Raman Light Source For Cold Atoms And The Laser Frequency Chain

The phase-locked two laser beams with a tunable and controllable frequency difference in the range of several GHz play a major role in the stimulated Raman transition, coherent population trapping, quantum state preparation and other researches in quantum manipulation. In recent years people have paid great attention to obtain it with simple and reliable means and several methods have been presented to create such kind of light source, such as:injection locking of two slave lasers with a laser modulated by AOM or EOM, injection locking of two slave lasers with the laser from the semiconductor laser with modulated current and coherent combining of the outputs of two semiconductor lasers using optical phase-lock loops. We have demonstrated the laser beams with a tunable frequency difference in the range of6.0GHz-9.3GHz. In particular, the frequency difference of6.835GHz and9.192GHz, corresponding to the ground state hyperfine splitting of Rb87and Cs133respectively, has been experimentally realized. The power of the modulated beam has been measured to be6.87mW which is high enough to generate deterministic single photons by the stimulated Raman Adiabatic Passage (STIRAP). With an antireflection-coated edge-emitting diode placed in an external cavity we can suppress the carrier completely when the modulation frequency is lower than4.0GHz by means of adjusting the external cavity length, the temperature, the current of the diode and power of the modulation. When the modulation is higher than4.0GHz we can’t fully suppress the carrier, but we can also get the laser beams with high modulation depth due to modulation enhancement by external cavity resonance. We can get the cw Raman laser easily by a mode filter, for example an etalon. Additionally, we discuss the scheme to prepare pulse Raman laser beams and deterministic generation of single photons based on the present experiment system.Another part of this thesis is the laser frequency chain, which plays an important role in locking the optical micro cavity of our new cavity QED system. We briefly introduce the history of the cavity QED experiment, the basic idea and mechanism of the laser frequency chain, its significance for the Cavity QED and the specific parameters of our new cavity QED system. We have also designed and made the transfer cavity for the laser frequency chain and tested the parameters. We have set up the laser frequency chain to lock two micro cavities and put forward into locking steps. It is demonstrated that the new transfer cavity is much more robust against the change of temperature than the former one. We can lock the852nm laser,828nm laser and the transfer cavity much better than the former frequency chain system. Hopefully the micro cavity can be locked much better. We will combine the laser frequency system and the cold atom system to study the entanglement of the two distant atoms in two cavities.