The Frequency Stabilization And Shifting Of Semiconductor Laser Diode

Cold atom is a hot spot in the field of physics research in recent years because of its contribution to the researches of basic physics, quantum physics and quantum information. Cold atoms were mainly got by laser cooling and trapping including"optical morasses"and Magneto-optical Trap.Laser source is a key factor in the experiment of atom cooling and trapping by laser. In this paper some works for the cooling and trapping of the Rb atoms by laser were introduced, including:(1)provide laser sources with narrow line-width and high stability.Cold atom is a kind of precise experiment, so it has a high level requirement for instruments and environment, especially in the Line width and stability of frequency of the laser source. The frequency of semiconductor laser used in the experiment is not stable ,in other words, it will shift a lot in long time. In order to overcome this disadvantage of semiconductor laser, we designed and realized a system to make the laser locked to the frequency of atom absorption spectrum by PI feedback control. We designed the PI controller with some amplifiers of high precision to improve the precision performance of laser frequency in stability. We also had some adjust part in the PI controller to accommodate some other environments. We had tested the system with the semiconductor laser. The result is that our system could lock the output frequency of the laser to the frequency of the absorption spectrum peak and it has ability of anti-inference and good performance of long time stability.(2)provide lasers of different frequency, and realize laser switch controlled by TTL signal to coordinate the time sequence control with other equipment.The cold atom experiment needs different kinds of laser in frequency to realize some different goals in physics. Our schematic is shifting the laser frequency with Acousto-optical Modulator. The main part of the work is to design a AOM driver. It generated a sin signal to make the AOM work. The frequency of the sin signal equals to the frequency offset of the laser. The frequency and amplitude of the signal could be adjusted. AOM driver was constituted by a VCO and microwave switches controlled by TTL signal.In the quantum memory experiment, it is necessary to read or write the quantum information of the cold atom by laser, so we need to have a on-off switch of the laser controlled by TTL signal. When the AOM works, the laser would not only have a offset in frequency but also have a deflection. With a grating was added after the AOM to block the laser without deflection. Then we could controlled the on-off switch of the laser by controlling the switch of the AOM driver. The test result is that the on-off isolation of AOM driver is -70dB; the switch rate– presented by the rising and falling time of the laser power signal detected at the end, was less than 100ns; the system delay was about 400ns, which could Meet the requirements of the experiment.