Frequency stabilization of a laser system for Rydberg spectroscopy
Date of Issue2016-05-09
School of Physical and Mathematical Sciences
Our purpose in this final year project is to stabilize the 780 nm diode laser system . The method that is adopted in this project is to lock the frequency of the laser beam onto the resonant frequency of a stable Fabry-Perot cavity. The laser and the resonator are included in a feedback loop. This feedback loop continuosly calculate the difference between the frequency of the laser and the resonant frequency of the resonator to generate the error signal. This error signal is then fedback into the laser in order to counteract any shift in the frequency of the laser. In order to generate the anti-symmetric error signal, the laser beam is first modulated before being fed into the cavity. The variation of the laser beam will lead to the variation of the intensity of the laser beam that is detected from the cavity using a fast photodiode. The signal detected from the cavity is then compared with the modulation signal using the mixer. The output signal from the mixer gives us the information about which side the frequency of the laser beam is currently on with respect to the resonant frequency and the how the intensity of the laser beam transmitted through the cavity change corresponds to the shift of the frequency of the laser beam. This information is used as an error signal to move the frequency of the laser beam back to the resonant frequency. In this project, we focus on studying the three methods that are used to modulate the laser beam: the first method is to use the acousto-optic modulator (AOM), the second one is to use the electro-optic modulator (EOM) and the third one is to directly apply the modulation signal to the injection current of the laser.
Final Year Project (FYP)