Physics and Engineering
The frequency of a laser-diode can be locked by providing a negative feedback voltage to the piezo-electric transducer in the laser cavity. By phase-modulating the light and placing side bands on the carrier frequency, the fluorescence of the atoms is modulated. The signal from this fluorescence is phase-sensitively compared with a phase-locked reference signal in a lock-in amplifier, and an asymmetric error signal is produced. With this feedback method a laser-diode is locked within a 75 Mhz doppler-broadened spectroscopic line width. The lock is robust enough to last a few hours at a time and is impervious to high amplitude, low frequency noise perturbations to the laser-diode and temperature changes that cause frequency drifting. The achievement and performance of this lock is essential for the stabilization of the five frequencies necessary to perform a magneto-optical trap of lithium atoms.
Peplinski, Brandon, "Phase Sensitive Detection: Frequency Locking of a Laser Diode for Lithium Cooling and Trapping" (2011). Honors Student Works. 3.
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