|M.Sc Student||Sinay Asif|
|Subject||Mechanisms that Influence the Performance of Coherent|
Population Trapping Atomic Clocks
|Department||Department of Physics||Supervisors||Professor Jeff Steinhauer|
|Dr. Amit Ben-Kish|
|Full Thesis text|
The process of Coherent Population Trapping (CPT) occurs when a three-level atom interacts with two radiation fields, which are resonant with two of the possible transitions. It turns out that under certain experimental conditions, the atom does not absorb the radiation fields, contrary to the original situation of radiation field at resonance (namely, the atomic medium is transparent to the radiation field). This phenomenon occurs because the atom is trapped in a coherent superposition of the two lower states, and the upper state is not stimulated (hence the name of the phenomenon - "Coherent Population Trapping"). It also turns out that this behavior is extremely sensitive to the frequency detuning between the two radiation fields. Under certain conditions, a line width of several Hertz can be achieved for the CPT process.
In recent years, much research had been conducted with this extremely narrow line width for various applications, such as accurate frequency standards or magnetometers.
In this research we address the basic theory of the CPT and its applications as accurate frequency standards. We provide a more precise model with a seven-level model, instead of the regular three-level model, which is used for better understanding the CPT effect and to predict some of the phenomenons such as population pumping to the end states, re-pumping of population back to the clock transitions with other orthogonal beams with linear polarization, which are called here the "Pi beams" and depolarization in the ground and upper levels. Then we characterize a number of the CPT resonance attributes, such as the Radio Frequency (RF), the contrast and the Full Width of the Half Maximum (FWHM) as a function of the laser intensity at different optical density.
We also demonstrate the technique, which uses additional two other lasers to increase the population in the m=0 states. We show the predicted increase in contrast and also find an effect of increase in FWHM due to the Pi beams. We demonstrate a technique to increase the contrast without increasing the FWHM, and then calculate the frequency stability of our system.
Finally, we conclude our work, discuses the results and suggest further work.