Investigation On Atomic Magnetometer In The Geophysical Field Ranee

Highly sensitive magnetometers capable of measuring magnetic fields are important for many applications such as geophysical surveying, space science, nuclear magnetic resonance, non-destructive testing, medical diagnoses and gravitational wave detection etc. This thesis is about the experimental implementation of measurement for magnetic field in the geophysical field range.We use a technique called coherent population trapping, which is usually observed with a bichromatic field consisting of two resonant laser fields with the frequency difference varying in the vicinity of the ground-state hyperfine splitting. In comparison with previous experimental configuration in atomic magnetometer by using circular polarization light, linear light scheme has raised a great deal of interest in atomic frequency references.The experimental results show that linear-linear transition scheme is a promising alternative to the conventional circular-circular transition scheme for atomic magnetometer. Comparing to circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometer. Therefore, linear-linear transition scheme provides a novel and promising atomic magnetometer prototype.We also demonstrate experimentally an atomic magnetometer based on optical pumping theory, a magnetic resonance induced by a radio frequency field, dependent on the magnetic field strength. The method is known since the1960’s and commercial lamp-based devices are used by archaeologists and geologists to measure variations of the earth’s magnetic field. Comparing to conventional amalgam vapor lamp magnetometer, diode laser pumped alkali magnetometer has significant advantages. It is generally known that fiber optics are non-magnetic, an optic fiber coupled device allows flexible location of the instrument without magnetic interference. And diode laser has the potential to be battery operated at room temperature, miniaturized, ruggedized for development of a compact magnetometer. Compare with the conventional method using one radiation field, which is used as not only probe beam but also pump beam, the additional re-pump beam can increase remarkably the amplitude of the signal. It is shown that the amplitude of magnetic field resonance signal can be increased more than55%by using an additional re-pump beam, which makes the magnetometer a higher sensitivity. We conduct a study on the modulation frequency influence the characterization of the signal, in the experiment, we increase the capture range by using a high modulation frequency. Finally, we investigate the relation between amplitude of the signal and re-pump laser power, and calculate the atomic population in the trapping states with density matrix equations. The physical interpretation has been given to show the validity of the results.The thesis is organized as following. In chapter one, we introduce current research and significance of magnetometer working in the geophysical field range. In chapter two, basic principles of magnetometer based on optical pumping are presented. In chapter three, we experimentally study the coherent population trapping magnetometer by linear polarization laser. In chapter four, we investigate the optical pumping magnetometer using two pump laser. Finally, we give a brief summary and promising prospect of the atomic magnetometer.