Han Seb Moon

Double resonance optical pumping spectrum and its application for frequency stabilization of a laser diode

We present double resonance optical pumping (DROP) spectra for the 5P3∕2–4D3∕2 transition and the 5P3∕2–4D5∕2 transition of R87b and we use these spectra for frequency stabilization in the 1.5μm region. The spectra, compared to the conventional double resonance spectrum, show a good signal-to-noise ratio and a narrow spectral linewidth for laser frequency stabilization. The different intensities of the hyperfine states were attributed to the different rates of double resonance optical pumping into the other ground state. When we stabilized the frequency of a 1.5μm laser diode to the DROP spectrum, the best frequency stability was 1×10−11 after 100s.

Laser frequency stabilizations using electromagnetically induced transparency

We present two techniques to lock a laser frequency on an atomic transition line by using an electromagnetically induced transparency (EIT) signals, which give optical and electric feedback. We employed these methods to the D2 line of 87Rb atoms. Spectral characteristics of subnatural linewidth EIT allow us to improve frequency stability. By optical feedback of EIT signals, we were able to obtain locking bandwidths of 12 MHz, while frequency stability was 5×10−13 at best after 100 s of integration using a frequency modulation technique.

Coupling-intensity effects in ladder-type electromagnetically induced transparency of rubidium atoms

We have studied electromagnetically induced transparency (EIT) in the 5S1/2−5P3/2−5D5/2 ladder-type system of Rb. We observed relative changing magnitude of EIT hyperfine structures depending on not only the polarizations of the lasers but also the intensity of the coupling laser. The coupling-intensity effects are attributed to the nonlinear increase of the EIT signal to the coupling intensity. EIT signals nonlinear on the coupling intensity are analyzed by considering coherent interaction between atom and laser fields.

Dependence of electromagnetically induced absorption on two combinations of orthogonal polarized beams

We observed quite different spectra for electromagnetically induced absorption (EIA) in two cases where the polarizations of the lasers was orthogonally linear and counter-rotating circular, respectively. By using the density matrix equation we were able to try to confirm that the difference between them may result from the spontaneous transfer process occurring between subsystems within the system. The experimental results agree qualitatively well with the simulated spectra in the Doppler-broadened system.

Atomic coherence changes caused by optical pumping applied to electromagnetically induced absorption

We have investigated atomic coherence changes caused by optical pumping applied to electromagnetically induced absorption (EIA) occurring at the open system, which consists of the transition between the Fg = 2 ground state and the Fe = 3 excited state in the 85Rb D1-line. For optical pumping, another laser resonantly tuned to the transition between the Fg = 3 ground state and the Fe = 2 excited state was used. We found that the atomic coherence for EIA can be changed not by increasing the pumping rate but by pumping differently populations into the Zeeman sublevels in the Fg = 2 ground state, which is realized by changing the polarization of the pumping laser. The experimental results were able to be analysed by density matrix equations in the simple model system.

Amplification without Inversion in the Four-level N-Type 87Rb D1-Line

We demonstrate amplification without inversion in the 87Rb D1-line pumped by an incoherent light. A closed N-type, four-level atomic system has been considered to obtain an insight into the origin of the gain as well as the conditions under which the system exhibits gain without population inversion in bare states. We investigate the gain as a function of the incoherent pumping rate, the coupling laser detuning, and Rabi frequency. The experimental results are in good agreement with the numerical calculations considering the velocity distribution of atoms.

Observation of the Electromagnetically Induced Transparency and Dispersion - like Structure in Trapped Cs Atoms

We report experiemtnal results demonstrating the electromagnetically induced transparency (EIT) in trapped Cs atoms. EIT occurs at the Λ-type configuration where the re0-pumping laser simultaneously plays a role as the coupling laser in the presence of a magneto-optical trapping and weak magnetic fields. Dependences of EIT signal on both the intensity and the detuning of the coupling laser were investigated. Linear absorption spectra for cold cesium atoms in the magneto-optical trap have been observed and shown the pronounced dispersion-like structure with sub-natural linewidth of 1 MHz due to the cooling laser.