Kyoungdae Kim

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.

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.

Slow light propagation in an atomic vapour under conditions of amplification without inversion

We report experimental results on slowing a light pulse in a system for amplification without inversion (AWI). We were able to control a subluminal group velocity continuously from Vg = c/2850 to c/7260 by just changing an incoherent pumping beam power from 0 to 12 mW in the AWI system. And several advantages, such as the controllable delay time and the pulse amplification, for slowing of the light in the AWI system compared to in an electromagnetically induced transparency system were found.

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.

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.

STUDENTS’ CONCEPTIONS ABOUT POLARIZED ELECTROMAGNETIC WAVES

A survey was conducted on students’ conceptions about polarized electromagnetic waves. Three research methods were used, including written responses, drawings, and interviews based on a questionnaire. As a result, students were found to have alternative conceptions of a plane wave related to the basic concepts of linear polarization. There was also a tendency to link an invisible EM wave with a visible water wave or rope wave. Furthermore, although most students were able to calculate the intensities of waves transmitted through two linear polarizers with an arbitrary angle between the transmission axes, they did not distinguish the mechanical structures from the polarization axes. As such, a slit was equated with a polarizer due to its similar geometrical description. Accordingly, the current results suggest that instruction on polarization should be based on the interaction between matter and light