J. B. Kim

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.

Coherence control using the ratio of Rabi frequencies for complete coherent inversion in a four-level λ system

For the purpose of an examination of coherence control, we study the dynamics of population inversion in the four-level λ system where initial populations are arbitrary coherently distributed in two lower levels. It is shown that the coherence control, which causes population transfer between the lower levels to be forbidden, is possible by using the ratio of Rabi frequencies. Under this condition, it is remarkable that the adiabatic following and the optimal detuning methods are useful to invert the four-level system completely, and it is shown that the two-photon coherences of the coupled three-level ladders are dispersive and absorptive in the former and the latter methods, respectively. From the geometrical interpretation, the Bloch vectors, describing the four-level inversions, could be defined as ones in a two-level system.

Electromagnetically induced photonic bandgap in hot Cs atoms

Three-level Λ-type thermal Cs atoms are used to demonstrate the phenomenon of a photonic bandgap induced by quantum coherence with a standing wave (SW). We observed the transmitted signals of probe field driven by several kinds of SW, which are formed by a strong forward-traveling field and a backward-traveling field when a mirror reflects the forward-traveling beam. Considering Doppler inhomogeneous broadenings with a SW drive, we employ Fourier transformation to solve density-matrix equations for simulation results. The simulation results are found to be consistent with the experimental results.

Group velocity control of a light pulse using giant nonlinearities

In this paper, we propose and demonstrate a scheme to enhance nonlinearities of a probe pulse at both cross-phase modulation (XPM) and self-phase modulation (SPM) in a four-level system. Based on standing wave grating generated by counter-propagating resonant signal fields and an additional off-resonant coupling field, a giant nonlinear refractive index of the resonant probe field is obtained with absorption suppressed. Group velocity of the probe pulse can be controlled by both XPM and SPM nonlinearities.

Observation of electromagnetically induced photonic band gaps in hot two-level atoms

In this paper, two-level thermal Cs atoms are used to observe electromagnetically induced photonic band gaps with a strong symmetric and two types of asymmetric standing-wave (SW) driving fields. One main band and two sidebands are measured for the transmitted and reflected spectra. We carry out physical interpretation about the observations in SW-dressed atom picture and employ method of Fourier transformation to solve density-matrix equations for hot two-level system to simulate the experimental results. The numerical analyses are consistent with the experimental observations for properties of electromagnetically induced photonic band gaps.

Enhanced group velocity dispersion and nonlinearity for a weak field using quantum coherence

We propose a scheme in a four level atomic system to enhance group velocity dispersion and nonlinearity for a weak field using photonic bandgap created by quantum coherence with standing fields, where weak probe pulse propagates fast or slowly controlled by interaction between atoms and coherent fields.

Electromagnetically induced transparency and four wave mixing in coherently coupled Λ system

We have measured electromagnetically induced transparency (EIT) and four wave mixing (FWM) signals in a three level atomic system to enhance nonlinearity for a weak field due to quantum coherence with standing fields. We were able to observe quite different EIT signals according to a traveling or standing coupling field. (1) We obtained EIT and FWM signals depending on detunings, polarization, (2) and power of the coupling field. Our results will be analyzed theoretically in viewpoint of a photonic band gap model.

Saturated-absorption spectroscopy of weak-field Zeeman splittings in rubidium: comment

High-resolution saturated absorption spectroscopy of the 85RbD1 line has been used for observation of the Zeeman effect by use of a diode laser with a narrow linewidth. Experimental results were compared with both Breit–Rabi theory related to shifted resonant frequencies and Nakayamas single-cycle optical pumping theory related to signal magnitudes of signal [J. Opt. Soc. Am. B2, 1431 (1985)]. A comparison of our results with those of Bowie [J. Opt. Soc. Am. B12, 1839 (1995)], who used perturbation theory to obtain the energy-level shifts, yielded experimental results that differ significantly in some respects.