Kyungwon An

We have demonstrated laser oscillation with one atom in an optical resonator. In our experiment a beam of $^{138}\mathrm{Ba}$ atoms traverses a single-mode cavity with a finesse of 8 \ifmmode\times\else\texttimes\fi{} ${10}^{5}$. The atoms are excited by a $\ensuremath{\pi}$ pulse from the $^{1}S_{0}$ ground state to the $^{3}P_{1}(m=0)$ excited state before they enter the cavity. Laser oscillation at 791 nm ($^{3}P_{1}\ensuremath{\rightarrow}^{1}S_{0}$) has been observed, with the mean number o

We have developed a new ring-down technique that does not require a shutter to turn a probe laser on and off. With a rapid cavity scan we can measure a simple exponential cavity decay from which a cavity finesse can be found. When the cavity is scanned slowly, the cavity decay exhibits an amplitude modulation, and an analytic expression is derived for this modulation. With this new technique we measured the ultraslow relative velocity of the mirrors (of the order of micrometers per second) as we

We have observed optical bistability caused by absorption-induced thermal expansion of mirrors forming a Fabry-Perot interferometer. From the resulting anomalous transmission line shapes, absorption coefficients of the mirror coatings as low as 0.2parts in 10(6) (ppm) have been successfully measured.

Reductions in hippocampal neurite complexity and synaptic plasticity are believed to contribute to the progressive impairment in episodic memory and the mild cognitive decline that occur particularly in the early stages of Alzheimer's disease (AD). Despite the functional and therapeutic importance for patients with AD, intervention to rescue or normalize dendritic elaboration and synaptic plasticity is scarcely provided. Here we show that overexpression of neuritin, an activity-dependent protein

The recent single-atom microlaser experiment [K. An et al., Phys. Rev. Lett. 73, 3375 (1994)], in which a stream of inverted two-level atoms is injected into an ultrahigh $Q$ cavity, can be understood in the context of a semiclassical four-level laser model. Transit time broadening due to short atom-cavity interaction time effectively introduces nonradiative decay of the two levels in the model. The steady-state solution of semiclassical photon and atom rate equations for the intracavity mean ph

We demonstrated traveling-wave atom-cavity interaction in the single-atom microlaser by tilting the atomic beam from its usual orientation of normal incidence with respect to the cavity mode. Laser-tuning curves, measured for various excitation pulse areas, are in good agreement with one-atom microlaser-maser theory.

We report laser oscillations in whispering-gallery modes (WGMs) of a microsphere with its cavity quality factor Q unchanged for varied optical pumping intensities well above the laser threshold. Laser gain was present only in the evanescent-wave region of the lasing WGM around the microsphere equator, and thus pumping-induced Q degradation could be minimized, resulting in Q values maintained at 8(2)×10 9 regardless of the pumping strength.

In the recently developed microlaser, a single two-level atom interacts with a single mode of the optical resonator to generate coherent radiation. The resonator mode is in the form of a standing wave. We present an analysis of the standing-wave features, based on an approximate solution of the fully quantized microlaser equations. The result explains the rapid increase in the observed signal when the average number of atoms in the cavity is of the order of 1.

Deflection of an inverted two-state atom by a standing-wave cavity vacuum is analyzed. It is shown that clean vacuum Rabi oscillations occur at a frequency of ${g}_{0}/2$ between the initial atom-field state and the state with the atomic transverse momentum displaced by $\ensuremath{\Elzxh}k$ if the cavity is tuned to the Doppler shift associated with the atomic motion along the cavity axis, given that the shift is much larger than the optimum atom-cavity coupling constant ${g}_{0}.$ Consequentl

A criterion for the validity of the single-atom approximation in the many-atom microlaser was proposed and its adequateness has been tested in semiclassical, quantum mechanical and quantum trajectory simulations. Through these studies we conclude that the single-atom approximation, employing the same emission probability formula for individual atoms as that of the single-atom micromaser theory is valid as long as the product of the atom-field coupling constant and the atom-field interaction time

The frequency of a commercial Ti:sapphire laser is stabilized directly relative to the Lamb-dip signal from an atomic vapor cell without the Fabry–Pérot cavity as in intermediate frequency reference. The laser spectrum is measured by means of a supercavity spectrum analyzer with a full width at half-maximum (FWHM) of 110 kHz, which is independently calibrated using a ring-down technique. The measured spectrum has a FWHM of 220 kHz, thus indicating the laser linewidth to be about 55 kHz RMS.

We report a schlieren-style stroboscopic phase-contrast field-amplitude imaging of two-dimensional acoustic whispering gallery modes in a circular shell cavity immersed in liquid. A schlieren signal is combined with a presplit reference beam to enable nonscan field-amplitude imaging. Excitation mechanisms of standing and traveling eigenmodes, respectively, are analyzed with acoustic ray simulations presented in a Poincaré surface of sections. The time evolutions for both standing and traveling e

Abstract We report operation of microcavity lasers based on the gain only in the evanes cent field region of whispering gallery modes. Two types of microcavities, microsphere and microcylinder, were used. First a cylindrical microcavity of 125 micron in diameter was surrounded by Rhodamine 6G dye molecules in ethanol solution of lower refractive index such that WGM's of the microcavity undergo laser oscillation when the dye molecules in the evanescent field region out side the cavity are excited