[en] We investigate the effects of the input laser beam's temporal pulse shape on a forward degenerate four-wave mixing (FDFWM) signal, assuming two-level saturable absorbers. Under conditions in which the coherence time is far shorter than the pulse-duration, we can calculate the signal easily in the time and frequency domains. From this result it is shown that, when the pulse duration is longer than ten times the population relaxation time, the calculated signal intensity is almost the same as that obtained by assuming a steady state throughout duration of the laser pulse. With this assumption, we obtain the signal by summing all the steady-state signals at each time-domain grid point during the pulse. The calculation is performed with three input beam temporal pulse shapes: square, Gaussian, and typical Q-switched pulses. After reaching a maximum, the signal intensity decreases. The rates of the signal increase and decrease depend strongly on the temporal shape of the input beam. For the same average power, the square-pulse input saturates the absorber faster than the other pulses. These results indicate that the weak part of the pulse input plays an important role in generating the signal, yielding differences in saturation behavior of the signal intensity and the spectral line shape. We compare the calculations with experiments by fitting the saturation curve of the FDFWM signal of argon atoms in a radio frequency inductively coupled plasma. Also, the spectral line shape of the DFWM signal is fitted with the calculation by use of published experimental data. Copyright 2001 Optical Society of America

[en] We have acquired images of polystyrene and fused-silica microsphere by using conventional optical microscopy, confocal microscopy and two-photon microscopy, and performed comparative analysis of these images. Different from conventional optical microscopy, confocal and two-photon microscopy had good optical sectioning capability. In addition, confocal microscopy and two-photon microscopy had better lateral resolution than conventional optical microscopy. These results are attributed to confocality and nonlinearity of confocal microscopy and two photon microscopy, respectively.

[en] In typical cavity quantum electrodynamics (QED)experiments, atoms traversing the optical cavity experience position dependent coupling constants due to the standing wave structure of the cavity mode. Most theories in the field of cavity QED, however, assume a spatially uniform coupling constant and even its tunability. We have realized this seemingly unrealistic feature by employing a nanopore lattice aperture along the path of the atoms. This specific aperture has nanometer scale holes in the form of a two dimensional lattice with a 791nm pitch, which is the same as the transition wavelength ("1"S"0"→"3"P"1")of atomic barium. Barium atoms that pass through this aperture interact with a high Q cavity in the cavity QED microlaser with an identical coupling strength. To reduce the spatial dispersion of the atomic beam, the cavity we newly fabricated has a special geometry so that the aperture can be placed very close (up to a distance of 500μm)to the cavity mode. When the horizontal position of the aperture is translated so as to make the vertical columns of nanopores aligned with the antinodes of the cavity, the atoms experience the maximum coupling. If the columns of nanopores and the nodes of the cavity field overlap each other, on the contrary, the atom cavity coupling vanishes. We have observed the controlled coupling constants by measuring the microlaser output as a function of the aperture translation. Our nanopore lattice technique provides a new opportunity to perform various cavity QED experiments with continuously tunable atom cavity coupling constants

[en] Resonance-enhanced degenerate four wave mixing is analyzed for two-level and three-level systems in both stedy-state and transient cases by means of a time-ordered Feynman-type diagrammatic representation. Particularly in the steady-state case, we introduce the atomic motional effects and field-polarization dependence into our diagrammatic analyses. Furthermore we present quantum-mechnical interpretations of the holographic analogy for the one-photon resonant case and the phenomenon of probe-beam amplification for any resonant case. (Author)

[en] This paper presents experimental evidence of enhancement of second-harmonic generation as a result of the combination of high electromagnetic mode density of states, low group velocity, and spatial phase locking of the fields near the photonic band edge

[en] The laser beam propagating through the resonant medium undergo severe deformation because of nonlinear interaction such as self-focusing, self-defocusing, etc. When strong pump beam coexists with the probe beam, propagation characteristics can be changed. We use samarium (Sm) vapor as the nonlinear medium. Probe laser is tuned around 4f⁶6s²⁷F₀ -> 4f⁶(⁷F)6s6p(¹P⁰) transition line of Sm (561.601 nm) and the pump laser is tuned around 4f⁶6s²⁷F₁ -> 4f⁶(⁷F)6s6p(¹P⁰) transition line of Sm (572.019 nm). The probe and the pump beams are Λ-type configuration. The transmission of the probe beam is changed as the intensity and the detuning of the pump beam are varied. The degree of self-focusing is also modified. (author)

[en] We have analyzed the statistical distribution of the fluorescence signal levels in a magneto-optical trap containing a few atoms and observed that it strongly depends on the relative size of the bin time with respect to the trap decay time. We derived analytic expressions for the signal distributions in two limiting cases, long and short bin time limits, and found good agreement with numerical simulations performed regardless of the size of the bin time. We found an optimal size of the bin time for minimizing the probability of indeterminate atom numbers while providing accurate information on the instantaneous number of atoms in the trap. These theoretical results are compared with actual experimental data. We observed super-Poisson counting statistics for the fluorescence from trapped atoms, which might be attributed to uncorrelated motion of trapped atoms in the inhomogeneous magnetic field in the trap

[en] We show that the optical mode filtering can be achieved by whispering gallery mode (WGM) microsphere that is in contact with a tapered-fiber. When the equator of the microsphere contacts with narrowest region of the tapered-fiber point by point, the WGM is well excited. We observed transmitted laser power of the tapered-fiber decreased about 15% at resonance with mode spacing of 2-3 GHz. This mode structure is due to the spitting of the degenerate modes of the microsphere caused by the deformation from perfect sphere.

[en] Spatial distortions, such as self-focusing, self-defocusing and conical emission, of the pulsed laser beam interacting with near-resonant samarium atoms are modified using electromagnetically induced transparency. Depending on the power and the detuning of the coupling and the probe lasers, beam shape is retrieved.

[en] We have measured the loading and loss rates in a magneto-optical trap only with a few atoms by directly counting atom-number changing events. Unambiguous formulas are presented for the calculation of those rates from a step-wise time sequence of the fluorescence of the trapped atoms. With a recently developed atom-number feedback technique we could efficiently measure the loading rate as a function of the magnetic field gradient for the initial number of trapped atoms of zero. We could also measure the one- and two-atom loss rates as functions of the trap laser intensity for a precisely prepared initial number of trapped atoms. Each of these rates has been measured independently by directly counting the corresponding atom-number-changing events, without any influence from or inference to the other rates