Y. Yoshikawa

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We present a simple modulation-free technique to stabilize a laser frequency to the Doppler-free spectra of an atomic vapor. Polarization spectroscopy with use of a balanced polarimeter allows us to obtain a background-free dispersion signal suitable for high-speed and robust frequency stabilization. We employed the method to the 5S(1/2) F = 2 --> 5P(3/2)(More)
Superradiant light scattering from noncondensed, thermal atomic vapors was experimentally studied. We found that superradiant gain is independent of quantum degeneracy and determined only by the shape of the atomic cloud and a contained number of atoms. Superradiant pump-probe spectroscopy was also developed to measure the atomic correlation function,(More)
[1] The accuracy of HF radar measurement in the Tsushima Strait is investigated. A comparison between radial velocities measured by HF radar and acoustic Doppler current profiler (ADCP), which provides an upper bound of HF radar measurement error, shows that the root-mean-square (RMS) velocity difference obtained from the principal component analysis is(More)
We have presented a novel design of a photonic crystal slab (PCS) nanocavity, in which the electric field of the cavity mode is strongly localized in free space. The feature of the cavity is a linear air slot introduced to the center of the mode-gap confined PCS cavity. Owing to the discontinuity of the dielectric constant, the electric field of the cavity(More)
We demonstrate a simple and versatile method for generating various configurations of optical vortices from a Gaussian light beam by using glass plates and an astigmatic mode converter (AMC). The glass plates are inserted into the Gaussian beam to imprint nodal lines along the edges, and the AMC then transforms the beam with the nodes into a vortex beam.(More)
We performed saturated absorption spectroscopy of acetylene (C₂H₂) ν₁ + ν₃ band transitions with an optical nanofiber (ONF). Owing to high-intensity light around the ONF, we observed a Lamb dip at relatively low-power laser (~10 mW) without a cavity. Our results showed that the simple ONF spectrometer is advantageous for performing saturation absorption(More)
We demonstrate superradiant conversion between a two-mode collective atomic state and a single-mode light field in an elongated cloud of Bose-condensed atoms. Two off-resonant write beams induce superradiant Raman scattering, producing two independent coherence gratings with different wave vectors in the cloud. By applying phase-matched read beams after a(More)
We measured the intensity correlation of true thermal light scattered from cold atoms in an optical molasses. Using a single-mode fiber as a transverse mode filter, measurement with maximally high spatial coherence was realized, allowing us to observe ideal photon bunching with unprecedented precision. The measured intensity correlation functions showed a(More)