Publications by authors named "Takahiro Kuga"

9 Publications

  • Page 1 of 1

A simplified 461-nm laser system using blue laser diodes and a hollow cathode lamp for laser cooling of Sr.

Rev Sci Instrum 2013 Jun;84(6):063101

Institute of Physics, The University of Tokyo, 3-8-1 Komaba, Tokyo 153-8902, Japan.

We develop a simplified light source at 461 nm for laser cooling of Sr without frequency-doubling crystals but with blue laser diodes. An anti-reflection coated blue laser diode in an external cavity (Littrow) configuration provides an output power of 40 mW at 461 nm. Another blue laser diode is used to amplify the laser power up to 110 mW by injection locking. For frequency stabilization, we demonstrate modulation-free polarization spectroscopy of Sr in a hollow cathode lamp. The simplification of the laser system achieved in this work is of great importance for the construction of transportable optical lattice clocks.
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http://dx.doi.org/10.1063/1.4808246DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3689831PMC
June 2013

Carbon nanotube/polymer composite coated tapered fiber for four wave mixing based wavelength conversion.

Opt Express 2013 Feb;21(3):3651-7

Department of Electrical Engineering and Information Systems, University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656, Japan.

In this paper, we demonstrate a nonlinear optical device based on a fiber taper coated with a carbon nanotube (CNT)/polymer composite. Using this device, four wave mixing (FWM) based wavelength conversion of 10 Gb/s Non-return-to-zero signal is achieved. In addition, we investigate wavelength tuning, two photon absorption and estimate the effective nonlinear coefficient of the CNTs embedded in the tapered fiber to be 1816.8 W(-1)km(-1).
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http://dx.doi.org/10.1364/OE.21.003651DOI Listing
February 2013

Saturated absorption spectroscopy of acetylene molecules with an optical nanofiber.

Opt Lett 2011 Apr;36(7):1254-6

Institute of Physics, University of Tokyo, 3-8-1, Meguro-ku, Komaba, Tokyo, 153-8902, Japan.

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 spectroscopy and serves as a practical low-cost wavelength reference in the optical fiber communication band.
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http://dx.doi.org/10.1364/OL.36.001254DOI Listing
April 2011

Precise intensity correlation measurement for atomic resonance fluorescence from optical molasses.

Opt Express 2010 Mar;18(7):6604-12

PRESTO, CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama, Japan.

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 definite bimodal structure with fast damped oscillation from the maximum value of 2.02(3) and slow monotonic decay toward unity. The oscillation can be understood as an interference between elastic and inelastic scattering fields in resonance fluorescence.
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http://dx.doi.org/10.1364/OE.18.006604DOI Listing
March 2010

Design of a high-Q air-slot cavity based on a width-modulated line-defect in a photonic crystal slab.

Opt Express 2008 Sep;16(18):13809-17

Institute of physics, University of Tokyo, Komaba, Tokyo, Japan.

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 mode is strongly enhanced inside the slot, allowing strong matter-field coupling and large interaction volume in free space. Using finite-difference time-domain method, we calculate the properties of the cavity mode as a function of the slot width. The calculated quality factor is still as high as 2 x 10(5) and the mode volume is as small as 0.14 of a cubic wavelength in a vacuum, even if 200-nm-wide slot is introduced to the PCS.
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http://dx.doi.org/10.1364/oe.16.013809DOI Listing
September 2008

Holographic storage of multiple coherence gratings in a Bose-Einstein condensate.

Phys Rev Lett 2007 Nov 29;99(22):220407. Epub 2007 Nov 29.

Institute of Physics, University of Tokyo, 3-8-1, Komaba, Tokyo 153-8902, Japan.

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 controllable delay, the gratings can be selectively converted into the light field also in a superradiant way. Because of the large optical density and the small velocity width of the condensate, a high conversion efficiency of >70% and a long storage time of >120 micros were achieved.
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http://dx.doi.org/10.1103/PhysRevLett.99.220407DOI Listing
November 2007

Superradiant light scattering from thermal atomic vapors.

Phys Rev Lett 2005 Mar 4;94(8):083602. Epub 2005 Mar 4.

Institute of Physics, University of Tokyo, 3-8-1 Meguro-ku, Komaba, Tokyo 153-8902, Japan.

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, revealing the Doppler-width-limited coherence time of the thermal gas and sudden buildup of long-lived coherence below the transition temperature.
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http://dx.doi.org/10.1103/PhysRevLett.94.083602DOI Listing
March 2005

Frequency stabilization of a laser diode with use of light-induced birefringence in an atomic vapor.

Appl Opt 2003 Nov;42(33):6645-9

Institute of Physics, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.

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) F' = 3 transition of 87Rb atoms. The achieved feedback bandwidth was approximately 100 kHz, and an efficient suppression of the frequency noise in a laboratory environment was attained.
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http://dx.doi.org/10.1364/ao.42.006645DOI Listing
November 2003

Control of light pulse propagation with only a few cold atoms in a high-finesse microcavity.

Phys Rev Lett 2002 Dec 15;89(23):233001. Epub 2002 Nov 15.

Institute of Physics, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.

Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.
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http://dx.doi.org/10.1103/PhysRevLett.89.233001DOI Listing
December 2002
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