Keisuke Nakamura

<jats:title>Abstract</jats:title><jats:p>We have developed a Yb-doped fiber amplifier (YDFA) using fusion splicing, and characterized its performance with numerical simulation, achieving a continuous output of above <jats:inline-formula><jats:alternatives><jats:tex-math>$10~{\mathrm{W } }$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>10</mml:mn> <mml:mspace /> <mml:mi>W</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> of <jats:inline-formula><jats:alternatives><jats:tex-math>$1064~{\mathrm{nm } }$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>1064</mml:mn> <mml:mspace /> <mml:mi>nm</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> light. The device has been conceptualized to have a configuration as simple as possible; a strategy for using fiber amplifiers in harsh environments where quick repairs and replacements may become necessary at unexpected times.</jats:p>

<jats:p>We have realized a comb system with a 30 GHz mode spacing, 62 % available wavelength coverage in the visible region, and nearly 40 dB spectral contrast by combining a robust erbium-doped-fiber-based femtosecond laser, mode filtering with newly designed optical cavities, and broadband-visible-range comb generation using a chirped periodically-poled LiNbO<jats:sub>3</jats:sub> ridge waveguide. Furthermore, it is suggested that this system produces a spectrum with little change over 29 months. These features of our comb will contribute to fields requiring broad-mode-spacing combs, including astronomical observations, such as exoplanet exploration and the verification of the cosmic accelerating expansion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We developed a laser frequency stabilization and an optical fiber transmission system for the the francium electric dipole moment search. The absolute accuracy of a laser frequency stabilization scheme using a state-of-the-art commercial wavelength meter was 0.48 MHz at ±2 nm and -1.33 MHz at ±200 nm from calibration wavelength, respectively, and the frequency instability is below 10<jats:sup>-9</jats:sup> with a standard deviation of 0.56 MHz over 60 hours. We also demonstrated that a 400 m long fiber laid between laboratories can transmit 30 mW of trapping laser light, which is sufficient for a magneto-optical trapping of francium. The polarization crosstalk in the fiber was stable at -25 dB over 12 hours of measurement.</jats:p>