title: Direct measurement of the group refractive index of air with interferometry between adjacent femtosecond pulses.
abstract: The group refractive index of air in laboratory conditions is measured directly between adjacent femtosecond laser pulses by a new interferometry technique. Measurement of the repetition rate of the mode-locked pulse train that gives the maximum amplitude of the interference-signal envelope enables us to determine the group refractive index of air within a standard deviation of 2 x 10(-7). This simple method without vacuum reference is attractive for measuring the group refractive index needed for precise distance measurements in open fields.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan. y-yamaoka@aist.go.jp
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Yamaoka
authors.forename: Kaoru
authors.initials: K
authors.lastname: Minoshima
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Matsumoto