title: Boiling effect in liquid nitrogen directly cooled Yb³⁺:YAG laser.
abstract: Liquid nitrogen (LN2) behavior on the surface of excited Yb(3+):YAG is investigated using fluorometry. From the time-resolved temperature variations and integrated fluorescence spectra intensity on this directly cooled Yb(3+):YAG surface, we observe a phase transition of LN2 from nucleate boiling to film boiling. As a result of this pool boiling, good beam quality should occur when the temperature and heat flux at an excited surface of Yb(3+):YAG are below 95 K and 15.8  W/cm2, respectively. That is, the LN2 should remain in a steady state of nucleate boiling to produce good beam quality using pool boiling.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Sakurai
authors.forename: Haik
authors.initials: H
authors.lastname: Chosrowjan
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Furuse
authors.forename: Seiji
authors.initials: S
authors.lastname: Taniguchi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kitamura
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujita
authors.forename: Shinya
authors.initials: S
authors.lastname: Ishii
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Izawa