Akagi, T. Araki, S. Hajima, R. Honda, Y. Kosuge, A. Mori, M. Nagai, R. Shizuma, T. Terunuma, N. Urakawa, J. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-THPOA50 English 1204-1206 THPOA50 cavity ion laser electron photon Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-THPOA50 https://jacow.org/napac2016/papers/thpoa50.pdf High-energy photons from the laser Compton scattering (LCS) sources are expected to be applied in various fields in a wide range photon energies from keV to GeV. High-flux and narrow-bandwidth LCS photon beam is realized in an energy recovery linac (ERL). An electron beam of high-average current and small-emittance collides with accumulating laser pulses in an enhancement cavity for generating high-flux LCS photon beam. We have developed the high-finesse bow-tie ring cavity for the LCS experiment at the Compact ERL (cERL) in KEK. In this presentation, we will report the detail of the optical cavity.