American Physical Society (APS) Acta Medica Okayama 2469-9926 113 4 2026 Analytical and numerical studies of periodic superradiance 043713 EN Hideaki Hara Research Institute for Interdisciplinary Science, Okayama University Yuki Miyamoto Research Institute for Interdisciplinary Science, Okayama University Junseok Han Research Institute for Interdisciplinary Science, Okayama University Riku Omoto Research Institute for Interdisciplinary Science, Okayama University Yasutaka Imai Research Institute for Interdisciplinary Science, Okayama University Akihiro Yoshimi Research Institute for Interdisciplinary Science, Okayama University Koji Yoshimura Research Institute for Interdisciplinary Science, Okayama University Motohiko Yoshimura Research Institute for Interdisciplinary Science, Okayama University Noboru Sasao Research Institute for Interdisciplinary Science, Okayama University We conduct a theoretical study to understand the periodic superradiance observed in an Er:YSO crystal. First, we construct a model based on the Maxwell-Bloch equations for a reduced level system, a pair of superradiance states, and a population reservoir state. Analysis of the eigenvalues of the linearized differential equations shows that periodic superradiance can be realized only for certain parameters. We also derive two-variable equations consisting of the coherence and population difference between the two superradiance states, which contain the essential feature of the periodic superradiance. The two-variable equations clarify the mathematical structure of this periodic phenomenon and give analytical forms of the period, pulse duration, and number of emitted photons. Our model successfully reproduces the periodic behavior, but the actual experimental parameters are found to be outside the parameter region for the periodic superradiance. This result implies that some other mechanism(s) is (are) required. As one example, assuming that the field decay rate varies with the electric field, the periodic superradiance can be reproduced even under the actual experimental conditions. No potential conflict of interest relevant to this article was reported.

American Physical Society (APS) Acta Medica Okayama 2643-1564 6 1 2024 Periodic superradiance in an Er:YSO crystal 013005 EN Hideaki Hara Research Institute for Interdisciplinary Science, Okayama University Junseok Han Research Institute for Interdisciplinary Science, Okayama University Yasutaka Imai Research Institute for Interdisciplinary Science, Okayama University Noboru Sasao Research Institute for Interdisciplinary Science, Okayama University Akihiro Yoshimi Research Institute for Interdisciplinary Science, Okayama University Koji Yoshimura Research Institute for Interdisciplinary Science, Okayama University Motohiko Yoshimura Research Institute for Interdisciplinary Science, Okayama University Yuki Miyamoto Research Institute for Interdisciplinary Science, Okayama University We observed periodic optical pulses from an Er:YSO crystal during irradiating with a continuous-wave excitation laser. We refer to this phenomenon as "periodic superradiance." This periodicity can be understood qualitatively by a simple model, in which a cyclic process of a continuous supply of population inversion and a sudden burst of superradiance is repeated. The excitation power dependences of peak interval and the pulse area can be interpreted with our simple model. In addition, the linewidth of superradiance is much narrower than an inhomogeneous broadening in a crystal. This result suggests that only Er3+ ions in a specific environment are involved in superradiance. No potential conflict of interest relevant to this article was reported.

Springer Acta Medica Okayama 14346044 79 2019 Raman stimulated neutrino pair emission 684 EN Hideaki Hara Research Institute for Interdisciplinary ScienceOkayama University Motohiko Yoshimura Research Institute for Interdisciplinary ScienceOkayama University A new scheme using macroscopic coherence is proposed to experimentally determine the neutrino mass matrix, in particular the absolute value of neutrino masses, and the mass type, Majorana or Dirac. The proposed process is a collective, coherent Raman scattering followed by neutrino-pair emission from | e of a long lifetime to | g ;.0 + | e .. + i j.i. j + | g with.i. j consisting of six massive neutrino-pairs. Calculated angular distribution has six (i j) thresholds which showup as steps at different angles. Angular locations of thresholds and event rates of the angular distribution make it possible to experimentally determine the smallest neutrino mass to the level of less than several meV, (accordingly all threemasses using neutrino oscillation data), the mass ordering pattern, normal or inverted, and to distinguish whether neutrinos are ofMajorana or Dirac type. Event rates of neutrino-pair emission, when the mechanism of macroscopic coherence amplification works, may become large enough for realistic experiments by carefully selecting certain types of target. The problem to be overcome is macro-coherently amplified quantum electrodynamic background of the process,.0 + | e .. +.2 +.3 + | g , when two extra photons,.2,.3, escape detection. We illustrate our idea using neutral Xe and trivalent Ho ion doped in dielectric crystals. No potential conflict of interest relevant to this article was reported.