1. Fan, H.Y., Jiang, N.Q.: Phys. Scr. 78, 045402 (2008)
2. Louisell, W.H.: Quantum statistical properties of radiation. Wiley, NY (1973)
3. Fan, H.Y., Xu, X.F.: Opt. Lett. 29, 1048 (2004)
4. Takahashi, Y., Umezawa, H.: Collective Phenom. 2, 55 (1975)
5. Wan, Z.L., Fan, H.Y.: Acta Phys. Sin. 64(10), 190302 (2015)