15:30-16:00

Semi-classical theory for population inversion of two-level atoms using photonic crystals in three-dimensional systems

Population inversion, in which a population at the excited state is larger than that at the ground one, is necessary for stimulated emission of lasers. Since it is generally considered that steady-state population inversion of two-level atoms is impossible, three-level or four-level atoms with special energy levels are necessary. From the viewpoint of the quantum theory [1-2], however, it is predicted that photonic crystals (PC’s) composed of periodic dielectric materials enable population inversion of two-level atoms. In PC’s, there appear photonic band gaps (PBG’s) in which light in a certain frequency region cannot propagate, and then, large contrasts of electromagnetic local densities of states (EM LDOS’s) can be obtained in the vicinity of photonic band edges. Since spontaneous emission rates are proportional to EM LDOS’s, spontaneous emission can be controlled by PC’s.

In my previous study [3], I have confirmed the control of spontaneous emission and population inversion of two-level atoms in idealized one-dimensional (1D) and two-dimensional PC’s with infinite structures perpendicular to periodic directions, based on the semi-classical Maxwell-Bloch equations. In the semi-classical theory, while electrons are quantized to ground and excited states, electromagnetic fields are treated classically. In three-dimensional (3D) systems, however, structures are finite in any direction.

In this talk, therefore, I focus on the realistic 1D PC’s with finite structures perpendicular to periodic directions. In such structures, there appear pseudo PBG’s in which light leaks into air regions, unlike complete PBG’s. Nevertheless, these pseudo PBG’s provide large contrasts of EM LDOS’s in the vicinity of the upper photonic band edges. I show that the realistic 1D PCs’ enable the control of spontaneous emission and population inversion of two-level atoms even in 3D systems.

[1] M. Florescu and S. John, Phys. Rev. A 64, 033801 (2001).

[2] M. Florescu and S. John, Phys. Rev. A 69, 053810 (2004).

[3] H. Takeda and S. John, Phys. Rev. A 83, 053811 (2011).

Speaker

Dr. Hiroyuki Takeda, ICYS-Sengen Researcher, NIMS

Chair

Dr. Kazuaki Sakoda, Unit Director, Photonic Materials Unit, NIMS

16:00-16:30

Successful synthesis of nanostructured reduced titanium oxides using an easy-to-prepare reduction technique

In this talk, I will present a novel synthetic method to prepare nanostructured reduced titanium oxides. Recently, there has been an increasing interest in the synthesis of nanostructured reduced oxides because of their attractive properties, for example, reduced titanium oxides exhibit high electroconductivity and visible light absorption that TiO₂ does not possess. However, the synthetic approach to nanostructured titanium oxides has not been established yet, so development of such a navel technique is highly demanded to make full use of their fascinating properties. Very recently, I have overcome this problem by employing a low-temperature reduction method which allows us to synthesize nanoparticles of a corundum structure Ti₂O₃ from nanoparticles of a rutile structure TiO₂

Speaker

Dr. Yoshihiro Tsujimoto, ICYS-MANA Researcher, NIMS

Chair

Dr. Alexei Belik, MANA Independent Scientist, NIMS