Browsing by Subject "Phase"

Now showing 1 - 3 of 3

Open Access
Control of the Responsivity and the detectivity of superconductive edge-transition YBa2Cu3O7-x bolometers through substrate properties
(Optical Society of America, 1999-08-01) Fardmanesh, M.; Scoles, K. J.; Rothwarf, A.
The detectivity D* limits of YBa2Cu3O7-x bolometer on 0.05-cm-thick crystalline substrates are investigated, and a method to increase D* to greater than 10(9) (cm Hz(1/2))/W at a 20-mu m wavelength is proposed. Because the response increases proportionally with the bias current I-b, whereas the noise near T-c (the transition or critical temperature) of our MgO and SrTiO3 substrate samples does not, an increase in D* of these samples is obtained by an increase in I-b. Another limiting factor is the de thermal conductance G(0) of the device, which, although controlled by the substrate-holder thermal boundary resistance for our samples, can be changed by means of thinning the substrate to increase D*. The optimal amount of thinning depends on the substrate's thermal parameters and the radiation modulation frequency. D* in our samples is also found to follow the spectral-radiation absorption of the substrate material.
Open Access
The Influence of the Rashba spin orbit coupling on the two dimensional magnetoexcitons
(IOP Publishing, 2011) Hakioglu, T.; Liberman, M. A.; Moskalenko, S. A.; Podlesny, I. V.
The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.
Open Access
Strongly linearly polarized low threshold lasing of all organic photonic quasicrystals
(Nature Publishing Group, 2012-09-04) Luo, D.; Du, Q. G.; Dai, H. T.; Demir, Hilmi Volkan; Yang, H. Z.; Ji, W.; Sun, X. W.
Lasing is obtained from a two-dimensional (2D) Penrose photonic quasicrystal made of a low index contrast material of holographic polymer dispersed liquid crystals (H-PDLCs) that enables a substantial reduction in the optical pumping threshold. This lasing architecture further allows for excellent linear polarization characteristics as well as wide directional dependence. The pumping threshold is fivefold lower than that obtained from the 2D defect-free photonic crystals fabricated under similar conditions. These properties make H-PDLC photonic quasicrystal promising for a new type of all organic miniature lasers.