Why does a metal-superconductor junction have a resistance?

This is a tutorial article based on a lecture delivered in June 1999 at the NATO Advanced Study Institute in Ankara. The phenomenon of Andreev reflection is introduced as the electronic analogue of optical phase-conjugation. In the optical problem, a disordered medium backed by a phase-conjugating mirror can become completely transparent. Yet, a disordered metal connected to a superconductor has the same resistance as in the normal state. The resolution of this paradox teaches us a fundamental difference between phase conjugation of light and electrons.Comment: 12 pages, 5 postscript figures [v2: all figures inline

Excess noise in low Fresnel number unstable resonators

Numerical calculations of excess noise factors in low Fresnel number unstable resonators are described in detail. Computed mode profiles in one transverse dimension together with associated Petermann K-factors are presented; dynamical considerations such as injected wave excitation are also examined. The properties of the zero-order modes are consistent with virtual source theory and with a simple formula for K based on a geometrical optics approximation. While virtual source theory is asymptotic, we find that it can make good predictions for Fresnel numbers as low as unity. Full numerical calculations are however needed to determine accurate mode profiles and K-factors in some regimes. A new technique for calculating accurate higher-order mode profiles is also developed and this is employed to evaluate K-factor dependencies of the first two higher-order even modes

Brewster cross polarization

We theoretically derive the polarization-resolved intensity distribution of a TM-polarized fundamental Gaussian beam reflected by an air-glass plane interface at Brewster incidence. The reflected beam has both a dominant (TM) and a cross-polarized (TM) component, carried by a TEM(10) and a TEM(01) Hermite-Gaussian spatial mode, respectively. Remarkably, we find that the TE-mode power scales quadratically with the angular spread of the incident beam and is comparable to the TM-mode power. Experimental confirmations of the theoretical results are also presented. (C) 2009 Optical Society of Americ

Photon band structure in a sagnac fiber-optic ring resonator

\u3cp\u3eWe show experimentally that propagation of light waves in an effectively rotating fiber-optic ring resonator leads to a photon band structure due to interference of elastically scattered waves. The rotation is simulated by means of a Faraday-active element in the ring.\u3c/p\u3

Demonstration of a quasi-scalar angular Goos-Hanchen effect

We show experimentally that the angular Goos-Hanchen (GH) effect can be easily observed, also without employing its resonant enhancement at Brewster incidence. An s-polarized beam was used to decouple the polarization from the propagation dynamics of the beam. We found that, in this case, the angular GH effect can be strongly enhanced by increasing the angular aperture of the Gaussian beam. Our experiments suggest a route toward observing the angular GH effect for true scalar waves, such as acoustic waves and quantum matter waves. (C) 2010 Optical Society of Americ

Fractal modes in unstable resonators

One of the simplest optical systems, consisting of two mirrors facing each other to form a resonator, turns out to have a surprising property. Here we show that the peculiar eigenmodes of unstable resonators are fractals, a finding that may lead to a better understanding of phenomena such as chaotic scattering and pattern formation. Our discovery may have practical application to lasers based on unstable resonator

Diffractive origin of fractal resonator modes

The modes of unstable optical resonators possess fractal character. In this paper, the fundamental question of how and why fractals originate in one of the simplest linear optical systems is addressed. The answer is related to the fact that unstable resonator modes consist of a superposition of Fresnel diffraction patterns with effectively random phases. A connection is established between the mode eigenvalues and their fractal dimensions, and the consequent prediction that higher-order modes should exhibit lower fractal dimension is confirmed by numerical demonstration

Goos-Hanchen shift for a rough metallic mirror

We investigate experimentally the dependence of the Goos-Hanchen shift on the surface properties of an air-metal interface. The shift depends on the microscopic roughness of the metal surface but it is insensitive to the large-scale variations associated with surface non-flatness. Both an effective medium model of roughness and the Rayleigh-Rice theory of scattering are used to interpret the observed phenomenon. (C) 2009 Optical Society of Americ