The problem of propagation and interaction of optical radiation in dielectric waveguides is cast in the coupled-mode formalism. This approach is useful for treating problems involving energy exchange between modes. A derivation of the general theory is followed by application to the specific cases of electrooptic modulation, photoelastic and magnetooptic modulation, and optical filtering. Also treated are nonlinear optical applications such as second-harmonic generation in thin films and phase matching.

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Coupled-mode theory for guided-wave optics

A review of optical limiting mechanisms and devices using organics, fullerenes, semiconductors and other materials

In a thermodynamic treatment electromagnetic radiation of any kind is described. The difference between thermal and non-thermal radiation is accounted for by introducing the chemical potential of photons. Instead of an effective temperature all kinds of radiation have the real temperature of the emitting material. As a result Planck's law for thermal radiation is extended to radiation of any kind. The concept of the chemical potential of radiation is discussed in detail in conjunction with light-emitting diodes, two-level systems, and lasers. It allows the calculation of absorption coefficients, of emission spectra of luminescent materials, and of radiative recombination lifetimes of electrons and holes in semiconductors. Theoretical emission spectra are compared with experimental data on GaAs light-emitting diodes and excellent agreement is obtained.

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The chemical potential of radiation

A single‐threshold quantum‐utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite‐threshold device. Such a hot‐carrier flat‐plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.

Efficiency of hot-carrier solar energy converters

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes These are two nanostructured forms of sp2 carbon materials that are of major current interest These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp2 carbon materials, with particular emphasis given to the field of photophysics Some coverage is also given to the close relatives of these sp2 carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nano

Raman spectroscopy of graphene and carbon nanotubes

Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 A. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3 to 10−4 parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.The experiments are ...

Long‐Transient Effects in Lasers with Inserted Liquid Samples

Multiple-Phonon Resonant Raman Scattering in CdS

Radiative Recombination from Photoexcited Hot Carriers in GaAs

Due to residual absorption, a self‐induced negative lens is formed when molecular liquids are inserted in the path of a CW laser beam. This lens has a power‐dependent focal length which allows for its application as a power controller. Experimental results show that control under 3% is obtained for a CW argon laser.

The Thermal Lens Effect as a Power-Limiting Device

Light scattering experiments on semiconductors are discussed in which the energy of the incident photon from the laser or that of the Raman-scattered photon is nearly coincident with that of an electronic transition in the scatterer. Experimental data on ZnTe, CdS, InAs, ZnSe, and GaP are analyzed, and a discussion of LO-overtone scattering mechanisms is presented. Some additional experiments are proposed and discussed.

R. C. C. Leite

Papers

Long‐Transient Effects in Lasers with Inserted Liquid Samples

Multiple-Phonon Resonant Raman Scattering in CdS

Radiative Recombination from Photoexcited Hot Carriers in GaAs

The Thermal Lens Effect as a Power-Limiting Device

Resonant Raman Effect in Semiconductors