Electronic Properties of Materials

Quantum Mechanical Treatment of the Optical Properties (Optical Properties of Materials)

Introduction We assumed in the preceding topic that the electrons behave like particles. This working hypothesis provided us (at least for small frequencies) with equations which reproduce the optical spectra of solids reasonably well. Unfortunately, the treatment had one flaw: For calculation and interpretation of the infrared (IR) absorption we used the concept that electrons […]

Applications (Optical Properties of Materials) Part 1

Measurement of the Optical Properties The measurement of the optical properties of solids is simple in principle, but can be involved in practice. This is so because many bulk solids (particularly metals) are opaque, so that the measurements have to be taken in reflection. Light penetrates about 10 nm into a metal (see Table 10.1). […]

Applications (Optical Properties of Materials) Part 2

Optical Spectra of Pure Metals Reflection Spectra The spectral dependence of the optical properties of metals was described and calculated in topic 11 by postulating that light interacts with a certain number of free electrons and a certain number of classical harmonic oscillators, or equivalently, by intraband and interband transitions. In the present section we […]

Applications (Optical Properties of Materials) Part 3

Optical Spectra of Alloys It was demonstrated in the previous sections that knowledge of the spectral dependence of the optical properties contributes to the understanding of the electronic structure of metals. We will now extend our discussion to alloys. Several decades ago, N.F. Mott suggested that when a small amount of metal A is added […]

Applications (Optical Properties of Materials) Part 4

Insulators (Dielectric Materials and Glass Fibers) As we know, insulators are characterized by completely filled valence bands and empty "conduction" bands. Thus, no intraband transitions, i.e., no classical IR absorption, takes place. Furthermore, the gap energy for insulators is fairly large (typically 5 eV or larger) so that interband transitions do not occur in the […]

Applications (Optical Properties of Materials) Part 5

Helium-Neon Laser A cavity about 2 mm in diameter is filled with 0.1 Torr Ne and 1 Torr He (Fig. 13.36(a)). A current that passes through the gas produces free electrons (and ions). The electrons are accelerated by the electric field and excite the helium gas by electron-atom collisions. Some of the helium levels are […]

Applications (Optical Properties of Materials) Part 6

Laser Amplifier The laser can also function as an optical amplifier, which is again used for telecommunication purposes. A weak optical signal enters a laser through one of its windows and there stimulates the emission of photons. The amplified signal leaves the other window after having passed the cavity only once. This traveling-wave laser is […]

Applications (Optical Properties of Materials) Part 7

Organic Photovoltaic Cells (OPVCs) We interrupt now the description of light emitting devices and explain in this section how organic solar cells are working. Elucidating OPVCs at this point makes sense since we have already laid the ground for their understanding in the previous section. In short, the principal design of an organic solar cell […]

Applications (Optical Properties of Materials) Part 8

Optical Modulators and Switches When discussing electronic devices in Section 8.7.12, we encountered a digital switch that is capable of turning the electric current on or off by applying a voltage to the gate of a MOSFET. An equivalent optical device is obtained by making use of the electro-optical waveguide (Fig. 13.56). In the present […]

Applications (Optical Properties of Materials) Part 9

The Optical Computer We have learned in Section 8.7 that transistors are used as switching devices. We know that a small voltage applied to the base terminal of a transistor triggers a large electron flow from emitter to collector. The question arises whether or not a purely optical switching device can be built for which […]

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