Optical radiation

7 Optical radiation (frequency range 3-1011cps to 3-1015cps, wavelength range 1 mm to 0.1 xm) 

Optical radiation - especially in the infrared range - can be absorbed by combustible gases and vapours by oscillatory transitions of the molecules and cause an increase in temperature. In addition, the radiation may be absorbed by non-metallic solids and effect a temperature rise up to a value sufficient to ignite them or the surrounding gas-air or vapour-air mixtures. 

E = electric field strength vector H = magnetic field strength vector 

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In order to describe the second-order nonlinear response from the interface of two centrosynnnetric media, the material system may be divided into tlnee regions the interface and the two bulk media. The interface is defined to be the transitional zone where the material properties—such as the electronic structure or molecular orientation of adsorbates—or the electromagnetic fields differ appreciably from the two bulk media. For most systems, this region occurs over a length scale of only a few Angstroms. With respect to the optical radiation, we can thus treat the nonlinearity of the interface as localized to a sheet of polarization. Fonnally, we can describe this sheet by a nonlinear dipole moment per unit area, -P ", which is related to a second-order bulk polarization by hy P - lx, y,r) = y. Flere z is the surface nonnal direction, and the... 

Schawlow A L and Townes C H 1958 Infrared and optical lasers Phys. Rev. 112 1940 Maiman T H 1960 Stimulated optical radiation in ruby Nature 187 493 Milonni P W and Eberly J H 1988 Taser (New York Wiley)... 

Many lens casters use the term hard-resin lenses for DADC products companies and trade names include American Optical (Aoflte ), Cobum (Supremacy I), Optical Radiation (Orcoflte), and Silor Optical (Orma 1000). Additional information can be obtained from the Optical Manufacturers Association, Falls Church, Va. Cast sheets of homopolymer and copolymers are suppHed by the SGL Homalite Company, Foster Grant, and others. 

Figure 4.25. Experimental configuration for optical pyrometry of shock temperatures induced in transparent minerals. Upon impact of projectile with driver plate, a shock wave is driven into the driver plate and then into the sample. Optical radiation from the sample is detected via six lens/interference filter channels and an array of six photodiodes. Signals from photodiode circuits are recorded on oscilloscopes operating in single sweep model. (After Ahrens et al. (1982).)...

Collecting optics, radiation detectors and some form of indicator are the basic elements of an industrial infrared instrument. The optical system collects radiant energy and focuses it upon a detector, which converts it into an electrical signal. The instrument s electronics amplifies the output signal and process it into a form which can be displayed. There are three general types of instruments that can be used for predictive maintenance infrared thermometers or spot radiometers line scanners and imaging systems. 

Infra-red homing is used in many air-to-air and some anti-aircraft types such as Sidewinder, Red Top and Redeye. Since it relies on optical radiation, this form of guidance is short range and dependent on reasonably clear skies... 

Mlelenz, K. D., Ed. Optical Radiation Measurements Measurement of Photoluminescence Academic Mew York, 1982 Vol. 3. 

Jersch, J., Demming, F., Hildenhagen, L. J. and Dickmann, K. (1998) Field enhancement of optical radiation in the nearfield of scanning probe microscope tips. Appl. Rhys. A, 66, 29-34. 

As already indicated above, what one may consider a surface depends on the property under consideration. Adhesion is very much an outer atomic layer issue, unless one is dealing with materials like fibreboard in which the polymer resin may also be involved in mechanical anchoring onto the wood particles. Gloss and other optical properties are related to the penetration depth of optical radiation. The latter depends on the optical properties of the material, but in general involves more than a few micrometer thickness and therewith much more than the outer atomic layers only. It is thus the penetration depth of the probing technique that needs to be suitably selected with respect to the surface problem under investigation. Examples selected for various depths (< 10 nm, 10 s of nm, 100 nm, micrometer scale) have been presented in Chapter 10 of the book by Garton on Infrared Spectroscopy of Polymer Blends, Composites and Surfaces... 

Here p is dipole operator and E(t) is electric field in optical radiation. Due to the application of V(t), the system becomes nonstationary and the rate of energy absorption can be calculated ... 

EL Dereniak, DG Crowe. Optical Radiation Detectors. Wiley Series in Pure and Applied Optics. Chichester Wiley, 1984. 

The most simple, but general, model to describe the interaction of optical radiation with solids is a classical model, due to Lorentz, in which it is assumed that the valence electrons are bound to specific atoms in the solid by harmonic forces. These harmonic forces are the Coulomb forces that tend to restore the valence electrons into specific orbits around the atomic nuclei. Therefore, the solid is considered as a collection of atomic oscillators, each one with its characteristic natural frequency. We presume that if we excite one of these atomic oscillators with its natural frequency (the resonance frequency), a resonant process will be produced. From the quantum viewpoint, these frequencies correspond to those needed to produce valence band to conduction band transitions. In the first approach we consider only a unique resonant frequency, >o in other words, the solid consists of a collection of equivalent atomic oscillators. In this approach, coq would correspond to the gap frequency. 

Chapter 4, presents details of the absorption and reflectivity spectra of pure crystals. The first part of this chapter coimects the optical magnimdes that can be measured by spectrophotometers with the dielectric constant. We then consider how the valence electrons of the solid units (atoms or ions) respond to the electromagnetic field of the optical radiation. This establishes a frequency dependence of the dielectric constant, so that the absorption and reflectivity spectrum (the transparency) of a solid can be predicted. The last part of this chapter focuses on the main features of the spectra associated with metals, insulators, and semiconductors. The absorption edge and excitonic structure of band gap (semiconductors or insulator) materials are also treated. 

Figure 8. An incoherent source of optical radiation of finite size.

Atomic fluorescence spectrometry is based on the absorption of optical radiation of suitable frequency (wavelength) by gaseous atoms and the resultant deactivation of the excited atoms with the release of radiation. The frequencies (wavelengths) emitted are characteristic of the atomic species. 

The temperature measurement devices which do not contact the hot surfaces, for example, optical -, radiation pyrometers, and infrared techniques, are not typical for high-pressure application. 

The theoretical light curve is shown in Pig. 1a together with the observed one (van Genderen A.M., The P.S., 1985, Space Sci. Rev., 39, 313). The theoretical curve properly reproduces the dimming timescale and the depth of the observed curve. Theoretical spectrum shown in Pig. 1b displays discrepancies with observations in short waves. The deficit of optical radiation can be explained only by non-uniformity of the dust envelope which increases the contribution of scattering. The slope of far infrared spectrum is due to the adopted extinction tables. Angular distribution of monochromatic brightness (normalized, in arbitrary units) is shown in Pig. 1d. 

Why diamond works so well is because of its two most desirable properties, namely. (I) it is the hardest substance known to science, and t2) it is very- transparent to optical radiation as well as to x-rays. Compared to diamond, tungsten carbide, which was used in older pressure generating devices, has a much lower compressive strength and, further, it is opaque to radiation. 

Optoelectronic—Pertaining to a device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electncal-to-optical or oplical-to-electrical transducer. 

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