Infrared range

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

Infrared ellipsometry is typically performed in the mid-infrared range of 400 to 5000 cm , but also in the near- and far-infrared. The resonances of molecular vibrations or phonons in the solid state generate typical features in the tanT and A spectra in the form of relative minima or maxima and dispersion-like structures. For the isotropic bulk calculation of optical constants - refractive index n and extinction coefficient k - is straightforward. For all other applications (thin films and anisotropic materials) iteration procedures are used. In ellipsometry only angles are measured. The results are also absolute values, obtained without the use of a standard. 

Molecules possess discrete levels of rotational and vibrational energy. Transitions between vibrational levels occur by absorption of photons with frequencies v in the infrared range (wavelength 1-1000 p,m, wavenumbers 10,000-10 cm , energy differences 1240-1.24 meV). The C-0 stretch vibration, for example, is at 2143 cm . For small deviations of the atoms in a vibrating diatomic molecule from their equilibrium positions, the potential energy V(r) can be approximated by that of the harmonic oscillator ... 

It should be clear that all bodies (even your own) radiate photons in the infrared range of energies. Yours is similar to that of the earth and probably peaks near to 10.0 microns or 10,000 A. If you place your hand on your face, you feel warmth because the emitted photons are reabsorbed by s our hand. 

Molecules possess discrete levels of rotational and vibrational energy, and transitions between vibrational levels occur by absorption of photons with frequencies in the mid-infrared range. There are four types of vibration ... 

In LIBS analysis, a pulsed laser is focused on the gem surface. The laser energy ablates a small amount of gem material which burns in a short-lived plasma. As the plasma cools, excited electrons decay into lower-energy orbitals, releasing energy in the form of photons in the ultraviolet-visible-infrared range. This light is collected by optic fiber, diffracted, and recorded as a spectrum, generally between 200 and 1000 nm. 

He GS, Yong K, Zheng Q, Sahoo Y, Baev A, Ryasnyanskiy Al, Prasad PN (2007) Multiphoton excitation properties of CdSe quantum dots solutions and optical limiting behavior in infrared range. Opt Exp 15 12818-12833... 

Figure 5.21 The integrated emission intensity of Er + ions (in the infrared range, 1.5-1.6 ixm) as a function of Er concentration (reproduced with premission from Daran et al., 1994).

It is a commonplace that FTIR-based analyzers are the predominant technology for mid-infrared applications. This arises from a unique tie-in between the inherent advantages of the FTIR method and serious limitations in the mid-infrared range. The most serious problem for mid-infrared spectroscopy is the very low emissivity of mid-infrared sources combined with the low detectivity of mid-infrared thermal detectors. 

The phyllic alteration zone coincides with a subtle but consistent shift in the dominant AlOH peak in the short-wave infrared spectrum ( 2210 nm) to slightly lower wavelengths, consistent with an inner white mica-ferroan carbonate mineral assemblage. A preliminary analysis of hyperspectral data over the visible to near infrared range suggests that ferroan carbonates may be detected but not reliably quantified. However, TIR data allow calcite and ferroan carbonate to be distinguished, and may also detect increasing Fe content in ferroan dolomite as mineralized structures are approached. 

Infrared light is divided into three zones the near-infrared, the mid-infrared, and the far-infrared, as shown in Table 12.2. The wavelength of the near-infrared is below 2.5 pm, that of the mid-infrared ranges from 2.5 pm to 25 pm, and that of the far-infrared is above 25 pm. Infrared emission between 3 pm and 30 pm is caused by vibrational modes of the molecules, while that above 30 pm is caused by rotational modes. 

Scheinost, A.C. Chavernas, A. Barron,V. Tor-rent, J. (1998) Use and limitations of second-derivative diffuse reflectance spectroscopy in the visible to near-infrared range to identify and quantify Fe oxide minerals in soils. Clay Min. Soc. 46 528-536... 

The infra region can be divided up as shown in Table 5.1. Table 5.1 Infrared ranges... 

From Figure 7.10 it is seen that spontaneous emission according to the Planck theory of Black body radiation as well as Einstein s work starts to dominate above 10 Hz at 300K, this corresponds to the infrared range of the electromagnetic spectram. Note, that if the temperature increases the zero crossing point moves into the visual and UV range. 

B) C.G. Klick J.H. Schulman, "Luminescence in Solids , USNRL (Second Edition of Vol 5, Solid State physics, edited by F. Seitz D. Turnbull, Academic Press (1957), p 106 C) Quantatron, Inc, Applied Physics Laboratories, Santa Monica, Calif, (Coherent Infrared Ranging System , 15 Mar 1962 (Second Quarterly Progress Report)... 

The kinetics of acrylate polymerization using this type of initiators have also been studied [ 172,177] in addition to allowing comparison of the effectiveness of different initiators, the kinetic behavior also provides support for a 2P mechanism for initiation with excitation in the visible and near-infrared range. The rate of a radical polymerization, Rp, is given by [178] ... 

Commonly used units are reciprocal second (s l or Hz) for frequency nanometre nm, I nm = 10 m) for wavelength IK = civ. where c is the speed of light) and ioule ( ) far energy. Because energy is frequently dealt with on a mole basis, the unit encountered is kl mol-1. Table 1.1 shows the relationship between these units for selected numerical values in the ultraviolet/visible/near-infrared range. 

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