Near 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. 

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. 

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 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. 

Thus the value of the dielectric constant at the sample/metal interface determines the shift of the resonance. When adsorption of molecules at the metal surface results in the change of the refractive index or of the local value of the dielectric constant, the change of reflectivity is observed. This phenomenon has been used as the mechanism for detection of gases (Fig. 9.18a) and of adsorbed biomolecules (Fig. 9.18b). The depth of penetration of the surface plasmon is comparable to that of the evanescent field, that is, 100-500 nm for the visible-near infrared range. 

The near infrared range (12800-4000 cm-1) as well as the mid-infrared range (400-4000 cm -1) has been used for spectroscopic detection of physi-... 

In general, the polymers with polyconjugated systems of double and triple bonds are photoeonductive in the UV and at least part of the visible range. In some cases the photoresponse extends to the near infrared range. Although their usefulness in practical applications has been many times suggested, the results have been more or less disappointing. The main problems still remain difficult synthesis, in most cases poorly identified structure, and with few exceptions insolubility and intractability of the polymers. The direct comparison with poly(N-vinyl carbazole) and other photoeonductive polymers is not possible for lack of comparative data. 

The free carrier concentration at room temperature was determined by Raman experiments using the Ai(LO) phonon-plasmon coupled mode and by the reflectance in the mid-infrared and the optical absorption in the near-infrared range. Each experiment for the GaN layer of 60 pm thickness showed a free carrier concentration in the order of 1017 cm 3. 

Fig. 4.1.18. Infrared spectrum of European beech (Fagus sylvatica L.) and bamboo (Bambusa sp.) MWLs in the near infrared range. (Instrument Nicolet 7000 Resolution 8cm l, 128 scans courtesy of J. Mink, Budapest)...

Figure 2.2-2 The visible, near, middle and far infrared region of the spectrum drawn in a scale linear in wavenumbers. The infrared (IR) and far-infrared (FIR) spectrum is recorded by absorption of light from a continuous spectrum in the range of A = 2.5. .. 100 pm = i) = 4000. .. 100 cm and A = 100. .. 1000 pm = 100. .. 10 cm". Raman spectra can be excited by monochromatic radiation, emitted by different lasers in the visible (VIS) or near-infrared range (NIR). Molecules emit Raman lines with a frequency difference AF to that of the exciting frequency >o between 0 and -f 4000 or - 4000 cm. Usually only the Raman spectrum which is shifted to. smaller wavenumbers, the Stokes Raman spectrum, is recorded. Its range is indicated by bars for different exciting lines Ar" " laser at 488 and 515 nm, HeNe laser at 623 nm, GaAs laser at 780 nm, and Nd YAG laser at 1064 nm.

These devices are based on the anisotropic absorption of light. Usually molecular crystals exhibit this property and tourmaline is the classical example for this. For practical purposes, however, micro crystals are oriented in polymer sheets. Polymers containing chromophors become after stretching dichroic polarizers. The devices produced in this manner are called polawids. They have found a broad application in many technologies. Their application in spectroscopy is limited to the near ultraviolet and to the visible and near infrared range of the spectrum. In vibrational spectroscopy polaroids are employed as analyzers only for Raman spectroscopy. 

A Raman spectrum is excited by irradiating a sample with coherent or non-coherent monochromatic radiation in the ultraviolet, the visible, or the near-infrared range. By an elementary process described in Sec. 2.4, the sample produces usually non-coherent radiation the strong Rayleigh line at the frequency of the exciting radiation and weak lines at frequencies. shifted from the frequency of the exciting radiation by definite quantities, the Raman spectrum. 

Excitation of Raman spectra in the near-infrared range excludes fluorescence of samples and impurities, which used to mask the Raman spectra of real life products. The very low intensity of Raman spectra in this range, which is proportional to the fourth power of the frequency, can be overcome by interferometers which employ the Jacquinot and multiplex advantage. Special features of NIR FT Raman spectroscopy are described in Sec. 3.5.5. 

The absorption spectroscopy in the UV-Vis-NIR is especially rich for the actinides, allowing for fairly simple determinations of the metal oxidation state. The primary absorption bands result from f f transitions, f d and ligand-to-metal charge transfers. The f — f transitions are typically weak since they are forbidden under the LaPorte selection rules. Distortions in symmetry allow for relaxation in these rules and bands in the visible to near-infrared range result. Complexes that contain an inversion syimnetry, for example Pu02CLt, have weaker f- -f transitions (e < 20 cm ). The direct interactions of the 5f orbitals... 

Comby, S., Imbert, D., Vandevyver, C., and Biinzli, J.-C.G (2007) A novel strategy for the design of 8-hydroxyquinoUnate-based lanthanide bioprobes that emit in the near infrared range. Chemistry - A European Journal, 13, 936. 

A typical 500 W tungsten lamp operates at 3000 K with an emissivity of 0.4. If the spectral radiance is plotted against wavelength, the spectral radiance will have a maximum at approximately 1000 nm and swiftly drops at approximately 300 and 5000 nm, so that the tungsten lamp is most useful in the visible and near-infrared range. 

C. T. Germer, A. Roggan, J. P. Ritz, C. Isbert, D. Albrecht, G. Muller, and H. J. Buhr, Optical Properties of Native and Coagulated Human Liver Tissue and Liver Metastases in the Near-Infrared Range, Lasers Surg. Med., 23(4), 194-203 (1998). 

Simulation Chamber Study of the Oxidation of Acetic Acid by OH Radicals Detection of Reaction Products by CW-CRDS in the Near-Infrared Range... 

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