Near IR

The study of small energy gaps in matter using the optical spectral region (say the near-IR, visible and UV) offers many advantages over direct one-photon spectroscopies in the IR, far IR or even the microwave. First,... 

It should be noted that this technique is not without some disadvantages. The blackbody emission background in the near IR limits the upper temperature of the sample to about 200°C [43]. Then there is the dependence of the Raman cross-section ( equation (B 1.3.16) and equation ( B1.3.20)-equation ( B 1.3.21)) which calls for an order of magnitude greater excitation intensity when exciting in the near-IR rather than in the visible to produce the same signal intensity [39]. 

RDOs is much smaller than that for the vibration itself, not to mention that for the near-IR FT-Raman teclmique already discussed. This is particularly striking for high energy modes such as the C-H vibrations [108]. Modem applications of I CRS now utilize a two-dimensional time-frequency detection scheme... 

Greenfield S R and Wasielewski M R 1995 Near-transform-limited visible and near-IR femtosecond pulses from optical parametric amplification using Type II p-barium borate Opt. Lett. 20 1394-6... 

The triplet-triplet absorjDtion spectmm reveals, similar to the singlet-singlet features, a maximum in the near-IR... 

Soper S A and Legendre B L Jr 1998 Single-molecule detection in the near-IR using continuous-wave diode laser... 

Figure C3.1.13. Experimentai configuration for far-UV nanosecond CD measurements using a frequency-upconverted Ti sapphire iaser as a probe source. Pj and P2 are Mgp2 Rochon poiarizers at cross orientations. SP is a strained transparent piate with about i ° of iinear birefringence for quasi-nuii eiiipsometric CD detection. Prism PMj and the iris Ij seiect the far-UV fourth hannonic of the argon iaser-pumped Ti-sapphire iaser s near-IR fundamentai output to probe the eiiipticity of the sampie. A second iaser beam at 532 nm is used to pump CD...

The easiest method for creating many vibrational excitations is to use convenient pulsed visible or near-UV lasers to pump electronic transitions of molecules which undergo fast nonradiative processes such as internal conversion (e.g. porjDhyrin [64, 65] or near-IR dyes [66, 62, 68 and 62]), photoisomerization (e.g. stilbene [12] or photodissociation (e.g. Hgl2 [8]). Creating a specific vibrational excitation D in a controlled way requires more finesse. The easiest method is to use visible or near-UV pulses to resonantly pump a vibronic transition (e.g. 

Optical Properties and Radiation Effects. Within the range of wavelengths measured (uv, visible, and near-ir radiation), Teflon PFA fluorocarbon film transmits slightly less energy than FEP film (29) (Table 6). In thin sections, the resin is colorless and transparent in thicker sections, it becomes translucent. It is highly transparent to it radiation uv absorption is low in thin sections. Weather-O-Meter tests indicate unlimited outdoor life. 

R the air—glass reflection coefficient. Transmission is a function of wavelength. In siUcate glasses, it is limited by the absorption of siUca at approximately 150 nm ia the uv and at 6000 nm ia the air. Iroa impurities further reduce transmission ia the uv and near ir. Dissolved water absorbs at 2700 nm and is a serious problem ia making ir transmitting glasses. 

A great disadvantage of PHB is the necessity to operate at very low temperatures (<20 K). Therefore, this recording technique currently has no practical significance but it is subject to intensive research activity (175). One future aspect which may be important, if room temperature materials become available, is the usage of inexpensive semiconductor lasers in the near ir-regime (176). 

PMD color or the nature of the electron transitions produces the widest appHcation for PMDs. Depending on the polymethine chain length, the end-group topology, and the electron shell occupation, polymethines can absorb light in uv, visible, and near-ir spectral regions. 

Electron Level Position. One essential condition of spectral sensitization by electron transfer is that the LUMO of the dye be positioned above the bottom of the conduction band, eg, > —3.23 eV in AgBr or > —4.25 eV in ZnO (108). To provide the desired frontier level position respectively to the valence and conduction bands of the semiconductor, it is necessary to use a polymethine with suitable electron-donor abiHty (Pq. Increasing the parameter (Pq leads to the frontier level shift up, and vice versa. Chain lengthening is known to be accompanied by a decrease of LUMO energy and hence by a decrease of sensitization properties. As a result, it is necessary to use dyes with high electron-donor abiHty for sensitization in the near-ir. The desired value of (Pq can be provided by end groups with the needed topological index Oq or suitable substituents (112). 

The near-ir spectmm of ethylene oxide shows two peaks between 1600—1700 nm, which are characteristic of an epoxide. Near-ir analyzers have been used for verification of ethylene oxide ia railcars. Photoionization detectors are used for the deterrnination of ethylene oxide ia air (229—232). These analyzers are extremely sensitive (lower limits of detection are - 0.1 ppm) and can compute 8-h time-weighted averages (TWAg). 

Photomultipliers are used as detectors in the single-channel instruments. GaAs cathode tubes give a flat frequency response over the visible spectrum to 800 nm in the near IR. Contemporary Raman spectrometers use computers for instrument control, and data collection and storage, and permit versatile displays. 

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