Laser excitation near infrared region

Laser excitation near infrared, which is known as 3D femtosecond imaging (3DFI) can be used as non-invasive fouling visualization technique. The laser is installed in series with a microscope and camera to observe the fouling layer directly on the flat sheet membrane in a crossflow membrane module [73]. The 3DFI can be used in conjunction with fluorescent label, similar to CLSM however it can only provide a laser range in the infrared region (see Chapter 8). 

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Figure 25 Transient absorption in (a) visible and (b) near-infrared regions together with (c) time dependences at 580 and 900 nm upon fs laser excitation of NS+TPB- in DME at room temperature.

Figure 3.3-5 Transmission of a quartz fiber in the near-infrared region, r is the transmittance of a fiber with a length of 1 km, below are the ranges of the Raman spectrum excited by the HeNe laser at 623 and the Nd YAG laser at 1064 nm.

Figure 3.5-3 Linear decadic absorption coefficient of H2O, D2O, Ethanol, and Cyclohexane in the near infrared region. Insertion range of the Raman spectrum, excited by the NdrYAG laser with radiation of A = 1064 nm.

Although first demonstrated by Chantry et al. in 1964, FT-Raman spectroscopy did not attract significant attention until the development of commercially available instrumentation with excitation in the near-infrared region (1064 nm) from a continuous wave Nd/YAG (neodymium-yttrium-aluminum-gamet) laser. The FT-Raman spectrometer is a frequency-division multiplexing system in which all (scattered) wave-... 

Unlike IR spectroscopy where nowadays FT instrumentation is solely used, in Raman spectroscopy both conventional dispersive and FT techniques have their applications, the choice being governed by several factors. The two techniques differ significantly in several performance criteria, and neither one is best for all applications. Contemporary dispersive Raman spectrometers are often equipped with silicon-based charge coupled device (CCD) multichannel detector systems, and laser sources with operating wavelength in the ultraviolet, visible or near-infrared region are employed. In FT Raman spectroscopy, the excitation is provided exclusively by near-infrared lasers (1064 nm or 780 nm). 

Raman spectra reviewed so far are almost exclusively resonantly enhanced, because the exciting laser light wavelength is more or less close to the optical absorptions of the polymer. As discussed in more detail in the following part, the optical absorption of PANI as well as of its relatives extends into the near infrared region (i.e., beyond A = 1000 nm). Excitation of PANI with laser light in this region also has been employed in structural studies of... 

Squaraines with ring substituents which absorb and emit in the red and near-infrared regions have also been developed [72]. When compared to conventional Cy5—NHS systems (open chain), these derivatives have several advantages. For example, these compounds can be excited not only with red lasers but also with blue lasers or with luminescent diodes being useful compounds, they can be excited all over the visible range of the electromagnetic spectrum. These compounds are particularly useful in biomedical applications due to their favorable spectral and photophysical properties, such as fluorescence [72]. 

However, the high frequency of the laser irradiation in the visible region may lead to photochemical reactions in the laser focus. Besides, fluorescence can often cover the whole Raman spectrum. Such problems can be avoided by using an excitation wavelength in the near-infrared (NIR) region, e.g. with an Nd YAG laser operating at 1064 nm. Deficits arising from the v dependence of the Raman intensity and the lower sensitivity of NIR detectors are compensated by the Fourier-Transform (IT) technique, which is widespread in IR spectroscopy . ... 

Heat. As mentioned above most molecules lose energy from the excited state as heat. The most efficient molecules for converting electromagnetic radiation into heat are those that absorb in the near-IR region, i.e., infrared absorbers (IRAs). There has been much interest in IRAs because of their use in laser thermal transfer, optical data storage [the older write-once read-many (WORM) and the newer compact disc recordable (CD-R) and digital versatile disc recordable (DVD-R) systems], computer-to-plate printing, and as solar screens for car windscreens and windows. 

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