Near-infrared experiments

With IR light sources like this one, a technology is available which, in terms of day-to-day reliability and long-term and short-term stability, is entirely comparable with Ti sapphire regenerative amplifiers. As shown in this article, it was possible to perform femtosecond experiments on all kinds of condensed phase phenomena involving vibrational transitions (such as energy relaxation, dephasing, spectral diffusion, coupled systems) with essentially the same facility and accuracy as can be achieved in visible and near-infrared experiments. 

Near infrared experiments on lanthanide]III) ions showed no well-defined second hydration shell [118). The residence times for water molecules in the second shells around Nd, Sm and Yb are 13, 12 and 18 ps respectively [70]. The slightly higher value for Yb can be related to its smaller ionic radius, rjon. 

Near-infrared experiments may also require their own source, typically a quartz halogen lamp. 

The above procedures, which have been incorporated into automatic computer programs, are a systematic way of producing spectra that are appropriate for comparison with both far-infrared and near-infrared experiments on van der Waals molecules. 

In the authors experience, the amount of carbon dioxide in 10 microliters of blood can readily be determined by adding the blood to an acid, through which bubbles an inert gas. The CO2 is then brought into the field of a long cuvette, of approximately 20" in length, and the carbon dioxide measured at the near infrared with a filter instrument. Instrumentation can be designed readily for measurement of the carbon dioxide content of as little as 1 l of plasma with this principle at the rate of approximately 40-60 per hour. 

These effects of second and third order optical non-linearity are just exploited in the generation of the second and third harmonics, respectively. In this connection, Figure 40 schematizes an experiment in which the incidence of a laser light working in the near infrared at X 1060 nm on a crystal of KU02(P04) emits a light of X = 532 nm.70... 

Experiments were conducted in our laboratory to evaluate many of the dynamical expectations for rapid laser heating of metals. One of the aims of this work was to identify those population distributions which were characteristic of thermally activated desorption processes as opposed to desorption processes which were driven by nontbennal energy sources. Visible and near-infrared laser pulses of nominally 10 ns duration were used to heat the substrate in a nonspecific fashion. Initial experiments were performed by Burgess etal. for the laser-induced desorption of NO from Pt(foil). Operating with a chamber base pressure 2 x 10 torr and with the sample at 200 K, initial irradiation of a freshly cleaned and dosed sample resulted in a short time transient (i.e. heightened desorption yield) followed by nearly steady state LID signals. The desorption yields slowly decreased with time due to depletion of the adsorbate layer at the rate of ca. 10 monolayer... 

The foregoing experiments using visible or near-infrared lasers hoped to explore desorption dynamics within a framework characterized by a thermal desorption picture. Hiere are two complementary studies that undertook to explore nonthermal desorptions. 

F.C. Jentoft, Ultraviolet-Visible-Near Infrared Spectroscopy in Catalysis Theory, Experiment, Analysis, and Application Under Reaction Conditions, Adv. CataL, 52, 129-211 (2009). 

LA. Cowe, J.W. McNicol and D.C. Cuthbertson, A designed experiment for the examination of techniques used in the analysis of near-infrared spectra. Part 2 Derivation and testing of regression models. Analyst 110,1233-1240 (1985). 

The raw data plots and experience with near-infrared reflectance spectroscopy indicates the need for preprocessing to miniinize the effects of scatter. However, to illustrate the effect of preprocessing on the analysis, no preprocessing will be performed for the first pass through the data. ... 

Raman spectroscopy, while typically used as a micro-analytical tool, can be conducted remotely. Performance of remote Raman analysis have been recently explored and reahzed for experiments on the surface of Mars (Sharma et al. 2001 Sharma et al. 2003). Raman spectroscopy is a powerful technique for mineralogical analysis, where the sharpness of spectral features of minerals allows for much less ambiguous detection, especially in the presence of mixtures. Visible, near-infrared, thermal, reflectance and in many cases emission spectroscopy of minerals all suffer from broad overlapping spectral features, which complicates interpretation of their spectra. On the other hand, Raman spectra of minerals exhibit sharp and largely non-overlapping features that are much more easily identified and assigned to various mineral species. 

Nelson, B. P., Frutos, A. G., Brockman, J. M. and Corn, R. M. (1999) Near-infrared surface plasmon resonance measurements of ultrathin films. 1. Angle shift and SPR imaging experiments. Anal. Chem. 71, 3928-3934. 

Os(NH3)5(NCS)]2+ was first prepared by the reaction of [Os-(NH3)5(OH2) ]3+ with KSCN in water (197), and, more recently, by the reaction of [0s(NH3)5(0S02CF3)]2+ with NH4SCN in acetone (198). It undergoes a reversible reduction to the Os(II) complex and an irreversible oxidation to Os(IV). A complete analysis of the Raman and IR spectra (including deuteration experiments) has been reported, and the electronic spectra, including near-infrared bands, are discussed. [Os-(NH3)4(NCS)2]+ and [Os(NH3)3(NCS)3] are by-products of the reactions, but have not been characterized (198). 

If near-infrared diode lasers have low-noise characteristics similar to those of mid-infrared diode lasers, and thus minimum absorbances of 10 5 or less are possible, then an approximate detection limit can be calculated for an absorption experiment. For a 200-m optical path, the calculated detection limit is 5 x 1010 molecules/cm3, which is well above levels of H02 expected to be found in the atmosphere. An absorption experiment in this spectral region apparently would require extremely long optical path lengths, and, indeed, a calculation with a 5-km path yields a calculated detection limit of 2 x 109 molecules/cm3, still rather high for tropospheric measurements. Other issues associated with the use of diode lasers in absorption spectroscopy are discussed in the next section. 

Most SHG studies involve incident energies in the visible or near-infrared spectrum. Infrared SHG studies are hindered by the current lack of sufficiently sensitive IR detectors. However, the sum frequency generation (SFG) technique allows one to obtain surface-specific vibrational spectra. In SFG, two lasers are focused on the sample surface, one with a fixed frequency in the visible and one with a tunable range of IR frequencies. The sample surface experiences the sum of these frequencies. When the frequency of the infrared component corresponds to a molecular vibrational mode, there is an increase in the total SHG signal, which is detected at the visible frequency [66]. The application of such... 

Fourth, while fluorescence was not a problem in this system, some bioreactor components may be highly fluorescent. Until more experience is gained, this makes it difficult to make generalizations about the likelihood of success with new systems. Finally, water is a weak Raman scatterer and can be hard to track. While Ulber etal. considered the challenge in obtaining a spectrum of the aqueous cell culture broth to be a disadvantage, others consider it an advantage since these solutions overwhelm mid- or near-infrared detectors.33 34 36... 

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