Radiation double-wavelength

Instruments with double monochromator configurations, or equivalent multi-pass configurations, can greatly reduce stray light (which is any radiation of wavelength other than that of the columnated light beam). Absorbance in the presence of stray light can be expressed as ... 

None of the polymers absorbed UV radiation at wavelengths higher than 220 nm. This rules out conjugated double bonds and indicates monomeric units are linked by O-C bonds. Absorptions from C=N and N-O-C linkages were present in IR/Raman spectra. The hexamer has, therefore, the cyclic structure N. 

The laser system used in the experiments consist of two excimer-pumped dye lasers. The dye lasers can produce narrow bandwidth laser radiation of wavelengths between 340 and 850 nm, which can be extended, with the use of second harmonic generation, down to 205 nm. The bandwidth is nominally about 5 GHz, but this can be reduced to 1 GHz by use of an intra cavity etalon. The energy resolution in the present experiments is limited solely by the linewidth of the laser. The maximum pulse energy is typically a few mJ in the visible wavelength region and a few hundred jiJ in the UV, after doubling. The laser intensity is measured after the... 

To overcome the problems faced by the single-wavelength radiation thermometer and the ratio pyrometer, a double-wavelength radiation thermometer (DWRT) measures the spectral radiance itself at two distinct wavelengths for surface temperature evaluation. For this method to be used, the emissivity compensation function e i = fl v) must be defined. A detailed description of the principle for DWRT can be found in Ref. 53. When the emissivity relation x.i = Ae ) at two distinct wavelengths e i = fl v) is established, the true temperature on the measured surface can be determined from the inferred temperature, which is defined as... 

American National Standard Institute American Society for Testing and Materials International Committee of Weights and Measures Double-Wavelength Radiation Thermometer International Practical Temperature Scale International Practical Temperature Scale of 1968 Instrument Society of America International Organization of Standardization International Temperature Scale International Temperature Scale of 1990 National Bureau of Standards... 

A novel device for efficiently generating intense radiation at wavelengths around 202 nm is shown in Fig. 5.110. A laser diode-pumped Nd YV04 laser is frequency doubled and delivers intense radiation at X = 532 nm, which is again frequency doubled to A. = 266 nm in a BBO crystal inside a ring resonator. The output from this resonator is superimposed in a third enhancement cavity with the output from a diode laser at A = 850 nm to generate radiation at A = 202 nm by sum-frequency mixing. This 202-nm radiation is polarized perpendicularly to that at the two other waves and can be therefore efficiently coupled out of the cavity by a Brewster plate [5.255]. 

When DNA is exposed to radiation at wavelengths of about 260 nm, adjacent pyrimidines become covalently linked by the formation of a four-member ring structure resulting from the saturation of their respective C5, C6 double bonds. The structure formed by this photochemical cycloaddition is referred to as a pyrimidine dimer. The pyrimidine bases in DNA are thymine and cytosine. 

With frequency-doubled tunable dye laser radiation the wavelength range down to 2176 K can be covered (see Sect.7.6), which allows three-photon spectroscopy at wavelengths as short as 723 X. 

There are several requirements for this to be a suitable deteetion method for a given moleeule. Obviously, tire moleeule must have a transition to a bound, exeited eleetronie state whose wavelength ean be reaehed with tunable laser radiation, and the band system must have been previously speetroseopioally assigned. If the moleeules are fonned with eonsiderable vibrational exeitation, the available speetroseopie data may not extend up to these vibrational levels. Transitions in the visible ean be aeeessed direetly by the output of a tunable dye laser, while transitions in the ultraviolet ean be reaehed by Ifequeney-doubled radiation. The... 

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

The i j -configuration of the 6,7-double bond in pre-vitamin D is critical to its subsequent thermal rearrangement to the active vitamin. A photochemical isomerization of pre-vitamin D to yield the inactive trans-isoTnen occurs under conditions of synthesis, and is especially detrimental if there is a significant short wavelength component, eg, 254 nm, to the radiation continuum used to effect the synthesis. This side reaction reduces overall yield of the process and limits conversion yields to ca 60% (71). Photochemical reconversion of the inactive side product, tachysterol, to pre-vitamin D allows recovery of the product which would otherwise be lost, and improves economics of the overall process (70). 

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