Light sources, high intensity

Presentations rely on strong light sources. High-intensity halogen lamps contain mainly dysprosium iodide. 

The determination of photochemical quantum yields is not a simple task, and, in some cases, approximations are required. Nevertheless, according to the parameters chosen, various well-known photochemical reactions can be used to measure irradiance, which is an essential quantity in the field of photokinetics. Finally, some selected chemical actinometers will be discussed with respect to their pros and cons and their best areas of application. At the end, special applications of actinometry such as measurements of polychromatic light and high-intensity light sources (lasers) will be described. The overall aim of this chapter is to help the reader to choose the best actinometers out of the numerous examples in the literature and avoid technical mistakes. 

Figure 88. Effect of light intensity on the photodegradation of nifedipine at room temperature. Light source , high-pressure mercury lamp sunlight , fluorescent lamp. (Reproduced from Ref. 403 with permission.)...

Before submicrosecond setups were foimd to be of use for measurements of thermophysical properties, they were used to provide pulsed light sources with intense light output, or as plasma sources with imusudly high material density... 

The foremost of the modem teclmiques is tlie use of lasers as spectroscopic tools. Lasers are extremely versatile light sources. They can be designed with many usetlil properties (not all in the same instmment) such as high intensity, narrow frequency bandwidth with high-frequency stability, tunability over reasonable frequency ranges, low-divergence beams which can be focused into very small spots, or pulsed beams with... 

Lasers (qv) and other high intensity or alternative light sources are usefiil in crime laboratories to visualize latent fingerprints, seminal fluid stains, obhterated writings, and erasures, and to aid in specialized photographic work. Infrared and ultraviolet light sources are also used to view items of evidence. 

Because the Raman cross-section of molecules is usually low, intense light sources and low-noise detectors must be used, and high sensitivities - as required for surface analysis - are difficult to achieve. Different approaches, singly and in combination, enable the detection of Raman spectroscopy bands from surfaces. 

The efficiency of a photochemical process [39] requiring high-intensity light sources, e.g., UV... 

In recent years, high-resolution x-ray diffraction has become a powerful method for studying layered strnctnres, films, interfaces, and surfaces. X-ray reflectivity involves the measurement of the angnlar dependence of the intensity of the x-ray beam reflected by planar interfaces. If there are multiple interfaces, interference between the reflected x-rays at the interfaces prodnces a series of minima and maxima, which allow determination of the thickness of the film. More detailed information about the film can be obtained by fitting the reflectivity curve to a model of the electron density profile. Usually, x-ray reflectivity scans are performed with a synchrotron light source. As with ellipsometry, x-ray reflectivity provides good vertical resolution [14,20] but poor lateral resolution, which is limited by the size of the probing beam, usually several tens of micrometers. 

S.3.4.3. Photodissociation It is also possible to use light as the activation method. Laser sources are especially useful because of their high intensity and narrow wavelength bandwidth. Photodissociation can be used to determine bond dissociation energies in ions directly, similar to what is done with threshold CID, or, alternatively, can be used in conjunction with direct ionization. 

---