Electromagnetic radiation radiant sources

Infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy (Chapter 14) both use a form of electromagnetic radiation as their energy source. To understand IR and NMR, therefore, you need to understand some of the properties of electromagnetic radiation— radiant energy having dual properties of both waves and particles. 

The various terms that are used for the description of the emission of electromagnetic radiation from a radiant source or for the receipt of electromagnetic radiation by a specified surface element are summarized in Tab. 3-9. The terminology of electromagnetic radiation measurement is divided into radiometry and the subset of photometry (Fig. 3-18). The former is the science that involves the energy measurement of electromagnetic radiation in general. The latter is applied for the same purpose when visible radiation is to be described or measured in relation to the human eye s response. Important photometric quantities are for example luminous flux, luminous intensity, illuminance and luminance (McCluney, 1994). Every photometric quantity has its counterpart in radiometry, and vice versa. 

Tab. 3.9 Classification of terms used to describe and measure electromagnetic radiation either received by a defined surface element or emitted by a surface element of a radiant source (for verbatim definitions refer to Serpone and Emeline, 2002, Bolton, 2000, 1999, Verhoeven, 1995, McCluney, 1994, Mills et al., 1993, Braun et al., 1991, and the glossary in this book)...

The impact of electromagnetic radiation, especially of UV radiation, on the human skin and on the eye may lead to severe adverse effects (see Fig. 2-4) including skin cancer, severe skin burning, conjunctivitis or cataract formation. Hence, appropriate protective measures must be considered while working with artificial radiant sources. This includes UV-blocking eyewear and face wear. Never look directly and unprotected at an operating UV or VUV lamp ... 

The sun is an intense source of corpuscular and electromagnetic radiation. The latter is called solar radiation. The sun is a spherical UV/VIS source with an average radius tgun of 6.9585 x 10 m, an average Earth-sun distance dg.g of 1.4957x10 m and a radiant power Pgu of 3.842x10 W. Therefore, the radiant exitance M of the sun calculates to Bolton, 1999). 

Plane-polarized electromagnetic radiation is produced by certain radiant energy sources. For example, the radio waves emanating from an antenna and the microwaves produced by a klystron tube are both plane polarized. Visible and ultraviolet radiation from relaxation of a single excited atom or molecule is also polarized, but the beam from such a source has no net... 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

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