Long-wave infrared

About 51 percent of solar energy incident at the top of the atmosphere reaches Earth s surface. Energetic solar ultraviolet radiation affects the chemistry of the atmosphere, especially the stratosphere where, through a series of photochemical reactions, it is responsible for the creation of ozone (O,). Ozone in the stratosphere absorbs most of the short-wave solar ultraviolet (UV) radiation, and some long-wave infrared radiation. Water vapor and carbon dioxide in the troposphere also absorb infrared radiation. 

Considerable energy is radiated back from Earth s surface into space as long-wave infrared radiation. The atmosphere absorbs some of this infrared radiation, preventing its loss to space. This trapping is sometimes referred to as the Greenhouse Effect. ... 

Present theoretical efforts that are directed toward a more complete and realistic analysis of the transport equations governing atmospheric relaxation and the propagation of artificial disturbances require detailed information of thermal opacities and long-wave infrared (LWIR) absorption in regions of temperature and pressure where molecular effects are important.2 3 Although various experimental techniques have been employed for both atomic and molecular systems, theoretical studies have been largely confined to an analysis of the properties (bound-bound, bound-free, and free-free) of atomic systems.4,5 This is mostly a consequence of the unavailability of reliable wave functions for diatomic molecular systems, and particularly for excited states or states of open-shell structures. More recently,6 9 reliable theoretical procedures have been prescribed for such systems that have resulted in the development of practical computational programs. 

As shown in Fig. 4-42, carbon dioxide (C02) absorbs the second largest amount of long-wave infrared radiation in the atmosphere (about 32% Mann and Lazier, 1996). Over Earth s history, the predominant natural source of CO2 in the atmosphere has been volcanic eruptions, and the vast majority of that C02 is now stored in ocean sediments and rocks derived from those sediments (Mann and Lazier, 1996). If Earth did not have oceans, the concentration of C02 in Earth s atmosphere would be far higher than it is currently. 

After water vapor and C02, methane (CH4) is the third most important greenhouse gas. Each additional molecule of CH4 added to the atmosphere absorbs about 20 times as much long-wave infrared radiation as does a molecule of carbon dioxide. This occurs in part because some of the absorption spectrum of methane lies in windows in the carbon dioxide absorption spectrum (see Fig. 4-42) therefore, methane absorbs wavelengths that are not already being highly attenuated by carbon dioxide. Currently, the global concentration of methane in the atmosphere is approximately 1.7 ppm and is increasing at an annual rate of approximately 0.01 ppm per year (Table 4-14). The seasonal fluctuations shown in Fig. 4-44 may correspond to seasonal... 

Nitrous oxide (N20), another greenhouse gas, is stable in the troposphere, but oxidizes to ozone-reactive NO in the stratosphere. Molecule for molecule, N20 is currently about 200 times more effective in absorbing long-wave infrared radiation than is carbon dioxide, and its atmospheric concentration... 

In Section 4.6.4, the role of CFCs in stratospheric ozone destruction was discussed. CFCs also are of concern because they are radiatively active in portions of the infrared spectrum not strongly attenuated by water vapor, C02, CH4, or N20. Currently, a CFC molecule added to the atmosphere absorbs about 10,000 times as much long-wave infrared radiation as does a C02 molecule. C02 has a radiative forcing of 1.8 X 10-5 W/(m2 ppb(v)), whereas CFCs range from 0.22 to 0.32 W/(m2 ppb(v)) (Prather et al., 1996). CFCs also have long atmospheric residence times, ranging from 50 to 1700 years. The locations of some CFC absorbance bands are shown in Fig. 4-42. Unlike the several radiatively active trace gases that have both natural and... 

LONG WAVE INFRARED AND TERAHERTZ-FREQUENCY LASING BASED ON SEMICONDUCTOR NANOCRYSTALS... 

AETAIR Center develops long-wave infrared (EWIR) and terahertz-frequeney (THz) lasers operating at room temperature employing intraband lumineseenee in eolloidal semieonduetor nanocrystals, in which the optical transition frequencies can be easily tuned to the desired values by an appropriate choice of the semiconductor material and radius of the nanocrystals. 

Keywords. Semiconductor nanocrystals. Terahertz lasers. Long-wave infrared lasers. 

Long-Wave Infrared and Terahertz-Frequency Lasing 339... 

The material of the prism is important in infrared spectroscopy, since it must be transparent to infrared light. The material most frequently used for analysis in the middle wavelength region is sodium chloride. Prism materials for the analysis of short and long wave infrared light are usually potassium bromide, cesium bromide, and cesium iodide. 

For structural-physical relevant temperatures, 0 = 253-343 K = -20 to 70°C, the energy curves for black-body radiators are shown in Fig. 5.19. As one can see, the maximum energy values lie in the long-wave infrared area. 

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