Wavelength “cutoff

Hg Cd Te is an example of a ternary detector, in which the value of x controls the cutoff wavelength. Photoconductive detectors are generally simpler to couple to low noise amplifiers photodiodes generally have lower power consumption because these have no external bias, and better high frequency performance (15,16). 

Photodetectors exhibit well-defined, cutoff wavelength thresholds, the positions of which are determined by the magnitudes of the band gap activation energy, E, or impurity-activation energy, E. The cutoff wavelength, corresponds to a photochemical activation energy, E, where. 

Fig. 3. Ideal photon detector sensitivity as a function of cutoff wavelength. Lower background flux generates less photon-induced noise giving higher sensitivity. The sensitivity limit for the condition of 300 K background temperature and hemispherical (27T) field of view is shown.

The choice of a detector for a specific appHcation should be made in order to minimize the cooling requirements and the magnitude of the background radiation noise therefore, in detector selection the cutoff wavelength should be only slightly greater than that required by the appHcation. If the... 

HgCdTe photodiode performance for the most part depends on high quantum efficiency and low dark current density (83,84) as expressed by equations 23 and 25. Typical values of at 77 K ate shown as a function of cutoff wavelength in Figure 16 (70). HgCdTe diodes sensitive out to a wavelength of 10.5 p.m have shown ideal diffusion current limitation down to 50 K. Values of have exceeded 1 x 10 . Spectral sensitivities for... 

Fluorescent ultraviolet lamps within an apparatus that allows condensation cycles rather than the water spray typical of xenon arc tests have been developed for plastics testing (279). The spectral cutoff wavelength of the lamps used in the apparatus determines the severity of the test. Ultraviolet B (UVB) 313 lamps allow a significant irradiance component below 290 nm, which is normally filtered out by the earth s atmosphere. Ultraviolet A (UVA)... 

Table 5. Variation of bandgap and cutoff wavelength of Hgi- Cd Te as a function of the concentration, x, of cadmium.

Some common solvents and their UV cutoff wavelengths... 

In the previous example, we have calculated the plasma frequency for metallic Na from the free electron density N. In Table 4.1, the measnred cutoff wavelengths, Xp, for different alkali metals are listed together with their free electron densities. The relatively good agreement between the experimental values of Xp and those calculated from Equation (4.20), within the ideal metal model, should be noted. It can also be observed that the N values range from abont 10 to about 10 cm leading to... 

Table 4.1 Calculated and measured cutoff wavelengths for alkali metals...

Typical UV Cutoff Wavelengths for Some Commonly Used HPLC Solvents and Buffer Components, Taken Primarily from Manufacturer Product Specifications... 

Table 25-2 Eluotropic series and ultraviolet cutoff wavelengths of solvents for adsorption chromatography on silica...

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