Black body source

There are few models with automatic test capability. Testing is usually limited to hand held devices only 2 meters (7 ft.) from the detector or directly on the lens test unit. It can be ineffective if ice forms on the lens. It is sensitive to modulated emissions from hot black body sources. Most of the detectors have fixed sensitivities. The standard being under five seconds to a petroleum fire of 0.1 square meter (1.08 sq. ft.) located 20 meters (66 ft.) from the device. Response times increase as the distance increases. It cannot be used in locations where the ambient temperatures could reach up to 75 °C (167 °F). It is resistant to contaminants that could affect a UV detector. Its response is dependent on fires possessing a flicker characteristic so that detection of high pressure gas flames may be difficult. 

The problem is praticularly serious for the very weak metal-adsorbate bonds which are expected in the far-infrared region. Recently the IR radiation from a synchrotron has been used as a source for in-situ measurements at the electrode-solution interface [19]. The far-IR radiation from a synchrotron has an intensity between 100 and 1000 times higher than standard black body sources. 

The actual color appearance of light that comes from a "black body" source is called its color temperature or chromaticity. Correlated color temperature (CCT) is the terminology used when referring to the color of an artificial source. Because the color temperature of an artificial source will most likely not fall on the normal black body curve, it is the accepted practice to refer to their temperature as the temperature of the closest CIE daylight (D) temperature value. Hence, a CCT of 6500 K means that its color temperature is closest to that of CIE D6500 daylight standard. 

Response Calibration with a Black-Body Source... 

Black-body sources have the attraction of being primary standards but are rather cumbersome. A quite hot furnace is required to produce sufficient intensity, particularly at visible wavelengths. In addition, the source is usually too large to be positioned near the sample region (assuming the spectrometer could tolerate the heat ), so coupling optics are required. These optics should attempt to position the source image at the normal laser and collection focus and may not introduce their own response function. At least for routine use, a black-body radiator is unlikely to be practical. 

Infrared radiation is essentially heat, and so hot wires, light bulbs, or glowing ceramics are used as sources. The energy distribution from the black-body sources tends to peak at about 100 to 2000 run (near-IR) and then tails off in the mid-IR. Infrared spectrometers usually operate from about 2 to 15 pm, and because of the relatively low-intensity radiation in this region, relatively large slits... 

An optimal optical design successfully focuses all of the available source photons onto the detector. Frequently, the limiting factor in these designs for black-body sources, is that the light emits in a 4k steradian angle, and is therefore difficult to completely... 

Principle of IR sensor with black-body source. 

There was also described and discussed the relatively new Fourier transform infrared emission spectroscopy (IRES), its principle, an appropriate FT-IRES setup and applications. FT-IRES is unique in that it does not require an external radiation source, because the sample itself is the source. The radiation emitted from the sample is collected and sent to the detector. The ratio of the sample signal to that from a black body source represents the spectrum. However, appli-... 

It is assumed that the reader is broadly familiar with the properties of semiconductors, from which most detectors of importance are prepared, and with semiconductor technology which allows the preparation of interfaces such as p — junctions and Schottky barriers. For those who are not familiar with these concepts, many good books are available, including those by Sze [2.25], Grove [2.26], Kittel [2.27], and Moll [2.28]. It is also assumed that the reader is aware of the nature of electromagnetic radiation, including the properties of monochromatic and black body sources. For further information on this topic see the appropriate chapters in [2.1-7]. 

Because the performance of infrared detectors is limited by noise, it is important to be able to specify a signal-to-noise ratio in response to incident radiant power. An area-independent figure of merit is D ( dee-star ) defined as the rms signal-to-noise ratio in a 1 Hz bandwidth per unit rms incident radiant power per square root of detector area. D can be defined in response to a monochromatic radiation source or in response to a black body source. In the former case it is known as the spectral D, symbolized by Df X, f, 1) where A is the source wavelength,/is the modulation frequency, and 1 represents the 1 Hz bandwidth. Similarly, the black body D is symbolized by Z> (T,/1), where T is the temperature of the reference black body, usually 500 K. Unless otherwise stated, it is assumed that the detector Held of view is hemispherical 2n ster). The units of D are cm Hz Vwatt. The relationship between )J measured at the wavelength of peak response and D" (500 K) for an ideal photon detector is illustrated in Fig. 2.14. For an ideal thermal detector, Df = D (T) at all wavelengths and temperatures. 

Table 2.6. Signal fluctuation limit for 500° K black body source, 1 Hz bandwidth, and unit quantum efficiency in terms of long wavelength limit 2o...

Fig. Z16l Dependence of the function G upon detector cutoff wavelength Aq for black body source temperatures of 290 K, 400 iC. and 500 K and field of view of 2n steradians (after Kruse el al. [2.3, p. 363])...

The radiance Le> particle radiance Z.p, and luminance Ly are important characteristic properties of sources, not radiation fields. For a black-body source, the radiance Le> for example, is dependent only on the frequency of the radiation and the temperature of the black body. The dependence is given by Planck s radiation law. In optical imaging, the radiance Le of an object turns out to show an invariant property. In correct imaging, the image always radiates with the same radiance Le as the object, independent of the magnification. 

The emissivity (e) for any black body source is defined as the ratio of the emitted radiance (p) by the source to the radiance of a black body (BB) at the same temperature and frequency (wavelength). The following illustrates this ... 

What is the energy density of radiation at 500 nm emitted by a black-body source at the surface temperature of the sun (6,600 K) ... 

If a sample absorbs IR radiation at characteristic wavenumbers, it is capable of emitting radiation at these wavenumbers. A thin sample of a material will emit radiation with a spectrum very similar to its absorption spectrum. By ratioing the emitted radiation from the thin film to that from a black body at the same temperature, an emissivity spectrum is obtained which generally has the appearance of an inverted transmission spectrum. Emission spectra used to be collected from samples heated well above r.t., typically to 40-100°C (to minimise sample degradation), with a black-body source (e.g. graphite) at the same temperature as a reference. With FTIR instruments, emission spectra can also be recorded at room temperature. 

The sample analysis process is quite simple using a modern spectrometer coupled with a powerful computer. Infrared energy is emitted from a glowing black-body source. This beam passes through an interferometer where the spectral encoding ... 

Figure 6 Optical layout of a practical Michelson interferometer. So is a black-body source and D an IR detector M3 and M4 are parabolic off-axis mirrors. M3 and M4 may also be normal parabolic mirrors as in Figure 7.

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