Focal planes

Kidder L H, Levin I W, Lewis E N, Kleiman V D and Heilweil E J 1997 Mercury cadmium telluride focal-plane array detection for mid-infrared Fourier-transform spectroscopic imaging Opt. Lett. 22 742-4... 

After propagation into the back focal plane of tire objective lens, the scattered electron wave can be expressed in tenns of the spatial frequency coordinates k as... 

Figure Bl.18.12. Illustration that only light reflected from object points in the focal plane contributes to the image. If the light is reflected from areas below the focal plane, only a small fraction can pass through the pinliole so that light from those areas does not contribute to the image. The pinliole in front of the detector is exaggerated in size for the sake of presentation.

The extension of the voxel in a radial direction gives infomiation on the lateral resolution. Since the lateral resolution has so far not been discussed in temis of the point spread function for the conventional microscope, it will be dealt with here for both conventional and confocal arrangements [13]. The radial intensity distribution in the focal plane (perpendicular to the optical axis) in the case of a conventional microscope is given by... 

Ions of differing m/z values are dispersed by a magnetic sector and reach foci, which are distributed along a focal plane,... 

The array system is discussed in Chapter 29. With array detection, resolution of m/z values depends both on the analyzer and the collector. Historically, the method for recording ions dispersed in space was to use a photographic plate, which was placed in the focal plane such that all ions struck the photographic plate simultaneously but at different positions along the plate, depending on m/z value. This method of detection is now rarely used because of the inconvenience of having to develop a photographic plate. 

From the early 1980s to present, infrared sensitive two dimensional arrays were mated to integrated circuits for signal processing and sensitivity to better than 0.03 K (see Photodetectors). These focal plane arrays of some 500 by 500 elements eliminate the need for scanning and provide good spatial resolution. Some versions have no special cooling requirements. The development trend is to increase the number of pixels to improve resolution, increase the field of view and keep the size and cost of the optics within acceptable bounds. 

Fig. 1. Schematic for thermographic imaging. The ambient thermal radiation is imaged on the focal plane which converts the infrared to an electrical signal for display on a video monitor. Sensors with uncooled focal planes are now the size of a minicam and cost 5 to 10 times as much.

Cooled focal plane Uncooled focal plane ... 

Fig. 5. The Night Sight commercial thermograph made for all-weather operation uses the uncooled pyroelectric focal plane.

The schlieren microscope is able to detect refractive index variations to six decimal places. Any small difference in optical path (index difference, film thickness, etc) is very precisely detected by the schlieren microscope, especially in the Dodd modification. It is, in effect, a darkfield method. The specimen is illuminated with light in a portion of the illuminating cone and that direct light is masked in the conjugate back focal plane of the objective (Fig. 3). The only light to pass through this plane is refracted, reflected, or diffracted by the specimen. 

Bandwidth Mode Temp., Material Pixel size. Focal plane Principle Cutoff Response Responsivi D, ... 

In the x-ray portion of the spectmm, scientific CCDs have been utilized as imaging spectrometers for astronomical mapping of the sun (45), galactic diffuse x-ray background (46), and other x-ray sources. Additionally, scientific CCDs designed for x-ray detection are also used in the fields of x-ray diffraction, materials analysis, medicine, and dentistry. CCD focal planes designed for infrared photon detection have also been demonstrated in InSb (47) and HgCdTe (48) but are not available commercially. 

AlGaAs quantum well infrared photodetector (QWIP) focal planes have achieved sufficient sensitivity out to 10-p.m wavelength to result in scene temperature sensitivity of ca 0.2°C when the focal plane is cooled to 77 K. Spectral sensitivity is shown in Eigure 9c and array information is given in Table 1. The supedattice, a newer tool for achieving controlled activation energy, should present many alternative infrared detection techniques. 

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