Recording and Readout Optics

RECORDING AND READOUT OPTICS 16.4.1 Smgle-nioton Recording... 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

The basic components of a spectrophotometer include (1) a light source (2) a means to isolate light of a desired wavelength (3) fiber optics (4) cuvets (5) a photodetector (6) a readout device (7) a recorder and (8) a microprocessor. 

The subsequent thermal processes201 give rise to diffusion of the polycarbonate substrate into the dye layer, decomposition of the dye, and mechanical deformation of the film due to thermal contraction. Each of these processes can contribute to a reduction in the optical path length of the low-intensity readout beam. The optics within the detector are designed such that phase differences due to the optical path length differences cause the light intensity falling on the detector to be reduced when the beam passes over a recorded mark .196... 

We shall assume that the spectrometer basically consists of an entrance slit of area A focused on an exit slit at 1 1 magnification (Fig. 1). The recorded image is blurred because of diffraction and aberrations in the optics between the two slits and because of electronic blur in the readout circuit. The ultimate aim is to deconvolve or restore the spectral image so as to retrieve the spectral pattern at the entrance slit the latter pattern is called the object. 

Summary of LIDA. An optical recording medium, based on the concept of laser induced dye diffusion, has been studied. One micron diameter marks can be generated in less than 10 7 sec with an exposure sensitivity of 100 mJ/cm2. The marks are permanent and a readout contrast density of unity (ODt — ODFlODF, where ODt and ODF are the optical density of the image and film, respectively) is obtained in the transmission mode. Due to the lateral... 

Practical optical memory media should have nondestructive readout capability. Photochromic reactions, in general, proceed in proportion to the number of photons absorbed by the compounds. Such linear-response characteristics cannot be used as the basis of memory media, because recorded memories are destroyed after many readout operations. There are two approaches to avoid such inconvenience one is to introduce gated photochromic reactivity to the molecules, and another is to read the recorded memories by using light whose energy cannot induce photochromic reactions. The former approach will be described in this section. The latter approach will be discussed in Section 7.4. 

The readout result with RCM optics is shown in Figure 16.15. The four recording layers are clearly detected. As a result, it has been determined that the reflection type confocal microscope configuration can be used as a readout system of multilayered optical memory by using the recording medium in which the photosensitive thin films and transparent films are piled up alternately. 

An alternative readout system is a scanning differential phase-contrast microscope with a split detector as shown in Figure 16.5. The optical configuration is compact and easy to align. The memory medium, in which the data bits have been recorded, is located at the focus of an objective lens. The band limit of the optical transfer function (OTF) is the same as that of a conventional microscope with incoherent illumination. The resolution, especially the axial resolution of the phase-contrast microscope, is similar to that obtained by Zemike s phase-contrast microscope. The contrast of the image is much improved compared to that of Zernike s phase-contrast microscope, however, because the nondiffracted components are completely eliminated by the subtraction of signals between two detectors. The readout system is therefore sensitive to small phase changes. 

Colorimetric assays use the optical density of the solution in the well or the kinetic change of the optical density as readout parameter. These assays are typically applied to study the functional activity of enzymes. With an appropriate substrate it is possible to measure the activity directly by recording the color change in the well that originates from the differences in the absorbance spectra between the educt and the product of the reaction. In cases where the educt and product are colorless, a further chemical reaction is carried out to produce a colored final product... 

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