Modulators, Shutters

As seen from Table 8.8, a-Si H modulators with ferroelectric liquid crystals (FLC) nearly satisfy the requirements listed above. A special type of modulator is liquid crystal shutters, which can be used either in optical data-processing systems or in more traditional applications, such as cameras or printing equipment. Higher operation speed linear arrays of shutters could be made on the basis of ferroelectric liquid crystals. The specification of one of these linear arrays is given in Table 8.9 [27]. 

Shutter arrays of this type are considered to be one of the most important details of the new type of high quality computer printers, and which can compete with the well-known laser jet printers. 

TABLE 8.8. Characteristics of different modulators (r is the total response time, C is the contrast, r is the resolution, and e is the switching energy). 

TABLE 8.9. Ferroelectric liquid crystal matrix array [27] of shutters (for printing machines). 

At present we do not know of any electrooptical effect which can compete in operation speed with ferroelectric liquid crystals. For instance, the record response time for nematic modulators, ever demonstrated [28], is only about 100 fJLS. 

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Shrouds and shutters are essential to cover all live parts in a feeder module that may be exposed to the operator when the feeder door is opened (see Figure 13.3). This is a safely requirement for the operator attending the feeder. There may be two types of... 

For instrument modules, relay and control modules or control panels or all power modules, where an interlock with the door is not possible or is not provided, a proper shroud or shutter must be provided on all exposed live parts rated above 240 V. 

This lest is conducted to establish the satisfactory functioning of mechanical parts, such as switching devices and their interlocks, shutter assembly, draw-out mechanisms and interchangeability between identical draw-out modules, A brief procedure to test these features is as follows. 

The basic experimental arrangements for photocurrent measurements under periodic square and sinusoidal light perturbation are schematically depicted in Fig. 19. In the previous section, we have already discussed experimental results based on chopped light and lock-in detection. This approach is particularly useful for measurement at a single frequency, generally above 5 Hz. At lower frequencies the performance of lock-in amplifier and mechanical choppers diminishes considerably. For rather slow dynamics, DC photocurrent transients employing optical shutters are more advisable. On the other hand, for kinetic studies of the various reaction steps under illumination, intensity modulated photocurrent spectroscopy (IMPS) has proved to be a very powerful approach [132,133,148-156]. For IMPS, the applied potential is kept constant and the light intensity is sinusoid-... 

B. E. Jones and R. C. Spooncer, An optical fibre pressure sensor using a holographic shutter modulator with two wavelength intensity referencing, SPIE Proc. 514, 223 (1984). 

Thin PLZT films deposited by, for example, sputtering are too thin (< 1 /im) to achieve the necessary retardation for transverse mode optical devices. There is, however, potential for films having thicknesses in the range typically 2-25 /mi. If these can be successfully and economically produced then they offer potential for a variety of devices including optical shutters, modulators and displays. 

A low speed shutter (S2) is used for making computer controlled dark current measurements. A high speed electromagnetic shutter (SI, 22-8411, Ealing Corp., South Natick, MA 01760) is used for controlling the time interval that the vidicon is illuminated. Exposure times are entered into the shutter control module from a multiplier and a decade switch register providing shutter times of from 30 ms to 10 s. 

The method of beam modulation used involved the attenuation of the beam by reflection off glass flats. The split bleach and monitoring beams were carefully recombined at the sample. Exposure of the sample to bleach beam was achieved using a computer controlled electronic shutter (UniBlitz SD 1000). The 1/e2 diameter of the Gaussian profile spot and the sample was 2.85 pm. The intensity of the attenuated laser beam was adjusted such that it was below the bleaching threshold of the fluorescent probe. The duration of the bleach pulse was kept below 10% of the recovery time of the sample under test. These measures ensured that the recovery time was not artificially prolonged by overbleaching the sample. The... 

Fig. 1 Descriptive scheme of the experimental setups for dengue virus detection. (A) Photon counting unit. (Al) Hamamatsu HC135-01 PMT Sensor Module. (A2) PMT fixation ring. (A3) Manual shutter (71430, Oriel). (A4) Fiber holder that prevents the movement of the fiber inside the photon counting unit. (A5) Fiber optic. (A6) Connection wire of PMT to computer. (A7) Electricity cable. (B) The outside handle of manual shutter that enables light access to the PMT. (C) Immobilization unit. (Cl) Fiber optic. (C2) lOOpl pipette tip. (C3) Conical tube cup. (C4) Point of fixation of fiber. (C5) Optical fiber core. (C6) Biorecognition elements according to MAC-ELISA chemiluminescent OFIS (Alias et al. 2009). (C7) Test samples. (E) Connection to computer...

Fig. 4.1. Schematic of an experimental set-up for absorption measurements at low temperature incorporating a Perkin-Elmer Model 99G monochromator. Si, S2 and S3 are IR sources selectable with plane mirrors Mi and M2. FM focusing spherical mirrors. Ei and E2 entrance and exit slits. CM off-axis paraboloid collimating mirror. G plane reflection grating. Beam 1 from Si is converted by CM into a parallel beam dispersed by G. One wavelength is diffracted in a direction where it can be intercepted by first mirror M as beam 2 and focused on the internal chopper Ch. Modulated beam 2 is redirected toward G as beam 3 and re-dispersed a second time as beam 4. Beam 4 intercepted by IM is focused on E2 and re-focused on the sample by FM. The divergent monochromatic beam is finally focused on thermocouple D by ellipsoidal mirror EFM. Fi, F2 and Pol are locations for transmission filters and a polarizer. Beam 1 can be blocked by shutter Sh (after [37]). With permission from the Institute of Physics...

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