Contrast Ratios

Contrast Ratio Cq The contrast ratio is established on the basis of the ratio of the amplitude of the unattenuated radiation to the amplitude after attenuation through a test piece. This test piece is a lead disk which is mounted in the middle of the image converter it masks approximately 10% of the surface of the image converter. 

An additional limit to the size of a passive array relates to the current which flows in an OLED when it is under reverse bias [189]. When a given pixel is turned on in the array, there are many possible parallel paths for the current, each involving two diodes in reverse bias and one forward. Hence, as the number of rows and columns increases, there is a higher level of background emission from non-selected pixels that limits the contrast ratio of the array. As a result, the contrast degrades as N increases. 

The upper limit for passive matrix OLEDs thus depends on many factors, including the reverse current of the diodes, the current delivery of the row drivers, the roll-off in OLED power efficiency, and the brightness and contrast ratio requirements of the application. The practical limit is probably less than VGA resolution (480 rows by 640 x 3 columns, where the factor of 3 reflects the RGB subpixels for color) for power-sensitive portable applications. However, such considerations are less important where a wall-plug is available and one company in Japan (Idemitsu Kosan [190]) has demonstrated full color television using passive OLED arrays. 

The main technique that has been used for the measurement of opacity has been to prepare a standard disc of AB cement 1-0 mm thick and aged for 24 hours at 37 °C. This disc, contained in a small trough of water to prevent desiccation, is placed in a reflectometer on a black background. It is then illuminated with diffuse light and the amount of light reflected from it, is measured. The disc is then placed on a white background of 70% reflectivity, and the new amount of reflected light, measured. The contrast ratio 7 o/ o is defined as the Cp., opacity (Crisp et al., 1979). 

Based on C-H versus C-D zero point vibrational differences, the authors estimated maximum classical kinetic isotope effects of 17, 53, and 260 for h/ d at -30, -100, and -150°C, respectively. In contrast, ratios of 80,1400, and 13,000 were measured experimentally at those temperatures. Based on the temperature dependence of the atom transfers, the difference in activation energies for H- versus D-abstraction was found to be significantly greater than the theoretical difference of 1.3kcal/mol. These results clearly reflected the smaller tunneling probability of the heavier deuterium atom. 

It is important, however, to realize that whilst many types of chemical species exhibit electro-chromism, only those with favorable electrochromic performance parameters1 are potentially useful in commercial applications. Thus, most applications require electrochromic materials with a high contrast ratio, coloration efficiency, cycle life, and write-erase efficiency.1 Some performance parameters are application dependent displays need low response times, whereas smart windows can tolerate response times of up to several minutes. 

Recent review articles ([16,17] and references therein) allow the interested reader to get a broader picture of this exciting research domain and related applications. In the following (Sect. 10.2), we will mainly devote ourselves to the principles of the main ion acceleration mechanism, and to the way the temporal profile of the laser pulse, and more specifically the beam contrast ratio, can influence it. In particular, we will briefly review the main theoretical and experimental published work concerning the action of a plasma gradient on ion acceleration characteristics. Section 10.3 presents the contrast improvement device we have implemented for our laser beam, and the related temporal profile measurements. In Sect. 10.4, we will show and discuss the main results obtained using ultra high contrast (UHC) laser pulses in laser-driven ion acceleration experiments. Finally, an example of the exploitation of the particular features of UHC pulses in laser-driven ion acceleration will be given in Sect. 10.5. 

As a consequence, the optimal thickness Lopt introduced above corresponds, for a given set of laser parameters (pulse duration and intensity, contrast ratio, and pre-pulse duration), to the thickness, allowing the perturbations due to the pre-pulse from the front surface, which travel at typical... 

Conical emission, 85, 89, 93 Constructive interference, 66 Continuous wavelet transforms, 145 Contrast ratio, 142-144, 191 Conversion efficiency, 96 Corona discharges, 110 Counter-propagating laser pulses, 171 CPA, 187 Critical power, 83 Cross section, 125... 

Fig. 8.12 Inverse of the detection factors using (a) homogeneous and (b) surface sensing, (c) contrast ratio, and (d) ON resonance dropping coefficient are plotted as a function of IF and Rc for a doubly coupled microring with a gap of 250 nm. Reprinted from Ref. 45 with permission. 2008 Institute of Electrical and Electronics Engineers...

Size Format Resolution Contrast ratio Full white brightness Power consumption Color gamut Luminance uniformity Pixel count... 

Contrast ratio (CR) of an OLED display is very much dependent on the ambient and the lighting conditions. The actual CR for an OLED display is based on the applications and is different depending on the products such as in-car audio, hand phone, etc. Usually for indoor... 

Copolymers of thiophenes and didodecyloxybenzenes have been synthesized as well, exhibiting multicolor electrochromism coupled with high contrast ratios and fast response times (Scheme 8) [45]. Since all three basic colors in the RGB (red-green-blue) system can be obtained, the material is a potential candidate for display applications. 

The polymer-dispersed liquid crystal was used as a modulating medium in optically controlled modulators instead of the liquid crystal [261-264], The sandwiched structure from polyimide photosensitive film and the polymer dispersed liquid crystal film - i.e. the optically controlled solid state modulator -had the characteristics presented in Fig. 36 [261]. Contrast ratio 35 1, response time > 400 ps, decay time 80 ms and sensitivity 5 x 10 sJcm 2 were obtained. 

Fig. 36. Contrast ratio (/), switch on (2) and switch off (3) times versus voltages for modulator with polymer dispersed liquid crystal. Photocon-ductor-polyimide film. Pulse regime [261]...

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