Nonlinear optical transmittance

Frequency Doubling. As the name implies, in frequency doubling a substance doubles the frequency of the incident laser radiation. This effect is important in telecommunications and optical data storage. For example, in telecommunications the most efficient way to transmit data is by using infrared radiation, e g., 1200 nm radiation from an indium phosphide laser [60], Detection of infrared radiation is inefficient. In contrast, visible radiation is much easier to detect but is an inefficient transmitter of data. Consequently, an important application of nonlinear optical (NLO) materials is to convert infrared radiation into visible and thus enable easier detection of the signal. 

OKS Measurements of PDA Microcrystals. In OKS experiments, the probe beam through two polarizers in a cross Nicol state was detected because of the induced birefringence resulting fi om high intensity gate light incident upon the sample. The value was evaluated by probe transmittance (T). Equations (1) and (2) show the relationship between T and the nonlinear optical coefficient (n2) as follow ... 

Optical properties Uniaxial Isotropic Nonlinear optical response Structure- dependent properties 97.7 % of optical transmittance... 

There is a close relation between NLO and optical limiting (OL) properties. The main mechanisms to achieve OL are nonlinear absorption (NLA) and nonlinear refraction (NLR), but other effects such as nonlinear scattering can also contribute to OL. Materials with a positive NLA coefficient exhibit reverse saturable absorption (RSA), causing a decrease in transmittance at high intensity levels, and so operate as optical limiters [14]. 

Up to now, most proposals for photobleaching image enhancement have relied on linear photochemistry, in which the transmittance is a function only of total dose, and not on the rate at which that dose is delivered. The kinetics of such linear photochemistry are well understood and have been described analytically (28). The exposure depends solely on a single parameter which is the product of extinction coefficient, quantum yield, intensity, and time. No increase in contrast can be obtained by changing extinction coefficient or quantum yield, since this merely scales the dose. Contrast can be increased only by increasing the initial optical density, which increases the dose requirement. Only with nonlinear (intensity dependent) photochemistry can one obtain steeper bleaching curves at a specified optical density. 

Most transducers converting chemical concentration into an electrical signal have a nonlinear response for example, electrode potential and optical transmission are not directly proportional to concentration. In general, this nonlinearity is easily and simply corrected in equilibrium analytical measurements. However, it is considerably more difficult to instrumentally correct the response-versus-concentration function in reaction-rate methods, and often the correction itself can introduce significant errors in the analytical results. For example, the simple nonlinear feedback elements employed in log-response operational-amplifier circuits are not sufficiently accurate in transforming transmittance into absorbance to be used for many analytical purposes. 

Optical limiting threshold (incident fluence at which the nonlinear transmittance is 50% of the linear one). 

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