Saturation high-intensity limit

High intensity limit (saturation). Consider the rate equation for level 2 of our simple atom, Equation 6a. In the limit of large energy density, this equation reduces to... 

At low exciting intensities the linewidths (Fig. 7(a)) reach a value of 7.3 + 0.8 MHz in agreement with the lifetime-limited value, and the fluorescence emission rate increases almost linearly. In the high-intensity limit, the peak fluorescence emission rate saturates at 7.2 + 0.7 x 10 photons/s (Fig. 7(b)). As the peak emission rate saturates, the emission rate in the wings of the excitation spectrum continues to increase with intensity, and the linewidth broadens as shown in Fig. 7(a). Actually,... 

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]. 

The threshold limits of chemical compounds can lie over a range of 10 orders of magnitude or more (Table 13-3). The saturated hydrocarbons and organic solvents have high threshold limits and are as a consequence relatively odorless. Esters of acrylic acid and a,fl-unsaturated ketones and aldehydes belong to intensive aroma compounds. 

To estimate /, which gives good correspondence between Eqs. (1) and (3) in the high-intensity range we equate (1) with (3) in asymptotic limit / —>oo. Then we omit all terms in the denominators in Eqs. (1) and (3) which do not contain the intensity / of the driving field and obtain the following expression for the saturation intensity ... 

The maximum attainable deceleration is obtained for very high light intensities, and is limited because the atom must then divide its time equally between ground and excited states. High intensity light can produce faster absorption, but it also causes considerable stimulated emission. This produces neither deceleration nor cooling because the momentum transfer is in the opposite direction to what it was in absorption. The deceleration therefore saturates at the value a(max) = hv/2McT where x is the excited state lifetime. 

Anodic dissolution of n-Si can also proceed at a polarization under illumination. The maximum current is limited by illumination intensity when the saturation photo current density is lower than the critical current, Ji. The characteristics of i-V curves of n-Si under a high illumination intensity, when the reaction is no longer limited by the availability of photo generated carriers, is identical to that for p-Si. Similar also to p-Si, formation of PS on n-Si occurs only below the critical current, Jx 24... 

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