Figure 3 describes the open-aperture z-scan data (80 fs at 830 nm excitation wavelength) resolving a two-photon absorption effect; that is, a diminishing transmittance at the focal plane can be seen.

Expression (6) clearly shows that the inverse of the transmittance ([T.sup.-1]) is a linear function of input irradiance, with the slope related to the two-photon absorption coefficient [beta].

It has been previously reported that two-photon absorption can be switched to saturated absorption in nanostructures by changing the wavelength that gives rise to the nonlinearity [26].

The increase in the pulse repetition rate of the laser system can result in the switch from saturated absorption to two-photon absorption in the sample, allowing attractive applications to be considered.

Solidification is performed in a highly localized volume because of the quadratic dependence of the

two-photon absorption probability on the laser intensity.

Two-photon absorption (TPA) is a third-order nonlinear absorption process which is closely related to the imaginary part of nonlinear susceptibility of the material [1].

Then, the electric field modulation effect of two-photon absorption coefficient (TPAC) in HgCdTe photodiode is simulated from a two-band model.

We compared the simulation results with the two-photon absorption experimental results of HgCdTe photodiode [6].

Rana, "Energy limits imposed by two-photon absorption for pulse amplification in high-power semiconductor optical amplifiers," Optics Letters, vol.

(21) have reported decrease of [[beta].sub.eff], with increasing [I.sub.o] for the thiophene oligomers, where they attributed to saturation of instantaneous

two-photon absorption.

Previously, efforts to create a silicon laser were thwarted by

two-photon absorption which hindered the light amplification.

Importantly, in order to increase even further the potential of the PSs presented in this project, I propose to also excite them via simultaneous

two-photon absorption (TPA) in the so-called two-photon excitation PDT (2 PE-PDT).