Enhancement Of Two-photon Absorption Research Articles

Mechanisms for enhancement of two-photon absorption in donor–acceptor conjugated chromophores

Abstract Two-photon absorption (TPA) is a nonlinear optical process that is gaining increasing attention since it can be exploited in a number of optical applications. Here, on the basis of correlated quantum-chemical calculations, we investigate the structure–TPA property relationships for donor–acceptor π-conjugated compounds. These relationships provide strategies to design dyes with large TPA cross-sections for fundamental photon wavelengths in the desired 0.6–1.0 μm range of wavelengths.

EFFECT OF FINITE BANDWIDTHS OF LASER FIELDS ON ELECTROMAGNETICALLY INDUCED TWO-PHOTON TRANSPARENCY AND ABSORPTION ENHANCEMENT

The effects of finite bandwidths of laser fields and Doppler broadening on electromagnetically induced two-photon transparency and absorption enhancement in a four-level system have been discussed in this paper.The optimum experimental arrangement of this system for reducing the Doppler effects of the three laser fields has been obtained by the calculation results.

Excitonic enhancement of two-photon absorption in semiconductor quantum-well structures

A theoretical treatment of the excitonic enhancement of two-photon absorption is presented for quasi-twodimensional quantum-well structures. The two-photon absorption coefficient and the nonlinear index of refraction are calculated for TM and TE polarizations. Significant enhancement is observed in the TM case as a result of excitonic effects. This treatment differs from previous ones in that simple analytical expressions are derived. Moreover, we consider the asymptotic behavior as the size of the quantum well increases toward a three-dimensional system.

Resonant enhancement of direct two-photon absorption in Tb3+:LiYF4.

Resonant enhancement by a factor of over 20 of direct two-photon absorption from the ground state $^{7}\mathrm{F}_{6}$ to the excited state $^{5}\mathrm{G}_{6}$ of the 4${f}^{8}$ configuration of the ${\mathrm{Tb}}^{3+}$ ion at 40 200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has been observed in time-resolved experiments with two separate pulsed lasers. The results provide clear evidence for resonant enhancement of two-photon absorption in rare-earth compounds and imply a similar enhancement for Raman scattering and nonlinear-optical mixing. Two separate contributions to the direct transition moment were observed. When a single laser frequency was used, the intermediate states which made the largest contribution were from excited configurations of opposite parity; those intermediate states were far from resonance. Detailed two-frequency experiments showed, however, that near a single photon $^{7}\mathrm{F}_{6}$${\mathrm{\ensuremath{-}}}^{5}$${\mathrm{D}}_{4}$ resonance, a much stronger contribution arose from the 4${f}^{8}$ configuration $^{5}\mathrm{D}_{4}$ intermediate state. Two-photon absorption was clearly isolated from two-step (incoherent) excitation by varying the timing of two separately triggered lasers.