Intense Two-photon Absorption Research Articles

Polarization dependence of two-photon absorption and electronic Raman scattering intensitiesin crystals

A formalism using the properties of the irreducible representation of the scattering tensors has been developed to predict up to the third order the polarization-dependent behavior of the electronic Raman-scattering intensities and the two-photon absorption intensities of transitions between Stark levels. The polarization behavior of ions in crystals are tabulated for the 32 crystallographic point groups. The theory provides a stringent test for the Judd-Ofelt-Axe theory for two-photon intensities between Stark levels.

The intensity of two-photon absorption in transition-metal ions: Ni2+ ions in octahedral symmetry

Recently, Campochiaro et al. [1] reported two-photon absorption (TPA) spectra of Ni2+ in MgO. The transitions between the ground state 3A2 and the spin-orbit components of 3T2 Level are of special interest since their intensities exhibit interesting polarization dependence with an anisotropy rate very far from predicted. In the present paper the TPA transition probabilities between the symmetry adapted weak field eigenstates of the Ni2+ ion have been calculated by means of methods developed by Racah [11] and followers [2, 3]. It appeared that within the simplest, second-order mechanism the polarization ratios are in good agreement with experimental data.

Study of the Lowest Electronic States in a Polythiophene Oligomer, α-Sexithienyl, by One and Two-Photon Spectroscopy

Abstract α-sexithienyl (T6) is a large rigid rod molecule with twelve conjugated double bonds. The electronic structure of T6 has been investigates by one-photon and two-photon spectroscopy as well as by photoconductivity. From the single crystal polarized spectra at 4.2K we observe that the lowest allowed π-π transition (λmax = 478 nm) is polarized parallel to the long molecular axis and a second intense transition at 370 nm is polarized parallel to the short in plane axis. The two-photon excitation spectra in polycristalline thin films have been investigated at 4.2 K in the spectral range between 910 and 1180 nm of the fundamental laser radiation. The intense two-photon absorption band at 544.9 nm is assigned to the 2lAg exciton band origin. The lowest “gerade” exciton level lies therefore at 898 cm−1 above the lowest one-photon allowed 11Bu exciton level. The photophysics of T6 is studied by photoconductivity and one-photon excitation spectroscopy. An efficient pathway for carrier generation open up at...

Location of the low-energy 1Ag state in a polythiophene oligomer by two-photon absorption spectroscopy: alpha -sexithienyl.

The two-photon excitation spectrum in polycrystalline α-sexithienyl (T 6 ) thin films has been investigated at 4.2 K in the spectral range between 910 and 1180 nm of the fundamental laser radiation. The intense two-photon absorption band at 18 350 cm -1 is assigned to the 2 1 A g exciton band origin. The comparison of the one-photon and two-photon excitation spectra shows that the lowest gerade exciton level lies at 898 cm -1 above the lowest one-photon-allowed 1 2 B u exciton level.

Coulomb correlations and two-photon spectra of conjugated polymers

Electron—electron correlations in conjugated polymers are shown to produce weak two-photon absorption (TPA) below the one-photon gap E g and intense TPA above E g. TPA intensities vary strongly with the alternation δ of transfer integrals t(1 ± δ) and with U/t in Hubbard models. Pariser—Parr—Pople (PPP) models reconcile TPA spectra of conjugated molecules and polymers.

Two-photon absorption in lanthanide complexes

A theoretical description for two-photon absorption (TPA) in lanthanide complexes developed in this paper is based on the independent systems model. The contributions to the TPA intensities coming from the static and dynamic coupling mechanisms, and cross terms between them, are calculated by tensorial techniques. An appropriate expression for manifold-to-manifold J-J' TPA transition intensity is calculated.

Two-photon absorption in lanthanide(III) systems: the effect of anisotropy of the ligand

A general model for two-photon absorption in lanthamde complexes based on the independent-systems model is presented. This model includes contributions arising from the static and dynamic coupling mechanisms. The ligand anisotropy is considered. In particular the expression for the manifold-to-manifold J— J' two-photon absorption intensity is calculated.

Intensity of two-photon excitonic absorption in two-band and three-band models

The intensity of two-photon absorption to Wannier excitons is estimated in simplified models. Both two-band and three-band models simultaneously contribute to the optical two-photon spectrum, but it is shown that the two-band model is favoured in crystals with relevant electron-hole interaction. As an example, it is explained why two-photon absorption spectrum in CuCl exhibits 1 s, 2 p, 3 p exciton states.