Polarization Dependence Of Two-photon Absorption Research Articles

Time-resolved two-photon excitation of long-lifetime polaritons

Recent studies of two-photon excitation of exciton-polaritons in microcavities have considered the possibility of an allowed absorption process into the 2p-state of the excitons that participate in the polariton effect. Here we report time-resolved measurements of two-photon excitation directly into the lower polariton states, invoking the 1s state of the excitons. Although this process is forbidden by symmetry for light at normal incidence, it is allowed at a nonzero angle of incidence due to state mixing. We examine the polarization dependence of two-photon absorption at finite k both theoretically and experimentally. Previous results should be reevaluated in light of the mechanism observed here.

Polarization dependence of a GaAs-based two-photon absorption microcavity photodetector

In this paper, the polarization response of a GaAs based two-photon absorption microcavity photodetector has been studied. The deviation in the dependence of the detector response from that of bulk GaAs is shown to be due to the birefringence of the cavity. A theoretical model based on the convolution of the cavity birefringence and the polarization dependence of two-photon absorption in GaAs is described and shown to match the measured polarization dependence of the microcavity detector very well.

Polarization Dependence of Two-Photon Absorption in Si Avalanche Photodiodes

The polarization dependence of two-photon absorption (TPA) in Si avalanche photodiodes was investigated experimentally at room and low temperatures. Cross-TPA was selectively detected by using a lock-in amplifier that detects photocurrent that is synchronized to the sum frequency of two mechanical choppers. The polarizations of the two beams were independently controlled. Polarization dependence is discussed in terms of the non-diagonal elements of the third-order nonlinear susceptibility tensor. When one of two beams is circularly polarized, the dependence of the TPA efficiency on the polarization of the other beam was very weak. However, the dependence becomes greater at low temperatures as a result of the temperature dependence of the nonlinear susceptibility tensor.

Polarization-insensitive cross correlation using two-photon absorption in a silicon photodiode.

We present experimental measurements of the polarization dependence of two-photon absorption in silicon photodiodes at 1550 nm, and we offer a simple theory that explains our observations. Based on this theory, we propose and demonstrate that it is possible to construct an optical cross-correlation system that is polarization insensitive, provided that one of the two input polarization states can be controlled.

Optical anisotropy investigation in multi-quantum wells by two-photon spectroscopy

The light polarization dependence of two-photon absorption (TPA) near half the band gap has been experimentally investigated in strained-layer multi-quantum wells. A detailed analysis of their TPA photoluminescence spectra, measured for two different polarization configurations of the exciting laser beam (perpendicular and parallel to the QW growth axis z), permitted us to sensitively probe the exciton anisotropy in quasi-bidimensional (Q2D) heterostructures. Fundamental and excited exciton states of different symmetry have been selectively detected by exploiting the strong anisotropic selection rules for TPA processes. In particular, the polarization along the z axis allowed us to obtain the first clear experimental evidence of higher-order light-hole excitons. Our experimental results are in good agreement with theoretical predictions of an analytical model of TPA in Q2D exciton systems, demonstrating the usefulness of a simplified approach for the case of photon energies close to half the band gap.

Polarization dependence of two-photon absorption in an AlGaAs waveguide autocorrelator

We have obtained the complete polarization dependence of the two-photon absorption coefficient beta by measuring the orientational dependence and the contrast ratio of the photocurrent in an Al(0.2) Ga(0.8) As waveguide autocorrelator at an optical frequency far above the half-bandgap. The measured polarization dependence is consistent with theory and previous picosecond nonlinear transmission experiments. The cubic symmetry of the nonlinearity provides a contrast ratio that exceeds 2, which is larger than would be obtained assuming an isotropic medium and Kleinmann symmetry. This device was used to obtain an autocorrelation of a mode-locked Nd:YLF laser.

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.

Polarization dependence of two-photon absorption in ZnSe-ZnSSe strained-layer superlattices

We report two-photon absorption photoluminescence excitation (TPA-PLE) measurements in ZnSe/ZnSSe strained-layer superlattices (SLS). Polarization dependent selection rules are observed in TPA spectra depending on the direction of the exciting field with respect to the growth axis of the SLS. Moreover a comparison between the theoretical predictions for TPA transition rates and experimental results has been attempted.

Theory of the Polarization Dependence of Two-photon Absorption in Zinc-blende Semiconductors

Abstract The polarization dependence of two-photon absorption is calculated for several zinc-blende semiconductors. The spectral dependence of the linear/circular dichroism is determined using an isotropic, four-band Kane band-structure model and is shown to have specific features associated with the split-off band. The crystalline orientational dependence is determined using an anisotropic band-structure model obtained by additionally including the next highest upper conduction band set. It is shown that the anisotropic behaviour of the two-photon absorption is small in InSb but is quite substantial in GaAs giving a variation in the two-photon absorption coefficient for linearly polarized light of around 70% at a wavelength of 1 μm.

One- and two-photon spectroscopy of monovalent copper ions in calcium fluoride

The spectroscopy of Cu+ ions embedded in an alkaline earth fluoride (CaF2) is reported for the first time. The absorption, emission and excitation spectra, as well as the lifetimes have been studied as a function of the temperature. It is shown that Cu+ ions occupy non-centro-symmetric sites. Furthermore, the analysis of the polarization dependence of two-photon absorption shows that, in fact, Cu+ ions appear to be located at sites of nearly cubic symmetry, in off-centre positions in the cube. The 1E and 1T2 singlet states are responsible for the main absorption in the near-UV range, and the emitting level is shown to be the 3T2 triplet state. This state is in fact split by the spin-orbit coupling into four components, but two close sub-levels could be responsible for the strong temperature dependence of the lifetime in the low-temperature range.

Solvent perturbations on the excited state symmetry of randomly oriented molecules by two-photon absorption

The polarization dependence of two-photon absorption is used to determine the excited state symmetry of solute molecules dissolved in room temperature liquids. Perturbations of excited state symmetry are interpreted as solvent induced state mixing in the solute. Using a first-order expansion in the zero-order system wave functions, an expression is derived which describes the effects of solute–solvent electric dipole interactions on the symmetry of the solute excited state. Measurements on the S0→S1 0–0 band of fluorene in nonassociating polar and nonpolar liquids are fit well by the derived expression, using continuum reaction field models. Deviations from the derived expression are found when fluorene is dissolved in liquids capable of self-association or complexation with aromatic solutes. In n-alcohol solvents, perturbations on the excited state symmetry of fluorene are adequately accounted for using Kirkwood g factors for the solvent.

Two-photon absorption and energy band structure of orthorhombic Hg2Cl2 crystals

Dependence of two-photon absorption (TPA) rate on the state of polarization of a laser beam is investigated in the low-temperature orthorhombic modification of Hg2Cl2 crystals. Theoretical calculations of the dependence of TPA rate on the direction of polarization vector of the beam are performed for centrosymmetric pointsγ, Y, Z, T, R andS of the Brillouin zone. The domain structure of real crystals is taken into consideration and it is shown that periodicity of the polarization dependence may indicate whether TPA is due to transitions either atγ, Y, Z, T orR, S points. The polarization dependence of TPA cannot, however, distinguish between points inside these two groups. Comparison of theory with a low-temperature (T ∼ 8·5 K) experimental curve of polarization dependence is discussed. It is shown that the experiment can be explained in main features by a model of noninteracting oriented linear dipoles. Further, on the basis of TPA measurements, a simple energy band structure of Hg2Cl2 is proposed regarding Hg2Cl2 crystal as a linear chain of molecules.

Photoacoustic study of two-photon absorption in hexagonal ZnS

Photoacoustic detection technique is employed to investigate two-photon absorption (TPA) effects in ZnS over a wide frequency range with polarized 5 nsec dye laser pulses. By analyzing the dispersion and polarization dependence of TPA, we find that near the band gap, the TPA in ZnS occurs via allowed-forbidden type one-step, two-photon transitions.

Polarization dependence of near-resonant two-photon absorption of Na 2 vapor

We report theoretically and experimentally on the polarization dependence of two-photon absorption of diatomic molecules for the case where only one intermediate rotationvibration level (off-resonance Δ) contributes to the transition strength. In this case, in the classical limit ( J → ∞), the polarization between is (i) independent of the electronic symmetries, and (ii) it can be different for the regime Δ ⪢ Δ v D and Δ ≈ Δν D, due to velocity-tuning. The experiments have been performed on the 16601.88 cm −1 two-photon transition of Na 2; they show that this transition belongs to the Q-branch.

Anisotropy in two-photon direct creation of biexcitons in CuBr cubic crystals

The polarization dependence of two-photon absorption is considered in the case of CuBr crystals. Geometrical selection rules for direct creation of Γ 1, Γ 3 and Γ 5 biexcitons are provided. Using the fact that the absorption to Γ 3 and Γ 5 final states exhibits anisotropy with respect to the crystal axes, several geometrical situations for separating experimentally biexciton lines are discussed.

Two-photon absorption at a band edge with spheroidal energy surface

Mahan's isotropic two-band model for the polarization dependence of two-photon absorption is generalized to the case of spheroidal energy bands in a cubic crystal.

Polarization Dependence of Two-Photon Absorption in Solids

The polarization dependence of the rate of two-photon absorption has been calculated for all 32 crystallographic point groups. The method used by Inoue and Toyozawa to compute the polarization dependence of transitions from a ${\ensuremath{\Gamma}}^{1}$ (identity representation) ground state to an excited state of symmetry ${\ensuremath{\Gamma}}^{\ensuremath{\alpha}}$ (any single-valued representation) is extended to include all allowed two-photon transitions between pairs of states, each transforming according to any representation of the point group, including the double-valued representations. The results, presented in tabular form, are applicable to the analysis of transitions at point defects, and of band-to-band and exciton transitions at the center of the Brillouin zone.