Role of optical interference effects in the enhancement of magnetization-induced second-harmonic generation

Received: 14 October 1998     

Nonlinear magneto-optical diffraction by two-dimensional magnetic superstructures

Nonlinear (at the second-harmonic frequency of the incident light) optical reflection by two-dimensional magnetic superstructures is theoretically studied. A square lattice of magnetic dots and a hexagonal lattice of magnetic bubbles (cylindrical magnetic domains) are considered. Because the periods of these structures are comparable with the wavelengths of the fundamental and the second-harmonic radiation, it would be possible to observe diffraction at the second-harmonic frequency. A polarization analysis of nonlinearly diffracted radiation is performed and the numbers of observable diffraction orders for the above structures are estimated. Received: 10 January 2002 / Published online: 11 June 2002     

Nonlinear surface magneto-optics of ferromagnetic Ni/Cu(001) from first principles

We present first-principles calculations of the nonlinear optical (NLO) response of a Ni/Cu(001) bilayer. The calculations are based on the full potential linearized augmented plane wave (FLAPW) method with the additional implementation of spin–orbit coupling (SOC). On the basis of this set of eigenstates the magneto-optical transition-matrix elements are evaluated. Using the surface-sheet model the optical reflection properties are determined for the cases of the magnetization vector perpendicular to the surface (polar magneto-optical configuration (MOC)) and for the in-plane magnetization (longitudinal MOC). The nonlinear optical susceptibility tensor elements χ⁽²⁾ _ijk for different magnetization directions as well as the spectral dependence of χ⁽²⁾ _ijk, the resulting intensities, and Kerr angles are presented for the Ni/Cu(001) bilayer. The results show that the magnetic tensor elements of the χ⁽²⁾ _ijk tensor are smaller than the nonmagnetic ones by only one order of magnitude, confirming the important role of magnetic properties in the NLO response. Received: 16 October 2001 / Revised version: 8 March 2002 / Published online: 29 May 2002     

Surface second-harmonic generation spectra of Si(111)-7×7 in the -–1.0 1.7eV fundamental photon energy

Received: 20 September 1998 / Revised version: 23 December 1998     

Magnetization-induced second-harmonic generation enhanced by surface plasmons in ultrathin Au/Co/Au metallic films

(2ω) to be distinguished. Received: 20 September 1998     

DC-electric-field-modified second-harmonic generation at the Si(100) surface

1 resonances for clean and H covered surfaces shift as a function of the dc field in agreement with experiment. This suggests the presence of built-in electric fields whose strength depends on the H coverage, and which are strongly localized in the subsurface region. Received: 20 September 1998     

Features of the simplest model of second-harmonic magneto-optical Kerr effects

A generalised formalism of characteristic matrices is presented to analyse second-harmonic magneto-optical Kerr effects in an optically anisotropic centrosymmetric ferromagnetically ordered multilayer if its response can be described in terms of electric polarisation. Features of the model associated with ideal (infinitely thin) interfaces are highlighted. These are due to both the existence of two versions of unconventional boundary conditions and an inevitable conventional approach to defining the surface polarisations through the fundamental electric field and surface-susceptibility tensors. New analytical results for linear and second-harmonic Kerr effects are shown to be advantageous for developing an effective algorithm for their numerical simulation. The linear approximation with respect to magnetisation is pursued, thereby also making our results suitable for investigating a great variety of magneto-optical effects and (in the second-harmonic case) effects related to anisotropy. Received: 16 October 2001 / Published online: 24 April 2002     

Quantum-chemistry simulations of second-harmonic and sum-frequency generation of organic layers

By using quantum-chemistry approaches, the second-order nonlinear optical responses of molecules and two-dimensional molecular arrays containing the p-nitroaniline chromophore are evaluated in order to highlight key features of the simulation of the second-harmonic and sum-frequency generation spectra of organic layers. For the electronic component, which dominates the second-harmonic generation response and which constitutes the weakly frequency-dependent background contribution to the vibrational sum-frequency generation phenomenon, the time-dependent Hartree–Fock scheme based on the semi-empirical AM1 parameterization is suitable for predicting the microscopic responses as well as for accounting for the surrounding effects within a simple multiplicative scheme. For the vibrational resonant part of the sum-frequency generation response, ab initio density functional theory approaches turn out to be necessary for locating the resonances and estimating their intensities. Received: 16 October 2001 / Published online: 29 May 2002     

Nonlinear magneto-optics of freestanding Fe monolayers from first principles

Received: 20 September 1998     

Homodyne detection of second-harmonic generation as a probe of electric fields

Received: 16 December 1998     

Thin noble metal films on Si (111) investigated by optical second-harmonic generation and photoemission

Thin noble metal films (Ag, Au and Cu) on Si (111) have been investigated by optical second-harmonic generation (SHG) in combination with synchrotron radiation photoemission spectroscopy. The valence band spectra of Ag films show a quantization of the sp-band in the 4-eV energy range from the Fermi level down to the onset of the d-bands. For Cu and Au the corresponding energy range is much narrower and quantization effects are less visible. Quantization effects in SHG are observed as oscillations in the signal as a function of film thickness. The oscillations are strongest for Ag and less pronounced for Cu, in agreement with valence band photoemission spectra. In the case of Au, a reacted layer floating on top of the Au film masks the observation of quantum well levels by photoemission. However, SHG shows a well-developed quantization of levels in the Au film below the reacted layer. For Ag films, the relation between film thickness and photon energy of the SHG resonances indicates different types of resonances, some of which involve both quantum well and substrate states. Received: 16 October 2001 / Revised version: 14 March 2002 / Published online: 29 May 2002     

About the depth sensitivity of second-harmonic radiation in ultra-thin metal films

Second-harmonic generation (SHG) results for Ni and Co films on Cu (001) have been reinvestigated regarding the depth sensitivity of this technique for thin films. We find that tangential components of the nonlinear susceptibility are much more sensitive to real film properties than normal components, which are confined to surfaces and interfaces. In consequence, for SHG experiments on ultra-thin metal films, polarization combinations should be favored that possess only tangential susceptibility components, even though the yield is weaker. Additional phase measurements are necessary to obtain full information about the film. Received: 20 January 2002 / Published online: 6 June 2002     

Determination of nonlinear absorption and refraction by single Z-scan method

We report a simplified Z-scan technique based on a study on the symmetric features of a typical Z-scan curve. The contributions from the two-photon absorption (TPA) and the nonlinear refraction (NLR) are easily separated from a closed-aperture Z-scan curve using this method. And the determination of the two nonlinearities is simplified and unambiguous. We demonstrate this method on ZnSe, CdS, and ZnTe semiconductors with 120-fs laser pulses. And the influence from the uncertainty of the focal plane (Z=0) position is discussed. It is also found that the TPA coefficient can be obtained independently without knowing the exact location of the focal point. Received: 8 July 1999 / Published online: 3 November 1999     

Analytical functions for the optimization of second-harmonic generation and parametric generation by focused Gaussian beams

An analytical function involving four parameters is proposed to express the second-harmonic generation efficiency as well as the parametric generation gain coefficient in the Boyd–Kleinman theory. The analytical function clearly reveals the dependence of conversion efficiency on the focusing parameter and the walk-off parameter. Moreover, the optimum focusing parameter and its corresponding maximum efficiency are explicitly given in the analytical function, leading to a straightforward evaluation of a given crystal performance. Received: 20 January 2003 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +886-35/7291-34, E-mail: yfchen@cc.nctu.edu.tw     

Group-theoretical analysis of second harmonic generation at (110) and (111) surfaces of antiferromagnets

Received: 20 September 1998     

Optical limiting in cobalt-doped polyvinylpyrrolidone

The results of optical limiting investigations of cobalt-doped polyvinylpyrrolidone solutions are presented. The optical limiting studies have shown that this process is due to self-defocusing at the wavelength of 1064 nm and also due to reverse saturable absorption and self-defocusing at the wavelength of 532 nm. The results of measurements on the non-linear optical characteristics of organometallic complexes are presented. Received: 10 July 2001 / Revised version: 15 October 2001 / Published online: 29 November 2001     

Phase matching of second-harmonic generation in birefringent porous silicon

Optical second-harmonic generation is investigated in free-standing (110) porous silicon films having strong in-plane birefringence. Based on the measured values of the refractive indices, the conditions of phase matching are calculated and verified in the experiments on angular and polarization dependences of second-harmonic generation. Filling pores with a transparent dielectric liquid allows phase matching to be achieved and the second-harmonic signal to be increased by two orders of magnitude. The results of these experiments suggest an opportunity to form new-type nonlinear-optical media consisting of birefringent porous silicon as a phase-matching matrix for the materials embedded in the pores. Received: 30 April 2001 / Published online: 7 June 2001     

Time-resolved photo-induced nonlinear magneto-optical Kerr effect for the study of spin dynamics at a GaAs(001) surface

Received: 20 September 1998     

Chemical-bond analysis of the nonlinear optical properties of the borate crystals LiB3O5, CsLiB6O10, and CsB3O5

The second-order nonlinear optical properties of practical borate crystals, LiB₃O₅, CsLiB₆O₁₀, and CsB₃O₅, which all contain the identical basic structural unit [the (B₃O₇)^5- group], have been quantitatively studied from the chemical-bond viewpoint. Differences in the nonlinear optical properties among these three borate crystals arise from the contributions of the different cations, i.e., the different interaction between the cation and the (B₃O₇)^5- anionic group. The chemical-bond method quantitatively expresses this important difference. At the same time, the current calculation also shows that the B₃O₇ group is a very important crystallographic frame in the crystalline borate solids; it offers different cations an excellent coordination environment. Received: 20 February 2001 / Accepted: 14 June 2001 / Published online: 30 August 2001     

SHG on ferromagnetic Gd films: indication of surface-state effects

The magnetization of 10-nm Gd films on W (110) has been investigated with second-harmonic generation (SHG). We observed a strong second-harmonic (SH) yield, which we attribute to resonance enhancement by the well-known Gd (0001) d-like surface state above the Fermi level. Since this state is spin-polarized it enhances the magnetic SHG contrast. The contrast, the relative phase between odd and even SH fields, and the amplitude ratio of these fields depend strongly on wavelength, which confirms the resonance enhancement. Further proof is provided by the fact that oxidation of the Gd surface reduces the SH yield by an order of magnitude. Received: 16 October 2001 / Revised version: 21 March 2002 / Published online: 11 June 2002