Non-linear Optical Spectroscopy

The index of refraction in a non-linear optical material can be written  

We employed a comparative Z-scan procedure, wherein we perform a reduced-aperture Z-scan on CS2 immediately followed by reduced and open-aperture Z- scans on the polymer solution at a particular wavelength. The peak on-axis intensity, Iq, is then calculated from the CS2 peak to valley transmission change using previously measured values for its non-linear axis of refraction. Based on the work of Sheik-Bahae et al., the equation for Iq is given by [17] 

For each EA spectrum, the transmission T was measured with the mechanical chopper in place and the electric field off. The differential transmission AT was subsequently measured without the chopper, with the electric field on, and with the lock-in amplifier set to detect signals at twice the electric-field modulation frequency. The 2/ dependency of the EA signal is due to the quadratic nature of EA in materials with definite parity. AT was then normalized to AT/T, which was free of the spectral response function. To a good approximation [18], the EA signal is related to the imaginary part of the optical third-order susceptibility  

Unlike linear optical effects such as absorption, reflection, and scattering, second order non-linear optical effects are inherently specific for surfaces and interfaces. These effects, namely second harmonic generation (SHG) and sum frequency generation (SFG), are dipole-forbidden in the bulk of centrosymmetric media. In the investigation of isotropic phases such as liquids, gases, and amorphous solids, in particular, signals arise exclusively from the surface or interface region, where the symmetry is disrupted. Non-linear optics are applicable in-situ without the need for a vacuum, and the time response is rapid. 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

SFG [4.309, 4.310] uses visible and infrared lasers for generation of their sum frequency. Tuning the infrared laser in a certain spectral range enables monitoring of molecular vibrations of adsorbed molecules with surface selectivity. SFG includes the capabilities of SHG and can, in addition, be used to identify molecules and their structure on the surface by analyzing the vibration modes. It has been used to observe surfactants at liquid surfaces and interfaces and the ordering of interfacial 

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Mukamel S 1995 Prf/rc/p/es of Non-linear Optical Spectroscopy (New York Oxford University Press)... 

McGlip J F 1990 Epioptics linear and non-linear optical spectroscopy of surfaces and interfaces J. Phys. Condens Matter 2 7985-8006... 

Kohei Uosaki received his B.Eng. and M.Eng. degrees from Osaka University and his Ph.D. in Physical Chemistry from flinders University of South Australia. He vas a Research Chemist at Mitsubishi Petrochemical Co. Ltd. from 1971 to 1978 and a Research Officer at Inorganic Chemistry Laboratory, Oxford University, U.K. bet veen 1978 and 1980 before joining Hokkaido University in 1980 as Assistant Professor in the Department of Chemistry. He vas promoted to Associate Professor in 1981 and Professor in 1990. He is also a Principal Investigator of International Center for Materials Nanoarchitectonics (MANA) Satellite, National Institute for Materials Science (NIMS) since 2008. His scientific interests include photoelectrochemistry of semiconductor electrodes, surface electrochemistry of single crystalline metal electrodes, electrocatalysis, modification of solid surfaces by molecular layers, and non-linear optical spectroscopy at interfaces. 

P. H. Vaccaro in H. Hirota, R. W. Field, J. P. Maier, S. Tsuchiya (Eds.), Non-linear Optical Spectroscopy for Molecular Structure and Dynamics, Blackwell Scientific, IUPAC... 

Refs. [i] Hoke R (2008) Surface and interface analysis an electrochemists toolbox. Springer, Berlin [ii] Tadjeddine A, Peremans A (1998) Non-linear optical spectroscopy of the electrochemical interface. In Clark RJH, Hester RE (eds) Advances in spectroscopy (spectroscopy for surface science), vol. 26. Wiley, Chichester, p 159 [iii] Shen YR (1990) In Gutierrez C, Melendres C (eds) Spectroscopic and diffraction techniques in interfacial electrochemistry (NATO ASI series C, vol. 320). Kluwer, Dordrecht, p 281 [iv] Shen YR (1986) Applications of optical second-harmonic generation to surface science. In Hall RB, Ellis AB (eds) Chemistry and structure at interfaces. VCH, Deerfield Beach, p 151 [v] Williams CT, Beattie DA (2002) SurfSci 500 545... 

Liquid Dynamics Studied by Higher Order Non-Linear Optical Spectroscopy... 

Professor in 1981 and Professor in 1990. He is also a Principal Investigator of International Center for Materials Nanoarchitectonics (MANA) Satellite, National Institute for Materials Science (NIMS) since 2008. His scientific interests include photoelectrochemistry of semiconductor electrodes, surface electrochemistry of single crystalline metal electrodes, electrocatalysis, modification of solid surfaces by molecular layers, and non-linear optical spectroscopy at interfaces. 

Tadjeddine A and Peremans A (1998) In Clark RJH and Hester RE (eds.) Non-linear Optical Spectroscopy of the Electrochemical Interface. Spectroscopy for Surface Science. London Wiley. 

A. Tadjeddine, A. Peremans, Non-linear optical spectroscopy of the electrochemical interface in Spectroscopy for Surface Science (Eds. R. J. H. Clark and R. E. Hester), Wiley Sons Ltd, Chichester, UK, 1998, pp. 159-216. 

S. Mukamel, Principles of Non-Linear Optical Spectroscopy (Oxford University Press, New York, 1995)... 

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