Acoustic effects on nonlinear optical processes

Abstract

We studied the effects of two types of ultrasonic waves, shear waves and longitudinal waves, using two nonlinear optical techniques, second-harmonic generation and hyper-Rayleigh scattering. Since shear waves hardly propagate in liquids, their influence on molecules at the interface between a surface and a liquid was studied using second-harmonic generation. Longitudinal waves propagate easily in solution, thus we used hyper-Rayleigh scattering to probe the ultrasonic effects on chromophores in solution. While we did not find shear waves to alter the second-harmonic generation from chromophores at the liquid/surface interface, the longitudinal waves caused effects comparable to our earlier observations. Longitudinal ultrasound caused a strong intensity modulation of the nonlinear optical signal according to a wave-pattern.

Conformational Changes of a Surface-Tethered Polymer during Radical Growth Probed with Second-Harmonic Generation

“…The polarization direction of the laser light was altered using a half-wave plate (HWP, Thorlabs WPH05M-808). The resulting SHG data were corrected for fluctuations in laser stability (see the Supporting Information). The polarization-dependent SHG data obtained from the in situ and ex situ grafted sample at various polymerization times are plotted as a function of the polarization angle of the incident laser light in Figure .…”

“…Such orientation, quasi-parallel to the surface, is often observed with these types of chromophores when they are physisorbed or chemisorbed on glass substrates. 35,36,39,40 If the true average tilt angle distribution remains relatively narrow, the tilt angle follows a steep decrease during the first 3 h and eventually halts at 56.6°± 0.1°. This angle should not be confused or compared to 57.4°, the magic angle for UV−vis measurements (the magic angle for SHG is 39.2°).…”