Q. H. F. Vrehen

Self-dispersive sum-frequency generation at interfaces.

We employ the self-dispersive nature of infrared-visible sum-frequency generation at interfaces to record sumfrequency spectra of molecular monolayers with a spectral resolution of a few inverse centimeters, using IR light with a spectral content of approximately 50 cm(-1).

Sum-frequency generation from thiophenol on silver in the mid and far-IR

Sum-frequency (SF) spectra of a monolayer of thiophenol on silver are reported in the mid and far-IR (infrared). The free-electron laser FELIX was used to reach wavelengths up to 54 μm. Molecular vibrations of thiophenol are observed at wavelengths near 10 μm (three modes), 14 μm (1 mode), and 24 μm (1 mode). The appearance of the different vibrational modes in the spectra varies dramatically due to interference between the resonant sum-frequency signal and the nonresonant sum-frequency signal from silver. The standard model used to describe line shapes in SF spectra is shown to be insufficient to explain the different line shapes for the various vibrational modes of thiophenol on silver.

High-resolution sum-frequency spectra using broadband laser sources

Abstract We employ the self-dispersive nature of infrared-visible sum-frequency generation at an interface to record high-resolution monolayer spectra. We achieve a resolution of a few cm −1 employing an IR free-electron laser having a spectral bandwidth of approximately 50 cm −1 .

Giant enhancement of sum-frequency generation upon excitation of a surface plasmon-polariton

The generation of the sum frequency of visible (0.5235 μm) and IR (10 μm) radiation on smooth and corrugated silver surfaces is investigated. The sum-frequency signal obtained with a visible-range surface plasmon-polariton excited on a corrugated silver-air interface is found to be more than four orders of magnitude stronger than the signal from a smooth silver surface.

Studies of interfacial regions by sum-frequency generation with a free-electron laser

The use of a Free-Electron Laser (FEL) allows the study of (non)linear optical properties of materials over unsurpassed large spectral intervals. As an example, we report on the use of a FEL as the infrared source in spectroscopic infrared-visible Sum-Frequency Generation (SFG). Employing the extremely wide tunability of the Free-Electron Laser for Infrared eXperiments (FELIX) at Rijnhuizen, we have studied the frequency dependence of the nonlinear susceptibility for sumfrequency generation in gallium phosphide between 20 and 32 μm in great detail. We have developed a shortpulse visible laser system that is highly synchronous with FELIX thereby creating a two-color setup that can be broadly applied. Resonantly enhanced SFG in alphaquartz has been used to study the relative timing stability of FELIX and the synchronized picosecond-laser system.

Efficient frequency doubling of ps-pulses from a free-electron laser in ZnGeP2☆

Abstract We report second-harmonic generation in ZnGeP 2 in the mid-IR using a high power, short pulse, free-electron laser. For fundamental wavelengths between 5.5 to 9.0 μm external efficiencies for second-harmonic generation up to 49% have been reached, which is close to the theoretical limit. At longer wavelengths the efficiency is reduced as a result of absorption in the crystal.

Nonlinear Optics with a Free-Electron Laser

Abstract We report on an experiment on spectroscopic infrared-visible Sum-Frequency Generation (SFG) with a Free-Electron Laser (FEL) as the IR-source. The SFG spectrum of gallium phosphide has been investigated in detail in an experiment covering the unsurpassed spectral range from 20 to 32 μm. This experiment demonstrates how the recent accessibility of FELs as truly widely tunable sources of coherent radiation can impact a well-established discipline.

Infrared‐visible sum‐frequency generation with a free‐electron laser

The feasibility of experiments on infrared‐visible sum‐frequency generation (SFG) with a free‐electron laser as a source of widely tunable narrowband coherent IR radiation is investigated. The SFG spectrum of Gallium Phosphide is studied over a large wavelength interval.

Enhancing the yield in surface sum-frequency generation by the use of surface polaritons

Summary form only given. Sum-frequency (SF) generation has developed into a convenient tool to investigate molecular layers at interfaces. One commonly associates this nonlinear optical technique with the use of tunable high-power laser sources. Given the finite power of the available sources much can be gained by optimally coupling the incident fields to the molecular layer and/or increasing its effective thickness. Surface polaritons provide a mechanism to achieve both these goals as we have demonstrated in a series of experiments on infrared-visible SFG at the air-silver interface. Two to four orders of magnitude increase in the SF yield have been observed when one of the input beams was coupled into a surface polariton.

Transmission reflection anomaly in second-harmonic generation from a monolayer.

We show experimentally that in second-harmonic generation from a monolayer the radiation propagating in transmission and that in reflection can have very different magnitudes. The origin of this difference lies in destructive and constructive interference of the components of the nonlinear polarization that drive the field at the second-harmonic frequency.