Observation Of Third-harmonic Generation Research Articles

Third harmonic generation from collective modes in disordered superconductors

The observation of third-harmonic generation (THG) in superconductors suggests that strong terahertz fields provide a preferential tool to excite collective excitations, e.g., the Higgs mode, which remain elusive in ordinary spectroscopy. From the theoretical point of view, disorder effects must be included. Here, the authors show that by treating disorder nonperturbatively the THG is strongly enhanced by disorder, and phase and charge fluctuations, neglected so far, give a substantial contribution to it. In addition, the computed polarization dependence of the signal within realistic band structures challenges the interpretation of recent experiments in cuprates.

Layer-Tunable Third-Harmonic Generation in Multilayer Black Phosphorus

Black phosphorus has been the subject of growing interest due to its unique band structure that is both layer dependent and anisotropic. While many have studied the linear optical response of black phosphorus, the nonlinear response has remained relatively unexplored. Here we report on the observation of third-harmonic generation in black phosphorus using an ultrafast near-IR laser and measure χ(3) experimentally for the first time. It was found that the third-harmonic emission is highly anisotropic, dependent on the incident polarization, and varies strongly with the number of layers present due to signal depletion and phase-matching conditions.

Observation of Third-Harmonic Generation in Polydiacetylene Films Using Internal Reflection Geometry

Abstract We have demonstrated technique for measuring the third-order nonlinear optical susceptibility χ(3)(-3ω, ω, ω, ω) based on internal reflection. Using this technique, we observed third-harmonic generation from a poly-DCH film deposited on oriented LB film of poly(3BCMU). Its χ(3) was 2.1 times as large as an another film with no LB film. This suggests that the oriented LB film contributes to the alignment of the DCH monomer deposited on it.

Identification of Coulomb Friction in Robot Drives and Other Mechanical Systems Through Observation of Third Harmonic Generation

One of the main difficulties in introducing improved robot control strategies is a lack of knowledge of the frictional behaviour of robot drive systems. The aim of the present paper is to describe a technique for the identification of Coulomb friction based on the response of the robot drive to a sinusoidal driving torque The presence of a third harmonic component in the resulting velocity is a consequence of the Coulomb non-linearity and it is shown theoretically, through computer simulation and in experimental tests, that the coefficient of Coulomb friction can be estimated from the amplitude of the third harmonic component. The identification method is shown to be applicable to any mechanical system that can be subjected to a sinusoidal forcing torque or force.

Observation of third harmonic generation in oriented Durham polyacetylene

Abstract Third harmonic generation has been observeb in samples of oriented, fully dense polyacetylene. A theoretical treatment is developed to relate the third harmonic intensity of a thick, absorbing film to its third order nonlinear optical susceptibility, χ(3). A value of χ(3) in excess of 10-8 esu parallel with the polymer chains is inferred from third harmonic intensity measurements. This exceptionally high value of the electronic χ(3) is believed to be the highest ever reported for an organic polymer, an order of magnitude higher than that of polydiacetylene toluene sulphonate.

Infrared third-harmonic generation in molecular gases

We report the first observation of third-harmonic generation (THG) in molecular gases. Using a CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> TEA laser and choosing molecules with vibrational transitions that contribute to a resonance enhancement of the third-order susceptibility tensor we have studied absolute conversion efficiencies, spectral response, and pressure dependences for THG in SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> , BCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , and CO and compared the results to theoretical predictions.