Highly Sensitive Determination of Dye Molecules on a Surface by the Second Harmonic Generation Technique

Recent Progress in Analytical SHG Spectroscopy

“…Accordingly, the SHG technique has been applied for investigations of chemical and physical phenomena at the interfaces (surfaces) by many research groups. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The SHG technique offers valuable information about events occurring at the interface region. For example, the second-order nonlinear susceptibility χ (2) of the solid/liquid interface can be expressed as the sum of three possible components:…”

“…The average molecular orientation can therefore be evaluated from the polarized SHG measurements, and has been carried out for various monolayer assemblies. [1][2][3][4][5][6][7][8][9][10][11][12][13] However, one should keep in mind that the adsorbed molecules are not always aligned in the same direction. The surface SHG reflects only noncentrosymmetric components of the adsorbed molecules.…”

Incident-Angle Dependence of the Sensitivity of Second-Harmonic Generation of an Oxacyanine Dye in an LB Film

“…1. Its optical units are essentially identical to that described previously, 8,13 except for a goniometer, which was installed in order to change the incident angle continuously. An Ar-ion laser (Coherent, Innova 310) exited Ti:Al2O3 laser (Coherent, MIRA900D; pulse width, 200 fs; average power, 1 W; pulse repetition rate, 76 MHz) was used as the excitation source.…”

“…This method has also been used for highly sensitive determinations in LB films. 13,14 However, the incident angle of the excitation laser is usually set at 45˚, and the incident-angle dependence of the SHG efficiency has scarcely been measured.In the present study, we constructed a new instrument to investigate the incident-angle dependence of SHG signals, and applied it for determining a cyanine dye (DOOC) in LB films. We found that the signal was dependent on the incident angle and that the detection limit could be improved by using the most efficient incident angle.…”

“…This method has also been used for highly sensitive determinations in LB films. 13,14 However, the incident angle of the excitation laser is usually set at 45˚, and the incident-angle dependence of the SHG efficiency has scarcely been measured.…”