Asymmetric β-sheet protein structures in spider silk should induce nonlinear optical interaction such as second harmonic generation (SHG) which is experimentally observed for a radial line and dragline spider silk by using an imaging femtosecond laser SHG microscope. By comparing different spider silks, we found that the SHG signal correlates with the existence of the protein β-sheets. Measurements of the polarization dependence of SHG from the dragline indicated that the β-sheet has a nonlinear response depending on the direction of the incident electric field. We propose a model of what orientation the β-sheet takes in spider silk.

We have detected a second-order nonlinear optical response from aggregates of the ampholytic megamolecular polysaccharide sacran extracted from cyanobacterial biomaterials, by using optical second harmonic generation (SHG) microscopy. The SHG images of sacran cotton-like lump, fibers, and cast films showed SHG intensity microspots of several tens of micrometers in size. The dependence of the SHG spot intensity on an excitation light polarization angle was observed to illustrate sacran molecular orientation in these microdomains. We also observed SHG signals around a special region of the cast film edges of sacran. These results show that sacran megamolecules aggregate in several different ways.

We have detected second-order nonlinear optical response from an amphoteric mega-saccharides named sacran under a needle/ring electrode stimulus by using an optical second harmonic generation (SHG) microscope. SHG was observed from sacran in the neighborhood of the negatively biased needle electrode below -4.5 V with respect to the outer ring electrode. From the incident light polarization dependence of SHG, this sacran was suggested to be oriented toward the electrode needle. SHG of the sacran polymer was judged to be induced by sacran aggregates with net positive charge.

We have studied hydrogen desorption from a flat H-Si (111)1 × 1 surface at 711 K by observing sum frequency generation (SFG) and second harmonic generation (SHG) spectra. Flat H-Si (111) surfaces were prepared by dosing hydrogen molecules in an ultra-high vacuum chamber with a base pressure of 10 À8 Pa. Combining the SFG and SHG methods, the desorption order has been clarified over the whole hydrogen coverage range from 1 monolayer (ML) to 0 ML. The hydrogen desorption was assigned as second order in the high coverage range of 1 ML-0.18 ML by using SFG spectroscopy and as first order in the coverage range of 0.18 ML-0.0 ML by using SHG spectroscopy.

We have performed time-resolved sum frequency (SF) spectroscopy of a H-Si(111)1×1 surface excited by pump visible pulses with the pulse width of ∼30 ps in ultra-high vacuum. Broad non-resonant SF signals as a function of the infrared wavenumber increased soon after the pump light irradiation, and decreased in ∼1 ns. A remarkable change in the intensity and the shape of the peak at 2085 cm −1 attributed to the Si-H stretching vibration is observed as a function of the delay time. After the pump light irradiation, the symmetric peak in the SF spectra disappeared at ∼60 ps and recovered gradually with an asymmetric shape.