We report spatially resolved measurement of third-harmonic generation (THG) emission from a Tin diselenide (SnSe2) multi-layer flake at a fundamental excitation wavelength of 1550 nm using a nonlinear optical microscopy system and study its thickness dependence. We also estimate the magnitude of the real part of the electronic nonlinearity susceptibility (χ(3) coefficient) by analyzing the thickness-dependence and found to be approximately 1.6×10-19 m2/V2, which is around 1500 times higher than that of the glass when measured with the same settings. We find excellent agreement between the measured THG thickness dependence and the analytical model considering absorption of harmonic emission in SnSe2 medium, phase mismatch and the multipath interference due to the underlying oxide/Si substrate. We also measure the second harmonic generation from same flake and find this to be maximum for thickness in the range of 10-12nm.
Type 1 Collagen is the most abundant member of the family of collagens, which are the dominant proteins constituting the extracellular matrix (ECM) of multicellular organisms. Within tissues, Type 1 collagen exhibits a fibrillar geometry that serves as a mechanical scaffold for cells. The latter remodel the collagen through the secretion of proteoglycans (proteins with long chains of sulfated glycosaminoglycans (GAGs)), both within physiological and pathological contexts. The dermatan sulfate proteoglycans (DS-PGs) are abundantly present within the developing organs and are known to be dysregulated in diseases such as cancer. How DS alters the fibrillar architecture of collagen is however, not well known. Herein, we have used second harmonic generation (SHG) microscopy to dissect the effects of DS GAGs on Type1 Collagen polymerization. We observe that the presence of DS during polymerization enhances the width and number of the fibers, the surface occupancy (which we define as the ability of the collagen matrix to fill a given volume) and the mean SHG signals. We then image polymerizing collagen matrices at temporal intervals: at very early time points (<6 h), the SHG signals in both control and DS-treated polymerizing Type-1 collagen are low and do not show any difference. However, there is a sudden increase in SHG signals 6 h onwards, with a sharper and significantly increased enhancement in the presence of DS. Our results suggest the presence of DS kinetically alters the collagen polymerization leading to significant changes in its eventual architecture.