The thin film of a heptamethine cyanine chromophore HC was prepared by spin-coating technique. Its surface morphology and linear optical property were characterized by atomic force microscopy (AFM) and UV-visible absorption spectroscopy. The results show that HC molecules are arranged in a well-ordered H-aggregate type. The third-order nonlinear optical properties of the spin-coating film were also measured by degenerate four-wave mixing (DFWM) measurement. Enhanced third-order nonlinear susceptibility can be attributed to molecular aggregation effects, and the corresponding mechanism was dealt with by collective electronic oscillator (CEO) approach.
Dependence of surface-enhanced Raman scattering （SERS） from Calf thymus DNA on anions is investigated. With the silver colloid, the bands at 732, 960 and 1333 cm^-1 for adenine （A）, 1466 cm^-1 for deoxyribose, and 1652 cm^-1 for the C=O group of thymine （T） are observably enhanced. With the presence of the Cl^- or SO4^2- anions, the bands at 732 and 1326/1329 cm^-1 for the symmetric stretching and skeletal vibrational modes of adenine （A） are dramatically enhanced, and the enhancement effect with the SO4^2- ion is more than that with the Cl^- ion. The experimental results show that the DNA molecule can be adsorbed on the silver colloid particles through the C6N and N7 of adenine （A） the C=O of thymine （T） and deoxyribose. Moreover, the formed hydrogen bonding of the Cl^- or SO4^2- ions to the C6NH2 group of adenine （A） can induce larger C6N electronegativity, which is favor for the C6N/N7 cooperative adsorption on the （Ag）^＋ colloid particles.
Raman spectroscopy has strong potential for providing non-invasion diagnosis of cancers. In this paper, micro-Raman spectroscopy is used to diagnose one most common liver cancer, hepatocellular carcinoma （HCC）. The statistical analyzes, including t-test, principal component analysis （PCA）, and linear discriminant analysis （LDA）, are performed on the Raman spectra of malignant and normal hepatocytes. The t-test-LDA results show that the 786- and 1004-cm^-1 bands of the malignant and normal hepatocytes are significantly different, and PCA-LDA results show an overall accuracy of 100% for the Raman spectroscopic identification of normal and malignant hepatocytes in our experiment.
A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.
Degenerate four-wave mixing measurements, using the 35 ps pulses at 532 nm, have been employed to investigate the third-order nonlinear optical parameters of two chromium tricarbonyl complexes η6-bonded to 3-amino-9-ethylcarbazole at either the NH2-substituted aryl ring (1) or the unsubstituted ring (2) and their precursor 3-amino-9-ethylcarbazole (AECz). The second-order hyperpolarizability γ of the compounds 1 and 2 were found to be 42.9×10-31 and 35.9×10-31 esu, respectively, approximately one order of magnitude greater than AECz. The relation between the molecular structure and second-order hyperpolarizability of the compounds 1 and 2 was explored in detail based on the three-level model and the density functional theory (DFT) calculation. The theoretical results indicate that the spatial distri-bution of electron density has the profound role in the third-order nonlinear optical properties.
