Abstract

Novel organic molecules with high nonlinear optical properties are an important subject of investigation because of their potential application in optical communication, frequency conversion, etc.¹ Here, we present the experimental results of spontaneous Raman, polarisation sensitive CARS (PS-CARS) and waveguide CARS of the newly synthesised organic molecule tetranitro-tetra-(n-propoxy)calix[4]arene (c₄₀h₄₄n₄o₁₂) in thin films. For assignment of most specific strong Raman bands of calix[4]arene, a comparative analysis and different derivatives of this molecule were used. In addition, the depolarisation ratios for most of the bands were estimated by polarisation sensitive spontaneous Raman and CARS independently. Several strong bands are present in the Raman spectrum of calix[4]arene: Ω = 1095 cm⁻¹, Ω = 1265 cm⁻¹, Ω = 1340 cm⁻¹, Ω = 1584 cm⁻¹. The strongest band at Ω = 1344 cm⁻¹ (ρ = 0.25) corresponds to the symmetric NO₂ stretch. In Fig. 1 the PS-CARS spectrum for calix[4]arene in chloroform (C = 20 mg/ml) is shown. The result of fitting the spectrum with depolarisation ratios, taking into account the various settings of the polarizers is also shown. The observed line shape changes at different analyser settings around the position of background suppression illustrate the polarised character of the different bands. For example, the different dispersive shape of the chloroform band at Ω = 1214 cm⁻¹ with ρ = 0.7 deviates from the bands of calix[4]arene with ρ < 0.7. In Table 1 the depolarisation ratios for calix[4]arene, as determined from the polarised Raman and PS-CARS spectra are summarised. The values agree well for both techniques.

© 1994 IEEE