High-frequency demodulation of multi-photon fluorescence in hyper-Rayleigh scattering

Abstract

A novel technique for suppression of the multi-photon fluorescence contribution in second-order nonlinear optical hyper-Rayleigh scattering experiments is described. The technique takes advantages of the demodulation and the phase shift in the frequency domain of the time-delayed (multi-photon) fluorescence in the time domain. We demonstrate the effectiveness of demodulation at high modulation frequencies of the fundamental laser beam by determining the molecular second-order nonlinear polarizability for a reference molecule under fluorescent conditions. The value that was obtained for crystal-violet in methanol with 9,10-diphenylanthracene added as a centrosymmetric fluorophore compares very well with the values that were previously obtained. The possibility of complete suppression of all fluorescence, based on phase-sensitive measurements in quadrature with the fluorescence, is also discussed.

Alkynyl Expanded Donor–Acceptor Calixarenes: Geometry and Second‐Order Nonlinear Optical Properties

“…[32] If no attention is devoted to the potential multiphoton fluorescence contribution to the HRS signal, a systematic overestimation of b can result. [33] This systematic error can be avoided by making the distinction between immediate scattering and time-delayed fluorescence in the spectral domain (spectrally broad fluorescence versus sharp scattering at the second-harmonic of the laser line only), in the time domain (a nanosecond fluorescence tail following the femtosecond laser pulse excitation), [34] or in the frequency domain.…”

Synthesis, Crystal Structure, and Second‐Order Nonlinear Optical Properties of Ruthenium(II) Complexes with Substituted Bipyridine and Phenylpyridine Ligands

“…This is experimentally verified by performing femtosecond hyper-Rayleigh scattering (HRS) ex-periments as a function of modulation frequency. [27] The finite lifetime associated with any fluorescence results in a demodulation (reduction of amplitude) for higher frequencies. [28] As exemplified in Figure 6, no such demodulation is observed in the case of [Ru(bpy) 2 6 ], thus implying that the HRS signal is not comprised of any multiphoton fluorescence contribution.…”

“…This setup was used as described before. [27] The samples were dissolved in acetonitrile and crystal violet (CV) dissolved in methanol was used as the reference (β xxx = 338 × 10 -30 cm 5 esu -1 ). [27] A concentration series ws measured and the slopes of the linear fitting compared.…”

Molecular engineering of chromophores for combined second-harmonic and two-photon fluorescence in cellular imaging

“…16 The ionic nature of some of the compounds inherently precluded the use of electric-field-induced second-harmonic generation and necessitated the nonlinear scattering technique that does not rely on the application of a DC electric field.…”