High-frequency demodulation of multiphoton fluorescence in long-wavelength hyper-Rayleigh scattering

Abstract

Suppression of the multiphoton fluorescence contribution to the hyper-Rayleigh (second-order nonlinear optical) scattering signal was recently achieved by intrinsic demodulation of the fluorescence at high amplitude-modulation (AM) frequencies [Olbrechts et al., Rev. Sci. Instrum. 69, 2233 (1998)]. These high AM frequencies were obtained from the high harmonic content in the Fourier spectrum of a repetitive train of femtosecond pulses from a Ti:sapphire laser emitting at 800 nm. We have used a femtosecond parametric oscillator to shift the fundamental wavelength to 1.3 mum . By further improving the detection electronics, we can now obtain fluorescence suppression at AM frequencies up to 600 MHz. Fluorescence-free hyperpolarizability values were obtained for fluorescent dipolar compounds as well as for an ionic fluorophore. The results also indicate that shifting the fundamental wavelength to the near infrared only is not a general solution to the multiphoton fluorescence problem in hyper-Rayleigh scattering.

Molecular Symmetry and Solution‐Phase Structure Interrogated by Hyper‐Rayleigh Depolarization Measurements: Elaborating Highly Hyperpolarizable D2‐Symmetric Chromophores

“…[11] Angewandte Chemie from essentially all of the chromophores probed in the HRS experiment. Given the differences in the solution-phase HRSactive conformeric populations between the MR f PZnM/ MPZnM and PZnMPZn chromophore families, it is important to stress other key factors that control the relative magnitudes of the measured b HRS values.…”

Strong Wavelength Dependence of Hyperpolarizability in the Near-Infrared Biological Window for Second-Harmonic Generation by Amphiphilic Porphyrins

“…Measurements at fundamental near-infrared wavelengths of 800 and 840 nm were carried out at a simplified version of this setup, which was previously described. 21 All experimental hyperpolarizabilities are reported in Table 2. To discriminate between the immediate nonlinear scattering and the time-delayed multiphoton fluorescence, we use high-frequency demodulation technique.…”

Organometallic complexes for nonlinear optics. 41: Syntheses and quadratic NLO properties of 4-{4-(4-nitrophenyl)diazophenyl}ethynylphenylethynyl complexes

“…With a high repetition rate of the laser, high frequency demodulation of fluorescence contributions can be effected, a full description being given in ref. [27]. All measurements were performed in tetrahydrofuran using disperse red 1 (DR1, b = 54 Â 10 À30 esu in chloroform) as a reference.…”