Dual beam transient thermal lens spectroscopy with high repetition pulsed IR-Laser Excitation: Photothermal and fluorescence quantum yields determination

Based on experimental results, we demonstrated that the most widely used model for the description of the dual beam transient thermal lens spectroscopy technique also works well when a high repetition frequency pulsed pump laser is used instead of a commonly employed continuous wave source. For this, for water samples colored with a tartrazine dye, we compared the optical absorbance obtained using a continuous and a pulsed laser source emitting at the same excitation wavelength. A close to 90 % photothermal quantum yield was obtained as a function of the dye concentration. As an application, we measured the near-infrared fluorescence quantum yield spectrum of a CF®800 dye (Biotium) dissolved in water. The thermal lens signal was recorded as a function of the photon's wavelength using a tunable MAI TAI BB laser oscillator (Spectra Physics) for pumping that generates light pulses of about 80 fs at a repetition frequency of 80 MHz between 710 and 980 nm. The quantum yield spectrum and a comparison of the optical absorbance spectra measured by the thermal lens technique and a conventional transmittance experiment show a significant fluorescence quenching due to water optical absorption.