title: Improved sensitivity for two-photon frequency-domain lifetime measurement.
abstract: We demonstrate a method to improve the measurement sensitivity of two-photon frequency-domain lifetime measurements in poor signal to background conditions. This technique uses sinusoidal modulation of the two-photon excitation source and detection of the second harmonic of the modulation frequency that appears in the emission. Additionally, we present the mathematical model which describes how the observed phase shift and amplitude demodulation factor of two-photon phosphorescence emission are related to the phosphorescence lifetime and modulation frequency. We demonstrate the validity of the model by showing the existence of new frequency terms in the phosphorescence emission generated from the quadratic nature of two-photon absorption and by showing that the phase shift and demodulation match theory for all frequency components.
authors.affiliation: Department of Biomedical Engineering, The University of Texas at Austin, 1 University Station, C0800, Austin, TX 78712, USA. ArnoldE@mail.utexas.edu
authors.forename: Arnold D
authors.initials: AD
authors.lastname: Estrada
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Dunn
mesh_terms: D004735:Energy Transfer; D004867:Equipment Design; D005453:Fluorescence; D049449:Luminescence; D008163:Luminescent Measurements / Q000295:instrumentation*; D017711:Nonlinear Dynamics; D055095:Optics and Photonics / Q000295:instrumentation* / Q000379:methods*; D017785:Photons