title: Nonlinear photoacoustic spectroscopy of hemoglobin.
abstract: As light intensity increases in photoacoustic imaging, the saturation of optical absorption and the temperature dependence of the thermal expansion coefficient result in a measurable nonlinear dependence of the photoacoustic (PA) signal on the excitation pulse fluence. Here, under controlled conditions, we investigate the intensity-dependent photoacoustic signals from oxygenated and deoxygenated hemoglobin at varied optical wavelengths and molecular concentrations. The wavelength and concentration dependencies of the nonlinear PA spectrum are found to be significantly greater in oxygenated hemoglobin than in deoxygenated hemoglobin. These effects are further influenced by the hemoglobin concentration. These nonlinear phenomena provide insights into applications of photoacoustics, such as measurements of average inter-molecular distances on a nm scale or with a tuned selection of wavelengths, a more accurate quantitative PA tomography.
authors.affiliation: Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis , One Brookings Drive, St. Louis, Missouri 63130, USA.
authors.forename: Amos
authors.initials: A
authors.lastname: Danielli
authors.affiliation: Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis , One Brookings Drive, St. Louis, Missouri 63130, USA.
authors.forename: Konstantin
authors.initials: K
authors.lastname: Maslov
authors.affiliation: Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis , One Brookings Drive, St. Louis, Missouri 63130, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Favazza
authors.affiliation: Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis , One Brookings Drive, St. Louis, Missouri 63130, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Xia
authors.affiliation: Optical Imaging Laboratory, Department of Biomedical Engineering, Washington University in St. Louis , One Brookings Drive, St. Louis, Missouri 63130, USA.
authors.forename: Lihong V
authors.initials: LV
authors.lastname: Wang