Picosecond absorption relaxation measured with nanosecond laser photoacoustics

Abstract

Picosecond absorption relaxation-central to many disciplines-is typically measured by ultrafast (femtosecond or picosecond) pump-probe techniques, which however are restricted to optically thin and weakly scattering materials or require artificial sample preparation. Here, we developed a reflection-mode relaxation photoacoustic microscope based on a nanosecond laser and measured picosecond absorption relaxation times. The relaxation times of oxygenated and deoxygenated hemoglobin molecules, both possessing extremely low fluorescence quantum yields, were measured at 576 nm. The added advantages in dispersion susceptibility, laser-wavelength availability, reflection sensing, and expense foster the study of natural-including strongly scattering and nonfluorescent-materials.

Figure 1

System diagrams. (a) Schematic of the optical-resolution photoacoustic microscopy (OR-PAM) system (b) Ultrasonic and optical beam coupling cube.

Figure 2

Average photoacoustic amplitude as a function of the incident laser fluence. (a) Saturable Absorber 580 dye, (b) DQOCI dye, (c) oxygenated lysed bovine blood, and (d) deoxygenated lysed bovine blood. Error bars represent the standard deviations of 1800 measurements.