A physiological monitoring system may use photoacoustic sensing to determine physiological information of a subject. The photoacoustic monitoring system may use a light source, such as a modulated continuous wave laser diode, to provide a frequency modulated photonic signal (e.g., a chirp signal) to the subject. An acoustic detector may be used to detect an acoustic pressure signal from the subject. The acoustic pressure signal may include two components corresponding to two wavelengths of light in the photonic signal. A signal ratio may be calculated based on the two components. The photoacoustic monitoring system may use the signal ratio to calculate one or more absorption coefficients. The photoacoustic monitoring system may use the one or more absorption coefficients to determine additional physiological information such as hemoglobin concentration, blood oxygen saturation, and temperature.