A photoacoustic apparatus, comprising: at least one optical amplifier, configured to produce light; at least one photonic integrated circuit, configured as a tunable light filter; light guiding means, wherein the at least one optical amplifier, at least one photonic integrated circuit and light guiding means are configured as an optical cavity to produce laser light having an optical path within the optical cavity; and at least one acoustic sensor configured to detect sound produced by analyte introduced into the optical path of the laser light.