Photoacoustic detecting device , intended to be applied, via a contact face , against a medium to be analysed, the device comprising: - a hollow cavity that emerges onto a first aperture , the first aperture being produced in the contact face; - a pulsed or amplitude-modulated light source configured to emit, in an emission spectral band (Δλ), an incident light wave through the cavity to the first aperture; - an acoustic transducer linked to the cavity and configured to detect a photoacoustic wave extending through the cavity; such that, under the effect of illumination of the medium, by the incident light wave, the acoustic transducer detects an acoustic wave produced by heating of the medium ; the device being characterized in that : - the volume of the cavity is smaller than 50 μL; - the device comprises an open tube extending between the cavity and the air lying outside the cavity, over a length comprised between 1 and 20 mm, the diameter of the tube being such that: • when the volume of the cavity is smaller than or equal to 15 μL, the diameter of the tube is comprised between 150 μm and 300 μm; • when the volume of the cavity is comprised between 15 μL and 30 μL, the diameter of the tube is comprised between 200 μm and 350 μm; • when the volume of the cavity is larger than 30 μL, the diameter of the tube is comprised between 250 μm and 500 μm. - a hollow cavity that emerges onto a first aperture , the first aperture being produced in the contact face; - a pulsed or amplitude-modulated light source configured to emit, in an emission spectral band (Δλ), an incident light wave through the cavity to the first aperture; - an acoustic transducer linked to the cavity and configured to detect a photoacoustic wave extending through the cavity; such that, under the effect of illumination of the medium, by the incident light wave, the acoustic transducer detects an acoustic wave produced by heating of the medium ; the device being characterized in that : - the volume of the cavity is smaller than 50 μL; - the device comprises an open tube extending between the cavity and the air lying outside the cavity, over a length comprised between 1 and 20 mm, the diameter of the tube being such that: • when the volume of the cavity is smaller than or equal to 15 μL, the diameter of the tube is comprised between 150 μm and 300 μm; • when the volume of the cavity is comprised between 15 μL and 30 μL, the diameter of the tube is comprised between 200 μm and 350 μm; • when the volume of the cavity is larger than 30 μL, the diameter of the tube is comprised between 250 μm and 500 μm. - the volume of the cavity is smaller than 50 μL; - the device comprises an open tube extending between the cavity and the air lying outside the cavity, over a length comprised between 1 and 20 mm, the diameter of the tube being such that: • when the volume of the cavity is smaller than or equal to 15 μL, the diameter of the tube is comprised between 150 μm and 300 μm; • when the volume of the cavity is comprised between 15 μL and 30 μL, the diameter of the tube is comprised between 200 μm and 350 μm; • when the volume of the cavity is larger than 30 μL, the diameter of the tube is comprised between 250 μm and 500 μm. • when the volume of the cavity is smaller than or equal to 15 μL, the diameter of the tube is comprised between 150 μm and 300 μm; • when the volume of the cavity is comprised between 15 μL and 30 μL, the diameter of the tube is comprised between 200 μm and 350 μm; • when the volume of the cavity is larger than 30 μL, the diameter of the tube is comprised between 250 μm and 500 μm. <EOS>