An arrangement for measuring a gas density comprises a sensor head having an oscillating body (1), excitation means for exciting the oscillating body (1) and detection means for measuring an amplitude of the oscillating body (1). The excitation means have an excitation light source (9) for generating excitation light (3). The sensor head is connected via at least one optical waveguide (2a, 2b) to an evaluation circuit, both excitation light being fed in and measuring light being guided out via these optical waveguides (2a, 2b). The oscillating body is designed as a tuning fork or a beam clamped on one side. <IMAGE>
