Disclosed is an optical flow cell (100, 300) and a method (400) for bioprocessing applications. The optical flow cell (100, 300) comprises a fluid inlet (102, 302), a fluid outlet (104, 304), and a fluid flow channel (106, 306) provided between said fluid inlet (102, 302) and said fluid outlet (104, 304). The optical flow cell (100, 300) also comprises an output optical waveguide (108, 308) configured to emit light into said fluid flow channel (106, 306), and a collector optical waveguide (110, 310) configured to collect light from said fluid flow channel (106, 306). An optical pathlength adjuster (120, 320) for varying the optical pathlength (130, 330) between said output optical waveguide (108, 308) and said collector optical waveguide (110, 310) is also provided.