A fluid separation system (10) for separating compounds of a sample fluid in a mobile phase comprises a detector (50) adapted to detect separated compounds by providing an optical stimulus signal to the sample fluid and receiving a response signal to the optical stimulus signal. The detector (50) comprises a light source (100) adapted to provide an output light beam (230) as the optical stimulus signal. The light source (100) comprises a plurality of light emitting elements (200, 200A, 200Z) each adapted to emit a light beam (210, 210A1, 210A2, 210Z1, 210Z2) having a respective wavelength,, and a diffracting element (220). The plurality of light emitting elements (200, 200A, 200Z) are arranged that emitted light beams (210, 210A1, 210A2, 210Z1, 210Z2) impinging, on the diffracting element (220) are diffracted by the diffracting element (220) to form the output light beam (230).