A tunable coherent radiation source comprises a pump laser which outputs a pump beam and a non-linear optical medium having a tuning pattern to provide tuning across a wavelength range. A translation system is arranged such that the pump beam is translated across the tuning pattern. The scanning pattern is formed such that translation of the pump beam across the tuning pattern provides one or more discontinuities in tuning across the wavelength range. A spectroscopic system and a hyperspectral imaging system comprising such a tunable coherent radiation source are described, as is a non-linear optical medium adapted for use in such a source. A method of providing coherent radiation tuned over a wavelength range is also described.