Optical techniques are disclosed for improving the range resolution of a radar system. An optical source produces chirped optical pulses whose frequency changes linearly with time, wherein the pulse duration is close to the repetition period (quasi cw radiation). The optical source illuminates the target that scatters a portion of the light back into collecting optics of the ladar's receiver. The delayed back-scattered optical waveform is mixed optically with a reference waveform in a non-linear medium to produce optical radiation at a new frequency. The spectral properties of the non-linearly generated light contains information about the distance to the target. Different approaches that may be chosen for non-linear optical mixing are disclosed including sum and difference frequency generation in non-linear crystals.