US Patent 7280568 Laser coherence control using homogeneous linewidth broadening

An apparatus and method for linewidth broadening applied to a laser that emits a light having an output frequency ν and an emission linewidth δE. The apparatus is equipped with an electro-optic modulator for intercepting the light and a noise generator for driving the electro-optic modulator with a radio-frequency (RF) noise signal spanning a frequency range selected to broaden the emission linewidth δE of the light passing through the electro-optic modulator to a broadened linewidth δB. The noise spectrum of the noise signal exhibits a continuous frequency range and can be flat or sloping. The range extends from low frequency ωL set below the emission linewidth δE of the light to a high frequency ωH set above the emission linewidth δE of the light. The electro-optic modulator can be selected from among many suitable devices including optical crystals. Further broadening can be achieved by employing one or more secondary EOMs operating in resonant or non-resonant modes. The lasers that benefit from the invention involve any type of inherently narrow bandwidth lasers operating in CW or pulsed modes.