A light source is disclosed, having a quasi-incoherent broadband pump source configured to produce a longitudinally and transversally multi-mode pump beam. The light source may include a means for narrowing the linewidth of the pump beam. The light source includes an optical parametric oscillator with an optical cavity containing a crystal. The optical parametric oscillator is configured to receive light from the pump source and produce a first output light beam and a second output light beam. An optical coupler is disposed between the pump source and the optical parametric oscillator. At least one of the first and second output light beams is a substantially single transversal mode light having a narrower linewidth than the pump source.
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