Patent ID: 8922873

Claim:
A tunable light source comprising: a first polarization rotator to rotate a pump beam before a first pass through an optical parametric generation source in a first direction; a first separator to separate the pump beam exiting the optical parametric generation source from a signal beam also exiting the optical parametric generation source; a narrowband wavelength filter positioned to receive the signal beam from the first separator and generate a seed beam; a linear-to-circular polarization device to polarize the pump beam directed back toward the optical parametric generation source, after reflecting off a first reflector, for a second pass therethrough in a second direction opposite the first direction; a second reflector or a reflective surface of the first reflector positioned to direct the seed beam along the pump beam path in the second direction to pass through the optical parametric generation source in the second direction along with the pump beam; and a second separator positioned to separate the seed beam from an idler beam after exiting the optical parametric generation source in the second direction; wherein a larger portion of the pump beam is frequency converted on the second pass through the optical parametric generation source compared to the first pass.