Laser

A laser apparatus comprising:

• a folded cavity defined by a first end mirror, a second end mirror and an output coupler;
• an optically isotropic active gain medium in the cavity between the first end mirror and the output coupler that generates fundamental optical radiation at a fundamental wavelength;
• and
• a non-linear crystal in the cavity between the second end mirror and the output coupler that converts the optical radiation at the fundamental wavelength to an output wavelength using type 1 phase matching;
• wherein
• the first end mirror has high reflectance at the fundamental wavelength,
• the second end mirror has high reflectance at the fundamental wavelength and high reflectance at the output wavelength, and
• the output coupler has high reflectance at one polarization of the fundamental radiation, low reflectance at an orthogonal polarization of the fundamental radiation, and high transmission at the output wavelength.