A laser apparatus configured to operate on any one of two or more frequencies of output laser light, the apparatus comprising: a resonator cavity comprising mirrors or reflectors (115, 119), and coatings thereon, to achieve high reflectivity for wavelengths of at least first and second laser light beams in the cavity, each beam being of a different wavelength to simultaneously resonate the at least first and second laser light beams; a solid state laser material located in the cavity to generate at least the first laser light beam; a pump source located outside of the cavity for pumping the solid state laser material with a pump beam, whereby the solid state laser material generates the first laser light beam; a Raman-active medium located in the cavity for Raman-shifting the wavelength of the cavity laser beam, to generate at least the second laser light beam; a tunable non-linear medium located in the cavity, which does not Raman frequency shift the laser light beams, capable to selectively frequency convert at least two different frequencies, disposed in the cavity to select at least one of the at least first and second laser light beams to be frequency converted to a frequency altered laser light beam comprising a single converted wavelength by tuning thereof, wherein the non-linear medium is configured to convert the selected laser beam or beams by a non-linear interaction selected from the group of second, third or fourth harmonic generation, sum frequency generation, difference frequency generation and other parametric non-linear conversion; a tuner to tune the tunable non-linear medium to select the at least one laser beam from the group of the at least first and second laser beams; an output coupler capable to output two or more different frequencies of output laser light for outputting the frequency altered laser light beam from the cavity, wherein the two or more different frequencies are derived by the nonlinear interaction from at least one of the selected at least first and second laser light beams, wherein the output coupler is a reflector being highly reflective at the frequency of each of the simultaneously resonating at least first and second laser light beams and transmissive at the frequency of the frequency altered laser light beam derived from the selected at least one of the first and second laser light beams; wherein the tuner and tunable non-linear medium are configured such that the tunable non-linear medium is tuned to selectively frequency convert at least one of the first and second laser light beams to the frequency altered laser light beam comprising a single converted visible wavelength. a resonator cavity comprising mirrors or reflectors (115, 119), and coatings thereon, to achieve high reflectivity for wavelengths of at least first and second laser light beams in the cavity, each beam being of a different wavelength to simultaneously resonate the at least first and second laser light beams; a solid state laser material located in the cavity to generate at least the first laser light beam; a pump source located outside of the cavity for pumping the solid state laser material with a pump beam, whereby the solid state laser material generates the first laser light beam; a Raman-active medium located in the cavity for Raman-shifting the wavelength of the cavity laser beam, to generate at least the second laser light beam; a tunable non-linear medium located in the cavity, which does not Raman frequency shift the laser light beams, capable to selectively frequency convert at least two different frequencies, disposed in the cavity to select at least one of the at least first and second laser light beams to be frequency converted to a frequency altered laser light beam comprising a single converted wavelength by tuning thereof, wherein the non-linear medium is configured to convert the selected laser beam or beams by a non-linear interaction selected from the group of second, third or fourth harmonic generation, sum frequency generation, difference frequency generation and other parametric non-linear conversion; a tuner to tune the tunable non-linear medium to select the at least one laser beam from the group of the at least first and second laser beams; an output coupler capable to output two or more different frequencies of output laser light for outputting the frequency altered laser light beam from the cavity, wherein the two or more different frequencies are derived by the nonlinear interaction from at least one of the selected at least first and second laser light beams, wherein the output coupler is a reflector being highly reflective at the frequency of each of the simultaneously resonating at least first and second laser light beams and transmissive at the frequency of the frequency altered laser light beam derived from the selected at least one of the first and second laser light beams; wherein the tuner and tunable non-linear medium are configured such that the tunable non-linear medium is tuned to selectively frequency convert at least one of the first and second laser light beams to the frequency altered laser light beam comprising a single converted visible wavelength.