A chip scale ultra violet laser source comprising: a substrate; a plurality of chip scale ultra violet-generating laser elements on the substrate, wherein each chip scale ultra violet-generating laser element comprises: a back cavity mirror; a tapered gain medium coupled to the back cavity mirror; a nonlinear crystal, wherein the front facet of the nonlinear crystal has a first coating that has anti-reflectivity AR to a fundamental wavelength of the laser element and high reflectivity HR to ultra violet wavelengths, and wherein an exit facet of the nonlinear crystal has a second coating that has HR to a fundamental wavelength of the laser element and AR to the ultra violet wavelengths such that the second coating and the back cavity mirror form a laser cavity; an outcoupler to which the front facet of the non linear crystal is coupled, the out coupler also being coupled to the tapered gain medium, the outcoupler being configured to couple a fraction of the fundamental wavelength out of the cavity; a photodetector coupled to the outcoupler; a phase modulator coupled to the photodetector and coupled to the back cavity mirror; and a single mode master laser diode on the substrate coupled to the phase modulator of each laser element and coupled to the photodetector of each laser element, the master diode being configured to emit at the fundamental wavelength; wherein the photodetector detects optical phases of both the fundamental wavelength of its respective chip and the fundamental wavelength of the single mode master laser diode; wherein the non-linear crystal is configured to convert the fundamental wavelength to an ultra violet wavelength so that each laser element emits an ultra violet beamlet from the exit facet; and wherein each laser element is frequency and phase locked to the master laser diode. a substrate; a plurality of chip scale ultra violet-generating laser elements on the substrate, wherein each chip scale ultra violet-generating laser element comprises: a back cavity mirror; a tapered gain medium coupled to the back cavity mirror; a nonlinear crystal, wherein the front facet of the nonlinear crystal has a first coating that has anti-reflectivity AR to a fundamental wavelength of the laser element and high reflectivity HR to ultra violet wavelengths, and wherein an exit facet of the nonlinear crystal has a second coating that has HR to a fundamental wavelength of the laser element and AR to the ultra violet wavelengths such that the second coating and the back cavity mirror form a laser cavity; an outcoupler to which the front facet of the non linear crystal is coupled, the out coupler also being coupled to the tapered gain medium, the outcoupler being configured to couple a fraction of the fundamental wavelength out of the cavity; a photodetector coupled to the outcoupler; a phase modulator coupled to the photodetector and coupled to the back cavity mirror; and a single mode master laser diode on the substrate coupled to the phase modulator of each laser element and coupled to the photodetector of each laser element, the master diode being configured to emit at the fundamental wavelength; wherein the photodetector detects optical phases of both the fundamental wavelength of its respective chip and the fundamental wavelength of the single mode master laser diode; wherein the non-linear crystal is configured to convert the fundamental wavelength to an ultra violet wavelength so that each laser element emits an ultra violet beamlet from the exit facet; and wherein each laser element is frequency and phase locked to the master laser diode. a back cavity mirror; a tapered gain medium coupled to the back cavity mirror; a nonlinear crystal, wherein the front facet of the nonlinear crystal has a first coating that has anti-reflectivity AR to a fundamental wavelength of the laser element and high reflectivity HR to ultra violet wavelengths, and wherein an exit facet of the nonlinear crystal has a second coating that has HR to a fundamental wavelength of the laser element and AR to the ultra violet wavelengths such that the second coating and the back cavity mirror form a laser cavity; an outcoupler to which the front facet of the non linear crystal is coupled, the out coupler also being coupled to the tapered gain medium, the outcoupler being configured to couple a fraction of the fundamental wavelength out of the cavity; a photodetector coupled to the outcoupler; a phase modulator coupled to the photodetector and coupled to the back cavity mirror; and a single mode master laser diode on the substrate coupled to the phase modulator of each laser element and coupled to the photodetector of each laser element, the master diode being configured to emit at the fundamental wavelength; wherein the photodetector detects optical phases of both the fundamental wavelength of its respective chip and the fundamental wavelength of the single mode master laser diode; wherein the non-linear crystal is configured to convert the fundamental wavelength to an ultra violet wavelength so that each laser element emits an ultra violet beamlet from the exit facet; and wherein each laser element is frequency and phase locked to the master laser diode.