A dermatological laser system, comprising: a first laser source comprising first laser resonator, at least a first gain medium for generating a first optical field along a first optical axis; and at least one first Q-switch configured to control a resonance quality of the first laser resonator; a control circuit configured to control the first Q-switch to cause the first laser resonator to generate the first optical field as a first pulse train of laser pulses; a second laser source for generating a second optical field as a second pulse train of laser pulses along a second optical axis; at least one nonlinear medium for generating a third optical field along a third optical axis by a nonlinear interaction between the first optical field and the second optical field; a sensor (135, 235, 236) configured to detect a property of at least one of the optical fields; wherein the control circuit is configured to control operation of the first Q-switch so as to adjust a relative timing of the laser pulses of the first pulse train and the laser pulses of the second pulse train responsive to the detected property; wherein the first optical field has a first wavelength, the second optical field has a second wavelength and the third optical field has a third wavelength different from the first and second wavelengths; wherein the control circuit is configured, responsive to a wavelength selection command or responsive to the detected property, to selectively control the relative timing so as to control a wavelength of an output radiation of the laser system in order to switch between a first laser output that includes the third wavelength and a second laser output that only includes the first and second wavelengths; wherein, when the pulses of the first and second pulse trains do not temporally overlap, the first and second optical fields propagate through the nonlinear medium without generating the third optical field, so that the output from the nonlinear medium is composed of the first and second optical fields; and wherein, when the pulses of the first and second pulse trains temporally overlap in the nonlinear medium, the third optical field is generated therein. a first laser source comprising first laser resonator, at least a first gain medium for generating a first optical field along a first optical axis; and at least one first Q-switch configured to control a resonance quality of the first laser resonator; a control circuit configured to control the first Q-switch to cause the first laser resonator to generate the first optical field as a first pulse train of laser pulses; a second laser source for generating a second optical field as a second pulse train of laser pulses along a second optical axis; at least one nonlinear medium for generating a third optical field along a third optical axis by a nonlinear interaction between the first optical field and the second optical field; a sensor (135, 235, 236) configured to detect a property of at least one of the optical fields; wherein the control circuit is configured to control operation of the first Q-switch so as to adjust a relative timing of the laser pulses of the first pulse train and the laser pulses of the second pulse train responsive to the detected property; wherein the first optical field has a first wavelength, the second optical field has a second wavelength and the third optical field has a third wavelength different from the first and second wavelengths; wherein the control circuit is configured, responsive to a wavelength selection command or responsive to the detected property, to selectively control the relative timing so as to control a wavelength of an output radiation of the laser system in order to switch between a first laser output that includes the third wavelength and a second laser output that only includes the first and second wavelengths; wherein, when the pulses of the first and second pulse trains do not temporally overlap, the first and second optical fields propagate through the nonlinear medium without generating the third optical field, so that the output from the nonlinear medium is composed of the first and second optical fields; and wherein, when the pulses of the first and second pulse trains temporally overlap in the nonlinear medium, the third optical field is generated therein.