An optoacoustic system includes first and second light sources capable of generating pulse of light at first and second wavelengths, first and second electrically controlled optical attenuators, first and second light sync detectors, and a combiner. A power meter that is calibrated to determine power at the first and second predominant wavelength measures power at the first wavelength after the first light sync is detected and measures power at the second wavelength after the second light sync is detected. The system includes a calibration mode wherein it electrically attenuates the first optical attenuator when the power measured by the power meter at the first wavelength after the first light sync is detected is above a first level, and electrically attenuated the second optical attenuator when the power measured by the power meter at the second wavelength after the second light sync is detected is above a second level.