A form of laser output noise that is caused by thermal, mechanical, or acoustical disturbances of the cavity length. Mode sweeping occurs when the length of the laser cavity changes as a result of environmental conditions or changes in temperature, which cause the longitudinal modes to sweep
across the gain curve causing fluctuations in output power. Very short lasers with a single longitudinal mode can fluctuate from max power to zero power and back to maximum power as temperature changes. The longer the laser the smaller the fluctuations of power.