A method and apparatus are provided for performing a medical procedure on a patient, for example a dermatological procedure, by use of electromagnetic radiation (EMR) having a relatively low peak power, and in particular a peak power low enough so as not to result in a phase change in the heater or chromophore absorbing radiation which would result in a significant reduction in its absorption, and of relatively long duration which is generally greater than, sometimes significantly greater than, the thermal relaxation time of the irradiated target.