In this study, the efficacy and optimal settings of the CO2, Diode and cw Thulium laser systems were compared for various clinical applications in ENT, Lung and Neurosurgery. The experiments were performed using a specially developed setup, based on color Schlieren techniques, which enable real-time imaging of dynamic temperature gradients complimented with thermocouple measurements in a transparent tissue model in air and water. The CO2 and cw Thulium laser are both efficient in superficial tissue ablation with minimal coagulation depth. The cw Thulium laser, however, is fiber delivered and can also be used in a water. The Diode laser has a relatively deep coagulation effect. The ablation efficacy was enhanced by coating the fiber tip with carbon particles. Our thermal imaging technique was useful to develop new strategies making use of the advantages and overcoming the drawbacks of laser systems. The CO2, Diode and cw Thulium laser can be applied for similar clinical procedures using the optimal strategy and settings for each laser type. The cw 2 μm Thulium laser shows to be a versatile laser system for a broad range of applications both in air and water.