Abstract: A system for actively heating and cooling an object contains a thermoelectric device having a Peltier junction. The system is capable of reversing the direction of DC current flow through the Peltier junction so that the thermoelectric cooler/heater either heats or cools the object, as selected. The DC power supply is preferably operated in switch-mode. The thermoelectric device is disposed in a laser diode module or in heat-conductive contact with a laser housing mounting plate in a high-density laser source bank.