A roaster oven for the heating of foodstuffs includes an outer housing with an opening and a heating element disposed proximate an interior surface for heating thereof. The centrifugal clutch includes a clutch basket, a cover plate, a hub, first clutch plates, second clutch plates and a dynamic expansion ring assembly having cam members. The tertiary mirror is located on a reflective optical path of the secondary mirror. The fluid flow configuration provides lower temperature, a more even temperature profile, a higher coolant exit temperature, and permits operation with higher air utilization and lower coolant flow. The semiconductor layer is formed to a thickness such that it does not yield due to temperature-induced strain at device processing temperatures.