A thermoelectric cooler (TEC)-based temperature control system is developed for the resonator tube wall of an optically pumped terahertz gas laser, which serves as the light source of a polarimeter–interferometer system applied in tokamak device diagnostics. The core objective of this system is to ensure the continuous and stable measurement performance of the polarimeter–interferometer during plasma diagnosis. The thermal module is composed of aluminum finned heat sinks that fully enclose the resonator tube wall, within which is embedded a semiconductor cooling element (TEC) and a PT1000 platinum resistance thermometer. The implementation of a fuzzy proportional–integral–derivative (PID) algorithm by a Field-Programmable Gate Array (FPGA)-based controller serves to regulate both the magnitude and polarity of the TEC drive current. This, in turn, maintains the temperature of the cavity wall. In the experiment, the temperature of the tube wall was maintained at 15 ± 0.25 °C. Concurrently, the laser output power was stabilized at 13 ± 0.2 mW. In addition, the unloaded thermal module displayed a temperature fluctuation of ±0.1 °C. The compact, high-precision design facilitates laser miniaturization and underlies the accuracy of interferometric plasma density diagnostics.
Zou et al. (Fri,) studied this question.