Spatially resolved surface temperature control using scanned laser heating

A scanned laser heating system with multiple point closed-loop control has been designed and tested for processes requiring thermal pattern and uniform temperature surface heating. The first phase of this thesis involved building a large infrared display system for infrared scene generation to simulate radiation seen by heat seeking devices and infrared detectors. The objective of this project was to create a 600 mm x 600 mm dynamic image display with spatial resolution on the order of 5 mm.; The actuation of the heating for the infrared display system is produced by three continuous wave CO₂ lasers raster-scanned over a thin Kapton screen. Rapid modulation of the laser coordinated with the scanning produces a pixilated heated image that emits infrared energy. An infrared camera provides surface temperature measurements required for closed-loop control. The system is divided into a background heating system that covers the entire screen and simulates environmental IR and a hotspot heating system that covers a 100 mm x 100 mm square subwindow and simulates a target. Temperatures in the hotspot region can reach up to 150°C while the background temperatures vary from 25–30°C. The system runs at 0.25 Hz frame rate simulating changing environmental conditions and a moving target.; The hotspot heating system from the infrared display was augmented with an improved control system to make a high accuracy uniform surface temperature controller. Such a controller is required in processes like Rapid Thermal Processing in which a uniform chemical reaction is needed on the surface of a wafer. The best closed-loop controllers achieved rms spatial temperature variations of less than 0.5°C for a commanded temperature of 30°C above ambient over an 11 mm square test section. To test the capabilities of the controller in rejecting disturbances, additional laser power was introduced to the system independent of the controller's knowledge. The controller was able to recognize and account for the disturbance so as to stabilize to within 2% of the desired temperature within 6 seconds.