My Note: Automation and Control Technology (ACT), appears now to be aggressively marketing the Advanced Photonix, (API), T-Gauge as part of ACT's new Envision M-Series.
The ACT webpage has several pages and links to THz related news:
To minimize raw material waste and improve product consistency, manufacturers of multi-layer non-ferous products now have a cost effective alternative in a single-sided Terahertz sensor from ACT. Traditional Nucleonic and X-Ray transmission or backscatter gauges, use radioactive sources and their use requires compliance with government regulations. However, the Terahertz sensor is a safe non-nucleonic device. The time domain terahertz pulsed source allows the simultaneous measurement of each layer: thickness, basis weight and moisture levels in extruded or cast multi-layer sheet products. Terahertz sensors are more accurate, safer and economical.
In addition, there are scholarly papers, such as the following one by David Pond, explaining why time-domain terahertz is particularly well-suited to industrial process control: