Schaefer, W., Li, L., Stegmann, P., & Terada, M. (2026). Technical Report on the TSTOF Measurement Method: Technical Basics, Historical Development, and Comparison with Other Laser-Based Measurement Methods. Photonics, 13(1), 56. https://doi.org/10.3390/photonics13010056
In this paper, we discuss the functionality and historical development of the Time-Shift Time-of-Flight (TSTOF) technique. In addition, we compare TSTOF with laser diffraction and Phase Doppler techniques to identify the respective application ranges of measurement instruments based on TSTOF, such as ParticleTensorAI®, SpraySpy®, and SprayQuantAI®.
Abstract
The TSTOF stands for the time-shift time-of-flight measurement method, which is used to characterize individual dynamic particles—such as droplets in droplet clouds or particles in flows—in various industrial applications. Over the past 15 years, this method has become increasingly important and is valued in particular for its ease of use and compact design. So far, however, there is no technical report that deals exclusively and systematically with TSTOF technology. In the scientific literature, the method is usually only treated in connection with specific applications—theoretical or experimental—but is rarely presented in its entirety. Often the citations are incomplete or do not refer to scientifically validated sources. Current technical developments are usually not adequately considered, while non-scientific publications often take up technical aspects uncritically without referring to verifiable data. This report describes the technical foundations of the TSTOF measurement method, presents its historical development, and systematically compares it with established laser-based methods.