Terahertz PHASR Scanner With 2 kHz, 100 ps Time-Domain Trace Acquisition Rate and an Extended Field-of-View Based on a Heliostat Design
Zachery B. Harris, M. Hassan Arbab
Abstract
Recently, we introduced a Portable HAndheld Spectral Reflection (PHASR) Scanner to allow terahertz time-domain spectroscopic (THz-TDS) imaging in clinical and industrial settings using a fiber-coupled and alignment-free telecentric beam-steering design. The key limitations of the version 1.0 of the PHASR Scanner were its field-of-view (FOV) and speed of time-domain trace acquisition. In this article, we address these limitations by introducing a heliostat geometry for beam scanning to achieve an extended FOV, and by reconfiguring the asynchronous optical sampling system to perform Electronically Controlled OPtical Sampling (ECOPS) measurements. The former change improved the deflection range of the beam, while also drastically reducing the coupling of the two scanning axes, the combination of which resulted in a larger than four-fold increase in the FOV area. The latter change significantly improves the acquisition speed and frequency-domain performance simultaneously by improving measurement efficiency. To accomplish this, we characterized the nonlinear time-axis sampling behavior of the electromechanical system in the ECOPS mode. We proposed methods to model and correct the nonlinear time-axis distortions and tested the performance of the high-speed ECOPS trace acquisition. Therefore, here, we introduce the PHASR Scanner version 2.0, which is capable of imaging a 40 × 27 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> FOV with 2000 traces/s over a 100 ps TDS range. This new scanner represents a significant leap toward translating the THz-TDS technology from the lab bench to the bedside for real-time clinical imaging applications.