Fast THz-TDS Reflection Imaging with ECOPS—Point-by-Point versus Line-by-Line Scanning

Abstract

We built a high-speed TDS setup with the use of electronically controlled optical sampling (ECOPS), which can measure up to 1600 terahertz pulses per second. The movement of the sample was provided by two fast-speed motorized linear stages constituting the gantry. We developed a flat-bar-based metal marker approach for the synchronization of continuous line-by-line scans. We carefully compared the performance of the terahertz reflection time-domain spectroscopy (TDS) scanner operating in a slow point-by-point and a one-hundred-times faster line-by-line imaging scheme. We analyzed images obtained for both schemes for a uniform metallic breadboard with holes, as well as a glass composite sample with defects. Although the measurement time was reduced by 100 times in terms of the line-by-line scheme, the overall performance in both schemes was almost identical in terms of the defects’ sizes, shapes and locations. The results proved that the proposed ECOPS TDS system can provide uniform and extremely fast scanning without any deterioration in image quality.

Identification of black plastics with terahertz time-domain spectroscopy and machine learning

“…However, THz-TDS can be carried out in a reflection geometry, and it has been proven possible to simultaneously measure the refractive index and thickness of a sample of silicon by including both the THz pulses reflected from the frontside and backside of the sample 50 . Recently, a new high-speed THz-TDS system providing 150 ps time traces at the rate of 1600 traces/s has been used to image a metallic structure reflection geometry 51 . Each linescan of the 500 mm long moving metallic structure was measured in 1.4 s corresponding to a measurement speed of > 350 mm/s with a resolution of 0.44 mm.…”

A Hardware Encoder-Based Synchronization Method for a Fast Terahertz TDS Imaging System Based on the ECOPS Scheme

“…The synchronization problem has been solved by using a marker, in the form of a metal ruler located at the edge of the scanning area [ 27 ]. This gives a characteristic result, the presence of which in the data series of each image line enables alignment of individual lines in the final image of the scanned sample.…”

Remote Spectral Identification in the THz Band with Reflection Spectroscopy in an Open Atmosphere

“…Spectroscopy in the terahertz (THz) band has developed significantly since the introduction of pulsed techniques. Basic research [1,2] and practical applications have benefited from THz technology development [3,4]. Since the attacks on 11 September 2001, law regulations have enforced their highest ever security measures.…”