System and method to measure the transit time position(s) of pulses in time domain data

Inventors

White, Jeffrey S. • Fichter, Gregory D. • Zimdars, David • Williamson, Steven

Assignees

PROACT MEDICAL Ltd • Laurus Labs Pvt Ltd • Luna Innovations Inc

Abstract

A system and method to measure, with increased precision, the transit time position(s) of pulses in a time domain data. An example data set would be the transit time of pulses in Time-Domain Terahertz (TD-THz) data. The precision of the pulse timing directly affects the precision of determined sample properties measurements (e.g., thickness). Additionally, an internal calibration etalon structure and algorithm method provides for continuous system precision/accuracy check method to increase sample measurement integrity. The etalon structure can improve the precision of sample property measurements (e.g., absolute thickness). Various hardware and system implementations of the above are described.

Core Innovation

The invention relates to interpreting a terahertz waveform using a terahertz transmitter and a terahertz receiver configured to output and receive a pulse of terahertz radiation. A first optical interface provides optical interference so that a first optical interface reflected portion of the pulse is reflected to the terahertz receiver, and a second optical interface provides optical interference so that a second optical interface reflected portion is reflected to the terahertz receiver. An etalon spacing defined between the first and second optical interfaces is configured to receive a sample to be irradiated by the pulse, where the sample reflects a first sample reflected portion and a second sample reflected portion to the terahertz receiver.

The described approach addresses improving sample-property measurement precision by increasing pulse timing precision for interpreting time-domain terahertz waveforms, including thickness-related error reduction for thin samples. The document presents multiple timing algorithms for determining transit time position(s), including using an edge midpoint with linear regression between maximum and minimum amplitude points, a model fitting approach using simplex optimization, and deconvolution using a reference instrument response followed by Tikhonov filtering and model fitting.

The invention further introduces an internal calibration etalon (ICE) in the sensor head to provide per-waveform timing and amplitude references for continuous calibration. The document states that this enables improved absolute thickness determination without requiring the sample refractive index, and it describes multipass sample chamber/etalon approaches that increase time-of-flight delay while mitigating drift effects such as thermal/mechanical drift. Computer system implementation details are discussed for data acquisition of the time-domain waveform window and subsequent processing for waveform interpretation.

Claims Coverage

The partial set includes two independent claims. Together, they cover a terahertz transmitter/receiver system with optical interference from one or two optical interfaces and an etalon spacing configured to receive a sample, and waveform interpretation based on reflected portions from the interfaces and the sample.

Across the independent claims, the core coverage is a terahertz waveform interpretation system that uses optical interference from an optical interface, and in one case two interfaces with an etalon spacing, together with reflected portions from the sample to be received by the terahertz receiver. Dependent claims further constrain the analysis by selecting specific time-domain waveform interpretation methods and by extracting thickness-related timing relationships.

Stated Advantages

Documented Applications