Terahertz Inspection Optics for Polarization-Based Backscatter Separation
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Solution Overview
Problem
Conventional terahertz wave measuring devices struggle to inspect targets located in lower layers of low-permeable materials due to weak terahertz wave transmission and low signal-to-noise ratios, exacerbated by strong backscatter components from the material surfaces obscuring the signal components from the targets.
Innovation Solution
An inspection device utilizing a light source to output pulsed excitation light, a nonlinear optical crystal to generate terahertz waves through optical wavelength conversion, and a polarization part to separate backscatter and signal components by exploiting differences in plane of polarization, allowing for effective detection of the signal components from the inspection targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a semiconductor device such as RTD or PCA is used as the terahertz wave transmitter, then the device complexity is reduced, but the terahertz wave output becomes weak and the signal-to-noise ratio becomes low
Solution Approach 1:
The patent replaces the semiconductor device-based terahertz transmitter with a photoconductive antenna system driven by pulsed laser light. This substitution uses optical energy to generate terahertz waves, achieving higher output power and improved signal-to-noise ratio while maintaining reasonable device complexity.
Solution Approach 2:
The patent changes the operating parameters by using ultrafast pulsed laser excitation with specific pulse widths (10 ps to 10 ns) to generate strong terahertz waves from the photoconductive antenna, thereby increasing the terahertz wave output power and signal-to-noise ratio.
2Power
If a beam light source such as chip laser is used to generate stronger terahertz waves, then the terahertz wave output increases, but the backscatter component from the low-permeable material surface becomes stronger and obscures the signal component
Solution Approach 1:
The patent extracts the harmful backscatter component from the total received signal by using a polarization part. The polarization part separates the reflected wave into components based on their polarization states, allowing the signal component from the inspection target to be isolated from the backscatter component generated by the low-permeable material surface.
Solution Approach 2:
The patent introduces a polarization part as an intermediary element between the received terahertz wave and the detector. This polarization part acts as a mediator that selectively transmits or blocks wave components based on their polarization orientation, thereby separating the desired signal from the unwanted backscatter.
3Loss of time
If the pulse width of excitation light is reduced to improve time resolution, then the temporal resolution improves, but the energy of the generated terahertz wave decreases
Solution Approach 1:
The patent uses a pulse width range (10 ps to 10 ns) that provides sufficient time resolution for distinguishing the signal component from the backscatter component, while maintaining enough energy in the excitation pulse to generate detectable terahertz waves. This partial optimization balances temporal resolution requirements with signal strength requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution enables the separation and detection of signal components from inspection targets buried within low-permeable materials, overcoming the limitations of conventional devices by improving signal clarity and reducing noise interference.
Implementation Method 1
a nonlinear optical crystal for generating a terahertz wave by optical wavelength conversion of the pulsed excitation light
Implementation Method 2
a polarization part for reflecting at least a part of a reflected wave of the terahertz wave reflected by an inspection target
Data Source
AI summary
An inspection device includes: a light source for outputting pulsed excitation light with a time width of 10 picoseconds to 10 nanoseconds; a nonlinear optical crystal for generating a terahertz wave by optical wavelength conversion of the pulsed excitation light; a polarization part for reflecting at least a part of a reflected wave of the terahertz wave reflected by an inspection target; and a detector for detecting the reflected wave reflected by the polarization part.