Terahertz Imaging via Non-Linear Optical Mixing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for evaluating and characterizing material surfaces and sub-surfaces, particularly composite materials, face challenges in achieving sufficient resolution and depth penetration using Terahertz radiation, as existing THz focal plane arrays lack the resolution of optical systems and struggle with the spectroscopic frequency band accessibility between 0.5 to 3 THz.
Innovation Solution
A method involving the simultaneous application of an optical source and a THz source, where the optical source emits radiation between 1000 nm to 300 nm and the THz source emits between 0.3 mm to 3 microns, generating a sum frequency output beam and a THz second harmonic output beam, allowing for non-invasive evaluation of substrate material characteristics by penetrating up to 2 mm beneath the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If THz focal plane arrays are used for surface imaging, then non-invasive material evaluation is achieved, but resolution is insufficient compared to optical systems
Solution Approach 1:
The patent combines optical sum frequency generation detection with THz second harmonic detection to achieve simultaneous surface and sub-surface evaluation. The optical detection path provides high-resolution surface imaging while the THz detection path penetrates to sub-surface depths, merging both capabilities in a single system.
Solution Approach 2:
The patent adds the temporal dimension by using ultrafast laser pulses to generate both optical and THz radiation simultaneously. This allows the system to capture surface and sub-surface information at the same moment, transitioning from sequential to simultaneous multi-dimensional detection.
2Power
If electronic sources like Gunn or Schottky diodes are used for THz generation, then high output levels are achieved up to 100 GHz, but efficiency drops in the sub-millimeter range
Solution Approach 1:
The patent replaces electronic THz generation methods with optical methods using ultrafast laser pulses. The optical field directly drives current in the photoconductive antenna, generating THz radiation more efficiently in the sub-millimeter range where electronic sources fail.
3Measurement precision
If direct optical sources like quantum cascade lasers are used, then frequencies above 5 THz are achieved, but operation requires cryogenic temperatures
Solution Approach 1:
The patent uses an optical laser as an intermediary to generate THz radiation indirectly through photoconductive antennas. This intermediary approach allows room-temperature operation while achieving the desired THz frequency range, avoiding the need for cryogenic cooling of quantum cascade lasers.
4Measurement precision
If CW THz systems are used for high frequency precision, then single MHz control is achieved, but measurement time increases to several minutes
Solution Approach 1:
The patent uses periodic ultrafast laser pulses to generate THz radiation, with the pulse repetition rate determining the frequency sampling. This periodic action enables rapid spectrum acquisition while maintaining frequency precision through the known laser repetition rate, achieving both speed and accuracy.
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
This approach provides accurate and cost-effective non-invasive evaluation of substrate material surface and sub-surface characteristics, including chemical composition, defects, and contamination, by leveraging the penetration capabilities of THz radiation while maintaining high resolution through simultaneous detection of sum frequency and second harmonic signals.
Implementation Method 1
The first input beam and the second input beam are mixed at the substrate material surface to provide a sum frequency output beam
Implementation Method 2
The second input beam penetrates the substrate material surface into the substrate material sub-surface to provide a THz second harmonic output beam comprising a THz second harmonic signal of the second input beam
Data Source
AI summary
Methods, systems and apparatuses are disclosed for interrogating characteristics of a substrate material surface and sub-surface by evaluating: 1) sum frequency output beams produced by combining an optical source input and a Terahertz source input, and 2) Terahertz second harmonic frequency output from a Terahertz source input.