Terahertz Near-Field Probe Total Internal Reflection
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Solution Overview
Problem
Terahertz spectroscopy is limited by the diffraction limit, which restricts the measurement of small, inhomogeneous samples and introduces background radiation that distorts near-field measurements, reducing signal-to-noise ratio and damaging terahertz probes.
Innovation Solution
A method and system for terahertz near-field microscopy involving total internal reflection of excitation light at an interface between the sample and a medium, positioning the terahertz near-field probe on one side of the interface to measure the electric field without interference from excitation light, allowing for higher spatial resolution and reduced probe interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional THz spectroscopy with wide-area excitation beams is used, then homogeneous illumination is achieved, but spatial resolution is limited by the diffraction limit to mm-scale
Solution Approach 1:
The patent segments the excitation beam into multiple independent laser beams, each targeting a specific region of the sample. This allows simultaneous high spatial resolution for individual regions while maintaining the ability to illuminate multiple areas, effectively overcoming the diffraction limit without requiring a single wide-area beam
Solution Approach 2:
The patent transitions from scanning in the lateral plane to scanning in the vertical dimension by tilting the sample. Multiple laser beams illuminate different regions simultaneously at oblique angles, enabling high-resolution near-field measurements while avoiding the need for wide-area homogeneous illumination in the traditional sense
2Measurement precision
If terahertz near-field probe is positioned close to the sample for high spatial resolution, then background radiation distorts measurements and reduces signal-to-noise ratio
Solution Approach 1:
The patent extracts the harmful background radiation from the measurement path by using oblique incidence geometry. The terahertz probe detects scattered radiation from the sample surface while the excitation beams arrive from a different direction, separating the useful signal from the background noise and improving signal-to-noise ratio
Solution Approach 2:
The patent introduces the sample surface as an intermediary that converts the optical excitation into terahertz radiation. The terahertz probe detects this converted radiation scattered from the surface, rather than directly detecting the optical excitation or the background radiation, thereby isolating the measurement from harmful interference
3Use of energy by moving object
If excitation light intensity is increased to excite large areas, then sufficient fluence is provided, but probe damage may occur due to direct interaction
Solution Approach 1:
The patent extracts the excitation light from the probe detection path by using oblique incidence geometry. The excitation beams illuminate the sample from angles that prevent direct interaction with the terahertz probe, allowing high fluence excitation without probe damage while the probe detects scattered terahertz radiation from a different direction
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 enhances the signal-to-noise ratio by minimizing background radiation distortion and prevents probe damage, enabling precise terahertz near-field measurements with improved spatial resolution and faster scanning capabilities.
Implementation Method 1
directing excitation light onto an interface between the sample and a medium under an angle of incidence such that total internal reflection of the excitation light occurs at the interface
Implementation Method 2
measuring said electric field using a terahertz near-field probe, wherein the terahertz near-field probe is positioned on one side of said interface and the excitation light approaches the interface on another side of said interface
Data Source
AI summary
This disclosure relates to a method for measuring an electric field in the near-field region of an optically excited sample. The method includes optically exciting at least part of the sample. This step includes directing excitation light onto an interface between the sample and a medium. The excitation light is incident onto the interface under an angle of incidence such that total internal reflection of the excitation light occurs at the interface. The method further includes measuring the electric field using a terahertz near-field probe, wherein the terahertz near-field probe is positioned on one side of the interface and the excitation light approaches the interface on another side of the interface. This disclosure further relates to a system and computer program for measuring an electric field in the near-field region of an optically excited sample.