Terahertz Wave Generating Element Convex Reflecting Face
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Solution Overview
Problem
Existing terahertz wave generating elements using Cherenkov radiation suffer from distortion in power distribution of the generated waves, leading to a small effective beam diameter, which is not suitable for transmission or measurement applications.
Innovation Solution
A terahertz wave generating element is designed with a nonlinear optical crystal and a coupling member featuring a convex reflecting face that corrects the wavefront of terahertz waves, ensuring the angle between the reflecting face and the light propagation direction is greater than 90 degrees minus the Cherenkov angle, and the radius of curvature decreases further downstream, reducing power distribution distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a collimator is used to shape the wavefront of terahertz waves, then the wavefront planarity is improved, but the power distribution distortion increases
Solution Approach 1:
The patent applies curvature to the reflecting face of the coupling member, transforming it from a flat surface to a convex spherical surface with a specific radius of curvature. This curved reflecting face selectively reflects terahertz waves at different positions to correct the conical wavefront into a planar wavefront, while the specific curvature radius is chosen to minimize power distribution distortion. The curved surface enables wavefront shaping through geometric optics principles without the severe power distribution issues caused by simple collimation.
2Productivity
If the angle between the reflecting face and light propagation direction is set to achieve wavefront shaping, then the terahertz waves can be extracted, but the effective beam diameter becomes small
Solution Approach 1:
The patent optimizes the angle parameter between the reflecting face and the light propagation direction to satisfy the condition: greater than 90 degrees minus the Cherenkov angle but smaller than 90 degrees. This parameter optimization enables effective extraction of terahertz waves generated by Cherenkov radiation while maintaining a sufficiently large effective beam diameter. The angle parameter is carefully selected to balance extraction efficiency with beam quality, preventing excessive beam convergence that would reduce the effective diameter.
3Device complexity
If a flat reflecting face is used in the coupling member, then the structure is simple, but the terahertz waves cannot be properly shaped
Solution Approach 1:
The patent introduces a convex spherical reflecting face with a specifically designed radius of curvature into the coupling member structure. This curved surface is mathematically designed to transform the conical wavefront of extracted terahertz waves into a planar wavefront. While this increases structural complexity compared to a flat surface, the curvature is precisely calculated to achieve wavefront correction, enabling the terahertz waves to be properly shaped for transmission and measurement applications.
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 solution effectively reduces distortion in the power distribution of terahertz waves, allowing for a more stable and efficient transmission and measurement of terahertz waves with improved beam convergence and planarity.
Implementation Method 1
a technique using electro-optical Cherenkov radiation phenomenon (hereinafter, 'Cherenkov radiation') is capable of generating intense and relatively wide bandwidth terahertz waves
Implementation Method 2
There are methods to generate terahertz waves using a secondary nonlinear phenomenon by a nonlinear optical crystal
Implementation Method 3
The coupling member includes a reflecting face configured to reflect at least a part of the terahertz waves generated by the nonlinear optical crystal
Data Source
AI summary
A terahertz wave generating element includes a nonlinear optical crystal generating terahertz waves by propagating light, and a coupling member propagating the generated terahertz waves. The coupling member includes a reflecting face reflecting at least part of the generated terahertz waves. The reflecting face is convex in a propagation direction of the generated terahertz waves. An angle at the coupling member side between the reflecting face and the propagation direction of the light is greater than 90 degrees−cos−1 (ng/nTHz) but smaller than 90 degrees at a plane including the light propagation direction. ng represents a group refractive index of the nonlinear optical crystal at a wavelength of the light, nTHz the refractive index of the coupling member at a wavelength of the generated terahertz waves. A curvature radius of the reflecting face, in a reflection region reflecting the radius terahertz waves, is smaller the farther downstream in the light propagation direction.