Tunable Coherent Radiation Source Using Segmented Nonlinear Crystal
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Solution Overview
Problem
Conventional tunable sources of coherent radiation are ineffective for real-time hyperspectral imaging in the mid and long wavelength infrared spectrum, as they cannot provide sufficient resolution over an extended spectral range in a short time for detecting molecular species at low concentrations.
Innovation Solution
A tunable coherent radiation source using a periodically poled nonlinear crystal, such as periodically poled lithium niobate or orientation patterned gallium arsenide, with a tailored tuning pattern that allows for rapid and effective tuning across specific wavelengths or continuous tuning, enabling efficient data collection by excluding non-interesting spectral regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional tunable source is used to scan across an extended spectral range, then the wavelength coverage is improved, but the detection speed and real-time capability deteriorate
Solution Approach 1:
The nonlinear optical medium is divided into multiple regions, each with a different periodic poling period corresponding to different wavelength ranges. This segmentation allows the system to cover an extended spectral range while maintaining the ability to rapidly switch between specific wavelength regions of interest, thereby improving detection speed for real-time applications.
Solution Approach 2:
The system dynamically switches between different regions of the nonlinear optical medium based on the specific detection requirements. By using a tunable pump laser and selectively exciting different poling periods within the segmented medium, the system can rapidly adjust the output wavelength without the need for slow mechanical scanning, thus maintaining both wide wavelength coverage and high detection speed.
2Adaptability or versatility
If a fan-out grating is used to provide continuous tuning, then the wavelength range is improved, but the data processing complexity and time consumption increase
Solution Approach 1:
Instead of using a fan-out grating that requires scanning and processing of the entire continuous spectrum, the invention extracts only the specific wavelength regions of interest by designing the nonlinear optical medium with discrete periodic poling periods. This allows the system to directly generate radiation at predetermined wavelengths without the need to process unnecessary spectral data, significantly reducing data processing time and complexity.
Solution Approach 2:
Different regions of the nonlinear optical medium are designed with specific local properties (different poling periods) optimized for particular wavelength ranges. This local quality approach allows the system to efficiently generate radiation at specific wavelengths needed for particular molecular detections, avoiding the generation and processing of irrelevant spectral data that would occur with continuous tuning approaches.
3Measurement precision
If the pump beam is scanned across a fan-out grating to vary wavelength, then the spectral resolution is improved, but the detection time increases
Solution Approach 1:
The nonlinear optical medium employs periodic poling structures with specific periods that correspond to different wavelength ranges. By using a tunable pump laser that can be rapidly adjusted in frequency, the system periodically excites different poling periods to generate radiation at specific wavelengths. This periodic action based on predefined structures maintains spectral resolution while enabling rapid switching between wavelength regions, thus reducing detection time compared to continuous mechanical scanning.
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
Enables real-time hyperspectral imaging by simplifying data processing and allowing for rapid detection of molecular species, reducing processing demands and improving detection speed, especially for volatile species like petroleum gas products and explosives.
Implementation Method 1
An OPO is a system which converts an input pump laser into light beams at two different frequencies by passing it through a nonlinear optical crystal
Implementation Method 2
Optical parametric oscillators (OPO) are a particularly effective type of tunable source of coherent radiation in this wavelength region
Implementation Method 3
The thickness of these layers, and hence domains, is chosen to achieve quasi-phase-matching, which results in an efficient flow of energy from the pump frequency to the signal and idler frequencies
Implementation Method 4
use a periodically poled grating of birefringent material
Data Source
Figure 1~4
Figure 2
AI summary
A tunable coherent radiation source comprises a pump laser which outputs a pump beam and a non-linear optical medium having a tuning pattern to provide tuning across a wavelength range. A translation system is arranged such that the pump beam is translated across the tuning pattern. The scanning pattern is formed such that translation of the pump beam across the tuning pattern provides one or more discontinuities in tuning across the wavelength range. A spectroscopic system and a hyperspectral imaging system comprising such a tunable coherent radiation source are described, as is a non-linear optical medium adapted for use in such a source. A method of providing coherent radiation tuned over a wavelength range is also described.