Differential Absorption Lidar With Polarization Combining
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Solution Overview
Problem
Existing remote gas emission monitoring systems face challenges in achieving high sensitivity, spatial resolution, and cost-effectiveness, particularly in simultaneously detecting gas concentrations and performing 3D topographical imaging, due to limitations in laser beam combining and energy profile matching, and require multiple passes over the area of interest.
Innovation Solution
The implementation of a Differential Absorption Lidar (DIAL) system utilizing Volume Bragg Gratings for laser wavelength and linewidth control, combined with polarization combining, circularization, reference pick-off, and fiber coupling, and incorporating a multiple pixel sensor array to enable flash DIAL, which allows for simultaneous 3D imaging and gas detection in a single sensor, improving spatial resolution and chemical sensitivity while reducing size, weight, and power requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Fourier transform spectrometers are used for high spectral resolution measurements, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the wavelength selection function from complex Fourier transform spectrometers and implements it using simpler tunable laser sources combined with narrowband optical filters. This separates the spectral resolution function from the entire spectrometer system, allowing high spectral resolution to be achieved with less complex components.
Solution Approach 2:
The patent creates a multi-functional system where a single integrated instrument performs both DIAL gas concentration measurements and 3D topographical imaging. The same laser and detector system serves dual purposes: measuring atmospheric gas absorption at specific wavelengths and capturing spatial information through time-of-flight ranging, eliminating the need for separate specialized instruments.
2Measurement precision
If cavity-based optical devices are used for narrow wavelength sensing, then measurement precision is improved, but signal to noise ratio deteriorates
Solution Approach 1:
The patent employs a composite optical filtering approach combining multiple narrowband filters with different spectral characteristics. By layering and combining filters with complementary transmission profiles, the system achieves superior wavelength selectivity while maintaining higher throughput and signal strength compared to single-cavity approaches, thus improving signal-to-noise ratio.
3Measurement precision
If gas-containing cells are used for filter characteristics, then measurement precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent replaces physical gas-containing cells with solid-state tunable laser sources and optical filters. This substitution eliminates the complexity of gas handling, cell sealing, and pressure control systems while achieving equivalent or superior spectral selectivity through laser wavelength tuning and filter selection, dramatically simplifying system manufacture and deployment.
4Measurement precision
If previous DIAL systems are used for gas sensing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple laser beams into a single combined beam using optical beam combining techniques. By co-propagating multiple laser sources through the same optical path and using constructive interference or spatial overlap, the system achieves the spectral diversity needed for DIAL measurements while simplifying the optical train and reducing the number of separate optical paths that would otherwise be required.
Solution Approach 2:
The patent creates a multi-functional system where a single integrated instrument performs both DIAL gas concentration measurements and 3D topographical imaging. The same laser and detector system serves dual purposes: measuring atmospheric gas absorption at specific wavelengths and capturing spatial information through time-of-flight ranging, eliminating the need for separate specialized instruments.
5Measurement precision
If separate DIAL sensor and imaging system are used, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent creates a multi-functional system where a single integrated instrument performs both DIAL gas concentration measurements and 3D topographical imaging. The same laser and detector system serves dual purposes: measuring atmospheric gas absorption at specific wavelengths and capturing spatial information through time-of-flight ranging, eliminating the need for separate specialized instruments.
Solution Approach 2:
The patent enables continuous simultaneous operation of gas detection and imaging functions within a single instrument. By using the same optical path and detector for both DIAL and ranging measurements, the system continuously gathers both gas concentration data and spatial information in real-time during a single platform pass, maximizing data acquisition efficiency.
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 enables efficient and cost-effective remote gas concentration measurement with improved spatial resolution and chemical sensitivity, allowing for real-time 3D imaging and gas detection in a single integrated sensor, reducing the need for multiple passes and enhancing the overall performance of gas emission monitoring systems.
Implementation Method 1
The DIAL system uses Volume Bragg Gratings (VBGs) for laser wavelength and linewidth control
Implementation Method 2
The DIAL system uses Volume Bragg Gratings (VBGs) for laser wavelength and linewidth control, combined with polarization combining
Implementation Method 3
The flash LIDAR topographic modality uses a single pulse to illuminate a whole scene imaged onto a focal plane array. The flash LIDAR focal plane array observes a pulse waveform from each pixel, giving the capability to calculate pulse time of flight and therefore distance at each pixel
Implementation Method 4
One way of obtaining information regarding the amount of atmospheric trace gases is to sense the spectral absorption of reflected sunlight
Data Source
AI summary
A system for remotely detecting gas concentration is provided. The system includes a plurality of light sources. At least a first one of the light sources generates light having a first wavelength and a first polarization, and at least a second one of the light sources generates light having a second, different wavelength and a second polarization that is orthogonal to the first polarization. The light from the light sources is placed on a common transmission path, and is directed to a target area by a steering mirror. Light reflected from the target area is received and directed to a detector. The detector provides information regarding the time of arrival and amplitude of the received light, allowing range and gas concentration information to be obtained. In some embodiments the detector is an imaging detector, allowing three-dimensional range information to be obtained from the target area from a single light pulse.