Rayleigh-Raman Polychromatic Laser Guide Star for Tilt Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing laser guide star systems struggle to accurately measure wavefront tilt due to the double-pass nature of laser beams through turbulent media, limiting their effectiveness and range, particularly in areas where natural stars are not bright enough, and relying on sodium LGSs is limited by wavelength and night-to-night variability.
Innovation Solution
Implementing Rayleigh-Raman polychromatic laser guide stars (RRPLGS) that utilize Rayleigh and Raman scattering to measure wavefront tilt at multiple wavelengths, eliminating ambiguity and providing scalable, flexible tilt measurements using air dispersion, enabling accurate tilt determination without relying on the object being viewed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If laser beams are projected through the atmosphere to create a laser guide star, then wavefront measurement can be performed in areas where natural stars are not bright enough, but the double-pass nature of the laser beam through turbulent media reduces measurement accuracy
Solution Approach 1:
The patent segments the wavefront measurement process by separating the tilt measurement function from the higher-order wavefront measurement function. It uses a dedicated tip-tilt sensor (quad detector) for tilt measurement and a wavefront sensor (Shack-Hartmann) for higher-order measurements, allowing each sensor to be optimized for its specific function and improving overall measurement accuracy despite the double-pass limitation
Solution Approach 2:
The patent introduces an intermediary approach by using the differential measurement between two wavelengths (Rayleigh and Raman) as a mediator to extract tilt information. The tilt sensor measures the differential displacement caused by atmospheric turbulence at different wavelengths, which serves as an intermediary signal to determine the wavefront tilt angle
2Reliability
If sodium laser guide stars are used, then wavefront measurement can be performed at specific wavelengths, but the system is limited by wavelength constraints and night-to-night variability
Solution Approach 1:
The patent changes the wavelength parameter by using two different laser wavelengths (Rayleigh scattering at the laser wavelength and Raman scattering at a shifted wavelength) instead of relying on a single sodium line wavelength. This allows the system to operate at multiple wavelengths and eliminates the night-to-night variability associated with sodium layer density changes
Solution Approach 2:
The patent makes the guide star system universal by using atmospheric molecules (nitrogen and oxygen) as the scattering medium instead of relying on the sodium layer. The Rayleigh-Raman polychromatic laser guide star can be created at any location in the atmosphere where these molecules are present, providing consistent performance regardless of nighttime conditions
3Length of stationary object
If conventional laser guide star systems are used, then wavefront measurement can be performed, but the effective range is limited to approximately 30 km
Solution Approach 1:
The patent adds another dimension to the measurement by utilizing the wavelength dimension. By measuring at two different wavelengths (Rayleigh and Raman) and exploiting the differential refraction effect, the system can determine tilt information from a single shot measurement, effectively extending the usable range beyond the conventional 30 km limitation while maintaining 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
RRPLGS systems offer improved accuracy and reliability in wavefront tilt measurement, overcoming limitations of conventional systems by leveraging differential tilt measurements at multiple wavelengths, enhancing image quality and extending the effective range beyond 30 km.
Implementation Method 1
Light from the laser beam is scattered by the components in the atmosphere
Implementation Method 2
Light from the laser beam is scattered by the components in the atmosphere
Implementation Method 3
separating spectral components of the received scattered light
Data Source
AI summary
Methods, devices and systems are described that enable improved determination of wavefront errors associated with light traveling through turbulent media, such as through the atmosphere. The described systems use a Rayleigh-Raman polychromatic laser guide star (RRPLGS) to measure the tilt at the wavelength of observation by making use of the dispersion of the refractive index of air and differential tilt measurements at multiple combinations of wavelengths based on the Rayleigh and Raman back-scattered light. The described RRPLGS systems have a number of advantages, including scalability of returned flux and flexibility in selection of short wavelengths, allowing for a combination of multiple tilt measurements, and enabling characterization of the turbulent media without relying on photons from the object of interest.