Spatio-Spectral Laser Characterization via Interferometric Scanning
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Solution Overview
Problem
Existing methods for spatio-spectral characterization of polychromatic pulsed laser sources, such as the TERMITES technique, become cumbersome and expensive when dealing with large-diameter laser beams, requiring complex setups like telescopes for alignment, which are difficult to use and costly.
Innovation Solution
A compact and inexpensive characterization method using focusing optics, an imaging system with a camera, and an amplitude division interferometer to create and recombine beam replicas, allowing for spatial interference pattern imaging and Fourier transform analysis to obtain spatio-temporal interferograms, enabling characterization of beams of arbitrary diameter and duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the TERMITES technique is used to characterize large-diameter laser beams, then spatio-spectral characterization can be achieved, but the device becomes cumbersome and expensive
Solution Approach 1:
The patent segments the beam characterization process into multiple measurements at different positions across the beam profile. Instead of requiring a single complex setup to characterize the entire large-diameter beam, the method divides the beam into smaller sections and characterizes each section separately, then combines the results to obtain complete spatio-spectral information.
Solution Approach 2:
The patent introduces an intermediary scanning mechanism that moves a smaller measurement setup across the beam profile. This intermediary approach allows the use of a compact, simple interferometer to characterize different portions of the large beam sequentially, avoiding the need for a cumbersome single-setup characterization of the entire beam.
2Length of moving object
If a telescope is used to reduce the size of large-diameter beams for TERMITES technique, then beam size is reduced, but the device becomes expensive and difficult to use due to critical alignment requirements
Solution Approach 1:
Instead of using a telescope to reduce the beam size before measurement, the patent inverts the approach by keeping the beam at its full size and moving the measurement probe across the beam profile. This eliminates the need for beam reduction optics and their associated alignment problems.
Solution Approach 2:
The patent creates multiple copies of the measurement process by scanning the interferometer across different positions of the beam profile. Each position provides a local measurement that is then combined to form the complete characterization, avoiding the need to modify the beam itself.
3Measurement precision
If focusing optics are used to characterize beams at their focal point, then accurate local characterization is achieved, but the setup becomes more complex
Solution Approach 1:
The patent designs the scanning interferometer setup to be universal and multi-functional. The same basic interferometer assembly can characterize beams at different positions including the focal point, by simply moving the probe to different locations. This eliminates the need for specialized focusing optics for each measurement position.
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 method allows for precise spatio-spectral characterization of large-diameter pulsed lasers at their focal point, reducing equipment size and cost, and providing accurate spectral and phase information without the need for complex alignment, thus overcoming the limitations of existing techniques.
Implementation Method 1
an amplitude division interferometer arranged between the focusing optics and the camera and having first and second arms; the method comprising, for each of the first and second planes of the beam, the following steps: imaging the plane of the beam using the imaging system; creating first and second replicas of the beam using the first and second arms of the amplitude division interferometer; recombining the first and second replicas of the beam on the camera of the imaging system, so as to obtain an image in two spatial dimensions having spatial interference patterns
Implementation Method 2
calculating the 1D Fourier transform of each temporal interferogram or the 3D Fourier transform of the spatio-temporal interferogram, said Fourier transform comprising a central frequency peak and two lateral frequency peaks
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 2a~2b
AI summary
An aspect of the invention concerns a method for spatio-spectral characterization of a beam from a polychromatic pulsed laser source, comprising, for at least the first and second beam planes, the following steps: - imaging the beam plane using an imaging system; - creating first and second replicas of the beam using first and second arms of an amplitude division interferometer; - recombining the first and second replicas of the beam on a camera of the imaging system, so as to obtain an image in two spatial dimensions having spatial interference patterns; - measuring this image according to a time τ between the first and second replicas in order to obtain a temporal interferogram at each spatial point of the image, the set of temporal interferograms forming a spatio-temporal interferogram; - calculating the 1D Fourier transform of each temporal interferogram or the 3D Fourier transform of the spatio-temporal interferogram, said Fourier transform comprising a central frequency peak and two frequency side peaks; - filtering the Fourier transform so as to conserve only one of the two frequency side peaks; the method comprising, for each frequency of the polychromatic pulsed laser source, a step of reconstructing the frequency-resolved spatial phase profile using a first frequency-resolved spatial amplitude profile obtained for the first beam plane and a second frequency-resolved spatial amplitude profile obtained for the second beam plane.