Light Beam Characterization Using Lens Array Interferometry
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Solution Overview
Problem
Current techniques for characterizing large, high-power pulsed laser beams are limited by complexity, cost, and unsuitable for large beams, often requiring multiple laser shots and introducing phase fluctuations due to optical fibers, which complicates spatio-temporal coupling measurements.
Innovation Solution
A device and method utilizing a large reference beam with differing wavefront curvature to interfere with the beam to be characterized, allowing for complete reconstruction with good spatial and spectral sampling, using separating and recombining optics and a Fourier transform calculator to calculate intensity and spatial distribution, while accounting for light source fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical fibers are used to characterize the beam, then spatial sampling can be achieved, but phase fluctuations are introduced that complicate measurements
Solution Approach 1:
The patent extracts the spatial sampling function from optical fibers and implements it directly in the measurement plane using a lens array. Each lens focuses light from a specific spatial region onto a detector pixel, achieving spatial sampling without the phase fluctuations inherent in fiber-based systems.
Solution Approach 2:
The patent introduces a lens array as an intermediary optical element between the beam and detector. This lens array mediates the spatial sampling process by optically mapping different spatial regions to different detector pixels, eliminating the need for optical fibers that introduce phase noise.
2Measurement precision
If multiple laser shots are used to characterize the beam, then measurement accuracy can be improved, but measurement time increases
Solution Approach 1:
The patent transitions from temporal averaging (multiple shots) to spatial parallelism by using a lens array that simultaneously samples multiple spatial regions in a single shot. The 2D detector captures all spatial information at once, eliminating the need for repeated measurements.
Solution Approach 2:
The patent performs preliminary spatial encoding using the lens array before detection, so that all spatial information is captured and encoded in a single measurement. This preliminary spatial organization eliminates the need for subsequent temporal averaging.
3Ease of operation
If conventional characterization techniques are used, then implementation is simpler, but they are unsuitable for large beams
Solution Approach 1:
The patent applies local quality by using multiple lenses with different focal lengths or positions in the array, where each lens is optimized for a specific spatial region of the beam. This allows the system to handle large beams by dividing them into local zones that are processed by individual lenses.
Solution Approach 2:
The patent segments the large beam into multiple spatial zones using the lens array, where each lens handles a specific segment. The detector array then captures information from all segments simultaneously, making the system adaptable to large beam sizes while maintaining operational simplicity.
4Measurement precision
If spectral sampling is improved, then spatio-temporal coupling analysis is more accurate, but device complexity increases
Solution Approach 1:
The patent merges spatial and spectral sampling functions into a single integrated optical path. The lens array performs spatial sampling while the detector captures both spatial and spectral information simultaneously, eliminating the need for separate spectral sampling components.
Solution Approach 2:
The detector array serves multiple functions: it captures spatial information through the lens array mapping, spectral information through wavelength-dependent pixel responses, and temporal information through the ultrashort pulse characteristics. This multi-functionality reduces device complexity while improving measurement accuracy.
Data Source
Figure 1a~1b
Figure 2a
Figure 2b
AI summary
One aspect of the invention concerns a method for characterization of a light beam, comprising the following steps: - separation of the light beam by means of a separator optic into a first sub-beam and a second sub-beam; - propagation of the first sub-beam over a first optic and of the second sub-beam over a second optic, said first and second optics being respectively arranged so that the first sub-beam on leaving the first optic, referred to as the "reference beam", and the second sub-beam, on leaving the second optic, referred to as the "characterized beam", are separated by a time delay τ sweeping a time interval T1 with step P1; - recombination of the reference beam and the characterized beam by means of a recombiner optic in such a way that the beams spatially interfere and form a two-dimensional interference pattern; - measurement of said two-dimensional interference pattern by means of a measurement system, as a function of the time delay τ sweeping the time interval T1 with step P1, in order to obtain a temporal interferogram; - calculation of the Fourier transform in the frequency domain of at least one spatial point of the temporal interferogram, said Fourier transform in the frequency domain having a frequency central peak and first and second frequency side peaks; - calculation of the spectral amplitude AR(ω) and of the space-spectrum phase φR(x,y,ω) for one of said first and second frequency side peaks of said Fourier transform in the frequency domain.