Digital Holography Using Scattered Coherent Illumination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for 3D surface topography measurement, such as digital holography and optical coherence tomography, are limited by low power illumination and slow data acquisition rates, making them inefficient for large objects and prone to movement artifacts.
Innovation Solution
A digital multifrequency holography system using a scattered but fully coherent illumination wave, allowing higher power levels up to 10 W and enabling faster data acquisition by increasing the étendue of the illumination, which is achieved by scattering a TEM00 mode at a static diffusing plate, while maintaining spatial coherence for digital holography evaluation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fully coherent illumination is used for digital holography, then measurement precision is improved, but illumination power must be limited to milliwatt range to ensure eye safety
Solution Approach 1:
The illumination is segmented into multiple spatial radiation modes (TEM00, TEM01, TEM10, etc.) that are spatially coherent with each other. This segmentation allows the total power to be distributed across multiple modes while maintaining coherence, enabling higher total illumination power (0.1-10 W) compared to single-mode illumination (milliwatt range) while preserving measurement precision.
Solution Approach 2:
The patent transitions from single-mode illumination to multi-mode illumination by adding spatial dimensionality to the coherent illumination field. By using multiple spatial modes with fixed phase relationships, the system achieves higher total power in the illumination while maintaining the coherence required for digital holography, effectively moving from a 1D (single mode) to a 3D (multiple spatial modes) coherent field.
2Measurement precision
If optical coherence tomography is used for depth resolution, then depth configuration can be distinguished, but data acquisition becomes too slow for surface objects
Solution Approach 1:
The patent extracts only the depth resolution capability from optical coherence tomography while discarding its slow sequential scanning approach. By using multi-mode coherent illumination with fixed phase differences at multiple wavelengths, the system achieves depth resolution through digital holography evaluation without requiring the time-consuming wavelength tuning and Fourier transform reconstruction of OCT, thereby achieving fast surface topography measurement with depth information.
3Measurement precision
If conventional digital holography is used for 3D surveying, then surface configuration can be measured, but movement artifacts occur due to slow acquisition rates
Solution Approach 1:
The patent implements continuous multi-mode coherent illumination across multiple spatial modes simultaneously, rather than sequential scanning. The multi-mode illumination field (including TEM00, TEM01, TEM10 modes) illuminates the entire object surface at once, enabling continuous data acquisition without movement artifacts while maintaining surface configuration measurement 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
This approach allows for rapid and accurate measurement of large objects with reduced movement artifacts, achieving speeds at least 40 times higher than conventional systems and enabling high-depth resolution with increased laser power, while ensuring safety and minimizing hazards.
Implementation Method 1
a scattering element which prepares the illumination radiation in such a way that the radiation having traveled through the scattering element provides a two-dimensionally extended illumination field for illuminating the object, which field comprises more than one spatial radiation mode, the radiation modes being spatially and temporally coherent with one another but having a fixed phase difference from one another
Implementation Method 2
Illumination radiation scattered back at the surface of the object is superimposed with the reference radiation and then received by a detector. An interference signal of the superimposed radiations is thus obtained by the detector
Data Source
AI summary
A method for measuring the surface topography of an object including the following steps: a) providing source radiation and dividing the source radiation into illumination radiation and reference radiation, b) illuminating the surface of the object with illumination radiation in a planar illumination field, the surface of the object being illuminated simultaneously with more than one spatial radiation mode and the radiation modes of the illumination being spatially and temporally coherent, but with a fixed phase difference from one another, and c) overlaying the reference radiation on illumination radiation back-scattered at the surface of the object, and detecting an interference signal of the overlaid radiation with a detector. Steps a) to c) are carried out for at least two different, fixed wavelengths. The surface topography of the object is determined by means of digital holography.