Phase Retarding Plate for Zero-Intensity Doughnut Beams
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Solution Overview
Problem
Existing methods for creating zero-centered doughnut-shaped beams in microscopy are inadequate due to issues with wavelength dependence, phase errors, bulkiness, and the need for frequent adjustments, especially when dealing with broadband sources and the requirement for compact, accurate solutions that can fit within a microscope body.
Innovation Solution
A phase retarding plate composed of pairs of glass sheets with specific thicknesses, arranged in a 2×2 quadrant configuration, which provides a half-wavelength phase difference over a wide spectral range, allowing for the production of beams with zero intensity at the central axis or focus without requiring readjustment as the wavelength changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pyramid of glass triangles with a four-quadrant reflector is used to create the doughnut pattern, then the device can be corrected for two chosen wavelengths, but phase errors of even a small fraction of a wavelength can be detrimental to the performance, particularly over a large wavelength range
Solution Approach 1:
The phase retarding plate is divided into four quadrants, each with a different thickness of glass material. This segmentation allows each quadrant to introduce a specific phase delay, collectively creating the doughnut pattern while maintaining phase accuracy across a broad wavelength range. The segmented structure enables independent optimization of each quadrant's optical path length.
Solution Approach 2:
Different regions of the phase retarding plate have different glass thicknesses to create the required phase distribution. The central region has zero thickness (or a reference thickness), while the surrounding regions have progressively increasing thickness to generate the doughnut pattern. This local variation in quality (thickness) enables wavelength-independent operation.
2Adaptability or versatility
If an electronically programmable Spatial Light Modulator is used, then the beam can be reprogrammed as the wavelength is changed, but additional optics are required to direct the beam onto the SLM and pass the reflected beam to the rest of the system, creating opportunities for scattering, spurious reflection and introduction of additional phase errors
Solution Approach 1:
The invention extracts the wavelength-dependent phase modulation function from complex electronic systems (SLM) and implements it through a simple passive optical element (phase retarding plate). By removing the need for electronic programming and additional optical components, the solution eliminates scattering, spurious reflections, and phase errors while maintaining wavelength adaptability through the broadband nature of the glass material.
Solution Approach 2:
The phase retarding plate acts as an intermediary optical element that directly transforms the Gaussian beam into a doughnut pattern without requiring intermediate beam direction, expansion, or contraction optics. The glass plate mediates the wavelength adaptation function passively, eliminating the need for complex optical paths.
3Manufacturing precision
If the doughnut beam making means is located as close as possible to the microscope objective lens, then the quality of the doughnut beam is improved, but the fluorescent light emitted from the specimen would have to pass through said means in addition to both the excitation and quenching beams, and each of these bands of light would in general have different wavelengths
Solution Approach 1:
The phase retarding plate is designed to be wavelength-independent, serving as a universal optical element that functions correctly for multiple wavelength bands simultaneously. It can be positioned close to the objective lens and will correctly process the quenching beam regardless of its wavelength, while also being transparent to the excitation and fluorescent light bands. This multi-functionality allows a single element to handle multiple wavelength bands without requiring separate correction mechanisms.
4Measurement precision
If conventional methods are used to create zero-centered doughnut beams, then the resolution of the microscope is improved, but the ability to rapidly change wavelength or deal with broadband sources is limited
Solution Approach 1:
The invention replaces mechanical or electronic wavelength-tuning mechanisms with a passive optical system based on the interference of light waves passing through glass plates of different thicknesses. This substitution eliminates moving parts and electronic programming, enabling instantaneous wavelength adaptation for broadband sources while maintaining the high-resolution doughnut pattern required for microscopy.
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
The solution ensures accurate and compact generation of zero-centered doughnut beams across a wide range of wavelengths, improving microscopy resolution and compatibility with broadband sources without the need for additional optics or adjustments, thus enhancing the quality and versatility of microscopy techniques.
Implementation Method 1
A phase retarding plate composed of pairs of glass sheets with specific thicknesses, arranged in a 2×2 quadrant configuration, which provides a half-wavelength phase difference over a wide spectral range
Implementation Method 2
The solution ensures accurate and compact generation of zero-centered doughnut beams across a wide range of wavelengths
Data Source
AI summary
In order to produce a beam with a zero intensity axial ray or to produce a beam that when focused will produce an image of a doughnut shaped pattern with a zero intensity central point, a beam with a uniform or Gaussian profile is directed to a plurality of transparent plates, arranged in pairs on opposite sides of the beam axis, such that for at least one pair, the plates have a composition and thickness different from each other, and chosen so that the transmitted light has a phase difference of half a wavelength for at least three different wavelengths. An additional plate with a center on the perpendicular of the line connecting the first two plates has a composition and thickness such that the light transmitted through that additional plate has a phase difference of a quarter wavelength with respect to the light transmitted through one of the plates of said first pair of plates, at at least one wavelength.