TEM Intermediate Lens Assembly for Variable Diffraction Magnification
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Solution Overview
Problem
Current transmission electron microscopes (TEMs) lack flexibility in achieving different magnifications for diffraction planes, which limits the versatility and imaging capabilities, especially when using wave front manipulating devices like laser phase plates.
Innovation Solution
The design incorporates additional lenses and multiple ports for receiving wave front manipulating devices, allowing for the placement of these devices at various locations within the TEM. This configuration enables a range of magnifications by selectively deploying different lens combinations and wave front manipulating devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase plate is placed in the back focal plane, then the device size near the electron beam becomes large and contamination risk increases, but the phase contrast imaging capability is improved
Solution Approach 1:
The patent introduces a conjugate plane that is optically conjugate to the back focal plane but physically separated from it. This allows the phase plate to be placed in a different spatial location (another dimension in the optical path) while maintaining the same functional effect. The conjugate plane approach transfers the phase modulation function from the crowded back focal plane region to a more accessible location downstream, reducing contamination risk and improving accessibility while preserving phase contrast imaging capability.
2Manufacturing precision
If a laser phase plate is used, then a large effective focal length is required to achieve low cut-on frequency, but the hardware size near the electron beam becomes problematic
Solution Approach 1:
The patent uses an intermediate optical system consisting of relay lenses to create a conjugate plane. This intermediary mechanism allows the laser phase plate to be positioned at a location where the effective focal length can be optimized for low cut-on frequency without requiring the hardware to be near the electron beam. The relay optics act as an intermediary that decouples the phase plate positioning requirements from the electron beam interaction region, enabling independent optimization of both parameters.
3Adaptability or versatility
If multiple magnifications are to be achieved, then multiple diffraction planes or complex lens systems are needed, but device complexity increases
Solution Approach 1:
The patent implements a dynamic lens excitation system where the existing lenses can be selectively activated or deactivated to change the effective optical path and achieve different magnifications. By dynamically controlling which lenses are active and their excitation levels, the system can switch between multiple diffraction planes and magnification states without requiring physically separate optical paths. This dynamic configuration approach provides multi-magnification capability while avoiding the complexity of multiple fixed lens systems.
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 enhances the versatility of TEMs by allowing multiple magnifications to be achieved with a single instrument, improving imaging capabilities and adaptability when using wave front manipulating devices.
Implementation Method 1
a parallel beam illuminating the sample is focused by the objective lens after having passed through the sample, the so called back focal plane
Implementation Method 2
The phase plate causes a phase shift between scattered and unscattered electrons of e.g. π/2, thereby converting the sine-like behaviour of the CTF to a cosine-like behaviour
Implementation Method 3
An intermediate lens assembly is arranged between the objective lens and the projection assembly. The intermediate lens assembly is configured to receive the beam of electrons after leaving the objective lens and to produce a magnified image of a sample present in the sample holder
Data Source
AI summary
In a transmission electron microscope, an intermediate lens assembly receives a beam of electrons after leaving a primary lens and forms an image of a sample in a sample holder. The intermediate lens assembly comprises a first lens, a second lens, a first port in a first port plane and a second port in a second port plane. The first port and the second port receive a wave front manipulating device for manipulating the wave front of the beam. In a first mode, a controller controls the first and second lenses to direct the diffraction pattern into a second diffraction plane wherein the second diffraction plane is coincident with the first port plane. In a second mode, the controller controls the first and second lenses to direct the diffraction pattern into a third diffraction plane wherein the third diffraction plane is coincident with the second port plane.