TEM Intermediate Lens Layout for Variable Focal Length Phase Plates
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Solution Overview
Problem
Current transmission electron microscopes (TEMs) face challenges in achieving a range of magnifications and effectively using phase plates, particularly due to size constraints and contamination risks of laser phase plates in the objective lens region.
Innovation Solution
The design incorporates additional ports and lenses to allow for the placement of a wave front manipulating device, such as a laser phase plate, in alternative diffraction planes, enabling flexible magnification and reducing contamination risks by optimizing the effective focal length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser phase plate is placed in the objective lens region, then phase contrast is improved, but the hardware size becomes large and contamination risk increases
Solution Approach 1:
The patent introduces an intermediate optical system consisting of a relay lens and a conjugate plane that acts as a mediator between the objective lens and the phase plate. This intermediary arrangement allows the phase plate to be positioned away from the objective lens region while still achieving the desired phase contrast effect, thereby reducing contamination risk to the sensitive laser-optical elements.
2Measurement precision
If a laser phase plate is placed in the objective lens region, then phase contrast is improved, but hardware size constraints are violated
Solution Approach 1:
The relay lens system creates an intermediate image plane that is conjugate to the back focal plane of the objective lens. This intermediary plane allows the phase plate to be positioned in a location with sufficient space, avoiding the cramped objective lens region while maintaining the functional relationship needed for phase contrast imaging.
3Measurement precision
If the effective focal length is increased to reduce cut-on frequency, then low spatial frequencies are better imaged, but the system complexity increases
Solution Approach 1:
The patent changes the effective focal length parameter by introducing a relay lens with a specific focal length between the objective lens and the phase plate. This parameter change allows the system to achieve a larger effective focal length, which lowers the cut-on frequency and improves imaging of low spatial frequencies, while the added complexity is managed through the modular relay lens design.
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 configuration enhances the versatility of TEMs by allowing a range of magnifications to be achieved with a single microscope, improving image quality and phase contrast, while minimizing hardware size and contamination issues.
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
In such a conjugated plane, the diffraction pattern can be (de)magnified by a factor M
Data Source
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AI summary
A transmission electron microscope (TEM) comprises: a sample holder configured to hold a sample; an electron source configured to provide a beam of electrons towards the sample holder; and a primary lens configured to receive the beam of electrons after leaving the sample holder and to produce a diffraction pattern in a first diffraction plane. The TEM further comprises: an intermediate lens assembly configured to receive the beam of electrons after leaving the primary lens and to form an image of a sample present in the sample holder, wherein the intermediate lens assembly comprises, in sequence, a first lens occupying a first lens region and a second lens occupying a second lens region. The TEM further comprises: a projection assembly configured to receive the image of the sample, the projection assembly occupying a projection assembly region. The TEM further comprises: a first port in a first port plane and a second port in a second port plane. Each of the first port and the second port is configured to receive a wave front manipulating device for manipulating the wave front of the beam. Each of the first port and the second port is located in a different one of: the projection assembly region, the first lens region and the second lens region. A controller is configured to control excitation of the first lens and the second lens. In a first mode the controller is configured to control the first lens and the second lens 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 is configured to control the first lens and the second lens to direct the diffraction pattern into a third diffraction plane wherein the third diffraction plane is coincident with the second port plane.