Optical Force Measurement via Back Focal Plane Momentum Analysis
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Solution Overview
Problem
Existing methods for measuring optical forces on trapped microscopic samples are either impractical due to the need for complex recalibration and limited to spherical samples and homogeneous media, or require expensive and complex dual-beam setups that are not feasible for integration with commercial microscopes.
Innovation Solution
A system using a single high-numerical aperture light beam to trap and measure optical forces by capturing and analyzing the momentum structure of light at the back focal plane of a lens, allowing for direct force measurement without the need for complex recalibration or dual-beam setups, and enabling measurements in non-homogeneous media and with non-spherical samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If indirect single-beam methods are used to measure optical forces, then the measurement can be performed with a single laser beam, but the system requires complex recalibration procedures and specialized equipment making it impractical for commercial use
Solution Approach 1:
The system performs self-calibration by automatically determining trap stiffness and calibration factors through analysis of particle position fluctuations and power spectral density, eliminating the need for manual recalibration with piezo actuators and specialized equipment
Solution Approach 2:
The system changes measurement parameters dynamically by analyzing the power spectral density of particle position fluctuations at different frequencies to extract trap stiffness and calibration factors, replacing static manual calibration procedures
2Device complexity
If indirect single-beam methods are used, then the setup is simpler, but measurements are limited to spherical samples and homogeneous media only
Solution Approach 1:
The system achieves universal applicability by using advanced tracking algorithms that can handle particles of any shape or size, and by implementing refractive index mapping capabilities that adapt to different media types including heterogeneous and living cellular environments
3Measurement precision
If direct dual-beam methods are used to measure optical forces, then direct force measurement is achieved, but the system requires expensive duplicated optical components making it infeasible for integration with commercial microscopes
Solution Approach 1:
The system merges the trapping function and force measurement function into a single optical beam path, combining the advantages of direct force measurement with the simplicity of single-beam setups, eliminating the need for duplicated optical components
Solution Approach 2:
The single optical system performs multiple functions simultaneously: trapping particles, measuring forces directly through momentum analysis, and characterizing the trap stiffness, replacing the need for separate dual-beam 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 simplifies the measurement of optical forces, making it feasible for commercial use, allowing for measurements in various media and with samples of any shape, while reducing equipment costs and experimental complexity, and enabling integration with conventional microscopes.
Implementation Method 1
measuring the optical forces acting on a trapped particle
Implementation Method 2
determining the force components acting on a trapped particle in an optical tweezers assembly
Implementation Method 3
measuring the force directly by means of momentum changes
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An apparatus and method for measuring optical forces acting on a trapped particle. In one implementation the apparatus and method are adaptable for use in the optical train of an optical microscope that is configured to trap, with a single light beam, a particle suspended in a suspension medium between an entry cover and an exit cover of a chamber positioned on or within the microscope. The apparatus and method involves the use of a single collection lens system having a numerical aperture designed to be greater than or equal to an index of refraction index of the suspension medium intended to suspend the particle in the chamber which is placeable at or near the exit cover of the chamber of the microscope. A light sensing device is positioned at or near the back focal plane of the collection lens, or at an optical equivalent thereof, which is capable of directly or indirectly producing optical force measurements acting on the particle derived by the x and y coordinates of the centroid of the light distribution imaged onto the light sensing device by the collection lens.