Microscope Illumination System Using Controlled Beam Waists
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Solution Overview
Problem
In microscopes, especially laser scanning microscopes, achieving uniform illumination of the entrance pupil with laser light of multiple discrete wavelengths or a continuous spectrum is challenging due to the wavelength-dependent mode field diameter of optical fibers, leading to potential overillumination requirements and the need for high-powered laser sources.
Innovation Solution
An optical illumination system with a light source generating light at least two different wavelengths, coupled with an optical fiber and an optical focusing system that forms a predetermined number of beam waists along the propagation direction, ensuring the last beam waist determines the entrance pupil illumination, with a controlled increase in mode field diameter to maintain uniformity across wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the mode field diameter of the optical fiber is increased to achieve uniform illumination of the entrance pupil, then illumination uniformity is improved, but the wavelength dependence of the mode field diameter causes non-uniform illumination at different wavelengths
Solution Approach 1:
The patent changes the parameter of mode field diameter by selecting an optical fiber with specifically controlled wavelength dependence (less than 0.03 %/nm). This parameter selection ensures that the mode field diameter remains substantially constant across the wavelength range, achieving both uniform illumination and wavelength independence simultaneously
Solution Approach 2:
The patent creates an equipotential condition for the mode field diameter across different wavelengths by using an optical fiber where the mode field diameter is substantially independent of wavelength. This eliminates the variation that would otherwise cause non-uniform illumination at different wavelengths
2Illumination intensity
If a high powered laser light source is used to overilluminate the entrance pupil at certain wavelengths, then uniform illumination across all wavelengths is achieved, but the cost and power requirements increase
Solution Approach 1:
By changing the parameter of mode field diameter wavelength dependence to be less than 0.03 %/nm, the patent eliminates the need for overillumination. The uniform mode field diameter across wavelengths allows a single, optimized laser power level to illuminate all wavelengths uniformly, avoiding the need for high powered sources
3Length of moving object
If the mode field diameter varies with wavelength, then the beam diameter at the fiber end changes, but this prevents guaranteed uniform illumination of the entrance pupil for all wavelengths
Solution Approach 1:
The patent changes the parameter of mode field diameter wavelength dependence to be substantially independent (less than 0.03 %/nm). This ensures that the beam diameter at the fiber end remains constant across wavelengths, which in turn guarantees uniform illumination of the entrance pupil for all wavelengths without requiring additional correction
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 ensures uniform illumination of the entrance pupil independent of wavelength, allowing for the use of lower powered, cheaper illumination light sources and maintaining focus volume consistency, which is advantageous for applications like fluorescence correlation spectroscopy.
Implementation Method 1
an optical focusing system arranged between the fiber end and the objective and configured to illuminate the entrance pupil of the objective while forming a predetermined number of successive beam waists of the illumination light beam along a propagation direction thereof
Implementation Method 2
an optical fiber coupled to the light source and configured to form an illumination light beam that is emitted from a fiber end thereof
Data Source
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AI summary
An optical illumination system (102, 304) for a microscope (100, 300) comprises a light source configured to generate illumination light with at least two different wavelengths, an optical fiber (114, 302) coupled to the light source and configured to form an illumination light beam (110) that is emitted from a fiber end (116) thereof, an objective (104) having an entrance pupil (114) which is configured to be illuminated with the illumination light beam (110) for creating a focus volume illuminating a specimen (106), and an optical focusing system (118, 306) arranged between the fiber end (116) and the objective (104) and configured to illuminate the entrance pupil (114) of the objective (104) while forming a predetermined number of successive beam waists (202, 204, 205, 206) of the illumination light beam (110) along a propagation direction thereof, wherein the last beam waist (206) along the propagation direction determines the illumination of the entrance pupil (114) of the objective (104). An increase of a mode field diameter of the optical fiber (114, 302) with an increase from a shorter wavelength to a longer wavelength of the illumination light beam (110) is less than 0.03 %/nm and the predetermined number of beam waists (202, 204, 205, 206) is an even number. Alternatively, increase of the mode field diameter of the optical fiber (114, 302) with an increase from a shorter wavelength to a longer wavelength of the illumination light beam (110) is greater than or equal to 0.03 %/nm and the predetermined number of beam waists (204, 205, 206) is an odd number.