Three-Dimensional Focusing Measurement Method for Confocal Microscopy Based on Liquid Crystal Spatial Light Modulator
Abstract
:1. Introduction
2. Experimental Materials and Fabrication Methods
2.1. Study of LC-SLM Modulation Characteristics
2.2. Binary Fresnel Lens Construction Method
2.3. Analysis of Wavelength Effect of Incident Light
3. Experimental Methods
4. Results
4.1. Lateral Focusing Experiment
4.1.1. Experimental Data Acquisition
4.1.2. Experimental Data Analysis
4.1.3. Analysis of Abnormal Peaks
4.1.4. Experimental Error Analysis
- Laser Source: The laser used in this experiment is a small LED laser. Compared to the helium-neon lasers commonly used in laboratories, its light source is a square LED, which is focused by a lens at the laser head to form a quasi-point-like beam at a distant point. The beam quality is relatively poor, and its stability is slightly weaker. During prolonged operation, fluctuations in output power and frequency may occur, affecting the shape and brightness of the final spot;
- Optical Path Structure: The laser emits a Gaussian beam, where the center brightness is higher than the edges. Due to limitations in the experimental setup, no beam shaping was performed on the Gaussian beam. As a result, the light received by the LC-SLM has non-uniform brightness across its surface. During lateral modulation, the modulation region on the liquid crystal surface shifts, causing changes in the brightness of the focused spot, which, in turn, affects the final light intensity calculations;
- Measured Surface: Due to the influence of the polarizing beam splitter, a mirror could not be used as the measured surface. Instead, a white plastic block with high surface reflectivity was used as the measured object. While the surface appears smooth and flat to the naked eye, at the micro-nano scale, it may be relatively rough, affecting the light intensity values at each lateral modulation position. Additionally, if the measured surface is not perfectly perpendicular to the optical axis during installation, it can also lead to variations in the final measured light intensity values.
4.2. Axial Focusing Experiment
4.2.1. Experimental Data Acquisition
4.2.2. Experimental Data Analysis
4.2.3. Experimental Error Analysis
- Optical Path Structure: The laser emits a Gaussian beam, where the center brightness is higher than the edges. After passing through the collimating beam expander, it can be approximated as a plane wave; however, in reality, the light intensity distribution is non-uniform. Therefore, the light received by the LC-SLM also has non-uniform brightness across its surface. During axial modulation, the quasi-collimated beam obtained through the microscope objective has components with certain deflection angles. When the axial distance changes, the positions and intensities of these components also change, causing the captured spot images to vary irregularly with the defocus amount, showing only an overall trend in size changes;
- Alignment Precision: When setting up and aligning the optical system, the installation angles and heights of numerous components, such as the LC-SLM, PBS, microscope objective, and industrial camera, require manual adjustment, which affects the alignment of all subsequent components and devices. The final impact is that the components are not perfectly collimated or perpendicular, which affects the uniformity of the modulated beam in the focusing range, leading to deviations in the spot light intensity values during axial focusing;
- Ambient Light Interference: All images in this experiment were captured under dark conditions; however, the lights from electronic equipment around the laboratory are unavoidable. Additionally, the LC-SLM modulation, camera capture, and air-bearing platform control during the experiment are all operated via a computer; therefore, the confocal microscopy 3D focusing system is exposed to interference light from the display. The display screen changes during the experiment, causing the brightness of the interference light to vary accordingly. Although changes in pixel grayscale values are not visible to the naked eye, they may still interfere with the data acquisition process.
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
LC-SLM | Liquid crystal spatial light modulator |
DMD | Digital micromirror device |
SLM | Spatial light modulator |
FLC-SLM | Ferroelectric liquid crystal spatial light modulator |
R2 | Goodness of fit |
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Li, Y.; Li, Y. Three-Dimensional Focusing Measurement Method for Confocal Microscopy Based on Liquid Crystal Spatial Light Modulator. Sensors 2025, 25, 2620. https://doi.org/10.3390/s25082620
Li Y, Li Y. Three-Dimensional Focusing Measurement Method for Confocal Microscopy Based on Liquid Crystal Spatial Light Modulator. Sensors. 2025; 25(8):2620. https://doi.org/10.3390/s25082620
Chicago/Turabian StyleLi, Yupeng, and Yifan Li. 2025. "Three-Dimensional Focusing Measurement Method for Confocal Microscopy Based on Liquid Crystal Spatial Light Modulator" Sensors 25, no. 8: 2620. https://doi.org/10.3390/s25082620
APA StyleLi, Y., & Li, Y. (2025). Three-Dimensional Focusing Measurement Method for Confocal Microscopy Based on Liquid Crystal Spatial Light Modulator. Sensors, 25(8), 2620. https://doi.org/10.3390/s25082620