rus
Issue #3-4/2021
I.V.Yaminskiy, A.I.Akhmetova, S.A.Senotrusova
Optical microscopy with the use of microlenses
Optical microscopy with the use of microlenses
DOI: 10.22184/1993-8578.2021.14.3-4.184.187
Microscopy with the use of microspheres is a new method to obtain 3D images with ultra-high resolution due to the use of a transparent microsphere at visualization in a standard optical microscope. When using a microlens microscope it is possible to get an optical resolution up to a hundred of nanometers horizontally during visualization of blu-ray disc surface grooves. It does not require to introduce labels, it is just necessary to slightly upgrade the optical microscope. It is possible to improve the microlense microscopy capabilities using the interference microscopy which provides high sensitivity and image topography of ultra-high resolution.
Microscopy with the use of microspheres is a new method to obtain 3D images with ultra-high resolution due to the use of a transparent microsphere at visualization in a standard optical microscope. When using a microlens microscope it is possible to get an optical resolution up to a hundred of nanometers horizontally during visualization of blu-ray disc surface grooves. It does not require to introduce labels, it is just necessary to slightly upgrade the optical microscope. It is possible to improve the microlense microscopy capabilities using the interference microscopy which provides high sensitivity and image topography of ultra-high resolution.
Теги: blu-ray disk blu-ray-диск hardness interference microscopy microlens optical microscopy интерференционная микроскопия микролинзы оптическая микроскопия
INTRODUCTION
In 2011 Zengbo Wang et al. [1–3] experimentally demonstrated a principle of microscopy subdiffraction limit using glass microspheres in a standard optical microscope. This noninvasive visualization method in white light makes it possible to overcome a diffraction limit 2–3 times (λ/4 – λ/6). Our scientific team together with the Zengbo Wang research team is developing a unit that combines the probe, optical and microlens microscopy [4].
The principle of microscopy with the use of microspheres to obtain 2D images is to arrange a transparent microsphere between the studied sample and an optical microscope. It is important that the distance between the sample and the lens is minimal. A microsphere works as an optical amplifier and forms the magnified virtual image of the object. Afterwards the optical microscope lens collects the virtual image that is superior to the diffraction limit. Thus, the ultra-high resolution image without labels in nanoscale can be obtained using a microsphere and a lens of a standard optical microscope.
PRINCIPLE OF OPERATION AND DESIGN
In this work the Zeiss Model AxioSkop-40 optical microscope with aperture of 0.9 is used. Resolution of this model is nearby 350 nm. In order to check the accuracy of measurements, microchips, a calibration lattice for an optical microscope and blue-ray disc surface were used. Control of measurements using the FemtoScan probe microscope and image processing by FemtoScan Online software [5] were performed simultaneously.
Despite the fact that the phenomenon of the ultra-high resolution effect is currently not fully studied, the simulation results show the importance to select the geometric and optical parameters to increase and improve the lateral resolution: in particular, the diameter of the microsphere, the refractive index of the environment and the microsphere, as well as wavelengths.
The microsphere diameter affects not only the lateral resolution, but also the transverse viewing angle: the less the microsphere, the higher the resolution and the smaller the measurement area. The focal length is determined by the formula:
, (1)
here: n1 – refraction index of the environment,
n2 – lens refraction index,
R1 and R2 – radiuses of curvature of lens
For spheres with the refractive index 1 < n2 <2 the focus is located at some distance on the surface from the shadow side. If n2 = 2, the focus occurs on the shadow side. Finally, for all n2 > 2, the light focuses inside the lense. Following the Snell law, it is possible to find the focus of the geometric optics and calculate a distance:
. (2)
The focus distance is measured from the center of the sphere [6].
For measurements, are used the BTGMS-4.25 dia. 30–100 microns barium titanate microlenses of 4.22 g/cm3 density and 1.9 refractive index. When using a 15 μm microsphere, the focal length is 7.9 μm according to formula (2).
To reduce the refractive index n, it is possible to put a wter drop on the sphere, because it is not an absolute refractive index of the sphere which is important, but the ratio n sphere/n оenvironment. Thus, with the use of a drop of water the relative refractive index will be equal to n = 1.9/1.33 = 1.4286.
CONCLUSIONS
Another development is the combination of microlens microscopy with a probe microscopy. The combined microlens and probe microscope has several advantages: the presence of a large viewing field for a detailed approach with the aid of the probe microscope, visualization and mechanical manipulation of individual objects, obtaining 2D and 3D images of the sample as well as observation in air and liquid media with the controlled parameters. It should be noted that the optical image of the nanostructures beyond the boundary of the diffraction limit can also be obtained in the case of the confocal, interference, fluorescent and Raman microscopy. In the case of interference microscopy, the vertical spatial resolution can equal units of a nanometer.
ACKNOWLEDGEMENTS
The study was completed with the financial support of the RFBR and the London Royal Society No. 21-58-10005, RNF, Project No. 20-12-00389, RFBR, Project No. 20-32-90036. ■
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
In 2011 Zengbo Wang et al. [1–3] experimentally demonstrated a principle of microscopy subdiffraction limit using glass microspheres in a standard optical microscope. This noninvasive visualization method in white light makes it possible to overcome a diffraction limit 2–3 times (λ/4 – λ/6). Our scientific team together with the Zengbo Wang research team is developing a unit that combines the probe, optical and microlens microscopy [4].
The principle of microscopy with the use of microspheres to obtain 2D images is to arrange a transparent microsphere between the studied sample and an optical microscope. It is important that the distance between the sample and the lens is minimal. A microsphere works as an optical amplifier and forms the magnified virtual image of the object. Afterwards the optical microscope lens collects the virtual image that is superior to the diffraction limit. Thus, the ultra-high resolution image without labels in nanoscale can be obtained using a microsphere and a lens of a standard optical microscope.
PRINCIPLE OF OPERATION AND DESIGN
In this work the Zeiss Model AxioSkop-40 optical microscope with aperture of 0.9 is used. Resolution of this model is nearby 350 nm. In order to check the accuracy of measurements, microchips, a calibration lattice for an optical microscope and blue-ray disc surface were used. Control of measurements using the FemtoScan probe microscope and image processing by FemtoScan Online software [5] were performed simultaneously.
Despite the fact that the phenomenon of the ultra-high resolution effect is currently not fully studied, the simulation results show the importance to select the geometric and optical parameters to increase and improve the lateral resolution: in particular, the diameter of the microsphere, the refractive index of the environment and the microsphere, as well as wavelengths.
The microsphere diameter affects not only the lateral resolution, but also the transverse viewing angle: the less the microsphere, the higher the resolution and the smaller the measurement area. The focal length is determined by the formula:
, (1)
here: n1 – refraction index of the environment,
n2 – lens refraction index,
R1 and R2 – radiuses of curvature of lens
For spheres with the refractive index 1 < n2 <2 the focus is located at some distance on the surface from the shadow side. If n2 = 2, the focus occurs on the shadow side. Finally, for all n2 > 2, the light focuses inside the lense. Following the Snell law, it is possible to find the focus of the geometric optics and calculate a distance:
. (2)
The focus distance is measured from the center of the sphere [6].
For measurements, are used the BTGMS-4.25 dia. 30–100 microns barium titanate microlenses of 4.22 g/cm3 density and 1.9 refractive index. When using a 15 μm microsphere, the focal length is 7.9 μm according to formula (2).
To reduce the refractive index n, it is possible to put a wter drop on the sphere, because it is not an absolute refractive index of the sphere which is important, but the ratio n sphere/n оenvironment. Thus, with the use of a drop of water the relative refractive index will be equal to n = 1.9/1.33 = 1.4286.
CONCLUSIONS
Another development is the combination of microlens microscopy with a probe microscopy. The combined microlens and probe microscope has several advantages: the presence of a large viewing field for a detailed approach with the aid of the probe microscope, visualization and mechanical manipulation of individual objects, obtaining 2D and 3D images of the sample as well as observation in air and liquid media with the controlled parameters. It should be noted that the optical image of the nanostructures beyond the boundary of the diffraction limit can also be obtained in the case of the confocal, interference, fluorescent and Raman microscopy. In the case of interference microscopy, the vertical spatial resolution can equal units of a nanometer.
ACKNOWLEDGEMENTS
The study was completed with the financial support of the RFBR and the London Royal Society No. 21-58-10005, RNF, Project No. 20-12-00389, RFBR, Project No. 20-32-90036. ■
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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