A lens is made by grinding a transparent material such as glass into a circular sheet so that both surfaces are curved or one side is flat. Its function is to make the beam converge or diverge through the refraction of its two surfaces, and form the image of the object at any required position.
Double glue lens is a lens obtained by gluing two lenses together. The combined lens formed by two lenses is an effective method to obtain short focal length, large magnification and better imaging quality. It has been widely used in astronomical telescopes and cameras.
Optical microscopy is an ancient subject that has been studied for more than a century. The non-destructive nature of optical microscopy is important in various fields, such as biology and material science. The main disadvantage of ordinary optical microscope is that the resolution is limited by the diffraction limit, and its resolution is an order of magnitude with the illumination wavelength; Another limitation is its limited focal depth. These limitations make it difficult to image objects with a certain thickness using ordinary optical microscopy, so three-dimensional (3D) imaging of thick samples is impossible.
In order to improve the resolution of ordinary lens and facilitate confocal 3-D imaging and high-density optical storage, many techniques of super-resolution are proposed by adding pupil filter to the lens of optical system. Such as ring with central occlusion, light leakage ring pupil, phase pupil and grating, etc. These pupils improve the resolution of 2-D imaging, but due to the extension of the focal depth in the axial direction, it is not suitable for confocal 3-D imaging. In addition, due to the method of adding pupil to the lens, the intensity of the light spot is reduced, some even more than 90%, which greatly reduces the signal-to-noise ratio of the optical system.
The combined lens formed by two lenses is an effective method to obtain short focal length, large magnification and better imaging quality. This method has been widely used in astronomical telescopes and cameras. In 1990, Mansfield et al. Applied two separate lenses (they are called solid immersion lenses) to near-field light storage, and proved that placing a hemispherical solid immersion lens on the imaging surface of the lens can improve the transverse resolution of the microscope by N times (n is the refractive index of the solid immersion lens). Recently, many literatures have further studied the lateral resolution and polarization characteristics of solid immersion lens, and some literatures use two separate lenses to obtain high numerical aperture lens to improve the resolution of optical system,. The diffraction imaging characteristics of two closely glued double glued thin lenses are analyzed by scalar diffraction theory. It is found that it has not only better transverse resolution, but also higher axial resolution. It can be used as an ideal optical element for confocal 3-D imaging.
