Принцип на близко поле оптично микроскопия
Traditional optical microscopes consist of optical lenses that can magnify objects several thousand times to observe details. Due to the diffraction effect of light waves, it is impossible to increase the magnification infinitely, as the diffraction limit of light waves will be encountered. The resolution of traditional optical microscopes cannot exceed half of the wavelength of light. For example, using green light with a wavelength of λ=400nm as the light source can only distinguish two objects with a distance of 200nm. In practical applications, when λ>400nm, the resolution is lower. This is because general optical observations are made at a distance (>>λ) от обекта.
Базирани откриването и изображенията принципите от не радиационни полета, близко поле оптични микроскопи можете пробив дифракцията границата на обикновените оптични микроскопите и проводимостта наномащабни оптични изображения и спектрални изследвания в ултрависока оптична разделителна способност.
The near-field optical microscope consists of a probe, signal transmission device, scanning control, signal processing, and signal feedback system. The principle of near-field generation and detection: The incident light shines on an object with many small and fine structures on the surface. These fine structures, under the action of the incident light field, produce reflected waves including evanescent waves limited to the surface of the object and propagating waves towards the distance. Evanescent waves come from fine structures within objects (objects smaller than the wavelength). The propagating waves come from the rough structures in the object (objects larger than the wavelength), which do not contain any information about the fine structure of the object. If a very small scattering center is used as a nanodetector (such as a probe) and placed close enough to the surface of the object, the evanescent wave is excited, causing it to emit light again. The light generated by this excitation also includes undetectable evanescent waves and propagation waves that can propagate to distant detection, completing the near-field detection process. The transition between the evanescent field and the propagation field is linear, and the propagation field accurately reflects the changes in the latent field. If a scattering center is used to scan the surface of an object, a two-dimensional image can be obtained. According to the principle of mutual inversion, the interaction between the irradiation light source and the nanodetector is swapped, and the sample is irradiated with a nanolight source (evanescent field). Due to the scattering effect of the object's fine structure compared to the emission field, the evanescent wave is converted into a propagating wave that can be detected at a distance, and the results are completely identical.
Near field optical microscopy is a digital imaging technique that involves scanning and recording a probe point by point on the surface of a sample. Figure 1 is an imaging principle diagram of a near-field optical microscope. The rough approximation method of x-y-z in the figure can adjust the distance between the probe and the sample with an accuracy of tens of nanometers; The x-y scanning and z-control can control the probe scanning and z-direction feedback with a 1nm accuracy. The incident laser in the figure is introduced into the probe through a fiber optic and can change the polarization state of the incident light according to requirements. When the incident laser irradiates the sample, the detector can separately collect the transmission signal and reflection signal modulated by the sample, which are amplified by a photomultiplier tube. Then, they are directly converted from analog to digital and collected by a computer or entered into a spectrometer through a spectroscopic system to obtain spectral information. System control, data acquisition, image display, and data processing are all completed by computers. From the above imaging process, it can be seen that near-field optical microscopy can simultaneously collect three types of information, namely the surface morphology of the sample, near-field optical signals, and spectral signals.
