Development And Application Of Raman Spectroscopy And Nonlinear Optical Imaging Instruments

The study of advanced instruments is one of the most important factors that drive the development of science and technology.It can provide researchers with new tools,and help them understand many special properties of matter.So many application fields can be easily explored.Optical instrument is a common type of equipment in many fields of scientific research.Existing optical instruments include different types of light sources,imaging equipments suitable for observation from macro to micro scales,optical manipulation and processing equipments,etc.Since the energy of light has the the same order of magnitude with the energy level of molecules,when light interacts with matter,it can exchange energy with them and carry the structure information of molecules.By analyzing the composition of light,researchers can identify the composition and state of matter.Therefore,optical instruments are one of the most commonly used instruments in the field of analysis and detection,especially spectral instruments.They play important roles in the process of understanding the world.At present,the common commercial spectrometers include UV-VIS absorption spectrometer,fluorescence spectrometer,IR absorption spectrometer,Raman spectrometer,etc.In addition to these spectrometers,there are also many imaging instruments based on spectral effects,such as fluorescence microscope,multispectral camera and so on.Researchers have developed many analytical methods based on different types of spectral instruments.They can be effectively used for sample detection under different conditions.However,although these instruments have been able to provide a large amount of data for scientific research,it is still difficult to meet the functional requirements of many specific application areas.So,it is of great significance to design and develop spectral instruments based on new physical principles,combining with technological innovation or for special application areas.In this paper,we mainly introduce the instruments of spectral detection and spectral imaging.Based on detailed analysis of the function and structure of existing instruments,we develop three different kinds of instruments.The types of these works include the development of miniature Raman spectrometer for special application,the functional extension of traditional Raman spectrometer by combining with other scientific instruments,and the build of multi-mode imaging instrument based on nonlinear spectral effects.The paper will introduce the basic principles,the engineering design and the construction process of these instruments.Also the performance of these instruments will be given by sample testing.The three parts are described in detail as follows:1)Development of integrated Raman spectrometer special for microfluidic chip detection.The real samples in daily life usually have extremely complex composition.Their detection cannot be done directly by using the existing instruments.Some pretreating such as separation,enrichment,reaction and so on,are usually needed to be done with these samples before they are detected.Microfluidic chip is a chemical chip that can realize various conventional operations in the chemical laboratory.It can greatly improve the pretreatment efficiency of the sample.While Raman spectroscopy is a rapid,non-contact detection method,which can collect the fingerprint spectra of the sample.It is also very sensitive that suitable for the detection of extremely few samples since the appearance of surface enhanced Raman spectroscopy technique.Therefore,we fully considered the characteristics of these two techniques,and developed a new Raman spectrometer.The new instrument is more suitable for microfluidic chip detection than the existing instruments,and can bring together the advantages of the two techniques.It has an inverted probe and an integrated micro-imaging spectral detection module.Also its probe is movable so that the sample can be fixed.In the optical module of the instrument,a dichroic beam splitter is used instead of the imaging switching light path in the traditional micro-imaging Raman spectrometer,which greatly improves the stability of the instrument.This instrument combines the sample processing and detection together and has a high integrated level.It will help to drive the development of rapid detection techniques for complex samples.2)Development of the joint detection instrument which combines phase detection based surface plasmon resonance(SPR)and Raman spectroscopy.The surface plasmon resonance technique is very sensitive to the change of refractive index of the matter.It is often applied to detecting the surface adsorbed samples.However,this technique can only reflect the adsorption state of the sample,but the change of the fine structure of the adsorbed molecules cannot be known.Raman spectra can accurately reflect the structure of molecules,but it has a very weak signal.Since when SPR phenomenon occurs,the electromagnetic field on the sensing surface will greatly enhance the Raman signal.By this way the extremely few sample on the sensing surface can be detected.So people combine the two techniques to achieve joint sensing.The traditional way is to use angle scanning system with light intensity detection to monitor the SPR phenomenon.In this paper,this method has been improved.We introduce the phase-shifting interference imaging technique to the system.When the SPR phenomenon occurs,both the phase change of the light and the Raman detection can have a very high sensitivity.By monitor the phase change,we don't need to scan the incident angle of the light repeatedly.This will help improve the stability of the light path.Also,the instrument can image the phase change at different locations on the sensing surface,so researchers can get both the image and the spectral information of sample.This instrument will show great application potential in the research of surface reactions.3)Development of nonlinear optical imaging system and their biological application.For various imaging techniques,the most important thing is to improve the contrast of the samples.Since many sample themselves have complex components and low contrast,which makes them difficult to be observed clearly through traditional optical imaging methods.Since different samples have different micro-structures.And they can have influence on different spectral effects.So,people can use spectral imaging technique to distinguish samples from the complex surrounding environment.Under strong laser excitation,many samples can also have effects on different nonlinear optical effects.They can change the nonlinear spectra,or greatly enhanced the sensitivity of some optical effects that exist under weak light irradiation.By this way,the traditional linear optical imaging methods can be replenished.So in this paper,we analyze the excitation and detection conditions of several nonlinear optical effects in detail.By reasonably selecting the hardware devices,we develop a muti-mode nonlinear optical imaging instrument which combines the function of single/dual laser beams excition,pulse delay adjustment,mirror scanning and light power or its change detection.The instrument can catch image of samples by several nonlinear optical effects.Then,we choose one of the nonlinear optical effects,the four-wave mixing,as the research tool.By marking the cell surface with silver nanoparticles,we detect the content and distribution of the sialic acid on cell surface.The experimental results show that the instrument has the ability of application in the field of biology.