Strong Focusing Effect Of Laser By Micron Dimension Tapered Glass Capillaries

At present, focused laser with small size and high intensity is used in a surging number of fields. It has become a hot topic since many research teams at home and abroad have been engaged in this area when traditional focusing system was difficult to meet such high intensity. In many people’s efforts, there are many ways to show the possibility of achieving this goal, but these methods also have some shortcomings. Such as small focal length, low efficiency and does not fully demonstrate the trend of focused laser with the changes of external parameters.Inspired by the fact that micron cone-shaped glass tube can guide the focused ion beam, this work attempts to use the tapered glass capillary of micron dimension instead of mirror or lens system to guide the focused laser. In order to obtain the ability to focus laser of the micron cone-shaped glass tube, we determine quantitatively the position, size and intensity of focused light spot which from focused laser using the tapered glass capillary of micron dimension in the way of scanning light spot by small aperture optical fiber which equipped on the five dimensional displacement table.It is found that the tapered glass capillary of micron dimension has a better capacity of focusing the laser through experiments. And there is a strong dependence on the inner diameter of the tapered glass capillary of micron dimension. With the decrease of tapered glass capillary ’s inner diameter, the focusing position constantly close to the nozzle. That is to say that the focal length is continuously reduced, and decreases with the decrease of the inner diameter of the outlet from a few hundred microns to tens of microns. Which showing the law of decreasing with the factor of approximate 1/2. At the same time, the size of focused light spot is also in constant decreases, approximately to the linear decrease with the decrease of inner diameter and about the 1/3 of the inner diameter. In addition, the intensity of focused laser is in the continuous increases, which has a direct link with the inner diameter of the outlet. That is to say, the amplification factor is increased following the rise of the square type with the decrease of the inner diameter of the outlet.To more conductive for application, we use a bunch of laser with small divergence angle incoming the micron cone-shaped glass tube. And we find that the focal length can be effectively extended in the case of no significant attenuation of the intensity. Which all based on the fact that the position of focus will extend backwards when the diffusion laser passes through the convex lens. This method provides a good help for the application of focused laser with long focal length which will be used for irradiation of single cell.At the beginning of the thesis, we mainly introduced several kinds of work in this field which have been published. Including the super lens which based on negative refractive index materials, metal film substrate cycle of subwavelength holes, multimode optical fiber with self-focusing effect, direct synthesis of angle spectrum and so on.The concept of two-dimensional finite difference time domain method(2D-FDTD) is firstly discussed in the second chapter. We make preliminary theoretical simulation for the strong focusing of laser which guided by tapered glass capillaries.The third chapter presents a series of experimental equipment used for strong focusing laser guided by tapered glass capillaries, including the principle of instrument selection and specific parameters.The fourth chapter introduced some preparation before the tapered glass capillaries guide laser strong focusing experiment some preparation before the experiment. Including the test of the photoelectric diode and laser intensity distribution measurement and calibration of video microscope.The fifth chapter concentrates on the experiment of tapered glass capillaries guide laser strong focusing, the result of experiment is shown. We analyzed and discussed the experimental results preliminary.The sixth chapter is the last chapter of this article. In this part, we summarized our work, looking forward to the subsequent application, and provided the planning and direction of further experiments.