Taking into account the nonlinear effect, dispersion, gain distribution and loss of amplifying medium of a laser amplifier, the physical model that depicts the propagation characteristics of an optical pulse in the medium is established. In the example of Ti:sapphire amplifying medium, split-step Fourier transform method is used to solve the model numerically. The frequency chirp produced by Kerr effect is analyzed and the influences of gain saturation, group velocity dispersion and Kerr effect on the optical pulse are discussed in detail. The results indicate that the gain saturation of amplifying medium introduces the optical pulse distortion. Group velocity dispersion does not affect the pulse propagation characteristics. Kerr effect produces a frequency chirp and the gain saturation brings a larger frequency chirp at the front edge than that at the lagging edge of the pulse. It is the combined action of Kerr effect and gain saturation that makes the peak of the pulse spectrum shift to low frequency region, thus losing the symmetry of its initial profile. Therefore, in high-power laser amplification system, gain saturation and nonlinear effect are main factors that cause deformation of optical pulse, so they have to be considered seriously.

In chirped pulse amplification, the amplification of an optical pulse in laser amplifying medium is a very important link. After considering dispersion, Kerr nonlinear effect, gain distribution and loss of the medium, the physical model that the optical pulse propagates in the medium has been established, which is suitable for the general situation where the optical pulse propagates in the amplifying medium. Using a split-step Fourier method, the propagation state of a chirped optical pulse in the amplifying medium has been numerically simulated, and the influences of the gain dispersion of the medium and the frequency detuning of the pulse on the optical pulse have been discussed emphatically. The results show that, with the amplification and propagation of the ultrashort chirped pulse in the amplifying medium, gain saturation and Kerr nonlinear effect of the medium will cause distortion of the optical pulse. For the optical pulse with a wideband spectrum, gain dispersion will cause the gain narrowing effect, so it is equivalent to a loss mechanism. The frequency detuning of the optical pulse will cause distortion of the pulse, which can be used to weaken the impact of gain saturation, thus reshaping the optical pulse.

Based on radiant sound field expression for single rectangular piezoelectric wafer,this paper gives analysis the infection each factor causing to sound pressure intensity and directivity,concrete methods to minimize major lobe while narrowing side lobes is put forward.As an example,the paper derives superimposed sound field formula for 16-wafer phased array probe,analyzes relationship of superimposed sound pressure and distance between focus and transducer,simulates and discusses influence on the quality of synthetic sound beam of phased array probe by factors such as element number,distance of adjacent elements.Simulation result is considerably consistent to related theory,which provides reference for evaluation and measurement for sound distribution and production of high-quality phased array probes.

The state of wheel tread is related to the safety of train operation, detecting the train wheel tread abrasion conditions is great significant for ensuring the safe operation of trains. This thesis researched the detection method of wheel tread flat of domestic and abroad, and researched a method based on flat wheel and rail impact, the data has been wave filtered and unified standard. Finally, the results of detection system and experimental result are compared, proved the reliability and feasibility of detection methods, indicated that the detection system has a certain reference value.

Taking into account dispersion,nonlinear effect,gain and loss of gain medium,the basic propagation equation that an ultrashort optical pulse meets in distributed fiber amplifier has been derived.The amplification and propagation states of a picosecond optical pulse have been simulated numerically using split-step Fourier transform method,and the influences of group velocity dispersion and the third-order dispersion on the characteristics of the optical pulse have been analysed mainly.

The physical model for the optical pulse propagating in the amplifier has been established. Within the normal dispersion region of the fiber, the evolution of the optical pulse in the amplifier has been simulated numerically, and the influence of gain dispersion on the propagation characteristics of the pulse has been discussed emphatically. The results show that, during the propagation of the ultrashort optical pulse in a distributed fiber amplifier, group velocity dispersion and Kerr nonlinear effect will affect the pulse profile and spectrum. For the ultrashort optical pulse with a wideband spectrum, the influence of gain spectrum on the propagation characteristics of the optical pulse, in essence, is that of gain dispersion, which is equivalent to a loss mechanism and will generate gain narrowing effect, so it should be considered in the design of an amplifier system.

In order to realize the automatic judgment flaw of ultrasonic detection through MATLAB and simplify image processing,taking the train wheels for example,the B scanning figure of ultrasonic testing is classified treatment.Based on the image registration method of mutual information,this paper deals with the complex background image,and the result from the image registration that it is operated and got the complement,finally realize the image of defects and the defects are marked through the MATLAB,then display the defects location information.This method completes the defects judgment of automatic ultrasonic testing successfully,has the function on improving the efficiency of the ultrasonic detection on judgment flaw.

The license plate location plays an important role in the License Plate Recognition (LPR). According to the vertical projection and the morphological operations, this paper proposes a kind of locating method based on binary image in order to obtain accurate location of vehicle plate quickly under complex background. First, this method carries out preprocessing such as the color image grays processing, the binarization, filtering and noise abatement. Then the projection approach based on texture feature of license plate character is adopted to realize the rough location. On this basis, the up-down and left-right boundary of the car license are all examined accurately in accordance with the projection and the morphological operations. Experimental results show that this method is excellent in accuracy with a rapid speed and is great in the robustness.

Tread scratch brings excess vibration while traveling,and affects the safety and life of train and railway establishment.On the basis of many common dynamic measurements ar home and abroad,this paper introduces an optical method of auto-detecting of tread scratch based on LD-PSD,and designs the detection system.Then during the data processing,low pass filtering,load conversion and threshold comparison are achieved by using MATLAB,consequently the information of the wheel scratch is got.

In order to study the amplification and propagation characteristics of optical pulse in ytterbium-doped fiber amplifier,the propagation equation of optical pulse in distributed fiber amplifier is established. Using split-step Fourier transform method,the propagation state of optical pulse is simulated,and influence of frequency detuning on characteristics of optical pulse is discussed especially.The results show that optical pulse is amplified and broadened simultaneously in ytterbium-doped fiber amplifier,so it has a deformed profile and a broadening power spectrum.For the case of frequency detuning,the amplification of optical pulse has declined and symmetry of the pulse dispears.If the center frequency of optical pulse deviates from the gain peak frequency in different directions,the deformation law of pulse is different.Therefore, the influence of dispersion and nonlinear effect of fiber amplifier and frequency detuning on the propagation characteristics of optical pulse should be considered in the design of amplification system.

The nonlinear effect and dispersion of fiber may modify profile and power spectrum of optical pulse when it propagates in fiber.After considering the influencing factors above,the basis for the selection of sampling interval to simulation correctly propagation of optical pulse in fiber using split-step Fourier transform method has been given.The profile and power spectrum of optical pulse on the output facet of fiber have been simulated under different sampling interval.From this,the influence of sampling interval on numerical simulation of optical pulse evolution in fiber has been discussed.The results of numerical simulation have verified the correctness of the basis for the selection of sampling interval.

Fiber amplifier is used to compensate for the transmission loss of optical signals in the fiber.It is key device in all-optical communication network.The physical model for propagation of optical soliton in the distributed fiber amplifier is established.The properties of propagation and amplification for optical soliton were simulated numerically using split-step Fourier transform method.The influence of gain dispersion on the profile and power spectrum of optical soliton was discussed finally.The results show that the chirped soliton is produced continuously with the amplification of optical soliton in the anomalous dispersion regime of amplifier.The power spectrum of soliton is widened and the oscillation structure is produced.The gain dispersion of amplification medium leads to optical soliton amplitude decreasing,width broadening and power spectrum narrowing.So the dispersion,nonlinear effect and gain dispersion of fiber amplifier all have influences on the propagation property of optical soliton.

Based on study of Bragg's diffraction of microwave by crystal simulation lattice,according to the theory of the experiment of Bragg's diffraction of microwave,line array simulation of crystal has been designed to replace simulated lattice crystal in this paper.The experiment of Bragg's diffraction of microwave based on different size of linear array plane spacing as well as different frequency of microwave by making use of microwave spectroscope has been operated.Analyze and compare the experimental result with theoretical calculations of Bragg's diffraction of microwave and verify that the design is reasonable.

In recent years,the improvement in the field of microelectronics and computer engineering has led to significant advances in ultrasonic signal processing and image construction techniques.The importance of the research on the ultrasonic phased array imaging has been described in this paper.It describes the technologies presently used for the ultrasonic phased array imaging and especially details the the principle and advantages of the new technique called sampling phased array.

Taking the group velocity dispersion,Kerr nonlinear effects,gain saturation and gain spectrum of gain medium into account,a equation describing the propagation of optical pulse in the medium is derived.The propagation state of a high power linear chirped pulse in the gain medium is simulated numerically using Split-step Fourier transform method,and the influence of gain dispersion on the profile and power spectrum of optical pulse is discussed emphatically.The results show that when propagating and amplified in the gain medium,the high power super-Gaussian optical pulse's shape becomes sharp,peak moves to pulse front edge,the spectral peak moves to lower frequency,and the asymmetric oscillation structure is formed in spectral edge.When the gain dispersion of medium increases,the spectrum width of optical pulse becomes narrow,and its peak power decreases.As a result,the gain dispersion will cause loss of the broadband spectrum pulse.

This paper describes a computer vision method for reconstruction of three-dimensional object which is capable of reconstructing the profile of the object real time and achieving high accuracy. The approach makes use of the light-section projecting a line-laser beam on the surface of an object. This work is distinguished by three key contributions. The first is the introduction of the light-section method and laser triangulation method. The space coordinates of points in the bright stripe which are considered as the first bright stripe outlining the measured object can be figured out by way of the laser triangulation method. The second contribution is algorithms of coordinate restoration, involved camera calibration and calibration of the central axis of turntable, which restores the space coordinates of the original points in the original bright stripe from that of being considered as the first bright stripe. The third is the profile reconstruction method for plotting the profile of the measured object using the OpenGL. In this paper, an experiment on a small disposal paper cup has been carried out and the three-dimensional profile of the paper cup has been obtained. The results meet the requirement of high accuracy and simplicity of computation.

Using Maxwell equations,after the influences of gain saturation,gain spectrum,group velocity dispersion and Kerr effect in Kerr amplifying medium were taken into consideration,the physical model to describe the propagation properties of ultrashort optical pulse in the medium has been built up.Using split-step Fourier method,the B integral to indicate the intensity of Kerr effect and frequency chirp generated by it have been obtained.Finally,the influence of Kerr effect on the profile and power spectrum of a optical pulse has been discussed.

With the growing capacity of optical communication and rapid development of high function of optical network,the rare earth doped fiber amplifier(RDFA) with C-band can not meet the development requirement.In order to find out the properties and development of RDFA,the RDFA with L-band and S-band can meet requirements,such as high capacity,wide band,high gain,low noise and so on,and greatly contribute to the development of dense wavelength division multiplexing(DWDM) system by introducing the construction of the RDFA,adopting the theories of energy level and working over three typical doped fiber amplifiers It has broad application prospect in the field of optical communication.

Electro-magnetic acoustic detection technique has become a new development trend of nondestructive testing because of its high detection efficiency, accurate detection results, etc, so it now has been widely adopted in the railway department of our country. When the signal is detected using electro-magnetic acoustic detection technique, the influence of the poor condition of wheel surface, the existing electromagnetic interference and other factors will enable different levels of noise to exist in the detected signal, which will affect the signal quality, thereby reducing the detection accuracy. After introducing the structure and principle of electro-magnetic acoustic detection system, this paper has put forward two noise suppression algorithms for the noise problem of the detection signal, namely, phase difference algorithm and adaptive filtering algorithm. On the premise of reserving the necessary signal waveform of system, the algorithms can effectively suppress the noise of a detected signal, improve the quality of a data waveform, and obtain good detection results. The paper also compares two algorithms and points out that the better detection accuracy can be obtained if combining the two algorithms. This work has certain inspiration to raise the accuracy of electro-magnetic acoustic detection results.

In recent years,as modern industry diagnostic and testing technology is experiencing fast development toward information and visualization,digital array phased ultrasonic testing technology has been highly recognized in domestic and foreign NDT research domain.This paper takes the case of ultrasonic phased array flaw detection on rain wheel,based on broad investigation and research,according to the basic principles of ultrasonic phased array and scanning imaging,the defects are recognised with image feature extraction technique.The result shows that the ultrasonic phased array system combined with digital image processing technology overcomes the disturbance from the inherent defects of the wheel,and recognizes accurately the correct wheel defect.So image processing technology not only improves the flaw detection capabilities of the ultrasound phased array system,but also provides some inspiration on the research of automatic inspection.