Ultrafast Pulse Laser Interference Technique And Its Application In The Diagnosis Of The Process Of Impact Dynamics

The pulse frequency-domain interferometry, developed ten years ago, is an advanced noncontact laser interferometric instrument with fs time resolution and nm displacement resolution.By adopting pump-probe technology,the interferometry can capture the physics parameters changed to time during the ultrafast dynamic process. As a important instrument,the frequency-domain interferometry is used widely to measure the dynamic paraments of experimental sample loaded by fs laser or ps laser.Nowadays,the frequency-domain interferometric technology has been developed in America,Britain,France and Japan.The significance to develop frequency-domain interferometry is to provide a method for investigating dynamic response character of material loaded by ultrafast pulse laser and accelerating the development of ultrafast dynamics physics.In order to promote the development of pulse frequency-domain interferometry in china, the author has carried out a systematic investigation for the pulse frequency-domain interferometry during the past years which can be used to measure the dynamic parameters during these experiments in which the sample is loaded by plane-distributed or centrosymmetric-distributed shock wave.In addition,the interferometric microscopy has also been investigated to measure the dynamic parameters during those experiments in which the sample is loaded by non-centrosymmetric-distributed shock wave.The dissertation introduces the work principle,design method,data processing method and experiment method for the above two interferometrys in detail.The primary content and innovation is as follow.1,On the basis of the illumination proved by E.Tokunaga in university of Tokyo,the author has studied the work principle of frequency-domain interferometry carefully.It is found that the condition for two laser pulses interfering in frequency domain is as follows Where c is the velocity of light.θis the diffraction angle of characteristic spectrum.d is the grating and T is the delay time between the two pulses came from one laser.By analyzing the character of frequency-domain interference,it is found that the light intensity equation I(f) of frequency-domain interference can be expressed as follows Where f is the frequency of light.T is the delay time between the two laser pulses.Φis the phase between the two laser pulses. R is the intensity ratio of the two laser pulses. I0(f) is the spectrum function of the laser.2,After analyzing the data processing method of Michelson interferometer,the author has brought forward a unique data processing method for frequency-domain interferometry. By adopted the Fourier transform arithmetic,it is easy to calculate the transfers-phase difference or transfers-time difference between the two laser pulses.In addition,the author has deduced the relation between the transfers-time difference or transfers-phase difference measured by fequency-domain interferometry,which is expressed as follows Where s is the dynamic displacement of moving surface. T is the transfers-time difference between the two laser pulses.Φis the transfers-phase difference between the two laser pulses.λis the work wavelength of the pulse laser.From the above formula,it is easy to be found that the movement displacement can be got by calculating the transfers-time difference or transfers-phase difference measured by frequency-domain interferometry.By Adopting the data processing method for transfers-phase difference,we can get 0.001fs time resolution and 0.1nm displacement resolution which is more high than by the one for transfers-time difference.3,By irradiated the probe light to the target surface slantways, a new frequency-domain interferometry, different with foreign ones,has been developed to conduct the parameters measurement for ultrafast physics process taking place within tens of picoseconds.Compared with the frequency-domain interferometry designed by R.Evans, the unique interferometry designed by the author is of more advanges such as easy to debugging and can be used to measure the shock wave velocity and free-surface velocity profile at the same time.4,After investigating the output character of frequency-domain interferometry in detail, it came to a conclusion that the stripe number will become more and more with the transfers-time difference increasing.On the other hand, the stripe number will become less and less with the transfers-time difference decreasing. By means of the phenomenon, we can make the pump pulse and probe pulse arrive at the measured target synchronously when only one stripe is appear in frequency-domain interferometry.5,On the basis of elaborate investigation to the work principle,the author has improved the frequency-domain interferometry which can work on spectrum mode and image mode.The viability of frequency-domain interferometry was demonstrated by measuring the shock wave velocity,variety of surface shape and free-surface moving velocity of 200nm-thickness aluminium foil load by pulse lase. 6,To measure the three-dimensional shape,the author has constructed a interferometric microscopy and given a detailed illustration for it's work principle,data processing method and design method.After elaborate analyzing for femtosecond-pulse interferometric microscopy in theory,it came to a conclusion that very wide spectrum is the result in the decreace of interference fringe visibility.7,By adopting theΦ2.5 orΦ1.25 measurement head and using the currently available conventional telecommunications elements,the authors have constructed a compact velocimeter called all-fiber displacement interferometry(AFDI). The velocimeter can measure the movement displacement profile of target loaded by picosecond pulse laser.Depend on the measurement result of AFDI,it is not only easy for us to set the parameters in those experiments using interferometric microscopy,but also help us to verify the viability of the interferometric microscopy.