Study On The Characteristics Of Propagation And Detection Resolution For Picosecond Laser

With the development of laser technology and the new crystal, the creation and use of ultra short laser pulses get tremendously progresses in the field of military affairs and the optical communication systems. However, unfortunately, there are many unknown phenomenons about the characteristics of ultra short propagation and the methods for measuring these pulses don't have corresponding progresses. In this case, we researched the characteristics of the propagation of the ultra Gaussion picosecond pulse, comprehensively considerated the Kerr nonlinear effect, group velocity dispersion of host and gain spectrum, gain saturation of active particle of the laser medium. At the same time, we designed a set of automatic detection of the picosecond laser. We used the 8051 MCU to communicate with the PC by UART. 8051 MCU was used to control the power supply of the picosecond laser and capture the signal of the picosecond laser, sending these signal to the PC by UART. We programmed an application software to control all these parts. So we could achieve the whole control automatically.This thesis is composed by the following parts:1. The theoretics model about the characteristics of the propagation of the ultra Gaussion picosecond pulse was deducted. Factors such as, the Kerr nonlinear effect, group velocity dispersion of host and gain spectrum, gain saturation of active particle of the laser medium which have important impacts on pulse characteristics have been taken into consideration simultaneously. We designed a software to simulate it, analyzed the effects of dispersion, gain spectrum , nonlinear, gain saturations. From the result of the simulation we can see that with the propagation of the pulse, the peak value of the ultra Gaussion pulse change needle from plainness, the half intensity change narrow from wide and the peak value move from the front of the pulse. Simultaneity, the nonlinear phase shift of the pulse becomes great graduallyand different positions of the pulse have different nonlinear phase shift.2. We studied the characteristics of the ultra Gaussion picosecond pulse propagation with the chirp on the ultra Gaussion picosecond pulse propagation contrastively and analyzed the effection of the chirp. We get this conclusion: when the ultra Gaussion picosecond pulse whose pulse width is 100ps and peak value intensity is 1GW/cm2 propagates in the Nd: Glass laser amplifying medium, the effection of the dispersion and the gain spectrum is very small, so it can be ignored. Because of the high intensity of the pulse, the effection of the nonlinear and the gain saturations are great, so we couldn't ignore it.3. We analyzed the theories of operation and the working process of the power supply of the laser. We used the 8051 MCU to communicate with the PC by UART. We can control the laser power supply to change the work state and repeat frequency etc. of the laser by the application software. Now this module has been finished and can operate steadily.4. A set of automatic detection of the picosecond laser was designed. It consists of PC (with video capture card), picosecond laser, CCD camera, automatic translation platform. We programmed the software to control all the modules. We used three methodes to realize the synchronous detection. One method is using the mouse to capture images, which is simple. Through an adjustable delay circuit whose signal from a photoelectric cell, the mouse can be touched off to capture the current image. In this method, the precision is not so high and the system is easily disturbed. Another method is using the photoelectric cell to convert the optical signal to electronical signal which was sent to 8051 MCU. Then, 8051 MCU immediately send a preconcerted signal to the PC by UART. When programming the application software, we let PC capture the images immediately once the preconcerted signal is detected. The precision of this method is high and the delay time is short but the design of hardware and software is relatively complex. In the last method, we donot use the photoelectric cell but directly use the software to control the delay. We set a prearranging delay time bofore capturing images when emitting laser. This prearranging delay time is confirmed by practical debugging. This method isrelatively simple but it is not so easy when confirmed the fixed delay time.All in all, we researched and designed the synchronous detection scheme, and it has some reference value in the automatic detection of the picosecond laser.