Measurement Of Ultra-short Pulse Based On Second Harmonic Wave

Since the second half of the 20 th century,lasers have developed rapidly,and pulsed lasers have been the research hotspot in recent years,especially femtosecond pulses,which can provide extremely high peak power.In recent years,ultra-short pulsed lasers have been widely used in biomedical,precision instruments and optical fiber communications.At the same time,because the pulse width of pulsed lasers is getting smaller and smaller,traditional oscilloscopes can no longer be used to measure such pulses.At present,the commonly used technique for measuring ultrashort pulses is the autocorrelation method,but this method cannot obtain the phase information inside the pulse and needs to make advance assumptions about the pulse shape.The frequency resolved autocorrelation method(Frequency Resolved Optical Gating,FROG)can measure the phase information without making assumptions about the pulse shape in advance,and has a set of mature algorithms to recover the pulse electric field.The frequency-resolved autocorrelation method is currently the most reliable method for measuring pulse phase information.The main work of this thesis is divided into the following parts:Firstly,a dispersion-managed dissipative soliton laser based on a positive dispersion cavity based on Nonlinear Polarization Rotation(NPR)is built.The pulse width is 5.9 ps,the output power is 624.8 ?W,and the repetition rate is 10.139 MHz.An Erbium-Doped Fiber Amplifier(EDFA)system was built to amplify the pulse.The pulse width of the amplified light was 3.98 ps,the output optical power was 48.4m W,and the peak power of the pulse was 1.20 k W,which was used for verification.At the same time,a frequency doubling system was built to verify the frequency doubling effect of the BBO nonlinear crystal,and the spectrum of the frequency doubled light was measured by a spectrometer.Then a frequency-resolved autocorrelator based on non-collinear form was built,and the basic optical path design,device selection,construction,control program writing,and intensity autocorrelation signal measurement and processing were completed.The intensity autocorrelation measurement of the managed dissipative soliton fiber laser was compared,and the results were consistent with the measurement results of commercial instruments.Finally,the measurement and algorithm recovery of the fiber laser were completed by using the built FROG.First,the NPR laser with a spectral width of 30 nm was measured.The stable state is consistent;secondly,adjust the polarization controller until the pulse is stable,and measure the intensity autocorrelation and FROG at the same time.Strong dispersion and strong chirp are consistent with the characteristics of dissipative solitons,and the spectrum of the restored pulsed light is also consistent with the actual spectrum trend;at the same time,the focal length of the focusing lens in the optical path is changed and the changes in the measurement results are analyzed.