Influence Of Amplitude Modulator On Time Frequency Characteristics Of Broadband Low Coherent Light

Studies have shown that low-coherent light pulses with precise time-shaping capability have important application potential in laser inertial confinement fusion.However,people’s cognition of the time-frequency characteristics of low-coherent light for precise time-shaping is not enough.Based on the application of Mach-Zehnder interferometric amplitude modulator in low-coherent shaping system,this paper selects the amplitude modulator of lithium niobate substrate to study the influence of amplitude modulator on time-frequency characteristics and time coherence of broadband low-coherent light,establishes research for the study of low-coherent light pulse shaping.The main work of this paper includes:Firstly,the advantages and disadvantages of the main high-power laser driver front-end technologies,the model and pulse shaping method of the broadband lowcoherent driver are introduced,and the theoretical basis of the time-frequency characteristic modulation of the broadband low-coherent light by the lithium niobate modulator is analyzed.Secondly,the influence of the bias voltage of the amplitude modulator with the waveguide length difference of 0 on the optical phase,light intensity and spectrum is simulated by MATLAB,and compared with the modulator with the waveguide length difference of 3613.6 nm.Finally,an experimental device was built.The broadband low-coherent light with a center wavelength of 1040 nm and a bandwidth of 58.84 nm was used as the seed source,and the electric signal generated by the arbitrary waveform generator was used to drive the amplitude modulator to perform arbitrary waveform modulation on the continuous seed light source.The effects of the RF coefficient,bias voltage of the amplitude modulator,the pulse width and amplitude of the loaded electrical pulse on the time-frequency characteristics of the low-coherent light,the effects of the filter and the half-wave plate on the optical modulation characteristics,and the light with different polarization directions are respectively studied.Whether to follow the modulation characteristics.Theoretical simulation of the effects of amplitude modulator bias voltage,RF coefficient and pulse width of input electrical pulses on the temporal coherence of light pulses.The research shows that the RF coefficient has no obvious modulation on the spectral composition and temporal coherence of the light pulse,and there is a fixed interval to make the waveform fidelity of the output light pulse the best.The bias voltage will affect the fidelity,spectral composition and time coherence of the output electrical pulse.When the bias voltage is at half-wave voltage,the time domain waveform fidelity of the light pulse is the best and the time coherence is the lowest.But the spectral components will be missing.When the bias voltage was at 3.712 V,the spectral fidelity of the light pulse was the best,but the temporal waveform was in the opposite direction to the loaded electrical pulse,and the temporal coherence was the lowest.The larger the pulse width of the loaded electrical pulse,the greater the intensity of the output light and the lower the temporal coherence.The filter and half-wave plate will affect the light intensity.Before and after using the PBS crystal,the modulation law of the amplitude modulator is almost the same.