Laser inertial confinement fusion (ICF) experiment puts forward high requirements on the energy, power balance and waveform consistency of the multiple pulses reaching the target. The uniform drive of the target surface requires precise beam synchronization to achieve accurate power balance, so the synchronization test and adjustment technology for multiple lasers is particularly important. In order to realize the time synchronization measurement of multiple beams directly at the target point, a target point synchronization measurement scheme based on optical Kerr medium refractive index change imaging was proposed. The optical Kerr effect occurs when ultrashort pulses with high power density pass through the optical Kerr medium, and a refractive index change occurs inside the optical Kerr medium. Since the refractive index of the area where the focused laser passes is different from the surrounding refractive index, if the diagnostic light can pass through the area where the refractive index changes within the time when the optical Kerr effect occurs, the image of the refractive index change can be displayed on the CCD. Pulse synchronization measurements can be achieved by monitoring the state of refractive index changes. The delay between the diagnostic light and the focused laser is determined by the presence or absence of refractive index changes on the CCD.The final experimental result showed that the synchronization accuracy was better than 2.5ps. In addition, the energy analysis of the pump light was carried out.
We proposed a self-referenced technique for measuring the spatiotemporal characteristics of ultrashort pulses using the coherent diffraction imaging. This technique includes the wavelength spatial multiplexing coherent diffraction imaging measurement and the three-dimensional spatiotemporal amplitude and phase reconstruction. In experiment, we verified the feasibility of this technique by measuring a pulse from the femtosecond laser oscillator. Wavelength spatial multiplexing was realized by the combination of two-dimensional diffracted optical element and narrow-band-pass filter, and the amplitude and phase information of each wavelength was recovered by ePIE (extended Ptychographic Iterative Engine) algorithm. This technique can measure the three-dimensional spatiotemporal amplitude and phase information of ultrashort pulses with high resolution and simplicity. In the future, it is expected to be an effective method for the comprehensive monitoring of the spatiotemporal optical field of ultrashort pulse lasers, and will be helpful for the laser performance improvement.
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