Research On Beam Smoothing Technology Based On Low-coherence Laser

Fusion energy is one of the important options for humans to solve energy problems.There are two main technical approaches to achieving a controlled fusion reaction:inertial confined fusion and magnetic confinement fusion.Inertial confinement nuclear fusion is based on the inertia of the fuel,by converting its kinetic energy into internal energy,a self-sustaining fusion reaction can be realized within the time limited by the inertia of the fuel.Laser driven inertial confinement fusion is currently the most promising inertial confinement fusion drive method for achieving fusion ignition.How to achieve efficient beam-target coupling is one of the major challenges for laser-driven methods.The beam-smoothing technology is a key technology for achieving efficient beam-target coupling.It has a great influence on many physical processes such as laser plasma interaction and symmetric compression of the target.This paper proposes a new beam-smoothing method that combines induced spatial incoherence technique and continuous phase plate to realize high-quality uniform-smoothing focal spot.This thesis mainly includes the following three parts:1.A new improved continuous phase plate design method,phase differential filtering G-S algorism is proposed.At the same time,the advantages and disadvantages of the new algorithm and the traditional G-S algorithm in designing the phase plate are compared and analyzed.The results show that under the condition of reasonable parameter selection,the far-field envelope of the phase plate based on the new algorithm is in good agreement with the objective function.It satisfies the focal spot shaping requirements well and has certain advantages.Statistical analysis of the far-field results shows that the electric field at the far-field fixed point can be equivalently determined by a vector with certain length,random-direction added to a round Gaussian random vector,and its amplitude is randomly distributed in the range of 0-2?,its amplitude follows the Rice distribution.2.A new beam smoothing method combine induced spatial incoherence and continuous phase plate(ISI+CPP)is proposed.The focal spot character of the new beam smoothing method is theoretical and numerically analyzed,statistical rules of instant focal spot distribution,focal spot intensity root mean square(RMS)time evolve rule,focal spot intensity normalized power spectrum(NPS)time evolve rules is given.The analyze shows that ISI+CPP could obtain a well-controlled focal spot shape,meanwhile the randomly changing character of ISI+CPP focal spot could further suppress laser and plasmas interaction.An optimal design method of continuous phase plate is proposed,too.Using the new beam smoothing method,with properly designed continuous phase plate,non-uniformity in spatial frequency 0.02?0.1 ?m-1 could be reduced to 0.02 in 116ps.3.A method to avoid near field intensity modulation in induced spatial incoherence by using of a two-lens aperture system is proposed.By theoretical and numerically analyzed,the effect using gaussian,round and square apertures are compared.The result shows that,when using square aperture with width of 0.8 diffraction limitation,the intensity modulation of new field with be lower,with smaller soften factor and higher transmissivity.The calculation of final focal spot shape shows that the using of two-lens aperture system with ISI+CPP could lower the near field intensity modulation and meanwhile obtain an even better uniformity in focal spot.