| As a crucial part of the facility driven by high-brightness electron beam,measurement of electron beam length is an indispensable tool for maintaining the quality of electron beam and keeping the facility stably operating.Converting pulsed electron beam into light beam is a common method for accurately measuring the beam length.Conventionally,radiated light,generated by the electron beam interacting with special material,is required to pass a transmission arrangement before entering the detector for optical path folding.Aiming at achieving the temporal accuracy measurement in picosecond,the propagation temporal difference of light beam induced by the folding system should be restricted within 1 ps.As a consequence,strictly maintaining the consistent wavefront of light beam,when propagating from source to detector,is in great demand.Wavefront consistency is normally referred as tiny wavefront difference or optical path difference,and therefore,temporal measurement error within 1ps is equivalent to the optical path difference between each fields and pupils within 0.3 mm at the detecting plane.In this dissertation,a newly-designed wavefront shaping system for wavefront consistency control is demonstrated and proposed,which holds great potentials for electron beam measuring.Firstly,on the basis of the object-image relationship and properties of ellipsoidal mirror,the equal path characteristics of light propagation between two focal points of ellipsoidal mirror are shown and illustrated.In addition,two optical arrangements,being composed of plane-ellipsoidal mirrors and double ellipsoidal mirrors,respectivley,are analyzed and optimized.Structural parameters of ellipsoidal mirrors,mainly including off-axis amounts and conic coefficient,that obviously impacts on the P-V value of wavefront,are calculated and simulated in detail.On the other hand,reeform surface mirror is employed in the wavefront shaping system,and the performance differences between the free-form surface mirror and the ellipsoidal mirror are compared and analyzed.In our design,both arrangements with 1.1 m transmission distance,are capable of implementing 0.085 mm and 0.031 mm optical path difference in various pupils,respectivley.Furthermore,the principle and application of Shack-Hartmann wavefront sensor in wavefront shaping system is studied.Taking the plane-ellipsoidal system as an example,the volume and material of two mirror are optimized,and the appropriate mechanical outer structure and adjustment mechanism of the mirrors are designed.Eventually,the experimtanl arrangment of plane-ellipsoidal mirror wavefront shaping system is built up.Important parameters of the reported system,such as length of optical path,wavefornt difference after propatation and transmission effiency,are measured and collected,which are consistent with the theoretical resulats.The proposed system with 1.1 m transmission distance and 60% average transmission efficiency are capable of implementing 0.0964±0.0002 mm optical path difference in various pupils,which is valuable for operation of electron beam measurment. |
