Research On All Optical Solid-state X-ray Detection With Picosecond Resolution Based On Refractive Index Modulation

Lots of picosecond single events exist in high energy density physics,astrophysics experiments and plasma radiation studies.In these fields,the picosecond time-resolved X-ray diagnostic technique has always been the emphasis of research and development.High time-resolved detection of X-ray using the semiconductor all optical modulation is a new ultrafast diagnosing concept recently proposed in the world.It attempts to develop an X-ray detection device having picosecond even sub-picosecond resolution and construct an all optical ultrafast detection system,aiming at solving the diagnosis of picosecond time-resolved problems existing in laser plasma interaction research.Based on the all optical modulation in semiconductor,an all optical solid X-ray detector with picosecond resolution was designed by combining X-ray Modulaotr（XM）and Beam Deflector Device（BDD）.Working mechanism of the All Optical Solid X-ray Detector（AOSXD）was theoretical studied and the detector was fabricated and tested basically.Influences of detector structure,material parameter and laser parameter on the detection performance were discussed respectively.It is proved that the principle of this all optical X-ray detector is feasible.The main work accomplished in this paper includes the following aspects:1.A novel all optical solid X-ray imaging detector was designed.Conversion of X-ray to optical was achieved through XM.Using of low temperature grown GaAs as sensitive area shortens the time response of detector to less than one picosecond.Using of Fabry-Perot cavity not only improves the detection efficiency but also turns phase change of the probe light to intensity change.Time to space transformation was achieved through BDD.Different compositions of AlxGa1-xAs were used as the waveguide core and cladding in BDD respectively in order to complete scanning deflection of the probe light cooperating with the design of prism mask plates.2.The influence of light generated carriers on refractivity in GaAs was discussed in detail and functional relationship between band filling effect,band gap narrowing,free carrier absorption effect and refractivity of GaAs was obtained.Through the simulation calculation,it is conclude that if the photon energy of probing light is slightly larger than the band gap energy,the intensity sensitivity of the system is relatively high.If the carrier concentration is large enough(10¹⁹cm^-3),variation of refractivity of GaAs could reach 10^-1 order of magnitude.3.Based on the pump-probe method,the carrier dynamics in semiconductor was experimentally studied,and the relationship which probe light reflective intensity changed with pump light intensity change was derived.Influences of free carrier,lattice temperature,state filling and carrier recombination on time resolution of the detector were analyzed.Results show that the time resolution of XM based on LTG-GaAshas access to picosecond even sub-picosecond order of magnitude.4.Influences of prism geometric design,probe light reflection,carrier diffusion and dispersion effect,pump light uniformity on time resolution and record length were analyzed in detail through theoretical calculation and numerical simulation.Also optimization measures were proposed.5.Both XM and BDD detectors were prepared,and then demonstration system of X-ray picosecond resolution was built.Static and dynamic tests of the AOSXD system were carried out.Testing results of AOSXD system are as follows: static spatial resolution is 5lp/mm,time resolution is about 6ps,and AOSXD system has the highest detection sensitivity with 800 nm probe light.Feasibility of AOSXD system is preliminary confirmed.The innovations of this paper are mainly reflected in four aspects:1.Based on the all optical modulation in semiconductor,an X-ray picosecond resolution imaging detection was achieved by combining XM and BDD.An all optical solid state detector model was built,preparing for the AOSXD system.Dynamic test results of AOSXD system were obtained and explained in theory.2.A theoretical model of light generated carriers induced refractivity changes in GaAs was built.Physical mechanism and quantitative description that X-ray induced GaAs refractivity changes were obtained in theory.It has provided a theoretical reference for high time-resolved detection of X-ray and other high energy particle.It is meaningful to promote the all optical solid detection method.3.Influences of material property,structure parameter,laser parameter on AOSXD detector time resolution were theoretical analyzed and optimization measures were proposed.The research results can direct the design and implementation of all optical solid state detectors.4.A new approach of X-ray picosecond resolution imaging detector using all optical solid state was explored.Research method established in this paper can be extended to other high energy particle detection field.Thus composed ultrafast imaging system can be widely used in deep space exploration,nuclear physics,high energy physics and other fields.