折射率调制脉冲射线探测技术原理验证

为验证折射率调制的脉冲射线束探测技术，建立了原理验证系统。该系统基于平行平板干涉原理，测量传感介质的折射率在射线激发下的瞬时变化。传感介质为GaAs，探针光为1310 nm单模激光，外界激发射线源平均能量为300 keV，脉宽为20 ns。使用带宽775 kHz的近红外InGaAs光电探测器，观测到了GaAs晶体在脉冲射线激发下的折射率变化。初步理论分析表明，射线脉冲在GaAs中产生的非平衡载流子浓度为1014 cm-3量级，折射率变化为10-6量级。折射率变化的实验结果与理论计算在量级上是符合的。实验结果表明，基于折射率调制的脉冲射线束探测技术基本可行，利用该系统可进一步发展高时间分辨的脉冲射线束探测技术。

Validation of radiation detecting technology based on refractive index modulation

The semiconductors refractive indexes change when they are exposed to radiation pulses. For short carrier lifetime, some semiconductors refractive indexes recover quickly. This process can be used to develop a new kind of pulse radiation detector. An interferometer was established to sense the change of refractive index of 300 um GaAs plate. The probe beam was provided by infrared (1310 nm) single mode continuous wave laser. The infrared beam illuminated GaAs with a certain angle. Two main branches of this beam interfered along the reflected path. One branch was reflected from front cover of GaAs. The other branch was the light refracted into GaAs and reflected back from the back cover of GaAs and then refracted out of GaAs. The interference light intensity changed with the change of refractive index of GaAs. The pump source was pulse radiation, 300 keV, 20 ns. The interfered light intensity was recorded by InGaAs infrared 775 kHz detector. Change of refractive index caused by the pulse radiation was detected. The nonequilibrium free carrier density and the change of refractive index were computed about 1014 cm-3 and 10-6, respectively. The experiment results were approximately consistent with the computed results, which suggests that the index modulation technology can be used for pulse radiation detection.