Study Of Detecting Terahertz Electromagnetic Wave By Weakly Ionized Plasma

Due to the unique characters of THz wave,it has important applications in biomedical,material analysis,nondestructive testing,homeland security and basic science and so on.As the key technology of terahertz science research,the current commonly used terahertz detection equipments are expensive and have complex structure,strict working environment temperature.Those actors limit the development of terahertz wave greatly.But using weakly ionized plasma detecting THz wave has the characteristics of fast response,room temperature operation,low cost and high electronic ruggedness.It's a very promising terahertz wave detecting method.This paper tests the discharge characteristic of the neon lamp.The light spot diameter of terahertz radiation of Gunn diode is 1 cm by tested using the blade method.The response of neon lamp weakly ionized plasma is tested mainly under terahertz radiation;the result Is that the current in the neon lamp weakly ionized plasma increases with incident terahertz wave.Compared with Schottky diode detection effect,the noise of neon lamp weakly ionized plasma is larger than the Schottky diode and the responsivity is smaller than the Schottky diode.Combined with the mechanism of weakly ionized plasma detecting microwave,we analyze the effect of weakly ionized plasma with incident terahertz wave.There are three results.(1)under certain conditions,the increase of electron kinetic energy density caused by incident terahertz wave is proportional to the power of incident terahertz wave.(2)the increase of ionization collision frequency caused by incident terahertz wave is proportional to the increase of electron kinetic energy.(3)the total current under the irradiation of incident terahertz wave is proportional to the power of terahertz wave.Finally,incident terahertz wave increases the discharge current of weakly ionized plasma.The paper analyzes the deficiency of the neon lamp itself;studies and designs one device to generate weakly ionized plasma based on the deficiency.We test the volt-ampere characteristic curve of generated weakly ionized plasma.And we mainly analyze the change rule of weakly ionized plasma responsivity in different gas pressure,discharge current and gas composition.It's concluded that when the gas pressure is 600 mmHg,discharge current is 1.4mA,neon and argon gas mixing ratio is 99.5:0.5,the responsivity of weakly ionized plasma is highest,can reach 194.4V/W,signal-to-noise ratio can reach 560 at the same time.The signal-to-noise ratio of weakly ionized plasma detecting THz wave is tested;it's 350,increases four times than neon.