| Terahertz GaAs photoconductive detection antenna is a kind of terahertz detector widely used in THz-TDS(terahertz time-domain spectroscopy).Improving the detection performance of terahertz GaAs photoconductive detection antenna and antenna array are the key to the development and application of terahertz time domain spectroscopy.In this paper,the basic characteristics of THz electromagnetic wave were described,and the detection method of THz wave and the working principle of TDS system were introduced in detail.Firstly,the current research status of GaAs photoconductive antenna is described,and the THz-TDS technology and the working principle of the system are briefly introduced.Secondly,the THz-TDS system was used to study the influence of the chip material characteristics,detection light energy and antenna electrode gap on the performance of a single antenna.In addition,the performance characterization of terahertz GaAs photoconductive detection antenna array was studied.Finally,the noise source of terahertz GaAs photoconductive detection antenna and the factors influencing the noise were analyzed theoretically and experimentally.The main research work and results of this paper are as follows:(1)In order to study the optimal detection femtosecond laser irradiation mode of THz-TDS system,in this paper,THz wave and femtosecond laser irradiate the front of the antenna electrode in the same plane,THz wave incident from the front of electrode and femtosecond laser irradiation from the back of electrode,and THz wave incident from the back of electrode and femtosecond laser irradiation from the front of electrode,these three methods were selected for comparative study through experiments.The test results show that THz wave and detecting femtosecond laser irradiate the front of the antenna electrode in the same plane was the best way to detect THz wave for the experimental system used in this paper.(2)The influences of terahertz GaAs photoconductive detection antenna chip material,optical energy of femtosecond laser and electrode gap of detection antenna on terahertz wave detection performance of a single antenna was studied.The results show that With the increase of the detection femtosecond laser energy,the amplitude of the test signal output from the detection antenna increases gradually.The output signal amplitude of the detection antenna was the largest and tends to be saturated,when the probe femtosecond laser energy was 120mW.The noise of the detection antenna made of semi-insulating GaAs material was smaller,and the output signal amplitude of the detection antenna made of low-temperature GaAs material was higher,under the condition of the same electrode gap and the same detection femtosecond laser energy.With the decrease of electrode gap,the amplitude of the detected THz wave become higher,under the condition of the same detected light energy and the same antenna material.(3)The difference between 2×1 and 1×2 THz GaAs photoconductive detection antenna arrays for THz wave detection was studied.The results show that the detection result of 2 × 1 detection antenna array was better than that of 1 × 2 detection antenna array,and the reverse current between adjacent the antenna elements lead to the low efficiency of experimental synthesis.Further verification experiments show that the carrier was distributed in the whole substrate,and the method of blocking the light source can not completely block the generation of reverse current.By analyzing and consulting the relevant literature,the array elements were cutted completely,and L-edit software was used to design the layout of the detection antenna array,so that the next experiment can be further carried out.(4)The results show that the noise of THz GaAs photoconductive detection antenna mainly comes from thermal noise and generation compound noise,and the noise signal is a random signal.(5)The noise of detection antenna was studied from four aspects:electrode gap,electrode shape,femtosecond laser energy and THz wave modulation frequency.The results show that the noise increases in a certain range with the decrease of electrode gap;noise decreases with the increase of THz modulation frequency and the experimental result was the best when the modulation frequency of THz wave is 2500Hz considering the noise of the detection antenna and the amplitude of the output test signal of the detection antenna.The experimental results show that the noise of 2 × 1 THz GaAs photoconductive detection antenna arrays was less than that of one of them as a single antenna. |
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