Time behavior of field screening effects in small-size GaAs photoconductive terahertz antenna

doi:10.1007/s12200-015-0488-9

Front. Optoelectron.

2015, Vol. 8

Issue (1) : 98-103 https://doi.org/10.1007/s12200-015-0488-9

RESEARCH ARTICLE

Time behavior of field screening effects in small-size GaAs photoconductive terahertz antenna

Tianyi WANG,Zhengang YANG(

),Si ZOU,Kejia WANG,Shenglie WANG,Jinsong LIU

Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China

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Abstract

The field screening effects in small-size GaAs photoconductive (PC) antenna are investigated via the well-known pump and probe terahertz (THz) generation technique. The peak amplitude of the THz pulses excited by the probe laser pulse as a function of the pump-probe time delay was measured. An equivalent-circuit model was used to simulate the experimental data. Based on the good agreement between the results of simulation and experiment, the time behavior of the radiation and space-charge fields was simulated. The results show that the space-charge screening dominantly determines the device response in the whole time, while the radiation filed screening plays a key role in initial time which strongly affects the peak THz field. The parameter analysis was performed, which may be valuable on the optimum design for the antenna as a THz emitter.

Keywords GaAs photoconductive (PC) antenna field screening effects terahertz (THz) emitter

Corresponding Author(s): Zhengang YANG

Issue Date: 13 February 2015

Cite this article:

Tianyi WANG,Zhengang YANG,Si ZOU, et al. Time behavior of field screening effects in small-size GaAs photoconductive terahertz antenna[J]. Front. Optoelectron., 2015, 8(1): 98-103.

URL:

https://academic.hep.com.cn/foe/EN/10.1007/s12200-015-0488-9
https://academic.hep.com.cn/foe/EN/Y2015/V8/I1/98

Fig.1 (a) Experimental setup; (b) measured peak amplitude of the THz pulses excited by the probe laser pulse as a function of the pump-probe time delay under different pump powers. The power of the probe beam is set to 2 mW. The applied bias voltage is 55 V (field across the gap: 11 kV/cm). The displayed data normalized to 100% for t = 0 . fs: femtosecond; BS: beam splitter; HWP: half-wave plate; PBS: polarization beam splitter

Fig.2 (a) Schematically representing the equivalent circuit of GaAs antenna, four circuit elements in series with each other, V b is the bias voltage of antenna, Z a is the antenna impedance accounted for the THz radiation screening, Z p ( t ) models the time-varying impedance of the photo gap, and V sc is the polarization induced by the separation of charge carries; (b) calculated and measured peak THz field as a function of the pump-probe time delay for fixed pump power at 10 mW

Fig.3 Measured (solid curves) and calculated peak THz field around t = 0 under different pump powers

Fig.4 Calculated time dependencies of (a) radiation field and (b) space-charge field under different pump laser powers. The inset in (a) shows the calculated temporal evolution of the local electric field in the antenna, plotted together with the radiation and space-charge fields for a fixed pump power at 20 mW

Fig.5 Calculated normalized peak THz field changes with (a) the strip-line spacing d , and (b) the trapping time τ c under different laser excitation powers

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