## 1 Introduction  
Terahertz (THz) radiation and millimeter waves (MMW) have attained widespread application in package inspection, quality control, nondestructive testing [1], medicine [2], communications [3], and spectroscopic characterization [4]. The preference to use THz and MMW is that there is no ionization hazard [5], penetration through dielectric materials is reasonably good, and the atmospheric scattering of MMW and THz radiation is relatively low [6]. This has led to the development of low-cost, fast, highly sensitive, compact, and room-temperature detectors. The most popular THz detectors are Schottky diodes, Golary cells, pyroelectric detectors, bolometers, and microbolometers [7, 8]. Golary cells and bolometer detectors have a long response time, even though they have large spectral and less noise-equivalent power [9]. Schottky diodes are fast and have lower noise-equivalent power (NEP) [10]. However, they are not intended for high-power THz pulses, are much less sensitive at higher frequencies of the THz band, and require much more local oscillator (LO) power as compared with currently convenient tuneable LO sources [11]. Furthermore, these three detectors are expensive. This paper demonstrates the use and responsivity of a glow-discharge detector (GDD) in the high-power millimeter-wave and terahertz frequency radiation region. Experiment results detected a single pulse of 0.1 THz and 5 KW using GDD. The GDD lamp has productive potential for THz detection due to its fast response time, electron dynamic broad range, efficiency at room temperature, and low price [12]. The GDD's detection mechanism is based on a slight change of current between the two electrodes of the lamp, defined by [13].  
\[\Delta I=\frac{Gq^{2}vn}{v_{i}m}(\frac{\tau}{\tau_{i}})\eta_{0}P_{D}(\frac{f}{ f^{2}+\omega^{2}})(1-e^{-\frac{t}{\tau}}) \tag{1}\]where \(G=\frac{exp(2f_{i}t_{d})}{2f_{i}t_{d}}\) is the internal signal amplification, \(q\) is electron charge, \(v\) is average electron velocity, \(n\) is electron density, \(v_{i}\) is gas ionization potential, \(m\) is electron mass, \(\tau\) is time response to create current changes, \(\tau_{i}\) is time between ionization collisions of electrons with gas atoms, \(\eta_{0}\) is free space impedance, \(P_{D}\) is incident THz power density, \(f\) is electron-neutral atom elastic collision frequency, \(\omega\) is electromagnetic radiation frequency, \(t_{d}\) is average electron drift time to the anode, and \(f_{i}\) is ionization collision frequency. Considering that the response time of the plasma inside the GDD is in the order of picoseconds, the detection mechanism is mainly dependent on visual detector response time rather than GDD circuit. The responsivity measures the electrical output per input THz power and is defined by [14]:  
\[Rep=\frac{A(V)}{P(W)}, \tag{2}\]  
where \(A\) is the THz signal amplitude, and \(P\) is the THz power. The responsivity of the GDD increases with the increase in bias current. NEP is a measure of the sensitivity of an optical detector system; a small NEP means a high signal-to-noise ratio (SNR). The NEP for the GDD is as low as \(10^{-8\text{w}}/\sqrt{\text{H}}\)[15], and is defined by [14]:  
\[NEP=\frac{\sqrt{N}}{R} \tag{3}\]  
where \(N\) is noise power spectral density, and \(R\) is responsivity.