# Improvement of an InfraRed Pyroelectric Detector Performances in THz Range Using the Terajet Effect  
[PERSON]  
1 School of Nondestructive Testing, Tomsk Polytechnic University, Lenin Avenue, 30, 634050 Tomsk, Russia; [EMAIL_ADDRESS]  
[PERSON]  
2 NanotechnologyGroup, Facultad de Ciencias, Salamanca University, Plaza de la Merced, Edificio Trilingue, 37008 Salamanca, Spain; [EMAIL_ADDRESS]  
[PERSON]  
2 NanotechnologyGroup, Facultad de Ciencias, Salamanca University, Plaza de la Merced, Edificio Trilingue, 37008 Salamanca, Spain; [EMAIL_ADDRESS]  
[PERSON]  
1 School of Nondestructive Testing, Tomsk Polytechnic University, Lenin Avenue, 30, 634050 Tomsk, Russia; [EMAIL_ADDRESS]  
Footnote 1: email: {Igor.V.Minin, 1,2,3,4,5,6,7,8  
special operation in the THz range. In our work, we consider the use of an IR detector for operation in a non-standard THz range not intended by the detector manufacturer and show for the first time that without changing its internal design, it is possible to increase its sensitivity not in the IR but in the THz range. A THz detector based on an IR-PD (LHI778, PerkinElmer), initially designed for a wavelength range of 7-14 \(\upmu\)m and used in THz imaging applications, was studied in [35]. A special amplification circuit to amplify and capture the signal from the sensor was designed. A responsivity of about 1.2 kV/W at 1.89 THz was achieved. However, direct application of conventional IR-PD to the THz band faces a problem of decreasing the detector's sensitivity. Commercial IR-PD (MG-33) is a good substitute for special THz detector. Though it is designed for IR, it retains sensitivity at THz frequencies. Single-element IR-PD has the operation wavelength range between 3 and 20 \(\upmu\)m [36] and is based on a free organic films of the PVDF type [23]. An active area of 1 \(\times\) 1 mm, ensure an NEP sensitivity threshold in the IR range lower than 5 \(\times\) 10\({}^{-10}\) W\(\cdot\)Hz\({}^{0.5}\) and a sensitivity greater than 10\({}^{5}\) V/W [37]. To enhance the PD sensitivity in the THz band [38; 39], a combination of a MG-33 detector and a metasurface-enabled absorber was considered in [40]. It was demonstrated that the efficient frequency- and polarization-selective detection in the range of 100-180 GHz with a degradation of NEP by a factor 2. However, this required a change in both the design of the detector itself (including the diameter of the optical window being specially increased from 3.5 mm to 5 mm in [40]) and the development of a new absorber. In addition, due to the nature of the metasurface, the detector has a pronounced resonance character. The aim of this work is to demonstrate the possibility of the effective use of commercially IR-PD in the THz range without changing their internal design. One of the new approaches to increase the sensitivity of THz detector is based on the so-called terajet effect [41; 42; 43; 44]. This effect is based on a reduction of the focused beam size caustic up to the sub-diffraction value at a distance close to the shadow surface of the wavelength-scaled particle-lens made from a conventional dielectric material [45]. The physics of the terajet effect is a complex interference and scattering phenomenon. The constructive interference between the incident field and diffracted and scattered fields by the wavelength-scaled dielectric particle leads to such a localization of electromagnetic wave in the form of terajet with a beam waist up to sub-diffraction limit. Like photonic jets in optics, it localizes intense electromagnetic beams formed near the shadow surface of a dielectric particle with a size greater or even equal to the illumination wavelength and propagating into the environment. It has recently been demonstrated that placing a dielectric cube in front of a sensitive area of strained silicon field effect transistor [32; 46] and point contact detector [31] allows the sensitivity of THz detectors to be increased due to the localization of the incident radiation with the slight decreasing of NEP value.