Titanium-Based Microbolometers: Control of Spatial Profile of Terahertz Emission in Weak Power Sources

Abstract

Terahertz (THz) imaging and spectroscopy set-ups require fine optical alignment or precise control of spatial mode profile. We demonstrate universal, convenient and easy-to-use imaging—resonant and broadband antenna coupled ultrasensitive titanium-based—dedicated to accurately adjust and control spatial mode profiles without additional focusing optical components of weak power THz sources. Versatile operation of the devices is shown using different kinds of THz—electronic multiplier sources, optical THz mixer-based frequency domain and femtosecond optoelectronic THz time-domain spectrometers as well as optically pumped molecular THz laser. Features of the microbolometers within 0.15–0.6 THz range are exposed and discussed, their ability to detect spatial mode profiles beyond the antennas resonances, up to 2.52 THz, are explored. Polarization-sensitive mode control possibilities are examined in details. The suitability of the resonant antenna-coupled microbolometers to resolve low-absorbing objects at 0.3 THz is revealed via direct, dark field and phase contrast imaging techniques as well.

Antenna-Coupled Titanium Microbolometers: Application for Precise Control of Radiation Patterns in Terahertz Time-Domain Systems

“…As is known, about 21 % of the incident power passes through silicon lens [ 25 ], on the other hand, without the lens radiation is dispersed over the large angles, therefore, only a small fraction of the total emitted power can be registered. Despite this fact, room temperature Ti- bolometers sensitivity of 200 kV/W including amplification circuit and NEP of 20 pW/ [ 23 ] is sufficient to register weak signal from photoconductive THz emitter even though the output beam is not effectively concentrated by the hyperhemispherical lens around the optical axis.…”

“…The titanium bridge of 12 m and 2 m in length and width respectively was electrodeposited on the silicon nitride (SiN) membrane of thickness of 2 m. The aluminum antenna and interconnection paths of area of approximately 500 m × 500 m, were formed around the active part of Ti- bolometer (see in top of the panel (a) in Figure 1 ). To reduce the heat capacitance and to increase the speed of operation, the Ti- bolometer was suspended in the air by etching out the underlying SiN membrane and was coupled either to resonant double-dipole or to wideband log-periodic type THz antenna (see panel (a) in Figure 1 ) [ 22 , 23 , 24 ]. Sensitivity of the device was enhanced resonantly by adjustment of a dipole antenna and resonant-cavity design: the back side reflection mirror was placed at the quarter wavelength distance ( Figure 1 a).…”

“…Very recently, we have demonstrated that optimised room temperature Ti- bolometers can serve as a convenient and easy-to-use imaging tool to accurately adjust low power THz sources without additional focusing components [ 23 ]. Radiation patterns and spatial modes profiles generated by electronic sources, frequency domain spectrometers, optically pumped molecular THz laser were measured and analyzed [ 23 ].…”

“…Very recently, we have demonstrated that optimised room temperature Ti- bolometers can serve as a convenient and easy-to-use imaging tool to accurately adjust low power THz sources without additional focusing components [ 23 ]. Radiation patterns and spatial modes profiles generated by electronic sources, frequency domain spectrometers, optically pumped molecular THz laser were measured and analyzed [ 23 ]. In addition, it was shown that these devices exhibiting room temperature sensitivity values of 200 kV/W, noise-equivalent power (NEP) of 20 pW/ , and the response time in the 5 s range are sensitive and fast enough to monitor precisely coherent THz emitters in optoelectronic time-domain systems.…”

“…The angles θ and φ in photo of the wideband detector are defined as sample rotation angle for polarization measurements and the polar angle of antenna fingers, respectively. The design is adapted from Refs [22,23]…”