Rapid Scan THz Imaging Using MEMS Bolometers

The impact of the response speed of a microelectromechanical system (MEMS) bolometer on the quality of terahertz (THz) imaging with rapid scan has been investigated and compared with a pyroelectric detector (PED). The imaging system was an active imaging composed of the MEMS bolometer, THz quantum cascade laser, and two-dimensional translation stage. The scanning process of the imaging system consisted of continuous scans in the X direction and step scans in the Z direction. The MEMS bolometer had a beam resonator with a resonant peak of 422 kHz, and it was operated in the frequency modulation detection mode. The frequency shifts in the resonant peak due to the irradiation of the THz waves were tracked using the phase-locked loop system built in the lock-in amplifier. In the measurement of the response characteristics using a 100-mu m pinhole, the peak intensity was almost constant against the stage speed in the case of the MEMS bolometer. For the PED, there was a decrease in the peak intensity and delay in the peak positions with increasing stage speed due to the insufficient response speed. When the images were acquired using the MEMS bolometer with a stage speed of 25 mm/s, fine structures of a metal bookmark were clearly observed and no degradation in the resolution was observed with changing stage speed. In the case of the PED, the resolution gradually degraded with increasing stage speed.