title: Real-time absolute frequency measurement of continuous-wave terahertz radiation based on dual terahertz combs of photocarriers with different frequency spacings.
abstract: Real-time measurement of the absolute frequency of continuous-wave terahertz (CW-THz) radiation is required for characterization and frequency calibration of practical CW-THz sources. We proposed a method for real-time monitoring of the absolute frequency of CW-THz radiation involving temporally parallel, i.e., simultaneous, measurement of two pairs of beat frequencies and laser repetition frequencies based on dual THz combs of photocarriers (PC-THz combs) with different frequency spacings. To demonstrate the method, THz-comb-referenced spectrum analyzers were constructed with a dual configuration based on dual femtosecond lasers. Regardless of the presence or absence of frequency control in the PC-THz combs, a frequency precision of 10(-11) was achieved at a measurement rate of 100 Hz. Furthermore, large fluctuation of the CW-THz frequencies, crossing several modes of the PC-THz combs, was correctly monitored in real time. The proposed method will be a powerful tool for the research and development of practical CW-THz sources, and other applications.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yasui
authors.forename: Kenta
authors.initials: K
authors.lastname: Hayashi
authors.forename: Ryuji
authors.initials: R
authors.lastname: Ichikawa
authors.forename: Harsono
authors.initials: H
authors.lastname: Cahyadi
authors.forename: Yi-Da
authors.initials: YD
authors.lastname: Hsieh
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Mizutani
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Iwata
authors.forename: Hajime
authors.initials: H
authors.lastname: Inaba
authors.forename: Kaoru
authors.initials: K
authors.lastname: Minoshima