Development of terahertz, mid- and far-infrared frequency standard toward ultra-broadband optical frequency measurement system

We are developing an unprecedented ultra-broadband optical frequency measurement system, which covers visible, infrared (IR) and terahertz (THz) frequency regions. An optical frequency comb technique is employed for absolute frequency measurement of various lasers and oscillators. The visible femtosecond-pulse Ti:sapphire laser frequency combs developed were applied for the absolute frequency measurement for optical clocks and confirmed to have the measurement precision in 10^-19 level by the optical heterodyne comparison. The near-IR erbium-doped-fiber laser frequency combs were also developed for the frequency calibration of optical-fiber communication lasers with 10^-16 level. Moreover, we have recently achieved the frequency measurement around 100 GHz by means of THz frequency comb with a photoconductive antenna with uncertainty at the 10^-17 level. By coherently linking these frequency combs developed and mid- and far-IR combs currently investigating, we can achieve the gap-free absolute frequency measurement with high precision. Such system will play an important role not only for metrology but scientific and industrial applications.