[Show abstract][Hide abstract] ABSTRACT: The spectral resolution and accuracy of asynchronous-optical-sampling terahertz time-domain spectroscopy (ASOPS-THz-TDS) were evaluated by examining low-pressure gas-phase samples. Use of dual 56-MHz, erbium (Er)-doped, mode-locked femtosecond fiber lasers enhanced the spectral resolution to as low as 50.5 MHz and the spectral accuracy to as low as 6.2 × 10(-6). The results indicate that ASOPS-THz-TDS has the potential to achieve high spectral resolution, high spectral accuracy, and wide spectral coverage at the same time. ASOPS-THz-TDS will open a new door to gas-phase spectroscopy of multiple chemical species in the field of atmospheric gas analysis.
[Show abstract][Hide abstract] ABSTRACT: We constructed a widely and continuously tunable terahertz frequency synthesizer traceable to a hydrogen maser linked to coordinated universal time. Photomixing of two optical frequency synthesizers, linked to the hydrogen maser via dual optical frequency combs, gave this THz synthesizer frequency uncertainty of 10⁻¹². To demonstrate the potential of wide and continuous tunability in the THz synthesizer, we tuned its output frequency up to 50 GHz discretely and 1.26 GHz continuously in the F-band while maintaining the unprecedented frequency uncertainty by using a uni-traveling-carrier photodiode as a photomixer. This THz synthesizer will be a powerful tool for broadband, high-precision THz spectroscopy and THz frequency metrology.
[Show abstract][Hide abstract] ABSTRACT: Spectral resolution and accuracy in asynchronous-optical-sampling THz-TDS was evaluated with the spectroscopy of low-pressure water vapor. The achieved resolution and accuracy were 72.9 MHz and 10−5 at the absorption line of 0.56 THz and 0.75 THz, respectively.
[Show abstract][Hide abstract] ABSTRACT: We developed a fiber-based, asynchronous-optical-sampling THz-TDS system by combination of mode-locked Er-fiber lasers and photoconductive antennas. Detail structure of the THz comb was clearly observed with a spectral resolution of 5.6 MHz.
[Show abstract][Hide abstract] ABSTRACT: We constructed a fiber-based, hybrid terahertz (THz) spectrometer having two working modes, asynchronous-optical-sampling THz time-domain spectroscopy (AOS-THz-TDS) and multiple-frequency-heterodyning THz comb spectroscopy (MFH-THz-CS), by use of dual fiber-laser-based frequency combs. A spectral range of 2THz and dynamic range of 100 was achieved at the single sweep measurement of 200ms in the AOS-THz-TDS mode, whereas the detailed structure of the THz frequency comb was clearly observed in the MFH-THz-CS mode. The spectrometer features compactness, robustness, flexibility, and cost effectiveness, in addition to high spectral resolution in rapid data acquisition, and has the potential to become a powerful tool for practical applications.
[Show abstract][Hide abstract] ABSTRACT: A continuously tunable, phase-locked, THz synthesizer has been demonstrated. This THz synthesizer is based on photomixing of two optical frequency synthesizers composed of CW laser and optical comb, and its output frequency has the same uncertainty as that of a microwave frequency standard used.
[Show abstract][Hide abstract] ABSTRACT: We propose a fiber-based, terahertz-comb-referenced spectrum analyzer which has the advantages of being a portable, alignment-free, robust, and flexible apparatus suitable for practical use. To this end, we constructed a 1550-nm mode-locked Er-doped fiber laser whose mode-locked frequency was stabilized precisely by referring to a rubidium frequency standard, and used it to generate a highly stable terahertz (THz) frequency comb in a photoconductive antenna or an electro-optic crystal. By standardizing the THz comb, we determined the frequency accuracy of an active-frequency-multiplier-chain (AFMC) source to be 2.4 x 10(-11). Furthermore, the potential of the THz spectrum analyzer was effectively demonstrated by real-time monitoring of the spectral behavior of the AFMC source and a photomixing source of two free-running CW lasers at adjacent wavelengths. (C) 2009 Optical Society of America
[Show abstract][Hide abstract] ABSTRACT: We proposed a fiber-based, asynchronous optical sampling THz time-domain spectroscopy system by combination of mode-locked Er-doped fiber lasers and photoconductive antennas. The proposed system will become a fast, compact, alignment-free, robust, and flexible apparatus without any mechanical moving parts.