Sources for high frequencies in the THz range are of interest in both precision measurements in spectroscopy as well as high carrier frequencies and bandwidth in next-generation communication. Optically generated THz frequencies allow for broad tunability based on telecom technologies. Optical frequency division via an optical frequency comb has the potential to generate ultralow phase-noise THz sources. We present a system that is capable of generating tunable THz frequencies of up to 10 THz at 0.5 THz/s scan rates, phase-locked to a common comb spectrum providing absolute frequency calibration. We show results of combining the photonic source with an electronic receiving system in the waveguide band WR 2.2 (330-500 GHz).

We demonstrate the capabilities of a novel frequency-domain terahertz spectrometer based on a comb-locked frequency synthesizer, which provides absolute frequency calibration. The inherent stability and repeatability of the scans allow for the combination of fast data acquisition with an average time-limited signal-to-noise ratio. We demonstrate kilohertz level frequency resolution in terahertz precision spectroscopy of ultra-high quality whispering-gallery-mode resonators. Spectra covering multiple free spectral ranges (>36 GHz) with sub-20 kHz resolution are acquired in 5 s. We analyze the coupling behavior and temperature tuning of single resonances and, for the first time, observe minute red and blue shifts of different mode families. The experimental results are supported with finite element simulations.

We present precision measurements of terahertz whispering gallery mode resonances using a novel comb-locked frequency domain spectrometer. Absolute long-term frequency stability and resolution allows to accurately resolve temperature shifts across multiple modes.

We report on ultra-high precision terahertz spectroscopy of a spherical microresonator using a novel comb-locked frequency domain spectrometer. With kilohertz frequency resolution and stability, the spectrometer enables the first observation of a minute red and blue shift of whispering gallery modes due to the coupling waveguide.

The high frequency region beyond 100 GHz considered for 6G poses challenges for future communication and measurement equipment. In this work we present a novel tunable THz system based on ultra-stable photonic sources and optical frequency comb technology covering the frequency range from a few GHz up to 500 GHz.

We present a novel frequency domain spectrometer, which is based on two external cavity diode lasers (ECDL) locked to a fibre-based erbium frequency comb, the repetition rate $\mathrm{f}_{rep}}$ of which is in turn referenced to a radio frequency (RF-) oscillator. By using an external endless frequency-shifter [1], one of the lasers is detuned by frequencies up to 10 THz, limited only by the spectral width of the comb. Within the locking bandwidth, the stability and phase noise of the RF reference is transferred to the difference frequency between both ECDLs [2].

We exploit a widely tunable comb-locked frequency-swept synthesizer to test a new optical approach to primary gas thermometry based on a global fitting of multiple molecular absorption lines of the same band at different pressures.

Optical Frequency Domain Reflectometry features high resolution and sensitivity. The resolution is limited by the laser scan range, linearity and noise. We introduce a laser source capable of precise > 10 THz wide and > 1 THz/s fast scans remaining phase locked to the optical comb. A resolution of 0.5E-6 at 20 km fiber is demonstrated.

We introduce a frequency-domain terahertz (THz) spectrometer based on a comb locked frequency synthesizer which combines > 3 THz scanning range at rates > 0.3 THz/s. We demonstrate kHz frequency resolution in THz precision spectroscopy of ultrahigh-Q whispering-gallery mode resonators.

Abstract In this paper we propose multispectrum rotational states distribution thermometry as an optical method for primary thermometry. It relies on a global fitting of multiple absorption lines of the same band at different pressures. The approach allows leveraging both the temperature-dependent Doppler width and the temperature-dependent distribution of line intensities across the ro-vibrational band. We provide a proof-of-principle demonstration of the approach on the 3ν 1 + ν 3 band of CO2, for which several accurate line-strength models of both theoretical and experimental origin are available for the global fitting. Our experimental conditions do not allow to test the methodology beyond a combined uncertainty of 530 ppm, but the comparative analysis between different line-strength models shows promise to reduce the error budget to few tens of ppm. As compared to Doppler-broadening thermometry, the approach is advantageous to mitigate systematic errors induced by a wrong modelling of absorption line-shapes and to reduce, for a given experimental dataset, the statistical uncertainty by a factor of 2. When applied in a reverse way, i.e. using a gas of known temperature, the approach becomes a stringent testbed for the accuracy of the adopted line-strength model.

Frequency combs have made optical metrology accessible to hundreds of laboratories worldwide and they have set new benchmarks in multi-species trace gas sensing for environmental, industrial and medical applications. However, current comb spectrometers privilege either frequency precision and sensitivity through interposition of a cw probe laser with limited tuning range, or spectral coverage and measurement time using the comb itself as an ultra-broadband probe. We overcome this restriction by introducing a comb-locked frequency-swept optical synthesizer that allows a continuous-wave laser to be swept in seconds over spectral ranges of several terahertz while remaining phase locked to an underlying frequency comb. This offers a unique degree of versatility, as the synthesizer can be either repeatedly scanned over a single absorption line to achieve ultimate precision and sensitivity, or swept in seconds over an entire rovibrational band to capture multiple species. The spectrometer enables us to determine line center frequencies with an absolute uncertainty of 30 kHz and at the same time to collect absorption spectra over more than 3 THz with state-of-the-art sensitivity of a few 10 −10 cm −1 . Beyond precision broadband spectroscopy, the proposed synthesizer is an extremely promising tool to force a breakthrough in terahertz metrology and coherent laser ranging.

We introduce a frequency-domain spectrometers (FDS) based on a comb locked optical frequency synthesizer which combines scanning ranges of more than 3 THz at scan rates >300 GHz/s with frequency resolution in the order of 10 kHz. The comb provides a narrow linewidth spectrum which is absolutely referenced to a frequency standard (e.g. GPS). The inherent stability allows for favorable signal-to-noise scaling with measurement time.