High-precision frequency measurements in the THz spectral region using an unstabilized femtosecond laser

Abstract

We perform high-precision frequency measurements in the THz frequency range using an unstabilized femtosecond laser. A simple and flexible algorithm is used to correct the beating signal resulting from the THz source and one comb line of the rectified optical comb for fluctuations of the laser repetition rate. Using this technique, we demonstrate an accuracy of our measurement device as high as (9 ± 3) · 10−14 for the measurement of a 100 GHz source. This is two orders of magnitude better than previous precision measurements in this frequency range employing femtosecond lasers.

Generation of ultra-narrow, stable and tunable millimeter- and terahertz- waves with very low phase noise

“…The spectral characteristics as well as the phase noise of the generated waveforms above a frequency of 110 GHz cannot be measured directly using commercially available equipment, although reports are provided in the research literature [47]. In order to demonstrate the downconversion mixing between two tones that are separated by more than 110 GHz, the wireless transmission link across a distance of 24.5 cm was manually interrupted by insertion of a metal plate.…”

Absolute Intensity Measurements of CW GHz and THz Radiation Using Electro-Optic Sampling

“…The experimental technique is based on the concept of THz frequency combs [2], [3], [12], [13] that are obtained from optical frequency combs [14]. Although we employ this technique for the measurement of CW GHz/THz signals, it can also easily be applied to the measurement of pulsed THz signals.…”

“…This signal is obtained from focusing the laser pulses onto a fast photodiode and mixing the resulting signal with the signal from a signal generator acting as a stable local oscillator [2]. A comparison between the two beating signals enables phase measurements of the GHz/THz source [3].…”

“…Nowadays National Metrology Institutes throughout the world are working on THz metrology such as frequency measurements [2], [3], radiometry [4]- [6], and spectrometer calibration [7]- [9]. Yet, the quantitative measurement of electric fields and intensities in this frequency range being even traceable to the International System of Units (SI) has so far not been paid much attention.…”

“…In previous studies, we have reported on precision frequency measurements as well as on spatially resolved measurements Manuscript of relative amplitude and phase using a THz frequency comb [2], [3]. Spatial resolution was obtained by moving the gigahertz (GHz) or THz sources [10].…”