Continuous terahertz radiation based on an L-band 500  MHz step-stable two laser beat-frequency source

This paper presents continuous terahertz (THz) radiation based on an L-Band 500 MHz step-stable two laser beat-frequency source (TL-BFS), with a frequency tuning range covering 0.1-2.7 THz. An all-polarization-maintaining (PM) fiber link was designed, including a PM isolator, a PM coupler, and a PM erbium-doped optical fiber amplifier (EDFA), to maintain a consistent polarization state between the two beams of light. An InGaAs high-performance photoconductive antenna (PCA) is excited by TL-BFS, generating continuous 0.1-2.7 THz radiation within the wavelength range of 1568.8-1589.6 nm. The THz power and frequency were tested respectively using a Golay detector and a THz scanning Fabry-Perot interferometer (TSFPI). The results show that the power instability of THz waves within 25 min is within 4%, and the frequency of 0.1, 0.5, and 1 THz are highly consistent with the interval frequencies of the TL-BFS. High-precision tuning of 500 MHz was achieved within the range of 0.95-1 THz, corresponding to a wavelength interval of 0.004 nm. At the same time, it was also proven in the THz absorption spectroscopy analysis of tyrosine samples, with a distinct absorption peak successfully detected at 0.968 THz. These results demonstrate the excellent tunning accuracy and stability of the system, highlighting its suitability for high-resolution spectroscopy.