Fiber-Coupled THz TDS System With mW-Level THz Power and up to 137-dB Dynamic Range

Abstract

Terahertz (THz) time-domain spectroscopy (TDS) offers considerable potential for a wide range of industrial applications, including thickness determination and defect identification through imaging. Fiber-coupled THz TDS systems are particularly promising due to their flexible and robust operation in a variety of environments. However, increasing the THz power of these systems remains a critical challenge for applications that require high dynamic range in very short acquisition times. Here, we present a significant improvement of a commercially available THz TDS system by combining a novel ultrafast Er-doped fiber laser and improved iron-doped InGaAs photoconductive THz emitters. The Er-doped fiber laser offers the combination of high average power up to 70 mW and ultrashort pulse duration down to 45 fs with a fiber delivery of 6.3 m to the THz antennas. The THz emitters are optimized in terms of the photoconductive material and gap size for excitation at optical power >50 mW and provide up to (958 ± 67) µW of emitted THz power. These improvements enable a record peak dynamic range of 117 dB for 60-s acquisition time and the highest peak dynamic range ever measured in a THz TDS setup of 137 dB.