Abstract
An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) with a footprintthe size of an A3 paper is presented. We improved the measurement performance of the is-TPG source for nondestructive inspection applications. A high pulse repetition rate up to 70 kHz and a low pulse timing jitter of a few tens of picoseconds, which is approximately one ten-thousandth of the conventional is-TPG, were achieved. THz waves exhibited excellent performance with a maximum average output power of 20 µW, a monochromatic spectrum linewidth of ∼20GHz, and a frequency tuning range of 1.7-3.0THz. This was achieved by designing the entire system configuration from the pump laser source to THz-wave generation. A new double-pass all-solid-state optical amplifier was developed with a high gain and low noise using an externally pulse-modulated laser diode (LD) as the master oscillator source. An achromatic optical injection system was developed for the is-TPG with a 40% reduction in the conventional path length. They were housed in a single enclosure in two layers. LDs and optical fiber amplifiers could be rack-mounted, and the outputs were delivered to the housing via optical fibers. The developed THz-wave source performed nondestructive imaging of a human hair sample fixed with Scotch tape on a test pattern in an envelope by irradiating 2.1THz waves. A clearly recognizable THz-wave image of an enclosed hair with a spatial resolution close to the THz wavelength was obtained.
Highlights
In recent years, there has been an increasing number of proposals for nondestructive testing applications that use terahertz (THz) waves
The results clearly show the spatial information from the differences in the transmitted signals at each point, resulting to sufficient visualization as parts of the hair, printed metal, and Scotch tape were used to hold the hair in place
This study demonstrated a compact injection-seeded terahertz (THz)-wave parametric generator (is-TPG) system with a low timing jitter of ∼30 ps and a high pulse repetition rate that has a maximum frequency of 70 kHz
Summary
There has been an increasing number of proposals for nondestructive testing applications that use terahertz (THz) waves. THz-wave optical coherence tomography (OCT) is increasingly being proposed for three-dimensional imaging, and there are reports of obtaining a high performance that exceeds the wavelength resolution.. THz-wave optical coherence tomography (OCT) is increasingly being proposed for three-dimensional imaging, and there are reports of obtaining a high performance that exceeds the wavelength resolution.9 It is difficult for most THz-wave sources to generate waves above 1 THz. In contrast, it is difficult for most THz-wave sources to generate waves above 1 THz This is because the output power of the antennastructured devices generally decreases dramatically at higher frequencies due to the cutoff frequency. Damage to the LN crystals can be avoided under a certain range of conditions This accomplishment provides design guidelines for high pulse repetition rates for the is-TPG. This study reports on the development of a compact and tunable THz-wave parametric source with a low pulse timing jitter while maintaining a pulse repetition rate in the kHz range. The entire design of the is-TPG system, including the pump source, optical amplifier, and optical injection system, was reviewed to develop a THz-wave source that can be widely used in THz-wave measurements
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