Injection-seeded terahertz-wave parametric generator with timing stabilized excitation for nondestructive testing applications

Abstract

An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) with a footprint the 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 ∼20 GHz, and a frequency tuning range of 1.7–3.0 THz. 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 2.1 THz waves. A clearly recognizable THz-wave image of an enclosed hair with a spatial resolution close to the THz wavelength was obtained.

Non-collinear phase-matching method for stimulated polariton scattering based on cross-pumping

“…Under strong near-infrared pump laser excitation, pump photons involved in the SPS process convert into Stokes photons with specific dispersion frequencies and corresponding THz waves. To achieve effective SPS, continuous stimulated emission and amplification of Stokes light and THz waves are necessary, requiring the pump light, Stokes light, and THz waves to satisfy the phase matching conditions determined by energy conservation and wave vector conservation [4] . However, due to the significant difference in refractive indices between THz waves and the pump light/Stokes light in the crystal, non-collinear phase matching or quasi-phase matching [5] can be employed.…”

Lightwave‐Driven Long‐Wavelength Photomultipliers

“…THz generation technology has matured tremendously over the past decades, enabling intense, coherent single-cycle pulses from table-top systems as well as accelerator-based sources with strong pulse energy and broad spectral coverage, [13][14][15] and high average powers at high repetition rates in collinear setups. [16][17][18] Important examples of quasi-monochromatic THz sources include photomixers, [19,20] quantum cascade lasers, [21,22] optically driven parametric generators, [23] and electronically driven resonant tunneling diodes. [24,25] The full potential of these advanced light sources can only be realized with versatile detectors that record the spatial, temporal, and spectral properties of the THz electromagnetic field.…”