Non-linear optical phenomena, such as parametric detection and amplification, manifest themselves in materials such as lithium niobate (LN) under the influence of a powerful optical pump beam. These processes have facilitated the practical realization of femtosecond (fs) pulse sources in the visible (VIS) and near infrared (NIR) spectra. They are also central to quantum detection, promising extremely sensitive detection of low-energy photons, particularly in the terahertz (THz) frequency range. To explore this innovative detection approach, we used an intense and powerful THz source taking advantage of optical rectification in lithium niobate (LN) crystals with an inclined-pulse front-end pumping configuration. By taking advantage of the high brightness of this source, we can acquire NIR signals in real time by upconversion and broadband using a standard CCD camera. In this presentation, we will look at the technical intricacies of the source and detection methodologies, as well as our goal of achieving single THz photon detection capability in the near future, all in the context of using ytterbium lasers.
The injection-seeded terahertz wave parametric generator (is-TPG) technology presented here is expected to enable measurements through thick shielding due to its wide dynamic range of over 120 dB in combination with detection methods that up-convert the terahertz wave to a near-infrared beam. Furthermore, recently machine learning has been applied to the fingerprint spectral analysis of reagents, which has enhanced identification accuracy. Real-time measurement has also been achieved by multi-wavelength generation and detection with image recognition of detection Stokes beams. We will present these improvements in is-TPG technology for non-destructive testing.
We achieved to extract terahertz (THz)-waves generated by cascade process (i.e., higher-order THz-waves) in an injection-seeded THz parametric generator (is-TPG), and realized higher-power output.
Because of the angular phase-matching condition, the higher-order THz-waves are generated deep in a crystal and extraction of them from the crystal was difficult due to the large absorption loss. In our setup, we used total reflection of the pump beam on the crystal surface to reduce absorption loss, and optimized the THz focusing lens and the position of Si-prism coupler. As a result, we succeeded in extracting higher-order THz waves and improved the output power.
In this work, we demonstrated real-time spectroscopy using a discreetly and fast wavelength tunable injection-seeded THz wave parametric generator (is-TPG). In our is-TPG, pump and seed beams shine the MgO:LiNbO3 crystal to generate the THz wave. At that time, the wavelength was tuned by changing the wavelength of the seed beam. Therefore, in order to achieve real-time measurement, we introduced fast wavelength switchable ECDL that we developed recently using a digital micromirror device (DMD) as a wavelength selector. As a result of this improvement, we achieved to identify the reagents hidden in cardboard box in real-time.
We developed a fast wavelength switchable external cavity diode laser (ECDL) using a DMD as a seed laser for an injection-seeded terahertz (THz) wave parametric generator (is-TPG). Generally, the wavelength of an ECDL is selected by the angle of the mirror or grating; however, in this case, a DMD is used as the wavelength selector. A power output of 300 mW and a tunable range of 26 nm were obtained. Furthermore, high-rate modulation at 6.55kHz was realized. This laser makes it possible to switch the THz wavelengths of is-TPG rapidly to match the absorption spectrum of a reagent.
We have been developing an injection-seeded terahertz (THz) parametric generator (is-TPG), detector, and amplifier. This THz generation and detection scheme have allowed us to develop a wide-dynamic range THz wave spectrometer which can be used for nondestructive inspection of illicit drugs under thick envelopes. In this work, we have improved the sensitivity of the THz parametric detector drastically using a multistage configuration, which consists of the up-conversion (pre-amplifier) and the main amplifier parts. Using this new configuration, we were able to suppress the broadband noise, and only an upconverted detection beam can be measured using the NIR detector. As a result of this improvement, the minimum sensitivity reached 130 zJ (zJ=10-21J), which equals to about 90 photons at 1.05 THz. Moreover, the principle of this multistage detection can be used for high gain THz amplification which has more than 6 billion-fold amplification factor.
An injection-seeded THz-wave parametric generator (is-TPG) uses a near-infrared (NIR) pump beam and seed beam input to the MgO:LiNbO3 crystal. In contrast, the THz parametric detector uses a THz wave as the seed beam instead of a NIR beam. In the detection configuration, when the pump beam and THz wave are input into the crystal, the THz wave is upconverted to the NIR idler beam by parametric processes in the crystal that are measured using a NIR detector. This THz generation and detection scheme has allowed us to develop a high dynamic range THz wave spectroscopic system that can be used for spectroscopic imaging of saccharides hidden in thick envelopes. Recently, we have improved the sensitivity of the THz parametric detector drastically using a multistage configuration in order to suppress the spontaneous THz emission and enhance the gain. In our new system, the THz parametric detectors were divided into two parts, i.e., for the up-conversion (pre-amplifier) and for the main amplifier. THz waves were upconverted to a NIR idler beam in the first part of the set-up. An iris positioned behind the upconverted region passed the idler beam and blocked the broadband spontaneous THz emission. Thus, in the amplification region, only the desired idler beam was clearly amplified. The amplified detection idler beam was then measured by a NIR beam profiler.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.