Longhuang Tang

China Academy of Engineering Physics · Institute of Fluid Physics

Optical up-conversion photonic Doppler velocimetry (PDV) based on stimulated Brillouin Scattering (SBS) with an all-fiber link structure is proposed in this article. Because SBS limits the laser power transmitted by a fiber over long distances, the probe does not have enough outgoing light to reach the measured surface and cannot receive the signal...

Efficient transceivers and antennas at terahertz frequencies are leading the development of 6G terahertz communication systems. The antenna design for high‐resolution terahertz spatial sensing and communication remains challenging, while emergent metallic metasurface antennas can address this issue but often suffer from low efficiency and complex m...

In this paper, we propose an all-fiber co-axial optical frequency-domain interferometer (OFDI) in a pulse-train mode with a sample rate of 9 kHz for measuring the vibrations in an internal structure without any contact. It was subjected to a range of 4.555 mm and had an accuracy level of 0.006 mm, as confirmed by a linear motion experiment. Due to...

A microwave absolute distance measurement method with ten-micron-level accuracy and meter-level range based on frequency domain interferometry is proposed and experimentally demonstrated for the first time. Theoretical analysis indicates that an interference phenomenon occurs instantaneously in the frequency domain when combining two homologous bro...

A terahertz (THz) fiber is of interest due to low loss and easy beam shaping. Graphene plays an important role in modulating the optical signal. In this paper, a graphene-coated D-shaped THz fiber modulator is proposed. The performance of the proposed modulator is investigated by the finite element method. The inference of geometric parameters of t...

Recently, tunable metagratings have attracted substantial attention in manipulating the diffraction of electromagnetic waves with considerable flexibility, but they are usually limited to inherent ohmic loss due to the metal layers. The all-dielectric schemes can address this issue, but its design and optimization remain challenging in the terahert...

Terahertz (THz) photonic crystal (PC) waveguides show promise as an efficient and versatile waveguiding platform for communication, sensing, and imaging. However, low-frequency THz PC waveguides with a low-cost and easy fabrication remain challenging. To address this issue, a THz PC waveguide with a lilac-shaped defect has been designed and fabrica...

Time-resolved temperature measurement of dynamic-compressed material is critical in the high-pressure research fields. For higher temporal resolution requirement of the dynamic experiments, a broadband optical pyrometer was developed, with a rise time of ∼70 ps and a measurable temperature range of 2500 K to higher than 10000 K. Expanding the detec...

Distance measurement technology can greatly aid scientific research and engineering applications. The optical frequency-domain interferometry ranging method (OFDI-RM) has attracted a great deal of attention as it can achieve accuracy down to the micron and nanometer resolution. However, the main drawback of OFDI-RM is its short measuring range, whi...

Femtosecond laser-excited generation of frequency-tunable microwave pulses, based on an unbalanced single-arm interferometer with frequency-to-time mapping, has been proposed and demonstrated with easy-to-obtain commercial devices. The optical wave-to-microwave frequency conversion, which involves continuous tuning in the range from 2.0 GHz to 19.7...

A high-energy, tunable, long-wave mid-infrared optical parametric oscillator (OPO) based on the ${\rm{BaG}}{{\rm{a}}_4}{\rm{S}}{{\rm{e}}_7}$ B a G a 4 S e 7 crystal was demonstrated in this Letter with 1064 nm laser pumping. The mid-infrared OPO was designed as a double-pass single resonant oscillator (DP-SRO) to reduce the threshold and improve th...

Terahertz (THz) imaging is an innovative technology used in many fields such as security, biology and hidden target detection. Region of interest (ROI) segmentation is essential for applications of THz imaging. However, THz images are often severely degraded by motion blur, poor resolution and severe noise. In this paper, a hybrid ROI segmentation...

A tunable dual-color KTP terahertz (THz) wave parametric oscillator (TPO) pumped by a dual-wavelength laser was proposed in this Letter. Theoretical analysis denotes that the emission of a tunable dual-color THz wave can be achieved by the simultaneous stimulated polariton scattering processes from multiple A1-symmetry phonon modes of the KTP cryst...

We have demonstrated a tunable mid-infrared tandem optical parametric oscillator (OPO) based on BaGa4Se7 (BGSe) crystal, which was intracavity-pumped by the tunable signal wave at ~1 μm generated from a ${\rm{KTiOPO_{4}-OPO}}$ (KTP-OPO) in doubly-resonant oscillator (DRO) configuration. Wavelength tuning of the mid-infrared tandem OPO was realize...

The optical properties of the α/β-BaTeMo2O9 (α/β-BTM) crystal in the terahertz range were characterized by the terahertz time domain spectroscopy (TDS) system. Frequency-dependent refractive indices and absorption coefficients of two crystals were measured from 0.2 to 2 THz, and discussions and comparisons were made on birefringence, absorption and...

Enhanced terahertz wave generation via Stokes wave recycling in a non-synchronously picosecond pulse pump configuration has been demonstrated. It is theoretically analyzed that under the condition of high pump peak power density, the oscillation of the strong 1st order Stokes wave could benefit the higher order Stokes wave emission and terahertz wa...

An injection pulse-seeded terahertz-wave parametric generator (ips-TPG) has been demonstrated with gain enhancement in wide tuning range. Theoretical analysis denotes that the compensation of initial Stokes energy is favorable to the THz gain enhancement in wide frequency range, which is attributed to the improvement on interaction of stimulated po...

A high-energy and tunable mid-infrared source based on BaGa4Se7 crystal was demonstrated by single-pass difference-frequency generation (DFG). Orthogonally polarized wave at 1064 nm (λ1) and tunable idler wave (λ2) generated by KTP-OPO, which could be tuned in the wavelength range of 1360–1600 nm, were used as the DFG dual-wavelength pump. The pump...

The energy scaling of THz wave based on surface-emitted ring-cavity terahertz parametric oscillator with pump recycling technique is demonstrated. The tunable range from 1.24 THz to 3.77 THz was achieved. The terahertz output energy and conversion efficiency increased more than seven times throughout the whole tuning range. The maximum enhancement...

A wide terahertz tuning range from 0.96 THz to 7.01 THz has been demonstrated based on ring-cavity THz wave parametric oscillator with a KTiOPO4 (KTP) crystal. The tuning range was observed intermittently from 0.96 THz to 1.87 THz, from 3.04 THz to 3.33 THz, from 4.17 THz to 4.48 THz, from 4.78 THz to 4.97 THz, from 5.125 THz to 5.168 THz, from 5.4...

Terahertz (THz) computed tomography (CT) is a promising technique to obtain the internal information of objects due to its properties of non-ionizing and high penetration of non-polar objects. However, THz CT is hindered by the strong refractive effect and Fresnel reflection loss when it is applied to high-refractive-index samples. In this paper, t...

Terahertz attenuated total reflection imaging has been used to develop preliminary applications without any in-depth analysis of the nature of present systems. Based on our proposed vertically scanning imaging system, an analysis of optimum prism design and polarization selection for error reduction is presented theoretically and experimentally, sh...

Edible oil is a significant source of human nutrition and energy, providing essential fatty acids for human body. Thus, the investigation on the optical properties of edible oils in THz region for component analysis and quality evaluation is considered to be of great importance. As a newly developed-technique, Terahertz time-domain attenuated total...

We investigate the optical properties of cadmium selenide (CdSe) crystals in a wide terahertz (THz) range from 0.2 to 6 THz by THz time-domain spectroscopy (THz-TDS) and Fourier transform infrared spec-troscopy (FTIR). The refractive index, absorption coefficient and transmittance are measured and analyzed. The properties are characterized by sever...

The imaging diagnosis and prognostication of different degrees of traumatic brain injury (TBI) is very important for early care and clinical treatment. Especially, the exact recognition of mild TBI is the bottleneck for current label-free imaging technologies in neurosurgery. Here, we report an automatic evaluation method for TBI recognition with t...

We demonstrated that different degrees of experimental traumatic brain injury (TBI) can be differentiated clearly in fresh slices of rat brain tissues using transmission-type terahertz (THz) imaging system. The high absorption region in THz images corresponded well with the injured area in visible images and magnetic resonance imaging results. The...

We have demonstrated a high-energy and broadly tunable monochromatic terahertz (THz) source based on difference frequency generation (DFG) in DAST crystal. The THz frequency was tuned randomly in the range of 0.3-19.6 THz. The highest energy of 870 nJ/pulse was obtained at 18.9 THz under the intense pump intensity of 247 MW/cm2. The THz energy emit...

The energy scaling of THz wave in wide range based on surface-emitted (SE) ring-cavity terahertz parametric oscillator (TPO) with pump recycling technique have been demonstrated. The tunable range of 1.38 to 3.42 THz was achieved. Comparing with the conventional SE ring-cavity TPO, the upper limit of the tuning frequency range expanded from 2.46 TH...

We have demonstrated a high-energy and broadly tunable monochromatic terahertz (THz) source based on difference frequency generation (DFG) in DAST crystal. A high-energy dual-wavelength optical parametric oscillator with two KTP crystals was constructed as a light source for DFG, where the effect of blue light was first observed accompanying with t...

A humidity sensor based on the intracavity sensing of a fiber ring laser is proposed and experimentally demonstrated. In the fiber ring laser, a humidity-sensitive fiber-optic multimode interferometer (MMI), fabricated by the single-mode-no-core-single-mode (SNCS) fiber coated with Agarose, works as the wavelength-selective filter for intracavity w...

A humidity sensor based on Fabry-Perot interferometer (FPI) and intracavity sensing of a fiber ring laser is proposed and experimentally demonstrated. A compact humidity-sensitive fiber-optic FPI is developed and inserted in a fiber ring laser. Because the output power of the fiber laser is modulated by the reflection loss of the FPI at different a...

We demonstrate an attenuated total internal reflection imaging system. The surface information of the sample on top of a prism can be acquired by two-dimensionally scanning this prism moving in the vertical plane with horizontally incident continuous terahertz waves at a fixed height. The principles and feasibility of this method are investigated....

A widely tunable, high-energy terahertz wave parametric oscillator based on 1 mol. % MgO-doped near-stoichiometric LiNbO3 crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The tunable range of 1.16 to 4.64 THz was achieved. The maximum THz wave output energy of 17.49 μJ was obtained at 1.88 THz under the pump energy of 165...

We have demonstrated a high-average-power, high-repetition-rate optical terahertz (THz) source based on difference frequency generation (DFG) in the GaSe crystal by using a near-degenerate 2 μm intracavity KTP optical parametric oscillator as the pump source. The power of the 2 μm dual-wavelength laser was up to 12.33 W with continuous tuning range...

Enhanced stimulated polariton scattering induced by 532 nm green laser in KTiOPO4 terahertz parametric oscillator was demonstrated in this paper. An expanded terahertz wave tuning range from 5.7 to 6.1 THz, from 7.4 to 7.8 THz, from 11.5 to 11.8 THz and from 13.3 to 13.5 THz was achieved. The maximum terahertz output energy was 1.61 μJ at 7.57 THz,...

A surface-emitted ring-cavity terahertz (THz) wave parametric oscillator has been demonstrated for high-energy THz output and fast frequency tuning in a wide frequency range. Through the special optical design with a galvano-optical scanner and four-mirror ring-cavity structure, the maximum THz wave output energy of 12.9 μJ/pulse is achieved at 1.3...

we demonstrate an active terahertz imaging method based on compressive sensing. With all modulation matrices engraved on one mask, the fast imaging has achieved. Recognizable result of letter “H” has obtained with PSNR of 10.21.

Anodic growth of TiO2 nanotube (NT) arrays has been proved very promising for energy conversion applications, e.g. photovoltaic devices and fuel cells. However, disordered “nano-grasses” layers were always found on the top of the anodic TiO2 NT arrays. In this paper, we demonstrate a novel and simple method using micromechanical cleavage technique...