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 ambient humidity, intracavity humidity sensing is induced. The experiment shows that the relative output power of the fiber laser has a good linear response to ambient humidity from 25 %RH to 95 %RH and the humidity sensitivity of 0.202 dB/%RH is obtained with a narrow 3-dB bandwidth and high signal-to-noise ratio (SNR). Furthermore, the excellent performance of the sensor for remote humidity detection is demonstrated. The sensor also shows a low temperature cross-sensitivity, fast time response, and good stability. The proposed sensor has a great potential in high-capacity sensor network and remote detections.

A high-energy, tunable, long-wave mid-infrared optical parametric oscillator (OPO) based on the 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 the outputs. Further optimization on the cavity length was theoretically and experimentally studied. With a short cavity length of 30 mm, the output energy of over 1 mJ/pulse at 11 µm was obtained with the pump energy of 39.5 mJ/pulse. In addition, a wide tuning range of 8–14 µm was experimentally achieved by rotating the B a G a 4 S e 7 crystal.

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 parameters including total pump energy and energy ratio were studied. Maximum pulse energy of 5.72 mJ at 3.58 μm was obtained at the dual-wavelength pump energy of 58.4 mJ/pulse. The wavelength tuning range was 3.36–4.27 μm with a flat tunability. Moreover, a saturation phenomenon of DFG output was observed and experimentally inferred to be related to the input energy of λ₂ in the BaGa₄Se₇ crystal.

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 polariton scattering (SPS) and difference frequency generation (DFG) processes. In the experiment, the THz frequency tuning range from 1.04 THz to 5.15 THz was achieved based on near-stoichiometric LiNbO₃ (SLN) crystal. Compared with the traditional terahertz parametric oscillator (TPO) under the same experimental conditions, a significant enhancement of THz output energy was occurred in high frequency range. As the THz frequency increased from 1.9 THz to 3.6 THz, the enhancement ratios from 1.6 times to 34.7 times were obtained. Besides, the 3dB bandwidth of ips-TPG was measured to be 2.1 THz, which was about 2.6 times that of SLN-TPO. This THz parametric source with a relative flat gain in wide frequency range is suitable to a variety of practical applications.

Anodic growth of TiO₂ nanotube (NT) arrays has been proved to be very promising for energy conversion applications, e.g. in photovoltaic devices and fuel cells. However, disordered “nano-grass” layers were always found on the top of the anodic TiO₂ NT arrays. In this paper, we demonstrate a novel and simple method using a micromechanical cleavage technique to peel off the disordered nanograss layer. Using this method, ∼1 × 1.5 cm⁻² of uncapped TiO₂ NT arrays with a high-aspect ratio can be easily obtained. The results further indicate that the treatment can improve the photovoltaic and photochemical performances. After the treatment, the conversion efficiency (η) of the dye sensitized solar cells (DSSCs) increased by 29.3%. This work facilitates the growth and applications of high aspect-ratio anodic TiO₂ NT arrays in related devices and systems.

Terahertz (THz) computed tomography (CT) is a promising technique to obtain the internal information of objects due to its properties of nonionizing and high penetration of nonpolar 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, the three-dimensional image of the sample is performed in the low absorption liquid, the refractive index of which is close to the sample. This novel experimental procedure can eliminate the refractive effect and Fresnel reflection loss effectively. Together with the data processing to eliminate the liquid absorption and to restrain the artifacts, the THz CT imaging of high-density polyethylene ( n = 1.53) cylinders and cubes is achieved successfully. The internal hole and metallic foreign body are shown accurately. In addition, the defects with different sizes inside the sample are measured with refractive index matching method. It shows that THz CT imaging based on refractive index matching method has high sensitivity to detect the small defect inside the sample as small as 0.5 mm diameter.