Tunable photoluminescence of NaYF4:Eu nanocrystals by Sr codoping

NaYF₄:Eu/Sr nanocrystals were synthesized by a hydrothermal method. Tunable photoluminescence of the NaYF₄:Eu nanocrystals was successfully achieved by codoping with Sr²⁺ ions. With increasing Sr²⁺ concentration, not only the X-ray diffraction peaks of the nanocrystals become broader, but also the positions of them shift toward larger lattice parameters. Eu³⁺ and Eu²⁺ have been found to coexist in an NaYF₄:Eu/Sr. The Eu³⁺/Eu²⁺ emission intensity ratio changed with the Sr²⁺ concentration and excitation wavelength. More interestingly, the spectral configurations of Eu²⁺ and Eu³⁺ also varied with the excitation wavelength, indicating that the nanocrystals have multiple luminescence centers or emitting states.     

High-power tunable terahertz generation from a surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals

A high-powered tunable terahertz wave (THz-wave) has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length was enlarged by employing two MgO:LiNbO₃ crystals. The tunable THz-wave radiation from 0.8 to 2.8 THz was realized via varying phase-matching angle between the pump wave and the Stokes wave. The maximum THz-wave radiation was 173.9 nJ/pulse at 1.7 THz as the pump energy was 82 mJ, corresponding to an energy conversion efficiency of about 2.12 × 10⁻⁶ and a photon conversion efficiency of about 0.035%. The first-order, the second-order and the third-order Stokes waves were observed during the experiments.     

宽带可调谐掺Yb3+双包层光纤激光器的研究

利用闪耀光栅构成可调谐Littrow外腔,对掺Yb³⁺双包层光纤激光器的波长调谐输出进行了实验研究.激光调谐输出波长范围70nm.针对光纤内的双折射效应对激光的输出功率的影响,实验中使用了在线光纤偏振控制器,从而有效地减小了调谐曲线的起伏及其与荧光谱的差别,并得到了窄线宽、线偏振、宽带调谐的激光输出.     

N2-broadening coefficients in the ν2 and ν4 bands of PH3

N₂-broadening coefficients are measured for 61 transitions of PH₃ in the ^QR branch of the ν₂ band and the ^PP, ^RP, ^SP, and ^PQ branches of the ν₄ band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 1 to 16 and K from 0 to 11 are located between 1008 and 1106 cm⁻¹. The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter models provide larger broadening coefficients than the Voigt model. These coefficients have also been calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. The theoretical results are in good agreement with the experimental data and reproduce the J dependence of the broadenings, but their decrease at high J values is overestimated for the ^QR (J, K) transitions.     

Coupled fused silica capillaries for rapid capillary zone electrophoresis of proteins

A novel two-dimensional electrophoretic system for the control of electroosmosis in capillary zone electrophoresis has been developed and evaluated for rapid separations of proteins. The system comprises uncoated and polyether-coated fused silica capillaries coupled in series. An equation relating the average electroosmotic flow velocity in the coupled capillaries to the intrinsic electroosmotic velocities of the connected segments and their corresponding lengths has been derived and verified experimentally. This approach has the advantage of enabling the electroosmotic flow to be tuned independently of the applied voltage. As a consequence, rapid protein analysis at relatively low field strength was achieved without sacrificing the high separation efficiencies obtained with surface-modified capillaries.     

Up to 30 mW of broadly tunable CW green-to-orange light, based on sum-frequency mixing of Cr:forsterite and Nd:YVO4 lasers

Efficient generation of continuous-wave (CW) tunable light in the yellow region is reported. The method is based on sum-frequency mixing of a tunable Cr⁴⁺:forsterite laser with a Nd:YVO₄ laser. A periodically poled lithium niobate crystal was placed intra-cavity in a Nd:YVO₄ laser, and the Cr⁴⁺:forsterite laser was single-passed through the non-linear media. With this setup, it was possible to generate up to 3 mW of yellow light smoothly tunable from 573 to 587 nm. This is the highest output demonstrated to date for a tunable diode pumped solid-state CW laser in this wavelength region. The ways to improve the efficiency further are discussed.     

Tunable optical filter based on Sagnac phase-shift using single optical ring resonator

In this paper, a single optical ring resonator connected to a Sagnac loop is used to demonstrate theoretically a novel narrow band optical filter response that is based on Sagnac phase-shift Δφ. The given filter structure permits the Sagnac rotation to control the filter response. It is shown that by changing the Sagnac rotation rate, we can tune the filter response for desired bandwidths. To increase the wavelength selectivity of the filter, the Sagnac phase-shift should be as small as possible that is limited by the loop length. For Δφ=0.1 rad, the obtained FWHM is 2.63 MHz for tuning loop length of 2 m. The simulation response agrees fairly with the recently reported experimental result.     

Thermally tunable THz filter made of semiconductors

By using the finite-difference time domain method, the transmission properties of terahertz wave passing through two different periodic subwavelength structures on InSb semiconductor slabs under different temperatures have been investigated. The results show that the peak transmittance increases and the transmittance peak has a blue shift when the temperature is increasing. It is extremely versatile to control the tunable THz filter by varying the temperature.     

Polymer Optical Fiber Photosensitivities and Highly Tunable Fiber Gratings

In this paper, recent progress in the investigation of photosensitivities of polymer optical fibers and the development of polymer optical fiber grating is reported. Photosensitivities in various polymer fibers, including doped and undoped, multimode and single-mode polymer fibers, have been experimentally characterized and evaluated for fiber grating application. In particular, the wavelength dependence of material absorption and photosensitivity has been found essential to the fabrication of polymer optical fiber grating. Based on the results of photosensitivity research, polymer optical fiber gratings have been successfully fabricated. More importantly, polymer optical fiber grating has been demonstrated highly tunable, with a tuning range more than 70 nm. The unique feature of high tunability in polymer optical fiber grating has great potential in various applications including optical fiber WDM systems and fiber sensor systems. Several important issues that remain to be investigated will also be discussed.     

A widely tunable dual-wavelength erbium-doped fiber ring laser operating in single longitudinal mode

A new mechanism to induce polarization hole burning effect in Er-doped fiber ring lasers is presented. By using this effect, incorporating with the counter-propagation of the two light beams, the inhomogeneous in the gain medium broadening was significantly increased, and thus a stable dual-frequency Er-doped fiber ring laser operating in single longitudinal mode and single-frequency was demonstrated. Frequency spacing was tunable from 0.47 GHz to THz.