A new coumarin laser dye 3-(benzothiazol-2-yl)-7-hydroxycoumarin

The electronic absorption, and emission spectra as well as fluorescence quantum yield of 3-(benzothiazol-2-yl)-7-hydroxycoumarin (BTHC) were measured in different solvents and are affected by solvent polarity (Δf). The deprotonation of BTHC by triethylamine is a reversible process. BTHC is relatively photostable, the quantum yield of photodecomposition (φ_c) was found to be 2×10⁻⁴ and 2.7×10⁻⁴ in EtOH and DMF, respectively. The fluorescence lifetimes of BTHC were measured in the absence and in the presence of molecular oxygen and were found to be 2.82 and 2.78 ns, respectively. BTHC acts as good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in ethanol and gives laser emission with maxima at 508 and 522 nm.     

Fiber grating sensors for high-temperature measurement

Two fiber grating sensors for high-temperature measurements are proposed and experimentally demonstrated. The interrogation technologies of the sensor systems are all simple, low cost but effective. In the first sensor system, the sensor head is comprised of one fiber Bragg grating (FBG) and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured based on the wavelength-shifts of the FBG induced by the strain. In the second sensor system, a long-period fiber grating (LPG) is used as the high-temperature sensor head. The LPG is very-high-temperature stable CO₂-laser-induced grating and has a linear function of wavelength–temperature in the range of 0–800 °C. A dynamic range of 0–800 °C and a resolution of 1 °C have been obtained by either the first or the second sensor system. The experimental results agree with theoretical analyses.     

基于WO3- Pd复合膜的D型光纤光栅氢气传感器

采用磁控溅射方法在侧边抛磨的光纤光栅（D型光纤光栅）上溅射40 nm WO3-Pd复合薄膜,制作了D型光纤光栅氢气传感器.40 nm WO3-Pd复合薄膜是由5 nm的WO3、5 nm的WO3/Pd混合膜和30 nm的Pd 薄膜组成.实验中,首先采用射频溅射技术向D型光纤光栅溅射5 nm WO3薄膜,再利用共溅射技术溅射5 nm WO3/Pd混合膜,最后用直流溅射技术溅射30 nm的Pd薄膜.SEM结果显示在多次通氢气后WO3-Pd薄膜仍然具有较好的表面形貌,这说明WO3-Pd复合薄膜具有较好的机械性能.实验结果表明:该氢气传感器具有较好的重复性,同镀有同样氢气敏感膜的普通FBG相比,D型光纤光栅的灵敏度提高了200%|在氢气体积浓度为6%时,D型光纤光栅传感器的波长变化为15pm.     

Experimental results of the performance of a laser fiber as a remote sensor of temperature

We present experimental results demonstrating the performance of an erbium-doped silica fiber as a remote temperature sensor. The sensor is based on the fluorescence intensity-ratio change of two spectral bands as a function of temperature in the wavelength interval from 515 to 570 nm. We apply a radiometric analysis to the fluorescence spectrum that we have measured to determine the optimal spectral bands to use in the power ratio of the sensor. The spectral bands used in the power ratio, with best performance, are 525–535 nm/555–565 nm, with a signal–noise ratio of 57 and 56 dB, respectively. The sensor sensitivity is about , and the resolution is approximately .     

Correlation between the birefringence and the structural parameter in photonic crystal fiber

In order to simply design a highly birefringent photonic crystal fiber (HB-PCF), we numerically simulated the correlation between the birefringence and the structural parameter of photonic crystal fiber with square-lattice or triangle-lattice air-holes by using multipole method. It is shown that the phase birefringence B(λ) and the group birefringence G(λ) can be modulated by the structure parameter of normalized wavelength λ/Λ and the relative air-hole size d/Λ. Numerical results show very high phase and group birefringence of the order of 10⁻². The group birefringence becomes negative in the region where phase birefringence increases with an increase in normalized wavelength that does not appear in traditional highly birefringent fibers.     

A multi-parameter optical fiber sensor with interrogation and discrimination capabilities

A multi-parameter and multi-function, but low-cost, optical fiber grating sensor with self-interrogation and self-discrimination capabilities is presented theoretically and experimentally. The sensor bases on three fiber Bragg gratings (FBG) and one fiber long period grating (LPG). Strain, vibration, pressure, ordinary temperature (−10 to 100 °C) and high temperature (100–800 °C) can be measured by the sensor. When high temperature (100–800 °C) is measured, the LPG is used as a high temperture sensor head and FBG₁ is used as an interrogation element. Alternatively, when one of the other four measurands is measured, FBG₁ (or FBG₂) is used as a sensor head and LPG is used as an interrogation element. When two of the other four measurands are measured simultaneously, FBG₁ and FBG₂ are used as sensor heads and LPG is used as a shared interrogation element. FBG₃ is used as a reference element to eliminate the errors resulted from light source fluctuation and the cross-sensitivity between measurand and environmental temperature. The measurands can be interrogated according to the signals of the photodiodes (PDs), which are related to the relative wavelength shift of the LPG and the FBGs. Experimental results agree well with theoretical analyses. The interrogation scheme is immune to light source fluctuation and the cross-sensitivity between measurands and enviromental temperature, and also the dynamic range is large.     

Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

We report the fluorescence upconversion properties of a class of improved pyridinium toluene-p-sulfonates having donor–π–acceptor (D–π–A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of 6.1%, and a maximum TPA cross-section of 8.74×10⁻⁴⁸ cm⁴ s/photon in these dyes.     

Two-photon excitation properties of a class of novel organic dye chloride

We present the two-photon excited (TPE) upconverted fluorescence and lasing efficiencies of a class of new pyridinium chloride having donor-π-acceptor (D-π-A) structure. Based on the excitation upon 40 ps laser pulses at 1064 nm, the experimental results showed that: the red-shift of TPE fluorescence emission peaks and the TPE fluorescence lifetime were gradually increased with the enhancement of electron-donating capability of the donor. To a certain extent, the enhanced donor would increase the two-photon pumped (TPP) upconversion lasing efficiencies, but the overlong alkyl chains would result in decreased lasing efficiencies. We could obtain TPE fluorescence lifetime of 754 ps, TPP upconversion lasing efficiency of ∼8.4%, and TPA cross-section of 6.14 × 10⁻⁴⁹cm⁴s/photon in these compounds.     

Resonant-cavity-enhanced photodetectors and LEDs in the mid-infrared

In this paper we outline the use of resonant-cavity enhancement for increasing the exterior coupling efficiency of photodetectors and light-emitting diodes (LEDs) in the mid-infrared (MIR) spectral region. This method is potentially very important in the MIR because encapsulation is not presently feasible due to the lack of suitable materials. Among other potential applications, resonant-cavity-enhanced (RCE) photodetectors and LEDs could be particularly suitable for greenhouse gas detection because of their ‘pre-tunable’ spectrally narrowed resonantly enhanced peaks. We also present the optical characterization of an InAs RCE photodetector aimed at the detection of methane gas (λ≈3.3 μm), and an InAs/InAs_0.91Sb_0.09 resonant-cavity LED (RCLED) aimed at carbon dioxide gas (λ≈4.2 μm). The high peak responsivity of the RCE photodetector was 34.7 A/W at λ=3.14 μm, and the RCLED peaked at λ=3.96 μm. These are among the longest operating wavelengths for III–V RCE photodetectors and RCLEDs reported in the literature.     

基于荧光淬灭原理的光纤氧传感器的实验研究

基于荧光淬灭原理的光纤氧传感器一直是许多研究工作的重点。介绍了一种制作简单、成本低的光纤氧传感器制造方法。该方法基于荧光淬灭原理，在光纤末端涂覆荧光材料铂八乙基卟啉(PtOEP)实现的。传感器中荧光材料被395nm的紫光激发，并由Y形光纤引导，使用广州犀谱光电USB2000+光谱仪记录荧光的发光强度时序图。最后得到的PtOEP的(I₀/I₁₀₀)-1的值为0.78，即光纤氧传感器的灵敏度为0.78，而且，斯特恩-沃尔默(Stern-Volmer)图显示出很好的线性特性。从氧气到空气环境的响应时间为24 s，从空气环境到氧气的响应时间是5 s。结果表明，基于荧光淬灭原理的光纤氧传感器具有较高的灵敏度和更快的响应时间。     

Electrochemical switching of fluorescence from europium ions dissolved in poly(ethylene oxide) oligomers

Europium salts were dissolved in poly(ethylene oxide) (PEO) oligomers. The europium ions were revealed to be electrochemically redox-active in PEO oligomers. Trivalent europium ions (Eu³⁺) showed red fluorescence (λ_em = 614 nm) in PEO oligomers, and a new intensive blue fluorescence (λ_em = 450 nm) was obtained after reducing the Eu³⁺ into Eu²⁺ by giving negative potential (−0.7 V versus Ag). Reversible fluorescence switching was also carried out by changing the given potential alternately. Sufficient color change required about 20 min because of slow electrode reaction. The fluorescence intensity from europium ions was affected by the molecular weight of matrix PEO. The amount of terminal hydroxyl groups and local viscosity were revealed to affect the fluorescence as the vibrational quenching and diffusion coefficient, respectively. The PEO oligomer with average molecular weight of 600 gave the most intensive fluorescence.     

Determination of Aberration Coefficient of Microoptic Arrays from Axial Confocal Response by Neural Method

We propose a high-speed and parallel method to determine lens aberrations from its confocal axial response. This method analyzes the intensity confocal response including the aberration information of the objective lens by means of neural network algorithm. This method is designed to work parallely for many microlenses, and simultaneously determines aberrations of each element of a microlens array. A prototype system can determine spherical aberration coefficients of a microlens in the range from −0.7λ to 0.3λ with less than 1% RMS error.     

Fluorescence sensor for Cu(II) based on R6G derivatives modified silicon nanowires

A fluorescence sensor for selective detection of Cu(II) is realized by covalently immobilizing derivatives of rhodamine6G (R6G) on the surface of silicon nanowires (SiNWs). It features the release of R6G from the SiNWs in the presence of Cu(II), which causes a significant enhancement of the fluorescence over other metal ions. The present Cu(II) sensor has good selectivity and sensitivity, and exhibits a linear response in the range of 0.0-7.0 μM Cu(II). Different from conventional Cu(II) sensor with fluorescence quenching, the present sensor based on fluorescence enhancement facilitates the practical application. Especially, the release of the R6G from SiNWs could be utilized as fluorescent labeling for Cu(II) in microenvironment.     

一种基于荧光猝灭原理的光纤氧气传感器

用钌 (Ⅱ ) 邻菲咯啉配合物作为指示剂 ,研制成功一种基于荧光猝灭原理的光纤氧气传感器。采用锁相放大技术 ,实现了对弱荧光信号的检测。该传感器的检测下限为 5× 10 -6,检测精度为 5× 10 -7,响应时间T≤ 10s,并具有较强的抗干扰能力、较好的重复性和稳定性。     

Singlet Oxygen Generation Enhanced by Silver-Pectin Nanoparticles

We demonstrate the potential application of silver-pectin nanoparticles on photodynamic therapy, on a solution-base platform. Photodynamic therapy is a medical technique which uses a combination of photosensitizing drugs and light to induce selective damage on the target tissue, by electronically excited and highly reactive singlet state of oxygen. Metal enhanced singlet oxygen generation in riboflavin water solution with silver-pectin nanoparticles was observed and quantified. Here 13 nm silver nanospheres enclosed by a pectin layer were synthesized and it interaction with riboflavin molecule was analyzed. Pectin, a complex carbohydrate found in plants primary cell walls, was used to increase the biocompatibility of the silver nanoparticles and to improve metal enhanced singlet oxygen generation (28.5 %) and metal-enhanced fluorescence (30.7 %) processes at room temperature. The singlet oxygen sensor fluorescent green reagent was used to quantify the enhancement of the riboflavin singlet oxygen production induced by the silver colloid. We report a 1.7-fold increase of riboflavin emission and a 1.8-fold enhancement of singlet oxygen production.     

Photophysical properties, laser activity and photoreactivity of a heteroaryl chalcone: A model of solvatochromic fluorophore

The absorption and fluorescence characteristics of 3-(4′-dimethylaminophenyl)-1-(2-thienyl)prop-2-en-1-one (DMATP) have been investigated in different solvents. DMATP dye exhibits a large red shift in both absorption and emission spectra as solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMATP gave an excimer like emission at 570 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. A dye solution ca. 10⁻³ mol dm⁻³ in CHCl₃ gave a good laser emission in the range 480–560 nm with emission maximum at 530 nm upon pumping by nitrogen laser (λ_ex=337.1 nm). The excitation energy transfer from 7-dimethylamino-4-methyl coumarine (DMC) to DMATP has been also studied in CHCl₃ and the values of energy transfer rate constant and critical transfer distance indicate a Főrster-type mechanism. The photoreactivity and net photochemical quantum yield of DMATP in chloromethane solvents are also determined. We applied semiempirical MO calculation using AMI and ZINO/S calculation to understand the geometric and electronic structure of DMATP molecule in both ground and excited states.     

Temperature-independent bending sensor with tilted fiber Bragg grating interacting with multimode fiber

A new type fiber bending sensor based on a tilted fiber Bragg grating (TFBG) interacting with a multimode fiber (MMF) is presented. The sensing head is formed by insertion of a small section of MMF between a single-mode fiber (SMF) and the TFBG. The average reflective power in the cladding modes decreases with the increase of curvature. The measurement range of the curvature from 0 to 2.5 m⁻¹ with a measurement sensitivity of −802.4 nW/m⁻¹ is achieved. The proposed sensor is also proved as temperature-independent from the experimental investigation.     

Fiber-optic sensors for the estimation of oxygen gradients within biofilms on metals

This paper presents an optical approach to measure the oxygen gradients in biofilms grown on stainless-steel 316L. The sensor is constructed by immobilizing an oxygen-quenchable fluorophore at the tip of an optical fiber. The response time and reversibility of fiber-optic sensor have been analyzed. By mounting the optical fiber using a computerized micromanipulator, the vertical profiles of oxygen are measured with 10 μm depth resolution across biofilms on metal coupons. Steep concentration gradients of oxygen have been observed within the biofilm, both perpendicular and parallel to the metal surface. Optical response of the biofilm grown metal surface is found to be a consistent measure of the oxygen profiles within biofilms.     

Light conversion in thin films of a mixture of mesotetraphenylporphyrin and erbium-doped yttrium vanadate crystallites: 2. Optical properties

The optical properties of two-component films composed of mesotetraphenylporphyrin (TPP) and erbium-doped yttrium vanadate Yt_0.95Er_0.05VO₄ prepared by spincoating have been studied for the first time. A decrease in the TPP content in the films leads to a hypsochromic shift of the Soret band peak by 1–9 nm; this finding suggests that the degree of aggregation of TPP decreases with decreasing TPP content in the film. The fluorescence peak of TPP is located at an emission wavelength of λ_em = 634 nm and an excitation wavelength of λ_ex = 420 nm. The fluorescence peaks of Y_0.95Er_0.05VO₄ at λ_em = 526, 546, and 555 nm (λ_ex = 300 nm) correspond to the following transitions of the Er3+ ion: the band at 526 nm, to the ² H _11/2 → ⁴ I _15/2 transition; the bands at 546 and 555 nm, to the ⁴ S _3/2 λ ⁴ I _15/2 transition. The fluorescence band peaks preserve their positions with a change in the ratio of components in the film; that is, the fluorescent characteristics of TPP and Y_0.95Er_0.05VO₄ clusters do not depend on their interaction. For both TPP and Y_0.95Er_0.05VO₄, the maximum fluorescence intensity is observed at a TPP content in the film of 40%; the gain with respect to single-component TPP and Y_0.95Er_0.05VO₄ films is 70 and 4–15%, respectively. In this case, a significant effect is exerted not so much by the nature and structure of the components and their interaction as by the topographic features of organization of the photoactive elements in the film, their ratio, and mutual orientation, which determine the energy capture probability.