Output Transmittance Research Articles

Watt-level output power and near-diffraction-limit beam quality mid-infrared Ho:GdVO4 self-Raman laser at 2.5 µm.

We demonstrate an efficient active Q-switched Ho:GdVO4 self-Raman laser at 2500 nm for the first time, to our knowledge. Using Ho:GdVO4 crystal as the gain medium for both the 2048nm fundamental laser and the 2500 nm Raman laser, the output performances of a new mid-infrared self-Raman laser were investigated. The maximum average output power of 1.45 W was achieved at an incident pump power of 22.5 W, with a slope efficiency of 25.8%, for an output transmittance of 30% and a pulse repetition frequency of 15 kHz. The maximum single pulse energy of 96.7 µJ with a pulse width of 11.35 ns was obtained, corresponding to the peak power of 8.5 kW. The beam quality was near diffraction limited with the M2 factors of 1.15 and 1.06 along the x and y directions. Moreover, adopting the two-end output way of the fundamental laser and the Raman laser, the Raman gain coefficient of Ho:GdVO4 crystal was estimated to be 1.14 cm/GW at 2048nm. This work shows that Ho:GdVO4 is an excellent self-Raman laser crystal for the generation of high power Raman laser at 2.5 µm.

A vibration-based Machine Learning type Structural Health Monitoring methodology for populations of composite aerostructures under uncertainty

A robust to uncertainty Machine Learning (ML) based Structural Health Monitoring methodology for populations of composite aerostructures is postulated. The methodology is founded upon a number of unsupervised ML algorithms for damage detection and a supervised counterpart for damage characterization. Damage detection is specifically based on two types of Healthy Subspace representations: A Multiple Model (MM) and a varying radii Hyper-Sphere (HS) type. Both are built upon response-only vibration acceleration and/or strain signals at properly selected sensor locations. Based on them, Multiple Input Single Output (MISO) Transmittance Function AutoRegressive with eXogenous (TF-ARX) excitation data driven models representing the partial structural dynamics are obtained. Decision making is then based on the model parameter vector that may be transformed and reduced via Principal Component Analysis (PCA). Damage detection is achieved via multi-level information fusion using acceleration and/or strain sensors. Damage characterization, referring to damage type, location, and level determination, is achieved via a hierarchical cosine similarity based algorithm. The methodology is successfully assessed via hundreds of experiments using a population of small-scale composite coupons for the detection and characterization of Delamination and Impact damage under material/manufacturing, temperature, excitation, and experimental uncertainty.

Crystal growth and laser properties of gradual concentration Nd-doped yttrium aluminum garnet serial crystals

The laser crystals of Nd:YAG and Nd:GdYAG with gradual concentration were grown successfully by a Kyropoulos Similar Method. The concentration of boule part of the three grown crystals were 0.17 ∼ 0.38 at% Nd:YAG, 0.95 ∼ 2.86 at% Nd:YAG, and 0.18 ∼ 0.32 at% Nd:GdYAG, respectively. Meanwhile, the absorption coefficients of boule part of the three crystals increased gradually along the growth direction near 808 nm. Three crystal rods with dimensions of Ф 3 × 40 mm were processed from boule part of the grown crystals. The laser performance of the three rods under different transmittance output mirrors and different pump directions were characterized. The optimal laser slope efficiency of 0.17 ∼ 0.38 at% Nd:YAG and 0.18 ∼ 0.32 at% Nd:GdYAG were 52.8% and 55.0%, respectively, when the transmittance of the output mirror was 15%. And the optimal laser slope efficiency of 0.95 ∼ 2.86 at% Nd:YAG was 47.4%, under a 30% transmittance output mirror. Moreover, when the high concentration end is the pump incident end, the laser slope efficiency is reduced. The results show that the laser efficiency can be greatly improved, when pumping along the low concentration end. The gradual concentration crystal is helpful to improve the laser performance.

PECULIARITIES OF THE FORMATION OF SCINCILLATION RESPONSE IN ORGANIC MATERIALS WITH STOCHASTIC CHARACTER OF LIGHT PROPAGATION

The paper examines the possibility of using an organic polycrystal as the “opaque” scintillator. Polycrystals are produced by pressing crystalline grains. When light propagates through a polycrystal, it is repeatedly reflected and refracted at the boundaries of the grains. This makes its propagation difficult. We studied the light output and optical transmittance of stilbene and p-terphenyl polycrystals with different fractions of crystalline grain: from 0.06…0.1 to 2.0…2.5 mm (the samples 20 mm in diameter and 2 mm in height) was conducted. Modelling of light propagation in polycrystalline samples of stilbene and p-terphenyl was carried out and the values of the light collection coefficients were calculated. It was found that in order to obtain the polycrystalline samples with sufficiently high light output and high efficiency of detection of local sites of interaction of ionizing radiations, grains in the range of 0.4…0.8 mm should be used.

Influence of neutron/gamma irradiation on damage and scintillation of Ga-doped ZnO thin films

As a new type of inorganic scintillator, ZnO crystal doped with Ga has been used for Ultra-fast scintillating detectors with fast response to detect X-ray, gamma, neutron, and charged particles. Moreover, due to the large bandgap energy and high threshold displacement energy, ZnO: Ga has a strong radiation resistance in theory. However, there is a lack of experimental studies on the change of scintillation properties of ZnO: Ga under an intense irradiation environment. This study deposited thin Ga-doped ZnO films on α-Al2O3(0001) substrate by dual-target reactive magnetron sputtering. The ZnO: Ga samples were irradiated by neutrons from 1010 to 7.1 × 1014 neutrons/cm2 (1 MeV neutron equivalent fluence) and γ rays from 500 to 10,000 Gy, respectively. The structural and optical properties of all irradiated samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), optical transmittance (TS), and effective light output at room temperature. The results indicated that all the irradiated samples are still in both hexagonal wurtzite structure and c-axis orientation. Compared with unirradiated samples, it is found that the samples' optical transmittance, energy resolution, and effective light output have little change due to irradiation, which has fully proved that the ZnO: Ga scintillation films have good radiation resistance under neutron and gamma irradiation. Hence, ZnO: Ga is an attractive candidate for radiation detectors with ultra-fast responses under extreme radiation environments.

DEVELOPMENT OF RADIATION RESISTANT SCINTILLATORS BASED ON RARE-EARTH ALUMINATES

LuYAG:Ce and YAG:Ce,Ca crystals were obtained by the Czochralski method using tungsten crucibles in reducing surroundings. Crystals (LuxY1-x)3Al5O12:1%Ce and crystals of YAG:Ce,Ca with different concentrations of Ce and Ca were grown. Studies and analyses of their characteristics were carried out. The analysis of their characteristics is based on experimental data that we obtained by measurements of light output, decay time, spectra of luminescence, excitation, and light transmittance.

Special issue “optical communications, sensing, and laser applications”

Special issue “optical communications, sensing, and laser applications”

Vibration Energy Harvesting from the Subwavelength Interface State of a Topological Metamaterial Beam.

Topological metamaterial has been a research hotpot in both physics and engineering due to its unique ability of wave manipulation. The topological interface state, which can efficiently and robustly centralize the elastic wave energy, is promising to attain high-performance energy harvesting. Since most of environmental vibration energy is in low frequency range, the interface state is required to be designed at subwavelength range. To this end, this paper developed a topological metamaterial beam with local resonators and studied its energy-harvesting performance. First, the unit cell of this topological metamaterial beam consists of a host beam with two pairs of parasitic beams with tip mass. Then, the band structure and topological features are determined. It is revealed that by tuning the distance between these two pairs of parasitic beams, band inversion where topological features inverse can be obtained. Then, two sub-chains, their design based on two topologically distinct unit cells, are assembled together with a piezoelectric transducer placed at the conjunction, yielding the locally resonant, topological, metamaterial, beam-based piezoelectric energy harvester. After that, its transmittance property and output power were obtained by using the frequency domain analysis of COMSOL Multiphysics. It is clear that the subwavelength interface state is obtained at the band-folding bandgap. Meanwhile, in the interface state, elastic wave energy is successfully centralized at the conjunction. From the response distribution, it is found that the maximum response takes place on the parasitic beam rather than the host beam. Therefore, the piezoelectric transducer is recommended to be placed on the parasitic beam rather than host beam. Finally, the robustness of the topological interface state and its potential advantages on energy harvesting were studied by introducing a local defect. It is clear that in the interface state, the maximum response is always located at the conjunction regardless of the defect degree and location. In other words, the piezoelectric transducer placed at the conjunction can maintain a stable and high-efficiency output power in the interface state, which makes the whole system very reliable in practical implementation.

Inverse design of a high‐quality factor multi‐purpose optical biosensor

This paper investigates a high-quality and multi-purposed biosensor with maximum stable output transmittance numerically by using the inverse design method. The proposed biosensor utilises particle swarm optimisation for inverse design which will be a helpful way of designing different kinds of precise sensors in the future. In this research, some parameters are introduced to the optimiser to find the best cavity parameters for developing a high-quality sensor to sense different targets. Many previous studies were on single-goal biosensors, or their quality factor and output spectrum were very low. The proposed sensor can sense different parts of blood components, the amount of glucose in the urine, and tear's glucose for the first time just in one device to the best of our knowledge. Compared to previous works, this structure detects the differences between refractive indexes analytes with a high-quality factor and a high and stable output transmittance spectrum. This structure contains two-dimensional photonic crystal microresonators to provide resonance frequencies in the photonic bandgap. The device works on a window of 1.55 μm with a quality factor equal to 24,000, the sensitivity is 500 nm/RIU (refractive index unit), and the resolution is equal to 4 × 10−5. In this paper, the scaling method, particle swarm optimisation, two-dimensional finite-difference dime domain, and Plane-Wave Expansion methods are utilised.

A Diode Pumped Middle Infrared Laser Based on Ho: GdVO4 Crystal

Ho: GdVO4 crystal is the host material for the production of laser working in the middle infrared range. In this contribution, the characteristic parameters of the Ho: GdVO4 crystal were measured, and the material was used as a gain medium to build a diode-pumped laser for the first time, to reach a laser output at 2047.9 nm. The output beam quality factor M2 was measured to be 1.4 and 1.3 in x-direction and y-direction, respectively. In addition, the influence of the transmittance of the output mirror on the generation of laser was obtained through exploration. The results showed that the laser wavelength blue-shifted as the output transmittance increased.

Actively Q-switched Tb:LiYF4 green lasers

In this work we have developed, for the first time to our knowledge, an actively Q-switched Tb:LiYF4 laser with emission directly into the green spectral region at 544 nm. Using an acousto-optical modulator, the laser delivered an average power of 445 mW at 3 kHz repetition rate for an incident pump power of 3 W at 488 nm. The laser pulse energy and the pulse duration were measured to be 148 μJ and 190 ns, respectively, indicating a pulse peak power of 580 W with output transmittance of 10%. The laser could be operated up to a repetition rate of 16 kHz with output transmittance of 2%.

Application of tungsten oxide thin film in the photonic crystal cavity for hydrogen sulfide gas sensing

In this work, we report the design and simulation of a high sensitivity hydrogen sulfide (H2S) gas sensor based on the Ln slot photonic crystal cavity. To improve the sensitivity of the sensor, a layer of tungsten oxide (WO3) is coated on the inner walls of the slot. Change in concentration of H2S varies the refractive index of WO3 and leads a more wavelength shift in the output transmittance spectrum of the sensor which increases the sensitivity. We showed that the proposed sensor possesses an ultra-high sensitivity up to 2.3× 105 nmRIU−1, and a high Q factor of 3 ×103.

Ultrathin Metasurface Wavelength-Selective Mirror for Millimeter/Terahertz Wave Fabry-Perot Cavities

We present an ultrathin metasurface working as both a highly reflective wavelength-selective mirror and a high transmittance output coupler for a semiconfocal Fabry-Perot cavity. The numerically optimized 2-μ m-thick metasurface achieves a peak reflectivity of R = 99.35% at ω0 = 94 GHz and peak transmittance of T ≈ 90% at the fourth harmonic (4ω0). Experimental results show that the metasurface FP cavity exhibits comparable quality factors to cavities enclosed by either a copper mirror or Bragg grating mirror. Our work highlights the potential for ultrathin metasurfaces to function as frequency selective mirrors in millimeter or terahertz wave cavities for various applications, such as nonlinear terahertz wave generation, material characterization, and imaging.

Efficient Continuous-Wave Diode-Pumped Ho :GTO Laser with a Pump Recycling Scheme

We demonstrate a novel continuous-wave 2.1 μm Ho :GTO laser pumped by a laser diode. Employing a pump recycling scheme and 30% output transmittance, we obtain an output power of 4.76 W and a single oscillating peak of 2068.4 nm with a slope efficiency of 55.3% with respect to the absorbed pump power. In addition, the M2 factor of the Ho :GTO laser is reckoned to be approximately 1.3 at the maximum output power.

Study on Scintillation Properties of Several Non-fluoride Halides under Low Energy241 Am radiation

A few of halide inorganic scintillation crystals have been applied as radiation detection materials and are playing important roles in nuclear medicine, high energy physics, security inspection, petroleum logging and so on, but most of them are on the way of research and development. In this paper, a series of novel halide scintillation crystals, LaBr3(Ce), LaCl3(Ce), SrI2(Eu), Cs2LiYCl6(Ce) and NaI(Tl) were studied using low energy 241Am radioactive source. The effect of reflective film thickness on low-energy ray transmittance and light output of encapsulated scintillators was investigated, Teflon thickness of 0.48 mm as reflective film is best choice to obtain higher light collection and better radiation transmittance. Among all these crystals, LaBr3(Ce) crystal has excellent energy resolution above 25keV gamma ray radiation, 9.3% at 26.34 keV, 8.4% at 59.54 keV and2.6% at 661.66 keV. Only NaI (Tl) crystal works fine below 25 keV X-rays radiation, with energy resolution of 17.68% at 13.9 keV, 14.16% at 17.8 keV and 13.42% at 20.8 keV.

Study on MgO: APLN Crystal for Multi-Optical Parametric Oscillation

In this paper, the expression of polarization structure for superlattice materials with phase mismatch and relative coefficient is established. Based on this method, a MgO:APLN crystal with two reciprocal lattice vectors is designed to generate 1.47μm, 3.84μm and 1.57μm, 3.3μm parametric light pumped by 1064 nm fundamental frequency light. Comparing the Fourier coefficients of MgO:APLN crystals with different structures, it is found that the Fourier coefficients of the two reciprocal lattice vectors are equal when the relative coefficient is 1:1. Based on this crystal, the experiment of external cavity MgO:APLN-MOPO is carried out to optimize the output transmittance of parametric optical coupling. With 20kHz high repetition rate 1064nm laser pumping, 1.57μm and 3.84 μm are achieved and the average power are 4.1W and 3.7W, respectively. The corresponding light-to-light conversion efficiency are 17.1% and 15.4%.

Efficient 2.1 μm laser action of an Ho:ScYSiO5 (Ho:SYSO) mixed crystal at room temperature

We present a new 2.1 μm Ho:SYSO laser, resonantly pumped by a 1940.3 nm Tm-fiber laser. With an output transmittance of 11.4%, the Ho:SYSO laser produced a 2097.7 nm continuous wave with up to 4.1 W of output power and 53.4% of slope efficiency with respect to the absorbed pump power. The measured beam quality factor (M2) of the Ho:SYSO laser was approximately 1.2 at the maximum output level.

Design of D shaped plasmon–photonic crystal fiber for bio sensing application

Abstract This article proposes D-shaped plasmon photonic crystals for bio sensing applications. It reports the enhanced sensitivity of 7000 n m / R I U . The sensing mechanism is attained by following coupled mode theory property. It is then calculated by obtaining the wavelength shift in the output transmittance spectra. The overall analysis of device is followed by the finite element method (FEM).

Analysis of nonreciprocal noise based on mode splitting in a high-Q optical microresonator

The whispering gallery mode optical microresonator offers a high quality factor, which enables it to act as the core component of a high sensitivity resonator optic gyro; however, nonreciprocal noise limits its precision. Considering the Sagnac effect, i.e. mode splitting in high-quality optical micro-resonators, we derive the explicit expression for the angular velocity versus the splitting amount, and verify the sensing mechanism by simulation using finite element method. Remarkably, the accuracy of the angular velocity measurement in the whispering gallery mode optical microresonator with a quality factor of 108 is 106 °/s. We obtain the optimal coupling position of the novel angular velocity sensing system by detecting the output transmittance spectra of different vertical coupling distances and axial coupling positions. In addition, the reason for the nonreciprocal phenomenon is determined by theoretical analysis of the evanescent distribution of a tapered fiber. These results will provide an effective method and a theoretical basis for suppression of the nonreciprocal noise.

Performance of Crystal Scintillators in a Severe Radiation Environment Caused by Protons

Future high energy physics experiments at the energy and intensity frontiers will face challenges from a severe radiation environment caused by both ionization dose and charged and neutral hadrons. This paper reports an investigation on proton induced radiation damage in various crystal scintillators. Large size BGO, LFS and PWO crystals of 18 to 22 cm long were irradiated by 800 MeV protons up to 3 × 1015 p/cm2 at the WNR facility of LANSCE with longitudinal transmittance measured in situ. LYSO plates of 14 × 4 × 1.5 mm3 were irradiated by 24 GeV protons up to 8.2 × 1015 p/cm2 at the IRRAD facility of CERN. Degradations in both transmittance and light output are reported. The results show an excellent radiation hardness of LYSO/LFS crystals against charged hadrons.