Photodetector Surface Research Articles

Quintic refractive index profile-based funnel-shaped silicon antireflective structures for enhanced photodetector performance

Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.

МОДЕЛИРОВАНИЕ КОНЦЕНТРИРОВАННОГО СОЛНЕЧНОГО ИЗЛУЧЕНИЯ ИНФРАКРАСНЫМ ДЛЯ ИЗМЕРЕНИЯ ТЕПЛОВЫХ ХАРАКТЕРИСТИК ТЕПЛОФОТОЭЛЕКТРИЧЕСКОГО МОДУЛЯ СОЛНЕЧНОЙ КОНЦЕНТРАТОРНОЙ УСТАНОВКИ

When developing renewable energy conversion devices, more and more attention is being paid to improving the efficiency of using renewable energy. The efficiency of modern mass-produced solar photovoltaic modules is about 20 percent. In order to increase the completeness of the use of solar energy, the direction of thermal photovoltaic systems is receiving significant development. Devices of this type realize the task of recycling the remaining 80 percent of energy into heat for its subsequent use. The conversion of concentrated solar energy into photoelectricity and heat is carried out by a thermal photovoltaic module. The study of its photovoltaic and thermal parameters is one of the main tasks when creating an appropriate installation. (Research Purpose) The research purpose is developing a methodology and creating a laboratory installation for studying the thermal characteristics of a thermal photovoltaic module. (Materials and methods) The design of the thermal photovoltaic module is presented. The spectral characteristics of the photodetector surface of the module in the visible and infrared spectral ranges have been studied by dispersion and Fourier spectroscopy. (Results and discussion) The analysis of the results of the study of the reflection spectra in the visible and infrared spectral ranges along with the spectral density of the infrared Planck radiation for the temperatures of the infrared emitter in the region of 250-300 degrees Celsius is carried out. The conversion coefficients of the intensities of concentrated solar radiation into the density of the Stefan-Boltzmann infrared radiation flux are obtained. A test measurement of the stationary temperature of the coolant at the output of the module was carried out, according to which the flux density of the heating infrared radiation was calculated. This value is correctly consistent with the independently measured intensity of infrared radiation. (Conclusions) A laboratory measuring stand has been created to simulate concentrated solar radiation with infrared radiation of the thermal range to measure the thermal characteristics of the thermal photovoltaic module of a solar concentrator installation.

Novel X-ray scanning technique for in-situ alignment of photo-detectors in the MEGII calorimeter

We describe and show results of a novel technique to measure with high precision the positions of photodetectors installed in the upgraded liquid xenon calorimeter of the MEG II experiment. The measurement was done by detecting the signal in individual photo-detectors as the front surface of the calorimeter was scanned in axial (Z) and azimuthal (ϕ) directions with a precisely controlled, thin, collimated beam of X-rays obtained from a 57Co X-ray source. The measurements were made when the calorimeter was cold and operational, under which conditions they could not otherwise be made. This technique is used to check for changes in the photodetector positions due to the effects of cooling and thermal cycling of the support structure and to provide a reference between the positions of the operational photodetectors and alignment markers on the cryostat exterior. The use of an essentially monochromatic X-ray source allowed ancillary measurements of photodetector properties, including pulse shape, relative gain, and variation in response over the photodetector surface. Measurement uncertainties below 0.6 mm in Z and 0.7 mrad in ϕ have been achieved, well within the requirements for the MEG II performance.

Optical path length self-calibration method based on form measured surface data

High-precision measurement of lenses and mirrors of free-form surface figures is necessary owing to the increasing functionality of optical elements. Previously, we developed a nanoprofiler measurement technology. The nano-profiler calculates the form from a slope distribution on the measurement surface. The slope distribution is calculated from the measurement result of the optical system that directly measures the slope of the surface using laser light and a quadrant photodiode, as well as the rotary encoder output that indicates the position of the optical system and the object to be measured. The slope distribution and optical path length are required to calculate the form. The geometrical length is between the measured surface of the object and the photodetector's surface. The optical path length was designed to be 400 mm when the instrument was manufactured; however, because assembly errors were included, the optical path length must be calibrated to obtain measurements with higher accuracy. Therefore, we herein propose a multistep self-calibration method to calibrate the optical path length. In this method, a plurality of forms is measured on the surface to be measured while changing the optical path length by a known amount. The optical path length was estimated based on the results of the multiple form measurements. Before the evaluation was performed, the optimum measurement conditions for the evaluation were determined via simulation, and the optical path length was obtained from the actual measurement results under the optimum conditions. The results show that the optical path length is 399.698 mm, and the standard deviation of the calculated variation in the optical path length is 5.3 μm.

Investigation of the damage to hybrid infrared photodetectors upon multiple cycles of cooling to liquid-nitrogen temperatures using an interference technique

The influence of the surface curvature of hybrid photodetectors on the gradual damage they undergo upon multiple cycles of cooling to the temperature of 77 K is investigated. The shape of the photodetector surface is controlled using the interference technique.

High performance wide response GaAs based photo detector with nano texture on nanopillar arrays structure

Nanopillar arrays structure deployed over a top photodetector surface exhibits high light coupling efficiency which is attributed to their unique optical and structural properties. The paper presents a proposed GaAs material based periodic pyramidal cut nanopillar structure array model deployed over a 50 µm × 50 µm detector’s surface area. From the geometric analysis of the proposed model structure a maximum 99.8% light absorption has been achieved. Enhanced detector’s performance in terms of 0.75 A/W responsivity, as well as 56.8% external quantum efficiency for a narrow 0.5 µm depletion width, has also been demonstrated.

Modeling the Heterodyne Efficiency of Array Detector Systems in the Presence of Target Speckle

To solve the speckle effect problem in heterodyne detection, an array detector is proposed; heterodyne efficiency is modeled by accounting for speckle and using an additional parameter to simulate coherent summation processing. Heterodyne efficiency is derived by mixing a Monte Carlo simulated speckle field with a planar local oscillator field on a photodetector surface to evaluate the array detector performance at improving signal-to-noise ratio (SNR) of the coherent optical system. From the simulation results, the array detector is shown to effectively improve the SNR of the heterodyne system. For low SNR, the heterodyne efficiency of an N × N array detector increases linearly with N .

Optimization of Parameters for a CsI(Tl) Scintillator Detector Using GEANT4-Based Monte Carlo Simulation Including Optical Photon Transport

GEANT4-based Monte Carlo simulation has been performed for a 2"φ × 2" L cylindrical CsI(Tl) single-crystal scintillator. The simulation includes transport of incident gamma photons as well as generation and transport of optical photons in the crystal up to the coupled photodetector. An optical photon detection spectrum was generated from the number of optical photons detected at the photodetector surface per incident primary gamma photon. This spectrum is equivalent to a conventional pulse-height spectrum, apart from the fact that its abscissa is only proportional, but not equal, to the actual pulse height (volts). This has an energy resolution of about 6.5% at 662 keV arising from the light generation and transport statistics. This spectrum was compared with an experimentally recorded pulse-height spectrum (after the abscissa of both the spectra were converted to energy scale) from a gamma spectrometer based on an in-house grown 2"φ × 2" L cylindrical CsI(Tl) crystal, thereby validating the simulation code. The effects of variation of scintillation and optical properties as well as physical and surface parameters on the simulated spectrum were subsequently studied in order to identify the important parameters. The quantum efficiency of the photodetector and the matching of its spectral response with the emission spectrum of the scintillator, reflectivity of the scintillator coating material, and the absolute light yield of the scintillator were identified as the parameters that influence the pulse-height spectrum in the most dominant way. Results of simulation presented in this paper are likely to facilitate the optimization of future detector setups.

A Novel Method for <inline-formula> <tex-math notation="LaTeX">$\gamma - \text{photons}$</tex-math> </inline-formula> Depth-of-Interaction Detection in Monolithic Scintillation Crystals

Achieved spatial resolution of the PET systems is often limited by the parallax error due to the lack of information about the Depth of Interaction (DoI) inside the crystal of the incoming 511 keV annihilation photons. The smaller the diameter of the PET ring and the thicker the scintillator are, the more this error affects imaging performance. In this work, a DoI calculator suitable for monolithic scintillation crystals and based on the shape of the scintillation light distribution at the photodetector surface has been proposed. To test the estimator performance, a test PET module with a $50 \times 50 \times 20\; \hbox{mm}$ monolithic LYSO crystal coupled to a $12 \times 12$ SiPM array has been employed. In addition, for calibration and validation of the method, Geant4 simulations have been also used. The key result of the application of the proposed DoI estimator is obtaining a continuous DoI estimation with an average DoI resolution of about 5 mm in the 20 mm-thick crystal. Benefiting from the DoI estimation capabilities of the method, it has been also possible to achieve additional important goals, first of all reducing the parallax error. First, because the scintillation light collection varies as a function of the 3D position of the interaction of the annihilation photon inside the crystal, a method to correct this response variation via a proper 3D look-up-table is proposed. This has led to an improvement of about 35% in energy resolution. Moreover, a DoI-dependent position algorithm has been proposed, allowing an improvement of both planar (X-Y) position linearity and planar spatial resolution. This algorithm is specifically developed for the rows/columns multi-channel readout logic, that reduces the number of independent channels from ${\rm N} \times {\rm N}$ to ${\rm N} + {\rm N}$ , where N is the number of SiPM photodetection elements (12 in our case) in each row and column. This development was performed in the framework of the MindView PET/MRI brain imaging project.

Зміна індукції флуоресценції хлорофілу у рослин ріпаку озимого залежно від мікродобрив

Determining the impact of various factors on the plant requires the use of express and informative methods which would allow to carry out tests in the laboratory and in the field with minimal violation of the integrity of the objects. These practices include induction of chlorophyll fluorescence method that is widely used in modern studies of photosynthetic processes. The shape of the curve induction is sensitive to changes of the photosynthetic apparatus as a result of unfavorable factors or physiologically active substances such as herbicides. The purpose of research . Detecting changes in the state of the photosynthetic apparatus of plants of winter rape for actions that various micronutrients using rapid diagnostic method of induction of chlorophyll fluorescence in the field. Materials and methods of research. The impact of drugs on agrobiological state of the photosynthetic apparatus of plants of winter rape varieties SnihovaKorolevaand Vezuvii studied using a portable biosensor Floratest, developed by the State Scientific and Engineering Center of the Institute of Microelectronics kibernentyky them. VN Glushkov, which allows you to record the fluorescence induction curve of the parameters which can determine the progress of light and dark phases of photosynthesis. The form of chlorophyll fluorescence induction (IFH) is sensitive to any changes in any unit of photosynthesis caused major environmental factors and endogenous. Study IFH changes were made in 3x repeated with a 3-minute duration of the measurement cycle. For the measurement of leaf plants placed in the optical unit. For this special pressing levers form a gap (2-4 mm) between the upper and lower lighting filing units. Leaf set against the source. Then slowly so as not to damage the leaf release levers. Soft fabric lining with dark sheet to protect from injury, prevent the penetration of external light on the photodetector and leaf surface area during the last adaptation to darkness. Plot sheet used for the measurement must be inverted upside to the light source, for it must be no thicker veins. Adapting to darkness lasted for 10 minutes, then be measured. The dependence of the fluorescence intensity of time after the start of lighting called chlorophyll fluorescence induction curve or induction curve. With the device Floratest was fixed as the kinetics of fast and slow changes in the signal interpretation and develop specific areas of induction curves. Results and discussion. According to the data revealed that in winter rape varieties SnihovaKorolevaand Vezuviiunder the influence of micronutrients WuxalMikroplant, AskofolTerios and saw an increase in the intensity of the background fluorestsentsyi (FO) compared with the control. More intensive growth of background observed in a variety fluorystsentsiyiSnihovaKorolevafor the actions of micronutrients WuxalMikroplant, Askofol, Terios index increased compared with control at 25.4%, 20.33%, 16.94% respectively, while the rapeseed plant varieties for the actions of Vezuvii the same micronutrients increased by 8.3%, 13.3%, 0.2% respectively. However, plants winter rape varieties Vezuvii for the actions of micronutrients WuxalMikroplant and Askofol and winter rape varieties SnihovaKorolevawith fertilizers WuxalAskofol and Terios significantly increased fixed level of fluorescence (F st), characterized by a dynamic equilibrium between the processes that lead to an increase in fluorescence . In winter rape varieties SnihovaKorolevawhen applying micronutrients WuxalAskofol and Terios observed increase in FV / Fmah compared to controls by 12.2% and 10.6%, indicating a significant stimulation of photosynthetic apparatus in leaves of rape under the influence of micronutrients. As a test indicator for early diagnosis recommended coefficient Kpl = (Fpl –Fo): (Fmah –Fo) in determining whether a viral infection in experimental plants. Value Kpl ≥ 0,4 0,5 indicate the presence of infection and significantly increases the probability of detection of viral lesions compared with visual observation. In plants winter rape varieties Vezuvii and the SnihovaKorolevaKpl index is within 0,28-0,27, indicating that the healthy state of the plants. Conclusions 1. More intensive growth of background fluorescence was observed in a variety SnihovaKorolevafor the actions of micronutrients WuxalMikroplant, Askofol, Terios index increased compared with control at 25.4%, 20.33%, 16.94% respectively, while the rapeseed plant variety Vezuviifor the actions of the same micronutrients increased by 8.3%, 13.3%, 0.2% respectively. 2. In winter rape varieties with the SnihovaKorolevaapplications and micronutrients WuxalAskofolTerios observed increase in FV / Fmah compared to controls by 12.2% and 10.6%, indicating a significant stimulation of photosynthetic apparatus in leaves of rape under the influence of micronutrients. 3. There was a passage stimulate photosynthesis in winter oilseed rape varieties Vezuvii for the actions of micronutrients WuxalMikroplant and Askofol, the rate of FV / Fmah increased by 10.3% and 11.76% respectively.

Effect of laser linewidth on the performance of heterodyne detection

According to the statistical theory, the influence of laser linewidth on the performance of optical heterodyne system is studied. Also, the effect of laser linewidth on the visibility of fringe pattern is discussed. The expressions of self-correlation function power-spectrum and definition of visibility of fringe patterns are obtained in this paper. Based on the analytical expressions, the numerical simulation is performed. The obtained results demonstrate that the laser linewidth influences the visibility of fringe patterns according to the result shown in Fig. 3, and that the intermediate frequency can be still detected by heterodyne detection technique as the laser linewidth increases. For different linewidths, the measurement of intermediate frequency is accurate without the influence of noise as the delay d between the received signal and locally generated signal is less than the coherence time c of laser source. If the delay d is greater than the coherence time c, the full width at half maximum of intermediate frequency in the frequency spectrum of the output signal of photodetector will broaden as the laser linewidth increases. However, for a wide linewidth, the measurement of intermediate frequency is inaccurate due to the influence of noise when the delay d is greater than the coherence time c. The wider the linewidth, the less accurate the measurement of intermediate frequency will be. In order to check the correctness of theoretical results, an experiment is carried out by using a laser with a linewidth of 1 MHz, which has an 8.1 km channel path. In our experimental set-up, a cooperative target is employed to modulate and reflect the transmitted beam. In this way, an echo signal is received. The mixing process of the received signal and local signal on the photodetector surface produces an electrical current known as the photomixing current. A spectrum analyzer is used to observe the output signal of detector. The obtained spectrum shows that intermediate frequency can be checked, which is in agreement with the theoretical result. In this work, the obtained conclusions can be directly used to choose a proper laser for optical heterodyne system. According to the target characteristics and measurement requirements, and by following the conclusions obtained in this paper, the laser linewidth can be evaluated.

First performance test of newly developed plastic scintillator for radiation detection

We present a plastic scintillator, developed in collaboration with Carlit Holdings Co., Ltd., that is fabricated using a liquid parent material cured at room temperature by adding a hardener. The new scintillator can incorporate heat-labile functional materials such as gadolinium to enhance neutron sensitivity. The characteristics of the new scintillator, in particular the light yield and attenuation length, were evaluated using a 90Sr β-ray source. The light yield was measured 7% Anthracene on the basis of a comparison with commercially available scintillator (BC-408) at a distance of 18cm from the photodetector surface. This light yield is dependent on the distance between the luminous point and the photodetector because of light attenuation. The attenuation length of the Gd-doped scintillator was about 50cm.

The Design of All Fiber Laser Heterodyne Detection System

The traditional method of heterodyne detection is improved in this paper based on the principle of laser heterodyne detection. The laser heterodyne detection system is designed with all-fiber laser radar in all fiber system, and the laser, the optical system, the receiving device and so on are connected via the passive component. The system can mix the local oscillation light with signal light of measured object information in the photodetector surface, and the difference frequency signal is obtained. Then the signal is filtered and amplified by the signal processing technique to eliminate the DC component, and the desired difference frequency signal is obtained. Through the analysis of the performance of all fiber laser heterodyne detection system, the system has a strong ability to detect weak signal, high conversion gain and signal to noise ratio, and has a good filtering effect. The system is very suitable for the application of laser ranging and so on.

Heterodyne efficiency of a detection system for partially coherent beams

We consider the heterodyne efficiency as a measure of quality for a coherent detection system. The heterodyne efficiency reflects the matching between the received beam and the local oscillator beam on the detector surface, and one can use this property for the alignment of the system. In this paper we derive a general expression for the heterodyne efficiency of a detection system for beams at any state of coherence, assuming that the propagation directions for the two signals (the received signal and the locally generated one) are slightly different. We derive an analytical expression for the heterodyne efficiency when mixing coherently two partially coherent Gaussian Schell-model beams on a photodetector surface. Numerical examples are given for the variation in the heterodyne efficiency with the misalignment angle, the detector radius, and the parameters of the overlapping beams. We show that partially coherent beams, although they suffer more than coherent beams from a decrease in the heterodyne efficiency, are less affected than coherent beams by the misalignment of the detection system.

Introducing speckle noise maps for Laser Vibrometry

When coherent light scatters from a surface, which is rough on the scale of the wavelength of the light, a speckle pattern is produced. The Laser Vibrometer measures target vibration velocity in the direction of the incident laser beam and typically samples a region of a speckle pattern on its photodetector. Target motions can cause the speckle pattern to change on the photodetector surface, particularly when target motions are non-normal to the direction of the laser beam. This speckle motion modulates the Doppler signal and adds noise to the demodulated output signal. Periodic target motions can cause the speckle noise to become pseudo-random and produce harmonic peaks, with the same fundamental frequency as the genuine target vibrations, which can be indistinguishable from the genuine target vibrations. Typical speckle noise levels are generally considered to be low-level, but they have not so far been adequately quantified. This paper reports preliminary results quantifying speckle noise levels using controlled experimental configurations incorporating periodic in-plane and tilt target motions. Working with commercial Laser Vibrometers, various target surface finishes and treatments are considered and speckle noise maps are produced for each configuration. For a tilting surface, speckle noise has been quantified at approximately 1 μm s −1/deg s −1 while, for surfaces with in-plane motion, the sensitivity to speckle noise has been estimated pessimistically at 0.1% of the in-plane velocity. Ultimately, these speckle noise maps will form a valuable practical resource for the Laser Vibrometer user.

An analysis of the spatial homogeneity of a photodetector surface in an infrared image converter using the fractal dimension

This paper analyses the spatial homogeneity of a large-diameter (100 mm) photodetector surface realized by recording the spatial distribution of the gas discharge light emission (DLE) in an ionization-type infrared image converter (ITIIC) with a GaAs photodetector. Analysis of the surface homogeneity is determined by the fractal dimension of the gas DLE when a current is passed through a converter cell. A fractal dimension estimation is found to be a powerful method because it enables both a non-destructive testing facility and use of the whole surface area of the photodetector surface in three dimensions. The effect on the roughness of the photodetector surface through plasmachemical processes at different experimental conditions was established. The effectiveness of the desorption process is proportional to the densities of bombarding particles as well as the stream of desorpted particles leaving the cathode surface. The surface images of the etched photodetector are analysed using both the profile and spatial distribution DLE intensity data showing the surface inhomogeneity in the photodetector plate. It is quantitatively concluded that plasma etching at certain experimental conditions can cause an improvement in surface homogeneity of the photodetector and spatial distribution DLE in an ITIIC.

Binary Optics Microlens Arrays in CdTe.

ABSTRACTArrays of miniature focusing optics located at the focal plane can improve the performance of focal plane systems. By more completely collecting the light at the focal plane and concentrating it into a smaller spot size on the detector plane, the photodetector area can be substantially reduced. Increased gamma radiation hardening and noise reduction result from the decrease in photodetector surface area. Binary optics technology, a process for fabricating large arrays of diffractive optical elements, is especially attractive for infrared materials. In this paper, diffractive Fresnel microlens arrays containing over six thousand F/0.9 lenslets are patterned in the surface of CdTe substrates by successive photolithographic and Ar+ ion-beam-etching steps. Results on smaller arrays of monolithically integrated binary-optics lenslets with II-VI detectors, demonstrating enhanced photodetector responsivities, are presented for the first time.

Laser-Doppler methods for the assessment of microcirculatory blood flow

A new principle for the measurement of microcirculatory blood flow is described. The laser Doppler flowmeter u tilises the fact that a laser light beam incident on tissue is scattered in static structures as well as in moving red cells. Light beams scattered in moving red cells undergo a frequency shift according to the Doppler effect, while beams scattered in static tissue alone remain unshifted in frequency. If shifted and unshifted light is mixed on a photodetector surface, beat notes are produced. The power spectral density of these beat notes is determined by red cell concentration and velocity. From the alternating portion of the photocurrent, an output signal that is related to flux of red cells in a specific tissue volume can be calculated. Some applications of the method are presented.

Incoherent optical heterodyne detection and its application to air pollution detection

Fundamental problems of incoherent optical heterodyne detection are analyzed. Output of the heterodyne detection depends on the spatial and temporal coherences of incoming incoherent signal light on the photodetector surface. The directivity of optical heterodyne detection is concluded to be the same as with that of direct detection in an ideal case in which the image of the object is well focused on the photodetector surface. This incoherent heterodyne detection is applied to air pollution monitoring. In the laboratory, the absorption spectra due to NH(3), Freon, and SF(6) are measured using an incoherent light source, and the concentrations of each gas were determined by using the least-squares method.

Noise reduction in optical measurement systems

The cost of conventional current and voltage measurement equipment has led to an increasing interest in systems using a minimum of expensive insulation. At CERL, several optical systems for the measurement of current and voltage have been produced. These devices are found to suffer from noise due to intensity fluctuations of the light source and the wandering of the light beam across the photodetector surface caused by vibration and atmospheric turbulence. In the paper several possible techniques to reduce this noise are outlined, and a novel modulation scheme which has produced an improvement in the signal/noise ratio of over 20 dB is described. A device for the simultaneous measurement of voltage and current, making use of this system, is soon to go on trial at a generating station.