Detection Wavelength Range Research Articles

Properties of Lead Telluride Mid-Infrared Imaging Devices of Focal Plane Arrays

We fabricated p–n-junction-type and Schottky barrier (SB)-type lead telluride (PbTe) mid-infrared focal plane arrays (FPAs) using a flip-chip bonder. The detection wavelength peak of the SB-type FPA shifted from 6.10 μm to 4.95 μm as the ambient temperature was increased from −258.15°C to −148.15°C. At −196.5°C, the detection wavelength peak and cut-off wavelength were 5.68μm and 6.16μm, respectively. The p–n-junction-type FPA yielded the sharpest photoconductivity spectrum among the investigated devices, presumably because of the Tl-related deep levels in its p-type PbTe epitaxial layer. These deep levels absorb the mid-infrared light and cut off the detection wavelength range. Thus, the p–n-junction-type FPAs are expected to be employed in vision cameras and sensors with selectable mid-infrared wavelengths. Meanwhile, the SB-type FPA has a high dielectric constant; consequently, it develops a wide depletion layer that detects a wide range of mid-infrared wavelengths. FPAs based on the PbTe system are potentially implementable in simple, highly sensitive, mid-infrared imaging devices with a wide scan range.

High-speed combustion diagnostics in a rapid compression machine by broadband supercontinuum absorption spectroscopy

The first results under fired internal combustion engine conditions based on a supercontinuum absorption spectrometer are presented and discussed. Temperature, pressure, and water mole fraction are inferred simultaneously from broadband H2O absorbance spectra ranging from 1340 nm to 1440 nm. The auto-ignition combustion process is monitored for two premixed n-heptane/air mixtures with 10 kHz in a rapid compression machine. Pressure and temperature levels during combustion exceed 65 bar and 1900 K, respectively. To allow for combustion measurements, the robustness of the spectrometer against beam steering has been improved compared to its previous version. Additionally, the detectable wavelength range has been extended further into the infrared region to allow for the acquisition of distinct high-temperature water transitions located in the P-branch above 1410 nm. Based on a theoretical study, line-of-sight (LOS) effects introduced by temperature stratification on the broadband fitting algorithm in the complete range from 1340 nm to 1440 nm are discussed. In this context, the recorded spectra during combustion were evaluated only within a narrower spectral region exhibiting almost no interference from low-temperature molecules (here, P-branch from 1410 nm to 1440 nm). It is shown that this strategy mitigates almost all of the LOS effects introduced by cold molecules and the evaluation of the spectrum in the entirely recorded wavelength range at engine combustion conditions.

Eye-safe near-infrared trace explosives detection and imaging.

We report the development of a non-contact no-reagents system operating in the eye-safe 1560-1800 nm wavelength range for standoff trace detection of explosives and high-speed imaging. Experimental results are provided for a number of chemicals including explosives on a variety of surfaces at sub-microgram per cm2 concentration. Chemically specific images were collected at 0.06 ms per pixel. Results from this effort indicate that the combination of modern industrial fiber lasers and nonlinear optical spectroscopy can address next generation eye-safe trace detection of chemicals including explosives.

Bloch Surface Wave-Coupled Emission at Ultra-Violet Wavelengths.

The interaction of fluorophores with nearby metallic structures is now an active area of research. Dielectric photonic structures offer some advantages over plasmonic structures, namely small energy losses and less quenching. We describe a dielectric one-dimensional photonic crystal (1DPC), which supports Bloch surface waves (BSWs) from 280 to 440 nm. This BSW structure is a quartz slide coated with alternating layers of SiO2 and Si3N4. We show that this structure displays BSWs and that the near-UV fluorophore, 2-aminopurine (2-AP), on the top surface of the structure couples with the BSWs. Fluorophores do not have to be inside the structure for coupling and show a narrow angular distribution, with an angular separation of wavelengths. The Bloch wave-coupled emission (BWCE) radiates through the dielectric layer. These BSW structures, with useful wavelength range for detection of intrinsic protein and cofactor fluorescence, provide opportunities for novel optical configurations for bioassays with surface-localized biomolecules and for optical imaging using the coupled emission.

High performance silicon carbide avalanche‐p‐i‐n ultraviolet photodiode with dual operation models

Silicon carbide-based quasi-separated-absorption-multiplication ultraviolet avalanche photodiode (APD) with a small-area multiplication region and a large-area absorption region, which comprises of a p+nn− junction encircled by a p+n− junction, is proposed, and its optoelectronic performance is modelled. The modelling results show a 4H-SiC APD with high performance can be achieved. Moreover, when operated at a low reverse bias (e.g. 5.0 V), the photodiode has almost the same optoelectronic characteristics as the 4H-SiC p-i-n photodiode. It is noted that the device has benefited advantages of both conventional separate absorption and multiplication APD and p-i-n photodiode in the wavelength range of ultraviolet detection, which enable the dual operation models of the device.

Research and analysis on lidar performance with intrinsic fluorescence biological aerosol measurements

Biological aerosols which could cause diseases of human beings, animals and plants, are living particles suspended in the atmosphere. Ultraviolet laser induced fluorescence has been developed as a standard technique used to discriminate between biological and non-biological particles. As an effective tool of remote sensing, fluorescence lidar is capable of detecting concentration of biological aerosols with high spatial and temporal resolutions. Intrinsic fluorescence, one of the most important characteristics of biological aerosols, has quite a large effect on the performances of fluorescence lidar. To investigate the effects of intrinsic fluorescence on biological aerosols, we design an ultraviolet laser induced fluorescence lidar at an excited wavelength of 266 nm, with a repetition rate of 10 Hz. Fluorescence signals are collected by a Cassegrain telescope with a diameter of 254 mm, in which fluorescence spectra of 300-800 nm are mainly considered. A spectrograph and a multichannel photomultiplier tube (PMT) array detector are employed to achieve the fine separation and highefficiency detection of fluorescence signals. According to the present configuration, we perform a series of simulations to estimate the measurement range and the concentration resolution of biological aerosols, with a certain pulse energy. With a relative error less than 10%, theoretical analysis shows that designed fluorescence lidar is able to detect the biological aerosols within a range of 1.5 km at a concentration of 1000 particles·L-1. When the detection distance enlarges to 2.1 km, detectable wavelength range is limited to 300-310 nm. In addition, the lidar is capable of identifying minimum concentrations of biological aerosols with 2 particles·L-1 and 4 particles·L-1 at fluorescence wavelengths of 350 nm and 600 nm, respectively, where the induced pulse energy is set to be 60 mJ and detected range 0.1 km. With setting energies of 40 mJ and 20 mJ, minimum concentrations of biological aerosols decrease to 3 particles·L-1 and 6 particles·L-1, respectively, at a fluorescence wavelength of 350 nm. The relative error of minimum concentration resolution is about 2 particles·L-1, increasing rapidly with range. For a fluorescence wavelength of 600 nm, both the minimum concentration and the relative error show relatively high values, 5 particles·L-1 at 40 mJ and 10 particles·L-1 at 20 mJ, where the relative errors are found to be 2 particles·L-1 and 4 particles·L-1, respectively. The results prove that a shorter intrinsic fluorescence wavelength has a better effect on biological aerosol measurement. We believe that a proper intrinsic fluorescence wavelength will further improve the detection accuracy of biological aerosols.

基于硅与锗材料的改进集成雪崩光电二极管

An advanced avalanche photodiode(APD) was put forword which was integrated by the Si Separate Absorption, Charge, Multiplication(SACM) and Ge SACM APDs. This advanced APD has enlarged the detected wavelength range to 200-1 400 nm. Furthermore, the key parameters which were used to characterize the APD performance, such as the electric field distribution, the dark current and photocurrent, the gain, and the sensitivity of the APD were researched. The simulation results demonstrated that the breakdown voltage of the advanced APD is 145 V, the peak response is 22 A/W at 900 nm wavelength as cathode is 140 V, and the current gain of the advanced APD could get 50 at 400 nm wavelength before breakdown. The fabrication process was also discussed.

Broadband photodetectors based on graphene-Bi2Te3 heterostructure.

Recently, research on graphene based photodetectors has drawn substantial attention due to ultrafast and broadband photoresponse of graphene. However, they usually have low responsivity and low photoconductive gain induced by the gapless nature of graphene, which greatly limit their applications. The synergetic integration of graphene with other two-dimensional (2D) materials to form van der Waals heterostructure is a very promising approach to overcome these shortcomings. Here we report the growth of graphene-Bi2Te3 heterostructure where Bi2Te3 is a small bandgap material from topological insulator family with a similar hexagonal symmetry to graphene. Because of the effective photocarrier generation and transfer at the interface between graphene and Bi2Te3, the device photocurrent can be effectively enhanced without sacrificing the detecting spectral width. Our results show that the graphene-Bi2Te3 photodetector has much higher photoresponsivity (35 AW(-1) at a wavelength of 532 nm) and higher sensitivity (photoconductive gain up to 83), as compared to the pure monolayer graphene-based devices. More interestingly, the detection wavelength range of our device is further expanded to near-infrared (980 nm) and telecommunication band (1550 nm), which is not observed on the devices based on heterostructures of graphene and transition metal dichalcogenides.

Development of an Amorphous Selenium-Based Photodetector Driven by a Diamond Cold Cathode

Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized.

Resolution Limits of Nanoimprinted Patterns by Fluorescence Microscopy

The authors investigated optical resolution limits to identify minimum distances between convex lines of fluorescent dye-doped nanoimprinted resist patterns by fluorescence microscopy. Fluorescent ultraviolet (UV)-curable resin and thermoplastic resin films were transformed into line-and-space patterns by UV nanoimprinting and thermal nanoimprinting, respectively. Fluorescence immersion observation needed an immersion medium immiscible to the resist films, and an ionic liquid of triisobutyl methylphosphonium tosylate was appropriate for soluble thermoplastic polystyrene patterns. Observation with various numerical aperture (NA) values and two detection wavelength ranges showed that the resolution limits were smaller than the values estimated by the Sparrow criterion. The space width to identify line patterns became narrower as the line width increased. The space width of 100 nm was demonstrated to be sufficient to resolve 300-nm-wide lines in the detection wavelength range of 575–625 nm using an objective lens of NA= 1.40.

Electro-optical characterisation of InP nanowire based p-n, p-i-n Infrared photodetectors

High speed photodetectors are most sophisticated optoelectronic devices, because it has high photo sensitivity, low noise, high conversion efficiency and allow a large wavelength range of detection ...

Sensitive and simultaneous detection of different disease markers using multiplexed gold nanorods

A multiplexed bioanalytical assay is produced by incorporating two types of gold nanorods (GNRs). Besides retaining the desirable features of common GNRs LSPR sensors, this sensor is easy to fabricate and requires only a visible–NIR spectrometer for detection. This assay can simultaneously detect different acceptor–ligand pairs by choosing the proper GNRs possessing various LPWs in a wide detection wavelength range and can be developed into a high-throughput detection method. This bioanalytical assay allows easy detection of human serum specimens infected by S. japonicum and tuberculosis (TB) from human serum specimens (human serum/Tris–HCl buffer ratio=1:104) without the need for sample pretreatment. The technique is very sensitive compared to other standard methods such as indirect hemagglutination assays (IHA) that require a serum concentration ratio of larger than 1:20 and enzyme-linked immunosorbent assays (ELISA) requiring a ratio larger than 1:100. This methodology can be readily extended to other immunoassays to realize wider diagnostic applications.

Simultaneous acquisition of the dissolution curves of two active ingredients in a binary pharmaceutical association, employing an on-line circulation system and chemometrics-assistance

The association of an on-line circulation system with a chemometrics-assisted UV detection strategy is described as a useful system to continuously monitor the dissolution of a pharmaceutical preparation containing two active ingredients, and as a tool for the simultaneous determination of the dissolution curves and dissolution profiles of the latter. Multivariate curve resolution with alternating least squares (MCR-ALS) was used as the chemometric tool to quantitate the analytes, while the hydrochlorothiazide–bisoprolol fumarate (HCT–BIS) association was employed as a model for method development. The experiments were carried out with a dissolution tester configured as apparatus II (paddles), under USP 32 official conditions. The suitability of the calibration procedure for quantitating the dissolved drugs was assessed according to ICH guidelines, with regards to linearity in the working range, specificity, accuracy and precision. Figures of merit, including limits of detection and quantitation were also determined, as well as the method's robustness with regards to detection wavelength range. The system was able to consistently provide very reproducible dissolution curves of commercial tablets, which were statistically similar to those furnished by a manual sampling technique, followed by HPLC analysis. To demonstrate the usefulness of the proposed system, the dissolution profiles of different lots of HCT-BIS tablets were acquired and three of them were conveniently compared at a 31 data point level, employing the f1 and f2 (“difference” and “similarity”) indexes. Use of multiple data points for comparison ensured reliability of the results.

Monolithically integrated tunable dual-wavelength photodetector with flat-top response

This paper elaborates the design and analysis of a novel monolithically integrated tunable dual-wavelength photodetector which can be formed by heteroepitaxial growth of an InP-based p-i-n absorption structure on a GaAs-based Fabry–Pérot filter. The photodetector presents two response peaks resulting from the introduction of 4-step Fabry–Pérot cavity. The wavelength spacing between the two peaks, as well as the peak shapes, can be accurately and easily tailored by adjusting the corresponding step height. This photodetector can be tuned via thermal-optic effect. With optimum design by using Transfer Matrix Method, the detectable wavelength range of the photodetector will be twice as that of its counterpart being with a uniform filter cavity; what is more, flat-top responses of the two peaks can also be obtained, simultaneously. We discuss the epitaxial growth and fabrication of the photodetector at the end, indicating the mature technique available for the device.

Ge-Photodetectors for Si-Based Optoelectronic Integration

High speed photodetectors are a key building block, which allow a large wavelength range of detection from 850 nm to telecommunication standards at optical fiber band passes of 1.3–1.55 μm. Such devices are key components in several applications such as local area networks, board to board, chip to chip and intrachip interconnects. Recent technological achievements in growth of high quality SiGe/Ge films on Si wafers have opened up the possibility of low cost Ge-based photodetectors for near infrared communication bands and high resolution spectral imaging with high quantum efficiencies. In this review article, the recent progress in the development and integration of Ge-photodetectors on Si-based photonics will be comprehensively reviewed, along with remaining technological issues to be overcome and future research trends.

Numerical simulation of impact ionization in Ge/AlxGa1−xAs avalanche photodiode

Impact ionization in Ge/AlxGa1−xAs p-i-n heterostructures has been studied using the Monte Carlo technique. The thin (<300 nm) Ge/AlxGa1−xAs single heterojunction structure was found to exhibit large hole (β) to electron (α) ionization coefficient ratio, owing to a higher β in the Ge layer and a lower α in the AlxGa1−xAs layer, together with the dead space effects. The Ge/AlxGa1−xAs avalanche photodiodes are attractive for applications where a wide wavelength detection range is required for compatibility with multiple sources such as in the emerging active optical cable and optical interconnect applications, as well as in the established optical fiber telecommunication systems.

Best dynamic wavelength range for shock detection via blood vessel density pattern

Diffuse reflectance spectroscopy is a non-invasive or minimally invasive medical diagnostic modality. Still challenges in noninvasive tools for early shock detection are unresolved especially in spatial resolution and broad range of sampling wavelength for reduced-/ oxy-hemoglobin concentrations detection from tissue sample. To minimize these limitations, we have developed a novel method based on spatially and spectrally resolved diffuse reflectance for shock detection. This study was performed to pick up best dynamic wavelength range sets to detect fine vessel density pattern modulation for shock detection.

Validated UV‐Spectrophotometric Methods for Determination of Gemifloxacin Mesylate in Pharmaceutical Tablet Dosage Forms

Two simple, economic and accurate UV spectrophotometric methods have been developed for determination of gemifloxacin mesylate in pharmaceutical tablet formulation. The first UV‐spectrophotometric method depends upon the measurement of absorption at the wavelength 263.8 nm. In second area under curve method the wavelength range for detection was selected from 268.5‐258.5 nm. Beer’s law was obeyed in the range of 2 to 12 μgmL-1 for both the methods. The proposed methods was validated statistically and applied successfully to determination of gemifloxacin mesylate in pharmaceutical formulation.

Strain and Absorption Coefficient of Finite Ge Structures on Si

A finite structure of Ge under tensile stress was investigated theoretically and experimentally focusing on applications to near-infrared photodetectors on (001) Si. We calculated the direct band gap energy of strained Ge between the conduction band and the heavy/light-hole valence band via the k·p theory. Three types of in-plane stresses were considered, i.e., a biaxial stress and uniaxial stresses along the <100> and <110> directions. On the basis of the direct band gap change, absorption spectra due to the direct transitions were calculated. The calculated absorption spectra showed that the biaxial stress is more effective than the uniaxial stresses in terms of the absorption red-shift, which increases the detection wavelength range. Localized strain measurements revealed that a selectively grown Ge mesa on (001) Si maintains a biaxial strain caused by the thermal expansion mismatch when its width is larger than 1 µm. A uniaxial stress probably develops owing to the strain relaxation in a finite Ge structure smaller than 1 µm. The application of Ge finite structures to waveguide photodetectors is discussed.

Femtosecond and nanosecond laser-induced breakdown spectroscopy of trinitrotoluene

Femtosecond and nanosecond laser-induced breakdown spectroscopy (LIBS) were used to study trinitrotoluene (TNT) deposited on aluminum substrates. Over the detection wavelength range of 200-785 nm, we have observed emission from CN and C(2) molecules as the marker for the explosive with femtosecond LIBS. In contrast, the signal for nanosecond LIBS of TNT is dominated by emission from the elemental constituents of the explosive. Aluminum emission lines from the substrate are also observed with both femtosecond and nanosecond excitation and indicate the role played by the substrate in the interaction.