Cooled Photon Detector Research Articles

Advancements in Uncooled Bolometer Technology: Shortwave Infrared Detection via CuFeSe2 Nanocrystal Colloidal Thin Films

Microbolometers have emerged as a cost‐effective alternative to cooled infrared photon detectors, albeit with certain trade‐offs in terms of responsivity (), detectivity (), and response time (). The research in this field is driven by the potential applications in night vision devices, military surveillance, and autonomous vehicles, leading to a growing interest in exploring new materials to bridge the performance gap between cooled photon detectors and uncooled bolometers. This study focuses on the optoelectronic and bolometric characteristics of nanocrystals (NCs) in a colloidal solution. These NCs exhibit a significant change in resistivity (ρ) when subjected to temperature variations ranging from 170 to 400 K. Specifically, the temperature coefficient of resistance (TCR), α, is 1.9% per Kelvin for a room temperature resistivity of 505 Ω cm. Furthermore, the responsivity of NCs is reported to be 0.101 A W−1, and the Hall mobility of the colloidal solution is determined as . Finally, a comprehensive comparison is conducted between the performance metrics of established bolometer materials, such as VOx and a‐Si, and those of colloidal NCs. Based on the results, colloidal NCs are a promising option for future bolometer technology.

Lock-in thermography using miniature infra-red cameras and integrated actuators for defect identification in composite materials

A novel approach for thermographic Non-Destructive Evaluation (NDE) of laminated polymer composite structures is presented. The technique is based on Lock-In Thermography (LIT), which traditionally uses an external heat source. Here a new means of internal heating, via a lightweight embedded actuator capable of providing highly repeatable and uniform heating is presented. The equipment cost, complexity and hence size is reduced by removing the need for high power external thermal excitation. Instead, the necessary temperature modulation of the internal actuator is achieved with a compact and low-cost Arduino controlled circuit. The size and cost of the equipment is further reduced by demonstrating that a miniature printed circuit board mounted thermal core type micro-bolometer can be used effectively for LIT. The performance of the thermal core is quantitatively compared with the more expensive and bulky traditional infra-red cameras. It is shown that the thermal core can detect defects with similar overall performance as a cooled photon detector and an uncooled micro-bolometer. The low-cost, compact nature and small mass of the thermal core offers great potential in thermographic inspection opening the possibility of deploying devices permanently on structures in conjunction with the embedded actuators for in-situ monitoring in the service environment.

Evaluating the spectroradiometric performance of an uncooled midwave infrared hyperspectral interferometer using a microbolometer array detector

Improved technology and emerging interferometric techniques have allowed the use of uncooled microbolometers in the long-wave infrared (LWIR; 8 to 14 μm) for hyperspectral imaging (HSI). The midwave infrared (MWIR; 3 to 5 μm) presents several advantages with respect to the LWIR for Earth and planetary science. For example, important atmospheric trace gases on Earth such as CO2 and CH4 are not masked by other atmospheric constituents in the MWIR. However, HSI in the MWIR is more challenging at ambient Earth temperatures because less radiance is available to measure. We describe how hyperspectral images in the MWIR can be acquired with an instrument using an uncooled microbolometer married to a Sagnac interferometer. Standard characterization tests are used to benchmark the performance of the microbolometer instrument with a cryogenically cooled photon detector with the same optical design. At a spectral resolution of 100 cm − 1 (17 bands between 3 and 5 μm), we measured a signal-to-noise ratio (SNR) of 100 at 30°C with the microbolometer instrument and an SNR of 50 at 50 cm − 1 (33 bands). Results from this work show that coupling microbolometers with interferometers allows for quality measurements with adequate SNR for high-temperature science applications.

An investigation of noise performance in optical lock-in thermography

An investigation into the noise performance of optical lock-in thermography (OLT) is described. The study aims to clarify the influence of infrared detector type and key inspection parameters such as illumination strength and lock-in duration on the quality of OLT amplitude and phase imagery. The study compares the performance of a state-of-the-art cooled photon detector with several lower-cost microbolometers. The results reveal a significant noise performance advantage to the photon detector. Under certain inspection regimes the advantage with respect to phase image quality is disproportionately high relative to detector sensitivities. This is shown to result from an explicit dependence in the phase signal variance on the ratio between the signal amplitude and the detector sensitivity. While this finding supports the preferred use of photon detectors for OLT inspections, it does not exclude microbolometers from a useful role. In cases where the significantly lower capital cost and improved practicality of microbolometers provide an advantage it is shown that performance shortfalls can be overcome with a relatively small factorial increase in optical illumination intensity.

Infra-red techniques for thermomechanical characterisation of materials and structures

The application of infra-red (IR) imaging techniques to the mechanics of materials and structures has grown considerably over past decades. The expansion is marked by the increased spatial and temporal resolution of the infra-red detectors, faster processing times and much greater temperature resolution. The improved sensitivity and more reliable temperature calibrations of the devices have meant that more accurate data can be obtained than were previously available. The purpose of the special issue is to bring together novel work on all aspects of thermomechanics with the focus on the application of IR imaging approaches. The main thrust is on the analysis of thermomechanical behavior of materials and using this behavior to elicit information on material characteristics, stress patterns, deformation mechanisms and failure modes. Of particular interest are strong thermomechanical couplings that result in complex, often nonlinear behaviour such as visco(thermos)elasticity, anisotropic heat diffusion mechanisms, strain and damage localisation and solid state phase changes. An objective is to share experience on how datarich experimental mechanics can help scientists and engineers to better understand and simulate the behavior of materials and structures. An important aspect is the use of other imaging techniques in conjunction with IR imaging, demonstrating how imaging is the route to a full thermomechanical characterization of both material behaviour and structural response. The special issue starts with a paper that uses a technique known as thermoelastic stress analysis (TSA), which exploits the thermoelastic coupling that exists in materials under load. The thermoelastic coupling was first observed in the 1830s and the mathematical formulation of the thermoelastic effect was derived in the 1850s by Lord Kelvin. Essentially when a material experiences a strain change in the elastic range a small temperature change occurs that can be related to the trace of the stress tensor. In the 1980s single cell scanning IR detection systems were developed to obtain the ‘thermoelastic response’, essentially the output from system was a digital level. The first commercially available system was called SPATE ‘Stress Pattern Analysis by Thermal Emissions’, which was developed in the UK by and organization called SIRA ‘Scientific Instruments Research Associations. The review by Lin, Saman, Khaja, and Rowlands, covers developments from the early days of SPATE to the present, where array based calibrated detection systems are used. One clear shortcoming of TSA is that can only deliver the sum of the principal stresses. The hybrid TSA approach described provides a route for determining the individual stress components by combining the measured thermal data with Airy stress functions. In developing the formulation for TSA it is assumed that the small temperature change occurs isentropically. This is achieved by cyclically loading the specimen in the elastic range (reversible) and at such a rate that the thermal diffusion length is small (adiabatic). A key component of TSA is the use of a lock-in algorithm, which uses a reference signal (usually from a test machine signal generator), to process the data. The IR detection systems used for TSA are costly as they are cryogenically cooled photon detectors with fast framing rates that enable sufficient data to be captured to reconstruct the cyclic thermal response with great accuracy. The second paper in the issue is by Pitarresi and proposes an off-line lock-in correlation algorithm enabling TSA and lock-in thermography A. Chrysochoos University of Montpellier, Montpellier, France

Thermoelastic stress analysis with a compact low-cost microbolometer system

This article describes the development and validation of a novel thermoelastic stress analysis (TSA) system based on a low-cost microbolometer device. The use of a microbolometer for a highly synchronous and delicate temperature measurement breaks a longstanding and exclusive reliance on high performance, cooled photon detectors for thermoelastic applications. It is shown that despite markedly inferior noise equivalent temperature detectivity and dynamic response specifications, microbolometers are capable of achieving comparable levels of stress measurement performance. The practical implications for experimental stress analysis are significant. Microbolometers are relatively low in capital cost, small in size, have good tolerance to shock and vibration and consume less power than their photon counterparts, attributes that confer enormous practical advantages. It is argued that the emergence of TSA systems that are more affordable and better suited to in-service application could help to promote a much broader use of this powerful technique in applications across the life cycle of high value civil, maritime and aerospace assets, from the validation of finite element modelling for design to in-service structural integrity assessment. A full-scale fatigue test of a flight-critical aircraft structural component is employed as a case study to demonstrate important aspects of the capability. Future directions in the development and application of low-cost miniaturised systems are also discussed.

Low temperature growth and laser-induced phase transformation of perovskite oxide films for uncooled IR detector applications

AbstractPyroelectric infrared (IR) detectors based on perovskite oxides are of interest in part because of their lack of need for cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. We are investigating two methods for low-cost growth of perovskite oxide thin films, namely, a bio-inspired, low-temperature synthesis method and a modified industry-standard metalorganic solution deposition (MOSD) method. Subsequent to film synthesis, we utilize direct-write laser phase conversion and micro-electro-mechanical systems (MEMS) fabrication for development of an uncooled IR focal plane array (FPA). Film growth, crystallization and MEMS processes are compatible with monolithic integration of the detector pixels directly onto Si readout integrated circuits (ROICs).

Characterization of an uncooled infrared thermographic system suitable for the solution of the 2-D inverse heat conduction problem

An experimental analysis and a data processing procedure, aimed to the characterization of an uncooled microbolometric infrared camera, have been carried out. The instrument performance test is addressed to the application of infrared thermography to the parameter estimation problem based on the solution of the inverse heat conduction problem. With this regard, a new figure of merit, which enables to estimate the local noise level in the thermal image, has been suggested. This parameter may be used to characterize the performance of IR and also of other thermographic devices, for applications common to a wide category of heat transfer measurements in which the spatial first or second derivatives of a thermal two-dimensional signal are needed. The instrument has been compared, in terms of local noise level, to an IR camera based on the cooled photon detector array technology.

Pyroelectric ceramics and devices for thermal infra-red detection and imaging

Abstract Pyroelectric detectors offer major advantages in terms of cost and ease-of-operation over cooled photon detectors of long wavelength infra-red radiation. This paper reviews the requirements of a pyroelectric material to maximise its effectiveness in different types of detector and compares the properties of ferroelectric ceramics with those of different single crystal materials. The control of the electrical properties of modified lead zirconate by doping is discussed. The concept of using a ferroelectric close to Tc under an applied electric bias as a dielectric bolometer is introduced and the properties of three different ferroelectric ceramics, barium strontium titanate, lanthanum-doped lead magnesium niobate and lead scandium tantalate are compared. It is shown that figures-of-merit can be achieved in lead scandium tantalate under DC bias which are up to three times greater than more conventional pyroelectric materials. Finally, the use of pyroelectric ceramics is illustrated by reference to ...

Liquid helium cooled photon detectors: Cause, prevention and remedy of contamination

Serious performance deterioration in commercial liquid helium cooled photon detectors was investigated. It was traced to electrical interference caused by atmospheric water deposits on the detector chip. It is shown that commonly applied design features favor such accumulations. Practical prevention and remedy measures are described.