Real-time imaging using a 2.8 THz quantum cascade laser and uncooled infrared microbolometer camera

Real-time imaging in the terahertz (THz) spectral range was achieved using a milliwatt-scale, 2.8 THz quantum cascade laser and an uncooled, 160 x 120 pixel microbolometer camera modified with Picarin optics. Noise equivalent temperature difference of the camera in the 1-5 THz frequency range was estimated to be at least 3 K, confirming the need for external THz illumination when imaging in this frequency regime. Despite the appearance of fringe patterns produced by multiple diffraction effects, single-frame and extended video imaging of obscured objects show high-contrast differentiation between metallic and plastic materials, supporting the viability of this imaging approach for use in future security screening applications.     

Probability analysis of position errors using uncooled IR stereo camera

This paper analyzes the random phenomenon of 3D positions when tracking moving objects using the infrared (IR) stereo camera, and proposes a probability model of 3D positions. The proposed probability model integrates two random error phenomena. One is the pixel quantization error which is caused by discrete sampling pixels in estimating disparity values of stereo camera. The other is the timing jitter which results from the irregular acquisition-timing in the uncooled IR cameras. This paper derives a probability distribution function by combining jitter model with pixel quantization error. To verify the proposed probability function of 3D positions, the experiments on tracking fast moving objects are performed using IR stereo camera system. The 3D depths of moving object are estimated by stereo matching, and be compared with the ground truth obtained by laser scanner system. According to the experiments, the 3D depths of moving object are estimated within the statistically reliable range which is well derived by the proposed probability distribution. It is expected that the proposed probability model of 3D positions can be applied to various IR stereo camera systems that deal with fast moving objects.     

Application of longitudinal multimode laser coherence properties to increase the holographic depth of field

It has been shown that the temporal coherence of a non-mode-locked laser is periodic in 2L/c. It has also been demonstrated that the limitations imposed on the depth of field in holography by the laser coherence properties may easily be overcome by illuminating the object with multiple beams. In such a system each object beam should travel the same distance to the holographic plate as the reference beam, or a multiple of 2L farther. For large objects (which would have large depths of field) multiple beam illumination is necessary anyway, to ensure uniform illumination of the object. In fact the limiting factor with regard to the size of an object and the depth of field should be the laser's power and not its coherence length. An advantage in this method of overcoming conventional limitations is that there is no reduction in the laser's output power as is involved in some other methods of coherence length improvement.     

高精度非致冷长波红外热像仪的辐射标定

为使非致冷长波红外热像仪在不同温度下保持较高的测温精度,建立了考虑探测器工作温度效应的非致冷长波红外热像仪的辐射标定模型。对非致冷长波红外热像仪进行辐射标定实验,在不同黑体温度和不同亮度增益值条件下,获得了16组图像灰度与探测器工作温度之间的函数关系,建立了目标温度的数学计算模型,并对定标结果进行了实验验证。结果表明：在25～40℃,探测器的工作温度效应可做线性化处理,且与目标温度无关。通过设定合适的亮度增益值可使红外热像仪的测温误差〈0.5℃,极大地提高了非致冷长波红外热像仪在不同温度环境下的测温精度。     

Validation of hard tooth tissue thermal diffusivity measurements applying an infrared camera

The problem concerns investigations of thermophysical properties of small biological specimens. Results of experimental verification of some thermal diffusivity data of hard tooth tissue are presented and discussed. The measurements have been performed on two sliced tooth specimens of different thicknesses. The temperature changes of one flat surface have been recorded applying an infrared camera while the opposite surface has been monotonously heated. The results of measurements have been analysed in order to identify the differences related to variations in thermal properties of hard tooth tissues. Distinct differences between heated enamel, crown dentine and root dentine structures have been revealed. Lack of analytical heat transfer formulae restricted the analysis to qualitative aspects of the problem. Conclusions concerning possible quantitative calculations and the methodology of such an analysis have been formulated.     

显微镜景深拓展技术研究

随着生命科学需求的日益迫切,显微镜的景深拓展成为显微领域的一个重要发展方向,为了更好地了解、研究显微景深问题,对景深拓展技术进行研究与总结。以显微景深的大幅提升为出发点,就光学切片扫描、空间光调制、波前编码及光场显微4个方面进行了全面的综合性论述。对这些技术的原理、方式及拓展水平进行了阐述,并就其技术缺陷、发展方向进行了归纳总结。随着技术水平的提高,显微景深较传统显微镜可提高1~2个数量级。     

Passive imaging of wind surface flow using an infrared camera

We present a method for passive imaging of wind motion against surfaces in a scene using an infrared video camera. Because the method does not require the introduction of contrast agents for visualization, it is possible to obtain real-time surface flow measurements across large areas and in natural outdoor conditions, without prior preparation of surfaces. We show that this method can be used not just for obtaining single snapshot images but also for real-time flow video, and demonstrate that it is possible to measure under a wide range of conditions.     

非制冷热像仪内部温升对测温精度的影响修正

随着非制冷型热像仪工作时间的增长,其内部器件、机械结构所积累的热量越来越多,其温升所导致的热辐射势必会对热像仪的测温精度产生严重影响。因此,要实现热像仪的准确测温,必须对其内部的各温升影响因素进行相应的修正。本文通过对影响测温精度的镜筒辐射温度、探测器靶面温度以及热像仪工作累积时间三个因素进行评估和建模,并对其相互关系进行评价,根据数据模型对热像仪辐射测温值进行修正。结果表明,在实验室条件下,经过修正,非制冷型红外热像仪测温精度可控制在±1℃以内,其稳定性可控制在±0.5℃以内。修正后的温度结果基本不受内部温升的影响,有效的提高了非制冷测温型热像仪的稳定性、可重复性以及测温精度。     

一种非致冷红外探测器真空封装的研究

介绍了一种非致冷红外探测器杜瓦组件的封装设计;对探测器件在真空封装过程中的关键工艺技术进行了比较深入的分析;阐述了影响组件真空寿命及可靠性的因素以及解决措施。     

Study of reactive film heterostructures with several interfaces using the thermal desorption spectroscopy

The thermal desorption spectroscopy is used to study the interaction of the chemisorbed oxygen and carbon monoxide molecules with the nanometer-thick ytterbium films that are formed on the surfaces of silicon substrates at room temperature. In accordance with the results at a temperature of 300 K, the O₂ and CO molecules are chemisorbed on the surface of a metal film and do not exhibit dissociation to atoms under such conditions. The molecular dissociation is observed at higher temperatures. The liberated oxygen is involved in reactions with ytterbium and silicon that lead to the formation of complicated silicates, which dissociate at even higher temperatures.     

Three-dimensional tracking of multiple particles in large depth of field using dual-objective bifocal plane imaging

Tracking moving particles in cells by single particle tracking is an important optical approach widely used in biological research. In order to track multiple particles within a whole cell simultaneously, a parallel tracking approach with large depth of field was put forward. It was based on distorted grating and dual-objective bifocal imaging, making use of the distorted grating to expand the depth of field, dual-objective to gather as many photons as possible, and bifocal plane imaging to realize three-dimensional localization. Simulation of parallel tracking of two particles moving along the z axis demonstrated that even when the two are axially separated by10 μm, they can both be localized simultaneously with transversal precision better than 5 nm and axial precision better than 20 nm.     

Influence of the errors in an infrared camera on the estimation of thermal conductivity and thermal capacity of a gypsum plaster sample

The present work studies how the errors of infrared cameras propagate during the estimation of thermophysical parameters. The errors in the camera were determined experimentally, and varied with both position and temperature. The thermal conductivity and thermal capacity were estimated by comparing the experimental and computational temperature evolution as a gypsum plaster sample was left to cool naturally in the air. For each study, one of the parameters was varied until the simulated temperature curve was adjusted to the experimental curve using the Levenberg–Marquardt Algorithm. We concluded that for the thermal capacity, there is a strong correlation between the error in the camera and the error of the parameter, which was not so clear in the case of the thermal conductivity. Another important conclusion is that the variation of the thermal conductivity presents a better adjustment of the curves even though the error in the estimated parameter was higher, indicating that reasonable results in the minimization process do not necessarily assure a good estimation. As a final conclusion, we stress the importance of using calibrated cameras, since in the extreme cases a mean deviation of 1.46 °C in the camera represented an error of 15% on the thermal capacity and a mean deviation of 0.81 °C in the camera represented an error of 25% on the thermal conductivity.     

Linear Tikhonov regularization against an edge field: an improved reconstruction algorithm in photothermal depth profilometry

This work introduces the concept of edge-field regularization into photothermal inverse depth profilometry problems. An edge field allows prior information concerning the depth location of material interfaces in a sample to be introduced into a Tikhonov regularization problem by a simple binary encoding. The edge-field regularization allows Nth-order Tikhonov stabilization constraints to be applied independently to multiple zones or segments of a depth profile between defined interface positions. This allows the reconstruction of continuous depth-profile information within known layers, without the globally imposed smoothing and edge oscillations of the classical regularization methods. This method successfully reconstructs both the amplitude of the interface discontinuities and the photothermal depth-contrast variations within the bounding edges, to a resolution limited by the resolving kernel for the underlying Nth-order Tikhonov constraint. The edge-field regularization dramatically reduces the errors associated with profiling photothermal contrast in bounded zones that are depth-displaced in the sample. Received: 19 September 2002 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-514/398-3797, E-mail: joan.power@mcgill.ca     

Determination of thermal wave reflection coefficient to better estimate defect depth using pulsed thermography

Thermography is a promising method for detecting subsurface defects, but accurate measurement of defect depth is still a big challenge because thermographic signals are typically corrupted by imaging noise and affected by 3D heat conduction. Existing methods based on numerical models are susceptible to signal noise and methods based on analytical models require rigorous assumptions that usually cannot be satisfied in practical applications. This paper presents a new method to improve the measurement accuracy of subsurface defect depth through determining the thermal wave reflection coefficient directly from observed data that is usually assumed to be pre-known. This target is achieved through introducing a new heat transfer model that includes multiple physical parameters to better describe the observed thermal behaviour in pulsed thermographic inspection. Numerical simulations are used to evaluate the performance of the proposed method against four selected state-of-the-art methods. Results show that the accuracy of depth measurement has been improved up to 10% when noise level is high and thermal wave reflection coefficients is low. The feasibility of the proposed method in real data is also validated through a case study on characterising flat-bottom holes in carbon fibre reinforced polymer (CFRP) laminates which has a wide application in various sectors of industry.     

空间相机内部隔热板的性能优化方法

针对空间相机内部隔热板起到隔离入射太阳光影响相机内部光学结构的作用,其厚度较小,一般不采用额外的散热措施,入射太阳光能量作用其上会引起较大的温升,温度增加的不均匀会增加相机内部的红外杂散辐射,提出一套完整的隔热板厚度优化方法。在保证隔热板体积不变的前提下,利用仿生优化原理,根据隔热板各处的温度梯度差异调整隔热板的厚度。对优化出的隔热板厚度函数进行高斯滤波处理,使隔热板的厚度变化均匀,便于加工。通过对比优化前后的温度场与红外场,发现优化后最高温度降低了3.8℃,其3 m ~5 m,8 m~12 m波段的红外辐出度降低了15%,该优化方法可以作为内部杂散辐射的抑制手段与其他方法一起实施。     

Extension of depth of field using amplitude and phase modulation of the pupil function

We analyze the extension of depth of field using both amplitude and phase modulation of the pupil function. In particular, we discuss the advantages and disadvantages of each approach and establish the range of applicability of each method based on the range of spatial frequencies of interest in the imaging system. To the best of our knowledge, this is the first such report on the range of applicability of amplitude and phase modulation to extend the depth of field.     

Wave propagation in an infinite piezoelectric crystal under a thermal field

The paper deals with the propagation of vibrational waves in an infinite piezoelectric crystal plate belonging toC ₂ (monoclinic system) when some sort of heat flow is maintained. The dispersion equations have been determined under a thermal field and also in the case when the heat flow is absent, both for small and large values of the frequency.The authors express their sincere thanks for the helpful criticism of the referee in improving the paper.