Thermal IR Detector Research Articles

TRIGLYCINE SULPHATE DYNAMICS OF DOMAINS IN RELATION WITH TEMPERATURE AND BIAS FIELD

Triglycine sulphate crystal (TGS) is a hybrid organic-inorganic ferroelectric crystal with a large electronic band-gap, transparent in visible spectra. It has large applications in electronics, as thermal IR detector. Pure and doped TGS crystals of 3-5 cm linear dimensions were grown at constant temperature in the paraelectric phase (52 oC), by slow solvent evaporation. Pure TGS samples show non-reproducible values of permittivity and losses in the ferroelectric phase after the “excursion” in the paraelectric phase. Walking up and down the crystal temperature, using a special program, the permitivity and losses were automatically recorded and analyzed. There is a continuous decrease of permittivity towards an equilibrium value during a long period of time. Previous AFM measurements from the literature have revealed peculiar aspects of domain dynamics. The relaxation process of permittivity was considered according to the equation er = A - B exp(-t/t). However, surprisingly, there is not a unique relaxation time t. For the first 500 sec (or so), the relaxation time is t » 7 minutes, while between the next time decades 1.000 - 10.000 - 100.000 sec, it is approximately 1 hour and 8 h respectively. The process is related with the ferroelectric domain’s dynamics, which are more or less strongly pined by dislocations or some other lattice defects.

An investigation of the generalized model of pyroelectric thermal IR detectors

In our work, a compact model of an infrared radiation detector based on a LiTaO3 pyroelectric material (lithium tantalate) is presented. Based on the developed model, the time-dependent characteristics of the pyroelectric current, voltage and the surface temperature of such detector were calculated. The obtained results can be used in the development of detectors of thermal images of objects operating in the wavelength range from 3 to 15 μm.

섬광의 적외선 특성 연구

To effectively utilize a flash and predict its effects on an infrared device, it is essential to know the infrared characteristics of the flash source. In this paper, a study of the IR characteristics of flash light sources is carried out. The IR characteristics of three flash sources, of which two are combustive and the other is explosive, are measured with an IR characteristic measurement system over the middle- and long-wavelength infrared ranges. From the measurements, the radiances over the two IR ranges and the radiative temperatures of the flashes are extracted. The IR radiance of flash A is found to be the strongest among the three, followed by those of sources C and B. It is also shown that the IR radiance of flash A is about 10 times stronger than that of flash B, even though these two sources are the same type of flash with the same powder. This means that the IR radiance intensity of a combustive flash source depends only on the amount of powder, not on the characteristics of the powder. From the measured radiance over MWIR and LWIR ranges for each flashes, the radiative temperatures of the flashes are extracted by fitting the measured data to blackbody radiance. The best-fit radiative temperatures (equivalent to black-body temperatures) of the three flash sources A, B, and C are 3300, 1120, and 1640 K respectively. From the radiance measurements and radiative temperatures of the three flash sources, it is shown that a combustive source radiates more IR energy than an explosive one; this mean, in turn, that the effects of a combustive flash on an IR device are more profound than those of an explosive flash source. The measured IR radiances and radiative temperatures of the flash sources in this study can be used to estimate the effects of flashes on various IR devices, and play a critical role for the modeling and simulation of the effects of a flash source on various IR devices.Keywords: Flash lights, Spectral radiance, Radiative temperature, Pyroelectric IR detectorOCIS codes: (040.3060) Infrared; (200.4560) Optical data processing, (350.5610) Radiation, (040.6808) Thermal (uncooled) IR detectors, arrays and imaging

Miniaturized integrated evanescent field IR-absorption sensor: Design and experimental verification with deteriorated lubrication oil

In industry, a vast variety of processes can be optimized by means of online measurement of chemical properties of fluids in order to reduce costs of maintenance or increase productivity as well as production quality. Since the absorption measurement in the mid-IR-region is a powerful method to determine the chemical composition of fluids, we propose a fully integrated absorption sensor based on IR-absorption in the evanescent field region of an integrated mono-mode waveguide utilizing thermally generated and detected IR-radiation. For the coupling, two grating couplers are employed, which couple broadband thermal IR-radiation into the waveguide and the attenuated IR-radiation towards a thermal IR-detector, respectively. To achieve a spectroscopic measurement, we utilize the dispersive feature of the grating coupler, which couples the IR-beams out of the waveguide at angles depending on the frequency. We report on the design of the fully integrated infrared absorption sensor, which is capable to determine chemical properties of, e.g., lubrication oil by investigating infrared absorption. Beside the theory related to an optimum design of the mono-mode waveguide, we discuss the applicability of the proposed concept to the monitoring of deterioration of lubrication oil.

Pyroelectric and dielectric bolometer properties of Sr modified BaTiO3 ceramics

The pyroelectric and dielectric bolometer properties of Sr modified BaTiO3 ceramics were investigated for thermal IR detector applications. The (Ba1−x, Srx)TiO3 solid solution ceramics have been prepared by adding 10–40 at % SrTiO3 to BaTiO3 and with different sintering conditions and under dc fields. The relationships of processing parameters, microstructures, dielectric/pyroelectric properties and dc fields are discussed. And the “figures of merit” are compared between pyroelectric-type and dielectric bolometer-type IR sensors based on the experimental results.

Controlled double-jet precipitation of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates

The synthesis of uniform colloidal crystalline particles of Zr- and Sr-doped barium titanates at a low temperature of 85 °C by the controlled double-jet precipitation (CDJP) technique is described. The stoichiometry of the powders can be precisely controlled by adjusting the compositions of the starting reactant solutions. Barium titanate with 20% Zr substitution, sintered at 1275 °C, satisfied the requirements for the Y5V multilayer capacitors application. The grain sizes are uniform and small, ranging from 1 to 3 μm. Solids with an extremely sharp change in the dielectric constant as a function of temperature, which are suitable for thermal IR detectors application, can be obtained when both Sr and Zr are incorporated as dopants.

Material characterization with a simple laser scanning microscope

<p>The design of a computer-controlled laser scanning microscope is described. It is capable of inspecting a 1 mm × 1 mm area in less than 1 s with an optical resolution of 2 µm. Three applications of the laser scanning microscope are presented: the observation of the ferroelectric-domain structure of sodium nitrite layers, the observation of the spatial distribution of the photocurrent in polycrystalline solar cells, and the observation of the lateral distribution of thermoelectric currents in a thermal IR detector for the determination of the thermal properties of its absorber foil.</p> <p>PACS: 0760P, 7240, 7780D.</p>

Application of interferometric enhancement to self-absorbing thin film thermal IR detectors

Uncooled thermal IR detectors require a suitable absorbing mechanism in order to achieve efficient radiation capture. For bulk detector materials such as ferroelectric ceramics this mechanism may be a broad-band absorber in the form of a metallic black layer, or a thin-film optical interference filter tuned for maximum absorption at the desired wavelength, deposited onto the surface of the detector. A thin metal film having a sheet resistance of 189 Ω per square can absorb 50% of incident radiation, and is employed in the metal film resistance bolometer detector and Golay cell. In this paper an interferometric technique for thin film thermal detectors is described, whereby a thermally sensitive material in the form of a semiconductor or dielectric layer becomes an integral component of a 3-layer absorber stack. The theory of this absorber structure is reviewed and compared with experimental data. It is shown that an effective absorption of 90% can be achieved over the waveband 8–13μm for a blackbody radiation source at 300 K temperature.

An optically coupled thermal imager

A novel scheme for thermal imaging is proposed, using a thermal IR detector whose temperature is sensed using a thermo-optic property, and the image is read electronically using a conventional television chip. As with other thermal IR detectors, the image is mechanically chopped, and the difference between fields calculated electronically. The particular scheme discussed uses a liquid crystal as the thermo-optic medium. Calculations of signal and measurements of noise are presented to deduce what the performance of such a thermal imager would be.