Vered Scharf

Four-band fiber-optic radiometry for determining the “true” temperature of gray bodies

Standard radiometric thermometry is based on measuring the infrared radiation emitted from a body in one broad spectral band. However, the “true” temperature, Tbody, can not be determined accurately if the emissivity, e, and the ambient temperature, Troom, are not known or change during the measurement. We constructed a “four band” fiber-optic radiometer for measurement of Tbody near room temperature, where measurements of the emitted radiation were carried out in four spectral bands. The radiometer was analyzed theoretically, and was then calibrated and tested on black and gray bodies. Good correlation between theory and experiment was achieved.

TEMPERATURE MEASUREMENTS USING PULSED PHOTOTHERMAL RADIOMETRY AND SILVER HALIDE INFRARED OPTICAL FIBERS

A novel technique for measuring temperature, based on pulsed photothermal radiometry and analysis of the spectral and temperature dependence of Planck’s blackbody equation, is described. In this technique a body is irradiated by a laser pulse and its temperature inferred from the time dependence of the emitted infrared signal curve. This technique was used for near ambient temperature measurements using a CO2 laser, an infrared detector, and infrared transmitting silver halide optical fibers. The experimental results are consistent with theory. This technique is independent of changes in emissivity or geometric factors and it will be useful for accurate and fast noncontact temperature measurements.

Single-mode mid-infrared silver halide planar waveguides

A single-mode silver halide symmetric step-index planar waveguide for 10.6 microm is described. We fabricate the waveguide from extruded multimode silver halide fiber by pressing the fiber between metal plates while heating. The device is therefore automatically pigtailed to a fiber, which could ease the difficulties of coupling light into it. We achieved single-mode confinement by suitably adjusting the refractive index of the core and the cladding and by reducing the core thickness to 30 microm. The output radiation from the planar waveguide was measured to confirm single-mode confinement. Silver halide single-mode waveguides for the mid-infrared can be used to enhance sensitivity in fiber-optic evanescent-wave infrared spectroscopy measurements or for the development of mid-infrared single-mode lasers and interferometers.

Fiber-optic infrared radiometer for accurate temperature measurements

A fiber-optic radiometer is developed for accurate noncontact temperature measurements. Of compact and novel design, it is based on replacing the usual chopper with a simple shutter. The radiometer operates in a spectral range of 5-20 microm and uses a silver-halide IR-transmitting optical fiber. The radiometer has a temperature resolution of 0.1 degrees C, a time response of 200 ms, and a spatial resolution of approximately 1 mm. Theory, simulation, radiometer design and construction, and examples of experimental measurements are shown. The novel radiometer can be used in diverse applications in science, medicine, and industry.

FIBER-OPTIC PULSED PHOTOTHERMAL RADIOMETRY FOR FAST SURFACE-TEMPERATURE MEASUREMENTS

Temperature measurement based on pulsed photothermal radiometry is described. In this technique a body is irradiated by a laser pulse and its temperature is inferred from the shape of the emitted photothermal-signal curve. A prototypical system based on a pulsed CO(2) laser, an IR detector, and IR-transmitting silver halide optical fibers was constructed and used to evaluate the feasibility of this technique. An important feature of the technique is that changes in sample emissivity or geometric factors do not introduce errors in the temperature determination. Theory, simulation, and experimental results are given and discussed.

Four-band fiber optic radiometry for true temperature measurements during an exothermal process

Four-band fiber optic radiometry is a method for noncontact temperature measurement of a sample with an unknown emissivity, assuming the emissivity is uniform in all four spectral bands. The method corrects the temperature calculation automatically, according to the emissivity calculation, during continuous measurements on the sample. This method may be particularly useful in determining the temperature of a material that undergoes a transition in which both temperature and emissivity change, such as phase transitions or exothermic processes. We report a radiometric four-band measurement in the mid-infrared region, for determining the true temperature of an epoxy resin during its curing.

Improved tympanic thermometer based on a fiber optic infrared radiometer and an otoscope and its use as a new diagnostic tool for acute otitis media

Clinical diagnosis of acute otitis media (AOM) in children is not easy. It was assumed that there is a difference ΔT between the Tympanic Membrane (TM) temperatures in the two ears in unilateral AOM and that an accurate measurement of ΔT may improve the diagnosis accuracy. An IR transmitting fiber, made of AgClBr, was coupled into a hand held otoscope and was used for the non-contact (radiometric) measurements of TT, the TM temperature. Experiments were carried out, first, on a laboratory model that simulated the human ear, including an artificial tympanic membrane and an artificial ear canal. Measurements carried out using commercially available tympanic thermometers shown that the temperature Tc of the ear canal affected the results. Tc did not affect the fiberoptic radiometer, and this device accurately measured the true temperature, TT of the tympanic membrane. A prospective blinded sampling of the TM temperature was then performed on 48 children with suspected AOM. The mean temperature difference between the ears, for children with unilateral AOM was ΔT = (0.68 ± 0.27)°C. For children with bilateral AOM it was ΔT = (0.14±0.10)°C (p<0.001). It was demonstrated that afor unilateral AOM the difference ΔT was proportional to the systemic temperature. In conclusion, the fiberoptic interferometric measurements of the TM can be a useful non-invasive diagnostic tool for AOM, when combined with other data.

Applications of fiber optic pulsed photothermal radiometry

Pulsed photothermal radiometry is a nondestructive technique for measurements of surface and subsurface thermal parameters of a wide variety of materials. A fiber optic pulsed photothermal radiometric system is constructed and its feasibility is demonstrated. The radiometric system includes a pulsed CO2 laser, an IR detector, and two IR transmitting silver halide optical fibers for delivering IR radiation to and from the sample. A weak laser pulse, absorbed by the sample, initially heats the sample surface. The time evolution of the transient emitted IR radiation is measured and analyzed. The results establish the feasibility of using the fiber optic pulsed photothermal radiometric system to measure coating thickness, to detect flaws, and to diagnose thermal damage in tissue. This fiber optic method would be useful for industrial and medical applications.

Medical applications of fiber optic pulsed photothermal radiometry

A fiber optic pulsed photothermal radiometric prototype system was constructed. The radiometric system includes a carbon dioxide laser, an infrared detector and two infrared transmitting silver-halide optical fibers for radiation delivery to and from the target. We used the pulsed photothermal radiometric system to heat up a sample by a short duration laser pulse and measured the decay time of the photothermal infrared signal emitted from a sample due to the absorption of the laser pulse in the sample. The fiber optic radiometric system was used to establish the feasibility of using the pulsed photothermal radiometric method for diagnosis of thermal damage in tissue.