Albert Zur

Fibers for low-temperature radiometric measurements.

Theoretical calculations are presented for the performance of a fiber-optic radiometer which makes use of infrared transmitting fibers to measure low temperatures (near room temperature). We calculate the radiometer spatial resolution, the dependence of the radiometer signal on the surface temperature, and the minimum resolvable temperature difference (MRDeltaAT) of the radiometer. The performance of the fiber-optic radiometer is compared with a conventional optical (thin lens) radiometer.

Research and development on silver halide fibers at Tel Aviv University

This paper presents a survey of current work at Tel Aviv University on properties and applications of silver halide infrared transmitting fibers. Various infrared spectral features of core-only fibers, extruded from pure mixed halide crystals of composition AgClBr1(O < x < 1), are presented and discussed. In the best fibers, total loss is as low as 0.15 dB per meter at a wavelength of 10.6 jim. The fibers can be repetitively bent on a 5 cm radius without degrading the transmission, up to thousands of bends. Fibers witha smooth core-clad structure have also been fabricated, but the optical losses are still relatively high. Novel applications of these fibers in spectrophotometry and radiometry are described.

Infrared radiometry using silver halide fibers and a cooled photonic detector

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer is capable of measuring in real time the temperature of tissue irradiated with a CO 2 laser. A silver halide IR fiber is used to deliver the CO 2 laser radiation to the target and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of detector blinding by reflected CO 2 radiation. A theory of operation for this silver halide fiber optic radiometer, based on lock-in amplifier techniques, is presented. A short discussion of the radiometer design and construction is given. This work forms a basis for the subject of measuring, in real time, fast radiometric signals caused by CO 2 laser irradiation. Such a radiometer is very useful when dealing with pulsed photo thermal radiation with 10.6-μm CO 2 laser radiation. This technique is very useful in medicine and industry.

Silver halide fiber optic radiometry for temperature monitoring and control of tissues heated by microwave

The heating of tissue by microwave radiation has attained a place of importance in various medical fields, such as the treatment of malignancies, urinary retention, and hypothermia. Accurate temperature measurements in these treated tissues is important for treatment planning and for the control of the heating process. It is also important to be able to measure spacial temperature distribution in the tissues because they are heated in a nonuniform way by the microwave radiation. Conventional temperature sensors used today are inaccurate in the presence of microwave radiation and require contact with the heated tissue. Fiber optic radiometry makes it possible to measure temperatures accurately in the presence of microwave radiation and does not require contact with the tissue. Accurate temperature measurements of tissues heated by microwave was obtained using a silver halide optic radiometer, enabling control of the heating process in other regions of the tissue samples. Temperature mappings of the heated tissues were performed and the nonuniform temperature distributions in these tissues was demonstrated.

Theory of fiber optic radiometry, emissivity of fibers, and distributed thermal sensors

This paper formulates a general radiometric theory of multimode step index fibers, covering in particular the region of mid- and far IR fibers. The optical fiber is treated both as a passive waveguide, guiding the external radiation injected into it, as well as an active waveguide, generating internal thermal radiation which is guided to both fiber endfaces. Several fiber absorption profiles are considered. In other words, the thermal radiation sources coupling radiation into the guided modes of the fiber are in one case considered to be distributed in the core, and in another, to be distributed in the cladding. The model is based on 3-D optical geometry of bounded and tunneling skew rays and yields an analytical expression for the angular power distribution along the length of the fiber. The radiation emissivity of multimode fibers is formulated. Based on the model, the theory of a new fiber optic distributed thermal sensor is presented. This sensor needs no external source of radiation for its operation and is based on the self-generation of thermal radiation in a modified IR fiber. Such a sensor can be produced by deliberately inducing surface or bulk absorption in the fiber core or coating (cladding) a bare fiber core with an IR absorbing material.

Silver halide fiber optic radiometer for temperature measurements of irradiated tissue

A fiber optic radiometer based on a cooled photonic detector was designed and constructed. The radiometer was capable of measuring in real time the temperature of a tissue irradiated with CO2 laser. A silver halide I.R. fiber was used to deliver the CO2 laser radiation needed to irradiate the target, and also to deliver the thermal radiation emitted from the target back to the detector. Two methods of measurements were examined, both of which solve the problem of the reflected CO2 radiation which blinds the detector. A theory for silver halide fiber optic radiometer based on lock in amplifier techniques is presented. Discussion of the radiometer design and construction is given. This work can be a good basis for the subject of measuring, in real time, radiometric signals caused by CO2 laser irradiation. Such a radiometer is of great use, when dealing with Photo Thermal Radiation, P.T.R., with 10.6 micrometers , CO2 laser wave length, which is very useful in medicine and industry.

Microwave warming of biological tissue and its control by IR fiber thermometry

The fiber-optic radiometric thermometry of surfaces with non-uniform temperature distribution was analyzed theoretically and optimization of fibers positioning was considered. An infrared fiber-optic multi-channel radiometer was used to monitor and control the temperature of samples in a microwave (MW) heating system. Several heater control algorithms were investigated and the optimal control mode was obtained. Preliminary results of biological tissue warming by microwave heating were obtained. This novel control system is reliable and precise. Such a system should be very useful for medical and industrial applications.

Theory of noncontact point thermal sensing by fiber-optic radiometry.

This paper formulates a theory of noncontact point thermal sensing by fiber-optic radiometry. This theory covers the field of mid- and far-infrared fibers that are suitable for low-temperature radiometry. However, new problems arise in the infrared range, the emission of thermal radiation from the fiber itself due to infrared absorption introduces perturbations into the radiometry, and this must be taken into consideration. The model presented is based on three-dimensional optical geometry of bounded and tunneling skew rays and yields an analytical expression for the inclination and the skewness angle distribution of the guided power collected by the fiber from various layers of a thermal body. The effective field of view, the surface resolution, and the temperature resolution of fiber-optic radiometry are discussed. Thermal sensing by direct coupling is shown to have an advantage over the coupling of a focusing lens located behind the fiber tip. A formulation of fiber emissivity is presented that quantifies the suppression of radiometric perturbations in fiber-optic thermal sensing. Bulk and surface absorption in the fiber core and cladding absorption are all taken into consideration deriving emissivity. Combining the transmissivity and emissivity of the fiber, we propose a measurable criterion, a figure of merit, for fiber-optic radiometry.

An infrared fiber-optic radiometer for controlled microwave heating

Describes an infrared fiberoptic radiometer which was used as a linear-feedback element for noncontact temperature control of a microwave heating system. The temperature of water was monitored and maintained at about 42 degrees C with a standard deviation of +or-0.15 degrees C and a maximum deviation of +or-0.45 degrees C. This controlled system would be very useful for medical, industrial, and domestic applications. >

Nonuniform temperature distribution monitoring with an IR fiber-optic radiometer.

A fiber-optic radiometric system based on IR AgB(x)Cl(1)-(x), fiber was developed and different nonuniform temperature distributions have been investigated. Experimental results show agreement with the theoretical model. The developed system enables us to monitor nonuniform surface temperature distribution with an accuracy of δT = ±0.1 ° C.