Crystalline IR fibers and hollow waveguides are increasingly being used in infrared sensor and laser power delivery applications. Polycrystalline fibers, made from ductile materials such as the silver halides, offer the advantage of low loss at 10.6 micrometers , wide infrared transparency, and good flexibility. In contrast to these solid-core fibers, hollow waveguides made from metallic or dielectric materials deliver CO2 laser powers in excess of 1000 W, have no end reflection losses, and are usually quite rugged. Currently, IR fibers are finding exciting new uses in remote spectroscopy of chemical species and for the delivery of laser power for surgical applications.

Experimental evidence for the effects of gravity on the crystallization of multiple phases in a Zr-Ba-La-Al-Na fluoride glass (ZBLAN) is presented. Thermal analysis (DTA) of ZBLAN bulk glass preforms showed the presence of two crystallization peaks under 1-g. Similarly, SEM analyses of thin filaments (drawn from these preforms and sealed in quartz ampules) heat treated in the range of 350 degree(s)C - 500 degree(s)C under 2-g for 20 seconds showed the crystallization of one/two phases. EDXA of these filaments indicated that the crystallized phases were either rich in Na and Al or deficient in Na and Al. On the other hand, filaments heat treated under 0-g did not show any evidence of crystallization.

The effect of high temperature aqueous solutions of various pH values on the mechanical properties of polymer coated optical fibers of an aluminum fluoride-based composition are examined. It was found that such fibers retain much more strength when aged in these aqueous environments than fibers of the more common zirconium fluoride-based composition. The aging is not affected by pH unless the fiber is under stress, in which case a low pH solution decreases the time to failure of the fiber. In static fatigue, the time to failure of the aluminum fluoride-based fibers is 20 times greater than that of the zirconium fluoride-based fibers.

Amorphous Materials (AMI) has served since 1977 as a source of high purity, optically homogeneous plates of selenium-based glasses used in passive IR (FLIR) night vision systems. Over the past three years, Amorphous Materials has used this chalcogenide glass technology and capability to develop a unique process to prepare optical fibers. The process is based on using 2 inch cores removed from a homogeneous plate and sealed in a chamber which can be heated so that fibers may be pulled from a small tube in the bottom. Methods for cladding and coating with thermal plastic using split dies have been developed. The method has been used to produce flexible, low attenuation fibers based on an As-Se-Te composition. High purity As2S3 glass has been used to produce fibers capable of transmitting substantial amounts of IR laser energy. Physical properties of both fibers are discussed.

Arsenic is introduced into the tellurium halide based glasses by substituting Se or Te. Glass transition temperature, Tg, is significantly increased and Tg as high as 150 degree(s)C has been obtained. These new glasses still have a multiphonon absorption situated in the region of 18 micrometers and they still have potential low losses in the 8 - 12 micrometers region. The first optical fibers obtained from these glasses show an attenuation of about 5 dB/m in the second atmospheric window and the losses are due to defects in the fibers.

It is shown that bi-tapering of a chalcogenide fiber results in a substantial increase in the number of reflections from the fiber boundary. Furthermore the average angle of incidence is closer to the critical angle. As a result the ATR absorption increases substantially when bi- tapered fibers, as compared to straight ones, are used. Hence higher sensing demands may be answered by bi-tapered fiber probes.

Flexibility resistance of silver-halide infrared fibers was investigated in the plastic bending regime, which is especially useful for internal medical applications. The CO2 laser transmission of the fibers was measured in several positions while being bent. The fibers have been found to operate even after large plastic deformations, and values for various fibers and bending conditions are reported.

Laser induced breakdown (LIB) thresholds of the AgClxBr1-x (0 2 lasers. Bulk and surface crystal/polycrystalline samples and fibers were investigated. The intrinsic LIB threshold of the crystals is dependent on x and are 3.8$CTR108W/cm2 for x equals 1; 8.2$CTR102W/cm2 for x equals 0 under 100 ns TEA CO2 laser excitation. The LIB threshold in fibers is roughly 2$CTR107W/cm2.

Optical IR fibers with core-clad structure are of great importance, because they have better qualities than unclad fibers for most IR fiber applications, especially in CO2 laser power delivery and radiometry. We have fabricated core-clad polycrystalline silver halide optical fibers with different compositions and core diameters. These fibers are easier to handle than unclad fibers and, in spite of their higher attenuation, they can transmit more power density than unclad fibers. The behavior of the scattering losses along these fibers and other optical properties were measured and compared with unclad silver halide fibers. We show that the higher losses in clad fibers result from excessive scattering. The improvement in the fabrication process of clad fibers enabled the production of new elements such as single-mode fibers and fiber bundles for thermal imaging.

Different mechanisms of extrinsic losses, including aging, in extruded mixed AgClxBr1-x fibers are discussed. Additional losses caused by changes in structure of fiber material have been investigated.

Spectroscopic measurements were used to evaluate the effect of water adsorption and desorption on IR fibers transmission. Water impurities attenuated the transmission of silver halide IR fibers at 2.94 micrometers , 6.32 micrometers , and at wavelengths longer than 10 micrometers . Water is adsorbed from the humidity of the air, and the adsorption is a slow exponential process that reaches saturation in a few months. Most of the water can be desorbed by heating the fibers to 110 - 140 degree(s)C for a few hours in air or in vacuum.

Single-crystal sapphire fibers were grown by the laser heated pedestal growth technique. Loss spectra are presented which show attenuation coefficients of less than 1 dB/m at the Er:YAG laser wavelength. Laser pulses of 600 mJ at this wavelength were delivered through the fibers with no laser induced damage. Flexural strength measurements made on these fibers indicate a 0.75% strain to failure when tested under 4-point loading. X-ray photography results show that the crystal quality of fibers grown by this technique is excellent. Initial experiments with a melt extruded teflon cladding on the sapphire fibers are very promising. The teflon is effective at preventing evanescent coupling to water, as might be expected.

A new method of fabricating long dielectric-coated metallic waveguides has been proposed by using vacuum evaporation and assembly techniques. Phosphor bronze waveguides have been fabricated whose inner 2 or 4 walls are coated by a thin PbF2 layer with a proper thickness. Waveguides with small losses have been obtained even when the waveguides are bent.

Plastic hollow fibers for IR transmission were characterized employing several physical and chemical methods. The dielectric layer was found to be (beta) -AgI or (delta) -AgI on the surface. The amount of iodine decreases gradually at deeper layers. The equivalent depth was determined from coulometric experiments; 0.3 - 1.6 micrometers .

Fiber buffer coatings, protective sheaths, and cable assembly techniques strongly impact mechanical and optical properties of infrared fiberoptics. Many materials common to silica fiber fabrication have strong infrared signature bands which may adversely affect the optical performance of infrared fiberoptics. Material selection and assembly methods for process hardening of infrared fibers for applications are discussed.

The evanescent-wave spectrum of a sample surrounding the core of an optical fiber is a complex function of the optical constants of the media involved as well as the geometry of the sensing fiber. We develop a simple theory for evanescent-wave absorption in the weak absorption limit where we show that the absorbance of a length of sensor fiber may be related linearly to the bulk sample absorption coefficient. We present experimental data that verifies the observed scaling between the evanescent-wave absorbance and the bulk absorption coefficient for an isopropanol sample. The application of evanescent-wave spectroscopy with different sensor fiber materials is discussed, along with experimental and theoretical data for the enhancement of evanescent-wave spectroscopy using tapered fibers. Finally we discuss the results of a numerical series of calculations based on the exact ray paths of radiation within the fiber and the fundamental theory of ATR absorption at an interface assuming a plane wave approximation. In the more complex theory the evanescent-wave absorption coefficient is a decreasing function of the bulk absorption coefficient.

The use of low V-number infrared transmitting fibers in the detection of gases, via the attenuation of the evanescent wave power in the porous polymer claddings, is discussed. The attenuation process is modelled, MDC values are predicted for some gases, and various intensity referencing techniques are suggested.

Evanescent wave spectroscopy measurements were performed using unclad silver halide fibers and tunable laser sources such as lead salts diode lasers and a CO2 laser. Spectra of liquids and gases were recorded. The system S/N ratio and resolution were better than those of FTIR spectrometers. This demonstrates the potential use of tunable lasers in fiberoptic evanescent wave spectroscopy.

We report on a devoted spectrometer setup for infrared fiber component characterization by lead chalcogenide diode laser radiation under the conditions met in sensitive infrared diode laser gas analyzers. Preliminary results obtained on zirconium fluoride fiber samples indicate, for example, that very low optical feedback levels, as are required in trace gas analysis can be achieved with proper care in fiber end preparation.

A high sensitive chemical analyzer of molecular gases is presented. It's based on measurements of high resolution molecular absorption spectra obtained with infrared tunable diode lasers (TDL). To transmit radiation from lasers to an analytical cell and back to detectors, infrared fibers with low optical losses are used. A multipass optical cell is used to enhance the essential sensitivity of the sensor. Various gaseous molecular objects could be detected by this analyzer due to the wide spectral range of available TDLs and fibers. Use of fibers for laser transfer could provide remote monitoring and multicomponent mixture analysis and evanescent spectroscopy of gases in the near future.

Chalcogenide optical fiber sensors for the measurement of chemical species are reported. An unclad chalcogenide glass fiber was used to collect evanescently excited spectral signals in the mid-IR region from both liquid and gaseous species. Important design parameters for evanescent field sensing have been investigated for their impact on sensitivity.

Fiber optic evanescent wave quantitative absorption measurements in liquids, using chalcogenide glass infrared fiber, are described. The sensor response dependence of each parameter (fiber length, fiber diameter, light beam launching condition, and wavelength) is theoretically analyzed and experimentally confirmed (deviation of less than 5% from the theoretical model calculated values).

Instrument accessories for remote infrared spectroscopy have been developed employing chalcogenide fiber. The fiber probes, designed for immersion in standard laboratory hardware, provide scientists with new possibilities for acquiring spectral signatures between 3400 cm-1 and 850 cm-1 for quantitative analysis of a wide variety of solutions, mixtures, sludge, mud, creams, and gels, including biological samples.

Er:YAG laser beams (2.94 micrometers ) have more strong absorbability by water than CO2 laser beams (10.6 micrometers ). Er:Yag lasers are expected as a treatment beam for water rich biotissue, we considered the application of Er:YAG lasers for medical use in the near future. When applying it for medical use, the delivery systems must be prepared. So we are investigating higher pulse power Er:YAG laser beam transmission with fluoride glass fibers, chalcogenide glass fibers, and hollow tube guides. From our experimental results, these beam delivery techniques are possible for Er:YAG lasers.

A series of FT-IR spectrometer based remote sensing systems have been developed taking advantage of the new technology of IR transmitting optical fibers. The systems may be used to monitor the chemical composition of solid, liquid and gas phase samples. An array of remote sensors may be interfaced to a single FT-IR spectrometer through a multi-fiber launch module. An optical channel selector (OCS) allows the sensors to be addressed with a single opto-mechanically multiplexed detector system. Remote collimated beam sensors have been developed for web monitoring and liquid and gas phase sensing. An optimized multi-detector web monitoring system has been developed for moving web sensing on optically dttuse webs. Quantitative data will be presented for a number of remote spectroscopic measurements.

ZnSe-coated Ag waveguides have been developed for transmitting high power CO2 laser light. The waveguides (1—rn length) are fabricated by using a polyimide tube with a smooth surface as well as an Al tube as a base material. A fabrication method including the sputtering condition for depositing ZnSe and Ag films is investigated experimentally. Transmission characteristics of the waveguides are evaiuated by measurements of loss spectra for incoherent light and bending losses for CO2 laser light. As a result, ZnSe-coated Ag waveguides fabricated by using a polyimide tube show remarkably low loss characteristics when the waveguides are bent.

Plastic hollow waveguides with different thicknesses of the dielectric layer were investigated. The AgI layer thickness (t) was found to be the main parameter which affects the transmission of radiation in the hollow waveguide. Waveguides with t equals 0.84 micrometers have a minimum attenuation for CO2 laser energy transmission ((lambda) equals 10.6 micrometers ). However, waveguides with t equals 1.32 micrometers have high attenuation, so they can be used as filters for this specific wavelength. The influence of the iodination parameters such as iodination time, concentration of iodine solution, and temperature of reaction on the dielectric layer thickness were also investigated. It was found that t rises with iodination time (r) as t equals r0.37, I2 concentration (parabolic form), and reaction temperature.

Earlier we presented papers concerning the development of planar hollow metallic waveguides (HMW) designed for transformation of middle IR-range laser emission. In these papers we analyzed the waveguides multimode operation characteristics. However, a single-mode operation is more desirable, since in this case the total emission intensity is transferred in the waveguide by weakly attenuated TE1 mode. In order to realize a single-mode transmission in a multimode waveguide, one has to excite a TE1 mode at the HMW input with efficiency higher than 96%. To achieve this, a precision alignment is necessary, since even a small shift results in excitation of higher TE2 and TE3 modes. The existence of the latter, along with a TE1 mode, gives use to the intermode interference which strongly effects the output intensity distribution and may result in misinterpretation of output mode content. (Thus, for example, the side maxima originating in TE1 and TE3 modes interference are often mistaken for diffractional maxima in a single mode operation.) In this paper we analyze the output intensity distribution and characteristics changes in intensity profile of interfering modes. We obtain, both numerically and experimentally, the relation between the intensity distributions in the near and far zones, which makes it possible to correct identification of a mode structure propagating in the HMW.

The development of new infrared transmitting optical fibers with low optical losses, sufficient mechanical strength, and temperature range to meet the demanding conditions of many process environments; and the availability of improved, ruggedized low-cost FTIR spectrometers have made in situ FTIR measurements possible. This paper discusses the development of in situ fiber optic remote FTIR spectroscopy and its application to the characterization of thin polymer coatings on substrates and the development of evanescent wave in situ fiber optic remote FTIR spectroscopy and its application to assaying components of biological fluids.

Two kinds of intrinsic luminescence in mixed AgBr1-xClx (1 io. Dependence of the parameters of this process on crystal composition has been investigated in terms of spatially well correlated Frenkel defect recombinations. The main effect found was the linear increase of the Agio migration energy with the crystal composition x. The second kind of luminescence arising due to exciton molecules has been shown to be sensitive to the solid solution composition and the quality of a crystal. It is shown that this luminescence correlates with the optical losses of the fibers studied.