The index of refraction n of the many mammalian tissues is an important but somewhat neglected optical constant. Archival and oral papers have quoted the use of values of n for tissue generally ranging from 1.35 to 1.55. However, these values are frequently without experimental basis. They have arbitrarily used values near that of water, which is a major component of mammalian tissue, or have calculated a theoretical n from the weighted elemental composition of tissue. Since these values have not been precise and little information is available on specific indices for each tissue, a study was undertaken to develop a simple, rapid, and reliable method for the experimental determination of n. This was done using the ubiquitous quartz optical fiber. By substituting the usual cladding found on commercial quartz optics by the tissue in question and utilizing the principle of internal reflection, the value of n for the specific tissue can be calculated. This is done by utilizing the known indices for air and quartz and measuring the angle of the emergent cone of light from the output of the optical fiber. A number of indices for mammalian tissue (bovine, porcine, canine, and human) have been determined at 632.8 nm. With few exceptions, for tissues at this wavelength, n was in the 1.38-1.41 range. The species type did not appear to be a factor. Bovine muscle showed normal dispersion characteristics through the visible wavelengths. The denaturation of tissue was shown to alter significantly the refractive index.

Refractive index of some mammalian tissues using a fiber optic cladding method.

A scanning device for reading indicia of differing light reflectivity, including bar code or matrix array symbols, has a single light emitter, such as a laser or light emitting diode, for generating a scanning light beam to visually illuminate sequential portions of the indicia. A sensor, such as a charge coupled or other solid state imaging device, simultaneously detects light reflected from portions of the indicia and generates an electrical signal representative of the spacial intensity variations the portions of the indicia. The scanning device may also include an ambient light sensor, range finder, a second light emitter for use only in aiming or orienting the scanning device. A photodetector may also be provided to separately detect one symbol virtually simultaneous with the detection of another symbol by the sensor or to provide dual modalities. A method for reading indicia is also provided.

Apparatus and method for reading indicia using charge coupled device and scanning laser beam technology

Devices and methods for measuring body fluid-related metric using spectrophotometry that may be used to facilitate diagnosis and therapeutic interventions aimed at restoring body fluid balance. In one embodiment, the present invention provides a device for measuring a body-tissue water content metric as a fraction of the fat-free tissue content of a patient using optical spectrophotometry. The device includes a probe housing configured to be placed near a tissue location which is being monitored; light emission optics connected to the housing and configured to direct radiation at the tissue location; light detection optics connected to the housing and configured to receive radiation from the tissue location; and a processing device configured to process radiation from the light emission optics and the light detection optics to compute the metric where the metric includes a ratio of the water content of a portion of patient's tissue in relation to the lean or fat-free content of a portion of patient's tissue.

Device and method for monitoring body fluid and electrolyte disorders

The refractive index of a material is one of the most important optical parameters. In this review article we have discussed different methods and techniques for the measurement of refractive indices of various materials. We have considered the literature of the past two decades from 1980 to 2001 and have shown how the techniques have been developed and improved for the measurement of refractive indices. Some applications of refractive index have also been discussed.

https://iopscience.iop.org/article/10.1238/Physica.Regular.065a00167/pdf

Refractive Index Measurement and its Applications

A fibre-optic evanescent field absorption sensor based on a U-shaped sensing probe is described. The influences of fibre core diameter, bending radius of the probe and the refractive index of the fluid on the sensitivity of the sensor are evaluated experimentally. The results are compared with the theoretical results obtained using geometrical optics and based on two-dimensional treatment. A good qualitative agreement is found between them.

Fibre-optic evanescent field absorption sensor based on a U-shaped probe

An optical fiber sensor for measuring a liquid refractive index is proposed. When an optical fiber is bent and part of its cladding is stripped off, the light energy (E) emerging from the fiber depends on the refractive index of the surrounding medium (nm). The change in nm can be found from E. The light output energy and the measuring sensitivity are calculated numerically as a function of nm for several values of the bending radius R. The fundamental characteristics of the sensor, made of a plastic fiber, are investigated using lamp oil and light oil as specimens, and a measurement accuracy of nm to the third decimal place is easily obtained. As applications of this sensor, measurement of liquid density and detection of oil are described.

https://iopscience.iop.org/article/10.1143/JJAP.21.1509/pdf

Optical Fiber Sensor for Measuring Refractive Index

We report a fiber-optic refractive-index sensor that is applicable to a long-distance measurement. The sensor consists of a silica glass fiber bent into a U shape with a bending radius of typically several hundred micrometers. The cladding at the tip of the sensor is stripped off. The sensing mechanism is based on the variation of the output intensity that is induced by radiation loss at the bend, which enables us to measure the refractive index of the outer medium. A fabrication method of fusing the sensor with a CO2 laser and etching with HF is described. Multipoint measurements of optical-time-domain reflectometry are also described.

Silica glass fiber photorefractometer.

A U-shaped fiber-optic refractometer is used to estimate the hydration state of human skin. The validity of the sensor in this application has been investigated by comparing the sensor output with the conductance of the skin to a high-frequency electrical current of 3.5 MHz, which has been reported to be a good measure of the skin hydration state. Results indicate that there is a relatively close relationship between the optical sensor output and the electrical conductance. A water sorption-desorption test conducted to confirm the above relationship has revealed that the fiber-optic probe can provide a convenient means for estimating the skin hydration state in an easy manner.

Skin hydration state estimation using a fiber-optic refractometer

Carbon atom densities in an inductively coupled radio frequency (13.56 MHz) CO and CO and H2 mixed plasmas were successfully measured for the first time using ultra-violet absorption spectroscopy (UVAS) with a carbon hollow cathode lamp. This method, developed for monitoring carbon atoms in-situ in the plasmas, is very useful for the investigation of etching and chemical vapor deposition (CVD) processes containing carbon atoms and the sputtering system employing a carbon target.

Measurement of Carbon Atom Density in High Density Plasma Process

An optical fiber photorefractometer is used for observing fluid mixtures. The concentration of alcohol or sugar into water is measured by noting the change in refractive index. The flow pattern of insoluble mixture is characterizable by a passage frequency, f, or an occupation ratio in time, α, of inclusions. These parameters are related to the mixture ratio. The flow velocity may be estimated from the cross-correlation between outputs of two photorefractometric sensors placed at distances along the path of flow.

Hajime Hattori

Papers

Optical Fiber Sensor for Measuring Refractive Index

Silica glass fiber photorefractometer.

Skin hydration state estimation using a fiber-optic refractometer

Measurement of Carbon Atom Density in High Density Plasma Process

Fluid Observation with an Optical Fiber Photorefractometer