Measurement of the optical absorption coefficient of a liquid by use of a time-resolved photoacoustic technique.

A time-resolved photoacoustic technique has been applied to the study of dissolved and dispersed absorbers in aqueous systems. The temporal pressure profiles generated from colloidal graphite and glucose solutions were measured, and it was found that the amplitude of the photoacoustic signal of both the glucose and the colloidal graphite solutions increase linearly with concentration and that acoustic signal time delay yields the acoustic velocity. The logarithm of the photoacoustic signal amplitude changes linearly with the time delay, with a slope that is proportional to the product of the acoustic velocity and the optical absorption that can thus be determined.

Advances in photoacoustic noninvasive glucose testing.

We report here on in vitro and in vivo experiments that are intended to explore the feasibility of photoacoustic spectroscopy as a tool for the noninvasive measurement of blood glucose. The in vivo results from oral glucose tests on eight subjects showed good correlation with clinical measurements but indicated that physiological factors and person-to-person variability are important. In vitro measurements showed that the sensitivity of the glucose measurement is unaffected by the presence of common blood analytes but that there can be substantial shifts in baseline values. The results indicate the need for spectroscopic data to develop algorithms for the detection of glucose in the presence of other analytes.

Application of pulsed photoacoustics in water at high pressure.

The application of pulsed photoacoustics to the study of liquids at pressures of up to 350 bars is discussed. The design and development of an in-line sensor for the subsea monitoring of crude oil concentrations in water is reported. Crude oil detection sensitivities at parts per million concentrations were achieved with prototype instrumentation. A comparison of experimental results and a theoretical prediction of the pressure dependence of the pulsed photoacoustic response from water is outlined. The results demonstrate that existing models that describe pulsed photoacoustic generation in liquids are applicable to high-pressure conditions.

Optical fiber interferometry for photoacoustic spectroscopy in liquids.

Optical fiber interferometry was used for measurement of the subnanometer surface and bulk displacements associated with photoacoustic pressure waves in methanol and water. The measurement system is both broadband and noncontacting, giving a pressure sensitivity of 0.1 Pa/ radicalHz.

Glucose determination by a pulsed photoacoustic technique: an experimental study using a gelatin-based tissue phantom.

A preliminary study of using a gelatin-based in vivo tissue model to investigate some of the near infrared photoacoustic characteristics that may influence the sensitivity of non-invasive photoacoustic detection of blood glucose in human tissue is described. It is shown that the optical absorption change due to glucose in the near infrared region is small and that the pulsed photoacoustic technique may offer a better detection sensitivity than other conventional optical transmission measurement systems being developed for blood glucose monitoring.

Laser photoacoustic determination of physiological glucose concentrations in human whole blood.

A glucose concentration analysis of human whole blood samples has been accomplished using pulsed laser photoacoustic spectroscopy (LPAS). Using a CO2 laser operating with microJ pulse energies, the technique has shown the required discrimination and sensitivity to determine glucose concentrations within the physiological range (18-450 mg dl-1) in whole blood samples. The sensitivity achieved with this system is comparable to that of the existing commercial enzyme-based diagnostic systems presently used in hospital clinical chemistry environments. The technique is compared with other optical methods that have recently been used for glucose determination, and its applicability for use in the development of an in vivo monitor is discussed.

Nonlinear refractive-index changes induced by carrier injection in an InSb étalon.

We report the bistable switching of an InSb étalon in a novel mode of operation where the necessary changes in refractive index are induced by minority carrier injection through a p-n junction. Refractive-index changes of approximately 10(-5) are achieved using 3-V pulses. Switch ON and switch OFF characteristics and projected performance are discussed.

Diffusive transverse coupling between adjacent InSb transphasor channels.

The proportionality of a transphasor signal to the photoexcited carrier density has been utilized to measure the transfer of the signal between adjacent optical channels and to estimate practical transphasor packing densities (~10(3) cm(-2)) for a pure, bulk étalon of InSb, 280 microm thick. By using the transphasor as a probe of the carrier population distribution produced by an adjacent beam, the ambipolar diffusion length was measured as 74 microm.

Carrier diffusion measurements in InSb by the angular dependence of degenerate four-wave mixing.

Studies of the angular dependence of cw degenerate four-wave mixing in n-type InSb have yielded a value for the diffusion length, l(D), of 60 +/- 2 microm. From this, the dependence of l(D) on photoexcited carrier concentration is calculated. A simple model has been developed to estimate the corresponding parallel-processing capabilities of semi-conductor-based, all-optical, parallel-processing digital computing systems.