A pulsed photothermal technique to calculate internal temperatures from noncontact surface temperature measurements is presented. The inversion process is based on approximating the integral equation describing the thermal interaction with a matrix equation. The matrix equation is then solved using singular-value decomposition. The method was evaluated using computer simulations and experiments with tissue phantoms and skin. The algorithm predicted internal temperatures within 10% for homogeneous samples down to a depth of about 500 μm. It did not predict internal temperatures accurately for inhomogeneous samples, but yielded fairly accurate estimates of the depths of subsurface absorbers and conserved energy. The uncertainty in the calculated depth of the absorber increased with depth. Currently this technique can probe depths to 500 μm.

The finite-difference time-domain (FDTD) technique is used to compute light scattering from biological cells in two dimensions. Results are presented for the computed scattering patterns of cells containing multiple organelles. This method provides considerably more flexibility than Mie theory because of its ability to model inhomogeneous objects such as cells.

Dentin was visualized using a new fluorescence technique and confocal laser scanning microscopy. Thirty extracted human teeth showing no clinical signs of caries were investigated. All teeth were horizontally sectioned to approximately 200 μm thickness and sections were subjected to different pretreatment conditions as follows: vacuum only, ultrasonication only, sodium hypochlorite only, sodium hypochlorite and vacuum, sodium hypochlorite and ultrasonication, and a combination of sodium hypochlorite, vacuum, and ultrasonication. Some samples were left untreated to serve as control. Following pretreatment, rhodamine 123 fluorescentdye was used for staining at concentrations ranging from 10^-3 to 10^-7M for 1 to 24 h at pH 6.0, 6.5, or 7.4. Optical staining occurred at pH 7.4 and concentrations ≥ 10^-5 M over 3 h or longer. Surface images obtained using confocal laser scanning microscopy were similar to those observed by scanning electron microscopy without the need for sample-altering conventional scanning electron microscope preparation techniques. Subsurface imaging to a depth of approximately 60 μm was achieved using confocal laser microscope techniques. This fluorescence technique offers a useful new alternative for visualization and quantification of dentin.

In order to enhance cell culture growth in bioreactors, biosensors such as those used for glucose detection must be developed that are capable of monitoring cell culture processes continuously and preferably noninvasively. The development of a unique noninvasive, optically based polarimetric glucose sensor is reported. The data were collected using a highly sensitive, lab-built polarimeter with digital feedback and a red laser diode source. A range of glucose concentrations was evaluated using both glucose-doped double-distilled water and a bovine serum-based medium. The serum-based medium is the nutritional environment in which the cell cultures are grown. Both media were examined across two glucose concentration ranges—a lower range of 100 mg/dl in 10-mg/dl increments and a higher range up to 600 mg/dl in 50-mg/dl increments. The linear regression in all experiments yielded standard errors of prediction of less than 8.5 mg/dl across both ranges.

A mathematical formulation of the problem of electromagnetic wave scattering by a system of two homogeneous triaxial dielectric ellipsoids of complex index of refraction is presented. The analysis is based on the Lippman–Schwinger integral equation for an electric field. The corresponding integral equation for the scattering, which contains two singular kernels, is transformed into a pair of nonsingular integral equations for the angular Fourier transform of the electric field inside each scatterer. The latter equations are solved by reducing them by quadrature into a matrix equation. The resulting solutions are used to calculate the scattering amplitude. As a numerical application, the case of a two red blood cell rouleau model is considered. Typical values of the appropriate discretization parameters, which proved sufficient for achieving convergence, are presented, along with validity tests. The effect of the electromagnetic coupling of the scatterers is also illustrated. Efficient techniques, which are capable of reducing the rather high computing demands of the analysis, such as parallel processing, are both suggested and applied.

A time-dependent, heat diffusion equation was used to predict the three-dimensional temperature distribution of Escherichia coli in liquid-suspension during irradiation by a high-power Nd:YAG laser. The model may be used to calculate the temperature rise and the transient 3-D temperature profile in the liquid suspension under arbitrary combinations of laser wavelength, pulse shape, pulse width, repetition rate, energy density, and for different concentrations of bacteria. The temperature profiles in the liquid, for a range of energy densities, were measured to validate the theoretical model. The experimental results were in good agreement with the theoretical ones. A temperature gradient was found in the sample in the radial and axial directions during laser irradiation. The model enables the parameters that affect the temperature distribution of the liquid suspension to be identified and optimized when designing laser sterilization systems.

A modified laser Doppler flowmetry technique that significantly improves the performance of the current technique in measuring pulpal blood flow is described. A preliminary model demonstrates that, by using a forward-scattered geometry, the detected signal will have a much higher signal-to-noise ratio and calibration capacity. The forward-scattered signal is readily detectable because teeth are relatively thin organs with moderate optical loss. Preliminary experiments comparing forward-scattered detection with conventional back-scattered detection were carried out using an extracted, perfused human molar. The results showed that: (1) the existing back-scattering method produced readings that fluctuated by as much as 187% in response to small changes in sensor position relative to the tooth and (2) the forward-scattered method produced consistent readings (within 10%) that were independent of the sensor position, a signal-to-noise ratio that was at least 5.6 times higher than that obtained by the back-scattering method, and a linear response to flow rate. The results validated the findings of the preliminary model and clearly showed the superiority of the forward-scattering geometry.

A novel mathematical model of light scattering by pathological and deformed erythrocytes is presented. An erythrocyte is modeled as a homogeneous triaxial dielectric ellipsoid of complex index of refraction. Both its position and orientation in a given cartesian coordinate system are considered arbitrary. The analysis is based on the Lippman–Schwinger integral equation for the electric field. The corresponding (singular) integral equation for the scattering is transformed into an integral equation for the Fourier transform of the electric field inside the scatterer. The latter equation has a nonsingular kernel. It is solved by reducing it by quadrature into a linear set of equations. The resulting solutions are used to calculate the scattering amplitude. Several tests ensuring the validity of the approach along with sample calculations are presented.

Determining the concentration of glucose in vivo by near-infrared spectroscopy is complicated by the effects of optical changes caused by fluctuations in temperature, tissue water content, and the concentration of other analytes. Mie theory and Monte Carlo computer simulation of light transport in optically absorbing and scattering media were used to investigate the magnitude of the changes in diffuse reflectance and transmittance from changes in glucose. Similarly, the possible interference in the glucose measurement from the other tissue parameters has been assessed and found to be significant.

The characteristics and the performance of a thermal lens detector, which uses a double-beam absorption scheme, were studied in a capillary electrophoresis system with various types of toxic pollutants, e.g., pesticides. The setup of the detector system was miniaturized using the smallest diverging path lengths between the cell and the pinhole (4 mm). The probe laser beam (He:Ne laser, 633 nm) and the excitation beam (Ar⁺ ion laser, 364, 457, 488, and 514 nm) with a crossed setup were directed by mirrors into two microscope objectives that focused the beam to a 5-μm waist inside the capillary. The detection volume was on the order of 75 nl when a 75-μm capillary was employed. The change in intensity of the probe beam was detected by a photodiode behind a pinhole, which was protected with different band-pass interference filters. The excitation laser can be used in the multiline order. Micellar electrokinetic methods are used for pesticide separation. Theperformance of the detector in capillary electrophoresis was assessed with various types of capillaries and compared with a conventional absorption detector. The limit of detection is at least one order of magnitude better than it is with the absorption detector.

Emission from a single-mode 100 mW diode laser at 840 nm is used to create optical tweezers: the trappinglaser beam is introduced into a microscope and focused by the objective. The microscope also allows monitoring of the motion of the trapped particles. The optical tweezers were monitored with objectives having different numerical apertures between 0.65 and 1.3. The optical trapping of polystyrene spheres with a radius between 0.11 and 7.45 μm and of biological objects, the flagellated alga Tetraselmis, with typical dimensions of 8×8×13 μm³ were studied. The efficiency of the optical tweezers has been characterized through a parameter Q and compared with theoretical models.