Experimental and numerical study of the colour appearance of tattoo models.

The colour of tattooed skin has been predicted by a Monte Carlo method based on the optical coefficient spectra of the skin and tattoo dyes. Slices of pig skin, a tattoo phantom and skin phantoms with different thickness were prepared, and their reflectance and transmittance spectra were measured using an integrating sphere at wavelengths varying from 400nm to 700nm. The absorption and scattering coefficient spectra of skin phantoms, pig skins and the tattoo phantom were each calculated using the inverse Monte Carlo method. The skin phantoms and pig skins were overlaid on the tattoo phantom, and the reflectance spectra of the two-layered structures were measured. The reflectance spectra of the two-layered structures were calculated from the optical coefficient spectra using the Monte Carlo method. They agreed well with the measured spectra. The colour differences between the calculated and measured spectra were also evaluated by the L*a*b* colour space distances and showed good agreement, with 3.49 for the skin phantoms and 8.27 for the pig skins.

Aberration measurement from confocal axial intensity response using neural network.

We propose a high-speed, parallel system for lens aberration measurement employing a confocal optical setup. This method uses a non-interferometric, conventional confocal axial response to determine the spherical aberration coefficient of a confocal objective. The aberration coefficients are successfully calculated from the intensity axial response by employing a neural network. It is estimated that the system can find out the aberration coefficients of 10,000 microlenses in 20 seconds of measurement and 1 second of calculation time. Our experimental results also demonstrate the practicality of this system.

Spectral interferometric optical coherence tomography with nonlinear beta-barium borate time gating.

A high-speed, all optical coherence tomography system was designed and constructed. This tomography system employs spectral interferometry and optical Fourier transformation to reduce the number of mechanical scanning dimensions required for multidimensional profilometry. The system also employs a time gate comprising a beta -barium borate crystal driven by a femtosecond laser pulse to improve measurement time. This system has 43-mum depth resolution and 150-fs temporal resolution and is capable of taking 1000 cross-sectional image frames per second.

Birefringence imaging of human skin by polarization-sensitive spectral interferometric optical coherence tomography.

We have developed a spectral interferometric optical coherence tomography (OCT) system with polarization sensitivity that is able to measure a two-dimensional tomographic image by means of one-dimensional mechanical scanning. Our system, which has an axial resolution of 32 mum , calculates the distribution of each element of the Müller matrix of a measured object from 16 OCT images. The OCT system successfully reveals the birefringent nature of human skin tissue.

Melanin and blood concentration in human skin studied by multiple regression analysis: experiments.

Knowledge of the mechanism of human skin colour and measurement of melanin and blood concentration in human skin are needed in the medical and cosmetic fields. The absorbance spectrum from reflectance at the visible wavelength of human skin increases under several conditions such as a sunburn or scalding. The change of the absorbance spectrum from reflectance including the scattering effect does not correspond to the molar absorption spectrum of melanin and blood. The modified Beer-Lambert law is applied to the change in the absorbance spectrum from reflectance of human skin as the change in melanin and blood is assumed to be small. The concentration of melanin and blood was estimated from the absorbance spectrum reflectance of human skin using multiple regression analysis. Estimated concentrations were compared with the measured one in a phantom experiment and this method was applied to in vivo skin.

Melanin and blood concentration in a human skin model studied by multiple regression analysis: assessment by Monte Carlo simulation.

Measurement of melanin and blood concentration in human skin is needed in the medical and the cosmetic fields because human skin colour is mainly determined by the colours of melanin and blood. It is difficult to measure these concentrations in human skin because skin has a multi-layered structure and scatters light strongly throughout the visible spectrum. The Monte Carlo simulation currently used for the analysis of skin colour requires long calculation times and knowledge of the specific optical properties of each skin layer. A regression analysis based on the modified Beer-Lambert law is presented as a method of measuring melanin and blood concentration in human skin in a shorter period of time and with fewer calculations. The accuracy of this method is assessed using Monte Carlo simulations.

Diffraction efficiency increase by corona discharge in photoinduced surface-relief gratings on an azo polymer film.

The diffraction efficiency of a surface-relief grating (SRG) was dramatically increased by corona discharge. We fabricated this SRG by applying surface modulation to azo polymer films, using laser interference fringes. The electric charge was deposited upon the SRG by a corona discharge in an oven. The first-order diffraction efficiency measured before and after corona discharge above the glass-transition temperature increased from ~2% to ~40% in a SRG written with a circularly polarized beam. The relief depth of the SRG as measured with an atomic-force microscope also increased, from ~130 nm to ~450 nm. The increase in diffraction efficiency was independent of the writing polarization.

Phase-resolved correlation and its application to analysis of low-coherence interferograms.

A new signal-processing technique is proposed that involves a phase-resolved correlation method that one can use to determine the phase distribution of low-coherence interferograms. This method improves the sensitivity and resolution of low-coherence interferometers. The depth structure of an aluminum oxide-coated aluminum mirror was determined by use of a low-coherence interferometer with this method. Three signal peaks were successfully extracted from a noisy interferogram.

Fringe pattern correlator for three-dimensional object recognition.

We propose a novel three-dimensional (3-D) object-recognition method based on a Fourier-transform profilometry technique and a two-dimensional (2-D) correlation technique. Height information on 3-D objects is transformed to phase information on 2-D complex amplitude by use of the Fourier-transform profilometry technique. 3-D objects are recognized using correlation by use of the transformed complex amplitude.

[Relation between temporomandibular joint disorder and subjective symptoms of fatigue].

An investigation was performed for the purpose of guaging the relation between temporomandibular joint disorder on the one hand and occupational category and subjective symptoms of fatigue on the other. Subjects were 2,414 workers (1,598 male, 816 female) in small and medium size enterprises at 67 workplaces in Hiroshima Prefecture. A comparison of cases with and without temporomandibular joint disorder showed that there were more complaints of fatigue among those with the disorder. Given these indications that temporomandibular joint disorder was related to occupation, it is possible that temporomandibular joint disease may be a work-related disease.

Activities of optical laboratories 1 and 2 at the Photon Factory.

Recent activities at optical laboratories 1 and 2 at the Photon Factory are presented. The activities are (i) construction of optical laboratory 1, (ii) reconstruction of optical laboratory 2, (iii) construction of a visible synchrotron radiation beam extraction mirror made of beryllium, (iv) small-beam-profile measurement by means of the image restoration method, (v) application of the adaptive optical system for correction of distorted wavefronts caused by deformation of the extraction mirror, (vi) construction of a synchrotron radiation interferometer for investigation of the spatial coherency of the visible synchrotron radiation beam and its application to the measurement of vertical beam profile and size.

Binary computer-generated holograms for security applications from a synthetic double-exposure method by electron-beam lithography.

We have developed a new multiplexing method for producing binary computer-generated holograms (CGH's) for security applications. This method is based on double recording of two types of coding method upon binary CGH's. The CGH synthesized by the proposed method can have multiple image planes from the region close to the hologram (image region) to infinity (Fraunhofer region) without severe degradation of reconstructed images in the image region. A CGH containing simultaneous image- and Fourier-type holograms is fabricated by electron-beam lithography. Some experimental results are presented.

Optics in Computing: Introduction to the Feature issue.

This feature issue of Applied Optics on optics in computing comprises 14 papers. Most of the papers are expanded versions of papers presented at the Optical Society of America Topical Meeting on Optics in Computing held 16-21 March 1997 in Lake Tahoe, Nevada.

Optical learning neural network with a pockels readout optical modulator.

We have constructed an optical neural-network system with learning capability by using a Pockels readout optical modulator. The system has a two-dimensional structure that permits easy optical alignment and can handle images without scanning. Learning signals are calculated optically with two liquid-crystal devices by a matrix-matrix outer-product method. The calculated learning signals are added directly to the weights memorized on the Pockels readout optical modulator. A two-layer network is implemented, and the learning and recognition of four alphabetical characters are realized according to the delta rule.

[The relation of dental examination results at corporation offices to occupation, subjective symptoms of fatigue and daily lifestyle--an investigation based on the number of missing teeth].

Our investigation was intended to find a relationship between the dental health of labourers and, their jobs, subjective symptoms of fatigue and daily lifestyle. Dentists checked the dental health of 2,565 corporation employees (790 male and 775 female) of small to medium-sized enterprises in Hiroshima prefecture. At the same time they examined the employees' occupation, subjective symptoms of fatigue and their health maintenance behavior according to Breslow's criteria. The data were divided into age groups spanning 10 years. Among males in their 30s, those engaged in transport/driving and engineering/production had more missing teeth than others. We found a relationship between the number of missing teeth and subjective symptoms of fatigue among men in their 30s. This suggests that the greater the number of missing teeth, the greater their subjective symptoms of fatigue. The results suggest that missing teeth cause malocclusion which leads to subjective symptoms of fatigue.

Quantized phase optimization of two-dimensional Fourier kinoforms by a genetic algorithm.

We have developed a phase optimization method of a quantized kinoform by a genetic algorithm. Because the genetic algorithm inherently deals with discrete values, the quantized phase of the kinoform can be easily estimated. The two-dimensional Fourier kinoform can utilize effectively the periodicity of the discrete Fourier transform in the genetic algorithm. This condition enables us to perform the crossover process that is one of the processes in genetic algorithm without a spatial bandwidth of the kinoform. The optimization has been performed successfully in computer simulation. The optically reconstructed image agrees well with the theoretical one.

Simple algorithm for large-grid phase reconstruction of lateral-shearing interferometry.

A simple zonal approach is proposed for estimating phase distribution on large grids. The estimation is based on phase differences that are precisely measured in two orthogonal directions by a lateral-shearing interferometer. It requires only O(N(2)) operations for reconstructing a phase distribution on an N × N grid. Computer simulation and experimental results are demonstrated to show the effectiveness of the new algorithm.

Phase optimization of a kinoform by simulated annealing.

The design of a kinoform by the use of simulated annealing is discussed. The simulated annealing process is applied to decrease the reconstruction noise and to adjust the phase distribution of the kinoform to the configuration of the recording device. A liquid-crystal spatial light modulator is used to display the kinoform. The reconstructed image of the optimized kinoform is found to be in good agreement with the computed image. Some experimental results obtained with a liquid-crystal spatial light modulator are presented. The phase quantization effect of the kinoform is discussed.