Anisotropic photon migration in human skeletal muscle.

It is demonstrated in the short head of the human biceps brachii of 16 healthy subjects (12 males and 4 females) that near infrared photon migration is anisotropic. The probability for a photon to travel along the direction of the muscle fibres is higher (approximately 0.4) than that of travelling along a perpendicular axis (approximately 0.3) while in the adipose tissue the probability is the same (approximately 0.33) in all directions. Considering that the muscle fibre orientation is different depending on the type of muscle considered, and that inside a given skeletal muscle the orientation may change, the present findings in part might explain the intrasubject variability observed in the physiological parameters measured by near infrared spectroscopy techniques. In other words, the observed regional differences might not only be physiological differences but also optical artefacts.

Laser-diode interferometric heterodyne vibrometer: application to linear motor control.

We describe an interferometric heterodyne vibrometer that uses a laser diode with a triangular modulation frequency. This optical sensor is used to probe a vibrating polished surface. As an illustration of the sensor performance, the control of nonuniform velocity of a linear motor is achieved. The technique can be used over a large bandwidth between a few hertz and several tens of kilohertz. Generalization of the technique to the sensing of frequency vibrations is also demonstrated theoretically.

Surface profiling by means of double spectral modulation.

Double modulation-in frequency and intensity-of the power spectral distribution of a light beam is proposed for interferometric profilometry. The procedure is based on two facts: (1) the continuous spectrum of a light source is frequency modulated by the path difference in an interferometric device, (2) the continuous spectrum of a light source is intensity modulated by the transparency of an object placed in the exit plane of a spectroscopic device. Both procedures can be used to measure the profile of a surface with high precision. Moreover, phase shifting is automatically performed by the continuous wavelength variation along the spectrum, so that no piezoelectric transducers are necessary. The method is adaptable for the analysis of remote surfaces through optical fibers.

Three methods of information assessment for optical data processing.

The determination of the specific information in a message has proved of interest in coding (for instance in a hologram) as well as in data processing itself. Also, simple considerations about the definition of optical information have grown into several groups of processing methods. At first the concept of characteristic spatial frequency bands, which describe essential features of any object, leads to compression of its Fourier terms in order to increase the transfer density of a transmitting system and the storage capacity of the recording media. With the emphasis being put on the informative value of the reference in holography, geometrical compression is applied in particular to the coding of printed texts. The second and third groups of methods apparently deal with opposite approaches. Assuming a given message, one may select some parts of its spectrum for further processing or carry out average signals from the collections it contains. Both cases-sampling and averaging-permit the extraction of a group of data belonging to a set of discrete signals. The following developments are presented: image replicating at a determined energy level, step-by-step phase sampling grids, study of the displacement law for moving objects by random sampling of disturbed wavefronts and recording of incoherent holograms, on the one hand, and construction of average letters for comparison between manuscripts, average Fourier holograms, and power spectra, on the other hand. A last illustration is provided in connection with the appraisal of psychological tests.