Silverio P. Almeida

Coherent Optical Spatial Filtering of Diatoms in Water Pollution Monitoring

SummaryThe use of Fourier transform coherent optical techniques in the pattern recognition of microscopic algae, i.e., diatoms, is described. The results of the construction of complex-valued filters for diatoms and their usefulness in algal identification are presented. Some general applications to water pollution monitoring and control are discussed.

Surface inspection via projection interferometry.

Projection fringe interferometry provides a useful technique for nondestructive surface analysis. Two beam interferometric fringes were projected onto a block of aluminum whose surface had various types of grooves cut into it. The fringes were digitized and analyzed via an automatic fringe tracking algorithm. Three-dimensional topographical maps of the surfaces microstructure are presented together with a statistical analysis of surface parameters including average roughness, height distributions, and the autocorrelation function.

The Dipole Model and Phase Transitions in Biological Membranes

Assuming the dipole model for a membrane, approximate calculations are made which employ a dipole-dipole interaction energy. The calculations are based upon the assumption of cooperative coupling of membrane polar molecules and make use of the Bragg-Williams approximation. A theoretical estimate is made of the critical temperature at which phase changes might occur in certain biological membranes. Proposals are presented which explain how the dipole transition might relate to the sometimes observed thermal phase transitions in biological membranes.

Root-mean-square difference between the intensities of non-Gaussian speckle at two different wavelengths

The root-mean-square difference between the speckle intensities of two different wavelengths produced in the far field by a rough surface has been studied theoretically and experimentally. The rms differences for various spot sizes, including differences comparable with the correlation length of the surface, are numerically evaluated. The possibility of estimating the correlation length of a rough surface by using speckles of two different wavelengths is discussed and demonstrated experimentally. The experimental results obtained with this optical method are compared with those obtained by a stylus instrument.

Holographic Microscopy of Diatoms

Hnlographic microscopy provides yet another means for enhancing the study of microscopic organisms in general. It has been suggested as one approach for recording biological and physical phenomena (1) and utilized with various microscopic organisms (2) (3). Diatoms occupy critical roles in the primary producer level of ecological food webs. In addition, these organisms possess detailed structure permitting further possibilities in optical studies. In the present report, we present one method for producing diatom holograms. Encasement in a fairly rigid silicon dioxide frustule and a reasonable degree of transparency are characterictic of this group of microorganims. The transparency factor led to a highly illuminated background which, in initial experiments, gave rise to poor holograms. However, subsequent modifications in technique later corrected this situation. DiatDms were collected from both fresh and brackish water ecosystems. Following preparation utilizing various standard diatom mounting techniques (4) several 75 X 25 mm glass slides were selected for a dominance of two species with grossly different morphological characteristics. The species chosen were a (1 ) pennate (linear) tTpe, e.g., N4viczlv sp.; and (2) a centric type, e.g., Cyclotella sp. The techniques employed here evolved from those using sideband holography coupled with a microscopic apparatus (5) (6) (7) (8) (9). Figure 1 displays a schematic of the optical system used to construct and reconstruct diatom holograms. A 15 mW Helium-Neon gas laser provided the coherent light source. After the variabIe beam splitter (VBS), two spatial filters SP1 and SP2 of 25 and 12 microns diameter respectively and

Automated Identification of Diatoms

Instrumentation permitting rapid automated identification of diatoms to be used in an environmental quality control system is described. A micro-optical processor, using input from an interference contrast microscope coherently illuminated by a Helium-Neon laser or an Argon laser, is the basic operational unit. Some of the options and problems in automated identification are discussed. (Accepted for publication 4 August 1981)

A Real-Time Hybrid Optical System for Pattern Recognition Applications

A description of a coherent optical processor which utilizes matched spatial filters in order to do pattern recognition is presented. The processor has been interfaced to a PDP-11-40 computer which controls the input film drive, the filter stage stepper motors, digitizes, and stores data and is used for data analysis. On-line to the computer are various peripherals including: a DEC-writer, a storage scope, a plotter, and a display terminal. As an example of a pattern recognition problem, we discuss the application of the system to the identification of biological specimens.

Trends in Optical Fibre Metrology and Standards

Trends on optical fibre technologies look very promising in terms of monetary market and technical advances. The maturing of the present and foreseen potential will rely on an adequate response in optical fibre measurements, metrology, standards and instrumentation. Key aspects of this evolutionary cycle, in which an important share of the investment goes in metrological activity are described stressing the exigencies brought by exploiting technical breakthroughs.

Converging beam optical Fourier transforms

The classical, most often used, system for performing the optical Fourier transform is by using parallel coherent beam illumination. Lenses used in this method can become quite costly. In this paper we present results obtained using converging beam illumination which is suitable for many applications and is less expensive than the parallel beam method. The input objects for which the Fourier transforms were made are transparencies of snowflakes.

A laser-based optical filtering system to analyze samples of diatom communities

Biomonitoring systems designed to protect the integrity of aquatic ecosystems must satisfy two complementary requirements if they are to be used in a successful management program. First, they must generate reliable information with respect to the current biological status of the ecosystem; second, they must be capable of reducing the lag time in the feedback of this information. This paper describes a biomonitoring system, currently being developed, that employs coherent optical spatial filtering techniques to rapidly identify diatoms and process species-abundance information. Preliminary results indicate that the optical problems associated with such a system can be overcome satisfactorily, although investigations are continuing into the problem of interfacing a microscope directly to the optical system. We envision that this system can eventually be employed in a management program along with chemical and physical data to obtain full beneficial use of the ecosystem without damage.