Optical: systems and elements – Holographic system or element – Having optical element between object and recording medium
Patent
1996-12-02
1999-04-06
Spyrou, Cassandra
Optical: systems and elements
Holographic system or element
Having optical element between object and recording medium
359 1, 358105, G03H 128, H04N 718
Patent
active
058926020
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention pertains to a method and a device for measuring the mobility distribution of particulate elements in a medium, using incoherent light holography.
BRIEF SUMMARY OF THE INVENTION
There are currently many technical domains in which being able to discriminate between the particulate elements of a medium is essential. This is particularly true, for example, in the field of fluid mechanics, in chemistry, in biology, or in genetics, where analysis requires the counting and/or the discrimination of molecules, particles, cells, or microspheres.
Studies have already been conducted to allow this type of discrimination or counting of particles.
Among these studies, one can mention the "Elapsed Time Method" (ETM). As represented in FIGS. 1a, and 1b, in such a method, a sample of particles, for instance labeled by using fluorescence, is introduced into a field of forces that act upon the particles. Within a determined period of time, the particles, all of which present different mobility parameters--mobility parameters including a velocity parameter and/or an acceleration parameter--migrated to different positions and are, therefore, physically separated. Particles exhibiting the least inertia are at the farthest from their point of departure, particles exhibiting the greatest inertia are at the closest to their point of departure, and those in the middle are spread among the aforesaid particles. An image of marked particles is recorded, allowing for an evaluation of mobility parameters, either visually or by calculation.
A variation of the precipitate method can be applied by placing a detector at a specified distance from the points of departure of the particles. The detector signal, during the migration of particles, is analyzed as a function of time. As represented in FIGS. 1c to 1f, particles presenting different mobility go through the field of view of detector DE at different times. The signal delivered by the detector represents the particles' mobility as a function of time.
Within this method, time and length of migration necessary to separate two particles of neighboring speed, V.sub.1 and V.sub.2, at the level of the field of the detector, are given by the relations: ##EQU1## where D represents an empirical bandwidth parameter which depends on the installation. This bandwidth parameter corresponds to a width, in the direction of migration, over which particles of approximately equal velocity, are spread at a particular point in time. Therefore, there exists a corresponding bandwidth D for a specific installation, and for each velocity value.
The precipitate method, in its two variations, allows measurement of mobility in media in which the intensity of a single particle's signal is below the noise level. Nevertheless, it does not allow individual measurements for each particle, the particles also being discriminated in terms of groups or particle bands presenting parameters of similar mobility, to the value of nearby bands--the signal relative to a band comprising, in fact, the sum of the elementary signals of each particle belonging to the band under consideration.
Consequently, the resolution or the power of discrimination for precipitate methods, as well as for their devices for application, is limited by the width value of the precipitate band. Particularly, in the aforementioned case for the implementation of this method, the particles are presented for a very brief instance in the field of the detector. Under such conditions, it is necessary to produce a highly elevated level of excitation energy, to assure that labeling by using fluorescence can be sufficient for appropriate conditions of detection. The thermal effects generated in these conditions increase the bandwidth parameter, which in itself reduces the system's resolving power.
Another method, consisting of a high speed recording of sequences of images of the medium and of the particles, was proposed with the object of measuring dynamic behavior. Such a method requires the identification of each particle
REFERENCES:
patent: 4320415 (1982-03-01), Jones
patent: 4648715 (1987-03-01), Ford, Jr. et al.
patent: 4976504 (1990-12-01), Sirat et al.
patent: 5081540 (1992-01-01), Dufresne et al.
Optiment, Optical Metrology Ltd.
Spyrou Cassandra
Treas Jared
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