Optics: measuring and testing – Crystal or gem examination
Patent
1987-02-03
1989-01-24
Evans, F. L.
Optics: measuring and testing
Crystal or gem examination
356301, G01J 344, G01N 2187
Patent
active
047997869
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an identification technique and more particularly relates to the identification of diamonds as opposed to artificial diamonds, zircon or similar materials.
It is often useful for example in the jewelry trade to unambiguously differentiate between cut diamonds (gem grade) and artificial diamonds such as those made from zircons. In Raman spectroscopy a monochromatic beam of light is directed onto a sample and observations are made on the scattered radiation. Monochromatic light sources of different frequencies can be used such as gas lasers. The Raman signal from a diamond has been found to be highly specific and the present invention relates to a device for identifying diamonds by use of this property.
Thus according to the present invention, there is provided a method for the identification of diamonds comprising the steps of (a) placing a sample to be identified in a beam of monochromatic laser radiation of pre-determined wavelength, (b) passing the scattered Raman radiation from the sample through a filtering means adapted to pass only scattered Raman radiation of frequency characteristic of a diamond, and (c) detecting the filtered radiation.
Preferably the source of radiation is a gas laser producing monochromatic radiation in the green parts of the spectrum. The means for detecting the excited Raman radiation is preferably the human eye or a detector based on a photocell but other suitable forms of detection may also be used. The filtering means is preferably located at right angles to the scattered beam of radiation. The filtering means may comprise a thin glass slide having a suitable coating. Filters are available from manufacturers (such as Melles Griot) and are characterized in terms of the wavelength of the incident radiation.
The invention also includes a device for the identification of diamonds comprising a source of laser radiation adapted to provide a monochromatic beam, means for supporting a sample to be identified in the path of the monochromatic beam, a filtering means adapted to pass only scattered Raman radiation of frequency characteristic of a diamond and means for detecting the scattered Raman radiation passed by the filtering means.
Conventional analysis of materials by Raman spectroscopic techniques involves the use of expensive optical equipment such as a monochromator together with a detector such as a photomultiplier tube or a diode array (see our copending UK patent application No. GB 2140555 A).
However it has been found that in the case of a diamond the Raman signal resulting from its irradiation with a monochromatic beam is relatively intense. By use of a narrow band pass filter a means of identification of diamonds from those of the artificial variety has been produced.
By the use of a gas laser giving an output in the green region of the visible spectrum, the Raman shift caused by a diamond is sufficiently towards the red region to allow ready identification using conventional laser safety goggles, the goggles filtering the unshifted laser radiation. A helium
eon laser which normally gives an output in the red region of the spectrum, near 632.8 nm can be modified to give an output near 543.5 nm. Such a laser is much less expensive than other green lasers and is suitable for observation of the Raman signal eye after removal of unshifted laser radiation by a suitable filter. The preferred range of wavelengths for the incident monochromatic laser radiation is from 450 to 650 nanometers.
The invention will now be described by way of example only and with reference to the accompanying drawing.
A low powered gas laser 1 of the helium
eon type (supplied by Melles-Griot (Netherlands)) was adapted to give an output near 543.5 nm and to direct a beam of monochromatic radiation 2 onto a sample 3 in a holder (not shown). A filter 4 adapted to pass radiation having a wavelength near 585.9 nm (the Raman signal of diamond) was positioned at right angles to the axis of the sample holder and the laser 1. A detector 5, in this case the human eye, was pos
REFERENCES:
patent: 4397556 (1983-08-01), Muller
patent: 4693377 (1987-09-01), Gerrard et al.
Melles Griot, Optics Guide 3, 1985, pp. 1, 333, 350, 351.
Solin et al., Physical Review B, vol. 1, No. 4, Feb. 15, 1970, pp. 1687-1698.
Evans F. L.
The British Petroleum Company p.l.c.
LandOfFree
Method of diamond identification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of diamond identification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of diamond identification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-416821