Optics: measuring and testing – By dispersed light spectroscopy – With raman type light scattering
Patent
1996-01-16
1997-06-10
Evans, F. L.
Optics: measuring and testing
By dispersed light spectroscopy
With raman type light scattering
356328, G01J 344, G01J 318, G01J 328
Patent
active
056381735
DESCRIPTION:
BRIEF SUMMARY
This invention relates to spectroscopic apparatus and methods. It is particularly useful in Raman spectroscopy, though it can equally be used in other forms of spectroscopy.
The Raman effect is a phenomenon in which a sample scatters incident light of a given frequency, into a frequency spectrum which has lines caused by interaction of the incident light with the molecules making up the sample. Different molecular species have different characteristic Raman spectra, and so the effect can be used to analyse the molecular species present.
A prior Raman analysis apparatus is described in our earlier European Patent Application No. EP 0543578. A sample is illuminated by a laser beam, and the resulting Raman scattered light is analysed, and then detected. The detector may be a charge-coupled device (CCD) comprising a two-dimensional array of pixels. The analysis of the Raman spectrum may be carried out by a dispersive device such as a diffraction grating, which disperses the spectrum produced from a point or line in the sample across the width of the CCD.
The apparatus may be arranged to disperse the spectrum widely across the CCD, to provide high spectral resolution. For a CCD of a given width, however, only a part of the spectrum can then be detected at any one time. To acquire data from a wider spectrum, one possible method is to expose one part of the spectrum onto the CCD for a sufficient time, and then to read all of the data relating to that part of the spectrum from the CCD into a computer. Next, the diffraction grating is indexed to a new rotary position, so that the next part of the spectrum is received by the CCD. Again, sufficient exposure time is allowed, and all the data from that part of the spectrum is read into the computer. This process is repeated as often as necessary. However, this step-and-repeat method has a disadvantage during subsequent computer processing of the data, because it can be difficult to join together in a seamless manner the separate blocks of data acquired from the separate parts of the spectrum. This is especially true if there have been changes in the background light level between the separate exposures, or if other conditions have altered. Furthermore, exposing the separate parts of the spectrum sequentially obviously increases the time required to analyse the complete spectrum, compared with a lower resolution system in which the whole spectrum of interest is dispersed more narrowly across the width of the CCD.
EP 0543578 describes a technique in which the CCD is scanned synchronously with rotation of the diffraction grating, to allow seamless acquisition of data from a widely dispersed spectrum. This technique overcomes the problem of joining together separate blocks of data with different background light levels, but still requires a similar length of time to analyse the full spectrum. Furthermore, both these methods require a precision rotary stage for mounting the diffraction grating, so that it can be rotated automatically into repeatable positions, preferably under computer control.
According to the present invention, there is provided spectrcscopic analysis apparatus comprising: a sample; direction; disperse a part of said spectrum across the detector in said first direction; and detector to split the scattered light to follow at least two different optical paths to the detector, the light reaching the detector by each of the optical paths being in different parts of said spectrum.
Preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic block diagram of a prior Raman analysis apparatus;
FIG. 2 is a schematic plan view of the analysing and detecting sections of a first embodiment of Raman analysis apparatus according to the invention;
FIG. 3 is a schematic perspective view of the apparatus of FIG. 2;
FIG. 4 is a schematic plan view of the analysing and detecting sections of a second embodiment of Raman analysis apparatus according to the invention;
FIG. 5 is a sch
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Baldwin Kurt J.
Batchelder David N.
Smith Brian J. E.
Evans F. L.
Renishaw plc
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