Optics: measuring and testing – By dispersed light spectroscopy – With raman type light scattering
Reexamination Certificate
2001-08-27
2004-03-16
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With raman type light scattering
C356S302000, C356S320000
Reexamination Certificate
active
06707548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to spectroscopy, in particular, devices and methods for spectrographic analyses that use filters to select wavelengths of electromagnetic radiation for measurement.
2. Description of Related Art
Spectroscopy can be characterized as the study of relationships between absorption and/or emission of electromagnetic radiation by certain substances as a function of the wavelength of the radiation. Absorption spectroscopy is in widespread use for the detection and identification of substances because a substance absorbs electromagnetic radiation better at certain wavelengths than at others. When a substance is exposed to a poorly absorbed wavelength of electromagnetic radiation, much of that radiation is reflected or transmitted back into the surrounding medium. A photodetector nearby can detect the radiation, and the amount of radiation can be quantified. In contrast, when a substance is exposed to an efficiently absorbed wavelength, little of that radiation is reflected into the surrounding medium, and consequently, the amount of radiation detected is less than for a poorly absorbed wavelength. Measurements are typically made over a range of wavelengths, and can include very short wavelengths (e.g., gamma- rays or x-rays) to very long wavelengths (e.g., radio frequency radiation). The relationship between radiation intensity and wavelength is herein termed a “spectrum.” As used here, the term “spectrum” includes, but is not limited to absorption, fluorescence, Raman, emission, or any other form or type of electromagnetic radiation. For many analytical applications, wavelengths in ultraviolet, visible and/or infrared ranges are especially useful.
Individual substances either absorb or emit characteristic wavelengths of electromagnetic radiation. Each substance thus has a characteristic spectrum, which can be used to identify and/or quantify the amount of a particular substance. Many volumes in the spectroscopic literature are devoted to the presentation of data regarding spectra of individual substances.
However, existing methods and apparatus have several drawbacks. Most spectroscopic apparatus rely upon varying the wavelength of emitted radiation from a radiation source by means of a dispersion device such as a prism or a diffraction grating. A dispersion device decomposes electromagnetic radiation of heterogeneous wavelengths into spatially resolved beams of fairly monochromatic radiation. The dispersion is achieved as follows: An electromagnetic radiation is collimated in a beam to allow the beam to fall onto a prism or grating under appropriate angle of incidence. Radiation of various wavelengths present in the beam interferes with such a dispersion device in a wavelength-dependent manner. This produces a plurality of fairly monochromatic beams radiated under various, wavelength-dependent angles. Each beam is collected onto the surface of a photosensitive device (such as a photo-multiplying tube, also called PMT, or photo-diode, or photo-sensitive film). The intensity of monochromatic light in such a beam is analyzed as the function of spatial position of the beam. The position is directly related to the wavelength in the beam. This way of spectra acquisition is broadly employed in various spectrophotometers and spectrographs. A major drawback of this approach is a high cost for such instrumentation, which is to a large extend due to a need for precise alignment of optical elements.
A source of electromagnetic radiation (e.g., a light source) produces a beam of radiation that enters a dispersion device. By way of example, a prism separates the different wavelengths at different angles depending on the index of refraction of each wavelength as it is transmitted through the prism. In the case of visible light, the result can be a “rainbow.” To expose an analyte sample to a particular wavelength, the prism is adjusted so that the angle of refraction of the radiation directs a relatively narrow range of wavelengths to the sample for spectroscopic measurement. To obtain a spectrum, the wavelength is varied by rotating the prism to direct other wavelengths to the sample. Similar methods can be applied to diffraction gratings. These processes are relatively slow, in that the rate of change of wavelength of illuminating radiation must be sufficiently slow to permit accurate measurement of absorption at each wavelength.
The length of time required to obtain a spectrum over a desired range of wavelengths depends upon the range desired, the discrimination between wavelengths, and upon the number of samples to be analyzed. For analyses of multiple samples, traditional spectroscopic methods can be impractically long. Moreover, prisms and diffraction gratings must be aligned carefully and misalignment can result in errors that may be difficult to detect.
SUMMARY OF THE INVENTION
To overcome these and other disadvantages of traditional spectroscopic devices and methods, certain embodiments of this invention use a plurality of narrow-band pass filters to select wavelengths of electromagnetic radiation for analysis. Each filter can be associated with an individual detector, for example, a charge coupled device (“CCD”), forming a “filter/detector unit”. Radiation emitted by a sample can penetrate through a filter and can be detected and/or quantified and can be displayed on an output device and/or stored in electronic form on a computer. The filter can absorb radiation of other wavelengths, preventing those wavelengths from being detected. Additional filters having desired transmittance at other, selected wavelengths can be used simultaneously to detect absorption at those desired wavelengths.
Multiple filter/detector units can be placed in a one- or two-dimensional arrangement relative to each other, permitting the simultaneous measurement of absorbed radiation at a number of different wavelengths from a single sample of the substance to be analyzed. Outputs from each detector can be displayed along, for example, a vertical axis of a two-dimensional plot, and the band-pass wavelength of the filter can be displayed along a horizontal axis, for example, similar to a conventional spectrogram. Thus, a spectrum can be obtained over a desired range of wavelengths. Addressable arrays of samples can be analyzed in an automated fashion. A series of samples can be applied to a substrate, each sample having a unique identifier, either position on the array, or by way of a unique chemical marker. Systems for spectrographic analysis can include servo-controlled probes that can acquire spectrographic information from each of a plurality of samples so arrayed.
It can be readily appreciated that similar strategies can be employed for emission, fluorescence, Raman, and any other kind of spectra, and other types of plots (e.g., three-dimensional displays) can be readily prepared.
In certain embodiments, filters can be chosen to permit passage of a relatively narrow wavelength band of radiation. Such embodiments can be useful in situations in which a desired spectrographic feature is narrow.
In certain other embodiments, filters can be chosen to permit passage of a relatively wide wavelength band of radiation. Such embodiments can be useful in situations in which desired spectrographic features are broad, or in which the desired information has sufficiently high intensity and is not masked by signals at other wavelengths within the band detected.
In yet other embodiments, a portion of a spectrum can be obtained using filter/detector units having wavelength bands that are sufficiently near each other to provide substantially complete coverage throughout a desired wavelength range. In other embodiments, it can be desirable to select only certain portions of a spectrum for analysis.
In additional embodiments of this invention, filter/detector units can include waveguides, including light pipes to transmit radiation from a sample to a remote detector.
Many configurations of sample, sample substrate, waveguides, focusing lenses and detectors
Kreimer David I.
Weber Robert
Yevin Oleg A.
Array Bioscience Corporation
Fliesler Dubb Meyer & Lovejoy LLP
Font Frank G.
Lauchman Layla
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