Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2001-10-05
2004-06-22
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C359S245000
Reexamination Certificate
active
06753959
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a shutter for blocking the path of a light beam in a spectroscopy instrument.
BACKGROUND
It is known that chemical analysis of samples can be accomplished by a variety of spectroscopy-based techniques. For example, the amount of various chemical elements in a sample can be ascertained by optical emission spectrometry or by atomic absorption spectrophotometry. The concentration of various chemical species in a sample can be ascertained by ultraviolet-visible absorption spectrometry or infrared absorption spectrophotometry, or by ultraviolet-visible fluorescence spectrophotometry. These are only a few examples of spectroscopy-based chemical analysis techniques.
Equipment for spectroscopy-based chemical analysis typically operates by measuring the intensity of light either as a function of wavelength or at one or more specific wavelengths. This may be done with a monochromator and a single detector collecting intensity data for each wavelength of interest in a serial fashion, but it is also possible to collect light intensity data for more than one wavelength simultaneously. Because of the greater time efficiency offered by simultaneous measurement, this approach is increasingly favoured for practical applications.
Modem simultaneous spectroscopic measurement apparatus typically includes an optical polychromator together with a solid state electronic detector device incorporating an array of optical sensor elements. The detector can be, for example, a charge-transfer device such as a charge-injection device (CID) or a charge-coupled device (CCD). A polychromator that is able to disperse the light in two dimensions (for example an echelle polychromator) can be employed, in which case a 2-dimensional array of optical sensor elements can be used with advantage as a detector. Alternatively a polychromator that provides dispersion in one dimension only (such as a single-grating-based polychromator) can be utilised, and a linear array detector used. The 2-dimensional approach offers better wavelength resolution for a given wavelength range and so is favoured for chemical analysis applications, particularly for elemental analysis by optical emission spectrometry.
Elemental analysis typically involves operation at optical wavelengths extending from the visible to the far ultraviolet, which places limitations on the types of detectors that can be used. Solid state detectors of various types are known to be suitable for this application, for example charge transfer devices, both CIDs and CCDs, are known to be useful. An example of such a detector is the CCD detector disclosed by Zander et al. in U.S. Pat. No. 5,596,407. This has a number of optically sensitive sites, generally referred to as pixels, that are distributed in a precise geometric arrangement over the surface of the detector to map accurately the optical image from the polychromator. Each optically sensitive site or pixel is capable of converting the energy of incoming light to free electrons, which are stored at the optically active site. The number of electrons, and thus the total charge, accumulated within each pixel will depend on the light intensity incident on that pixel and the time for which the pixel is exposed to said light, said time being usually referred to as the integration time.
Measuring the optical intensity therefore involves determining the amount of charge built up over a known integration period. In order to do this it is necessary first to collect the charge and then to transfer the charge accumulated at each pixel to appropriate readout electronics.
Two principal ways of carrying out this process are available. The first, used in the detector disclosed by Zander et al. in U.S. Pat. No. 5,596,407, duplicates each optically active pixel with an optically inactive pixel. The first step in the readout process is a parallel transfer operation that transfers the charge from each row of active pixels to the corresponding row of inactive pixels. The charge is then stepped through these inactive pixels as the shift register nodes. The second approach uses the optically active pixels themselves as shift register nodes, so that with each move operation the charge on every pixel moves to the next pixel along, with the charge of the last pixel moving to the readout circuit.
Both approaches have their attendant advantages and disadvantages. The second approach has the advantage that most of the surface area of the CCD can be covered by active pixels, thus maximising the light sensitivity of the whole device. It also avoids the need for any secondary structure. That is, this approach provides more efficient utilisation of available light in spectroscopic applications. It also permits the use of relatively inexpensive, off-the-shelf detectors.
The disadvantage of the second approach is that the pixels continue to accumulate electrons generated by any incoming light during the readout process. As a consequence, as the charge from one pixel moves through other pixels on its way to the readout circuitry, it accumulates additional charge, the amount of which depends on the light intensity incident at each of those other pixels and the speed of charge transfer. This has the effect of smearing the resultant image data, which is totally unacceptable in a spectroscopy application. To overcome this disadvantage it is proposed to provide an optical shutter that can block all light to the detector during the readout process.
Known optical interrupters for use in spectroscopic or photographic applications generally comprise one or more metal vanes driven by electromagnetic actuators. For example such devices are disclosed by Vincent in U.S. Pat. No. 3,427,576, U.S. Pat. No. 3,595,553 and U.S. Pat. No. 3,664,251, by Fletcher et al. in U.S. Pat. No. 3,804,506, by Saito et al. in U.S. Pat. No. 4,290,682 and by Krueger in U.S. Pat. No. 6,000,860. These mechanisms are relatively large, and consequently rather slow. This is a serious limitation in spectroscopic applications. The devices also tend to consume significant amount of power. Because of the number of moving parts the reliability and lifetime of this type of mechanism is uncertain. Furthermore, devices offering sufficiently long life tend to be relatively expensive.
Hikita et al. disclose in U.S. Pat. No. 5,268,974 an optical switch based on a piezoelectric bimorph. The use of a piezoelectric device is advantageous because such devices are silent, and they can be operated reliably for many millions of cycles. They are relatively inexpensive. They dissipate very little power and thus do not cause any significant local rise in temperature within the optical system of an instrument. Any such local rise in temperature is undesirable because it may lead to thermal expansion and consequent optical drift. Hikita et al disclose an optical switch having an optical shielding element at the free end of a cantilevered piezoelectric bimorph such that a light beam travelling parallel to the length of the bimorph is either intercepted by said optical shielding element or allowed to pass, depending on the polarity of the voltage applied to the bimorph. Light that is allowed to pass falls on a mirror close to the fixed end of the cantilevered bimorph and is reflected from said mirror and detected by an optical detector. The invention of Hikita et al. is suitable for use with narrow, well-collimated beams of light, such as laser beams, but it would not be suitable for the light beams in spectroscopic instruments. Such beams, although very narrow at certain points, converge rapidly towards such points and diverge rapidly away from them. This is a consequence of the need to capture as much light as possible from the spectroscopic source and transfer it to the detector. A light switch according to the teachings of Hikita et al. in U.S. Pat. No. 5,268,974 would not be suitable for use with a widely convergent or divergent beam because the device itself would partially obstruct the beam irrespective of the position of the optical shielding eleme
Campbell Stewart R.
Hammer Michael R.
Layton Peter G.
Masters Martin K.
Berkowitz Edward H.
Evans F. L.
Geisel Kara E.
Varian Australia PTY LTD
LandOfFree
Optical shutter for spectroscopy instrument does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical shutter for spectroscopy instrument, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical shutter for spectroscopy instrument will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3335701