Abstract:
Focusing a generated radiation signal on a detector is effected by a curvilinear surface. The radiation beam signal from the reflected surface is collimated or focused on the detector. Light scattered, Raman scattered, fluorescence, chemiluminescence, phosphorescence radiation signals from particles as a result of a chemical procedure or reaction is enhanced through this focusing technique. The enhanced signal which is detected is subsequently measured through different detection techniques.
Abstract:
There is disclosed a method and apparatus for implementing a narrow band rejection filter utilizing a liquid crystal cell. A liquid crystal cell is positioned in the path of a light beam between a pair of crossed or parallel polarizers with the optical axis of the cell at a 45.degree. angle to the optical axes of the polarizers. A voltage is applied to the cell to tune the cell to reject a given wavelength and to pass other wavelengths. In order to reject the given wavelength and pass all other wavelengths, the order of the cell is stepped to maintain rejection of a fixed wavelength and the detected signal from the light passing through the cell is averaged.
Abstract:
A light scattering photometer including a rotating segmented mirror intercepting light from a laser source and alternately directing the light into a sample zone along an optical axis in first and second opposite directions. A mask annulus coaxial with the optical axis intercepts light scattered from the sample in an incremental angle .DELTA..theta. at a selected angle .theta. with respect to the axis. As the direction of sample illumination alternates, the annulus alternately intercepts forward scatter and back scatter of light from the sample at angles .theta. and 180.degree.-.theta., respectively, and passes the forward and back scatter in alternate succession to a detector. The detector output signal is demodulated to derive near-simultaneous forward and back scatter measurements from the sample. The photometer permits measurement at small values of .theta. approaching 0.degree. and hence permits near-simultaneous scatter measurements at forward and back scatter angles spaced by an angle approaching 180.degree..
Abstract:
A method and apparatus for determining the wavelength of a light beam wherein the light beam is directed through a liquid crystal cell functioning as a variable retarder, wherein the voltage applied to the cell is ramped to vary the retardation of the cell between maximum and minimum values, wherein the light from the beam passing through the cell is detected, wherein the intensity of the detected light is monitored, which intensity alternately passes through maximum and minimum values as the retardation of the cell is varied between its maximum and minimum values, and wherein the number of times the intensity alternates between its maximum and minimum values is determined to provide an indication of the wavelength of the light beam.
Abstract:
A system and method are disclosed for optically aligning a capillary tube and an excitation laser beam for fluorescence detection applications by utilizing the Raman scatter signals of the capillary tube's contents. For example, Raman scatter by an electrophoretic separation matrix may be used for alignment in a capillary electrophoresis system. Fluorescent material may be present and may also be used for alignment purposes, but is not necessary. The invention employs a parabolic reflector, having apertures through which the capillary tube and the laser beam are guided so that they intersect, preferably at right angles and at the focal point of the reflector. The Raman scatter signals of the material within the capillary tube are collected via a series of filters and this information is used to reposition, if necessary, a focusing lens that directs the excitation beam into the reflector and the capillary tube, so that the Raman scatter signals are maximized. Maximal Raman scatter signals indicate proper alignment of the capillary tube and the excitation beam. Other signals, such as fluorescence emission from the sample, may then be gathered. Adjustment of the focusing lens may be automated so that alignment of the capillary tube and the beam is maintained throughout analysis of the tube's contents. Sequential alignment of an array of capillary tubes with an excitation beam is also disclosed.
Abstract:
A method of measuring and compensating stray light in absorbance analysis that use a multiple element array detector wherein one or more of the elements of the diode array are utilized to detect stray radiation in the absence of primary radiation including higher order diffracted radiation. In one aspect, the atmosphere is used to filter all primary radiation below a particular wavelength so that one or more array elements corresponding to detection below such wavelength can be dedicated to the detection of only stray radiation. Detection of higher order diffractions can be prevented by dividing the total spectrum into intervals and detecting these intervals in sequence. In another aspect, a diode array is designed to include additional elements along one side of the array outside the exposure of the primary radiation for the sole purpose of detecting stray radiation.
Abstract:
Methods for stray light measurement and compensation in spectrophotometers are disclosed. In one exemplary embodiment, stray light is determined as a convolution of a selected detected radiant power spectrum and a monochromator slit function. Such a stray light measurement may be made with or without the sample in an optical path between a source and detector within the spectrophotometer. When made with the sample in the optical path, the resulting stray light measurement may be used to compensate sample absorbance or transmittance measurements. In accordance with another embodiment of the present invention, sample absorbance or transmittance may be compensated in a method including measuring sample detected radiant power at a wavelength outside an interval of significant detected radiant power within which a sample measurement compensated for stray is desired.
Abstract:
A wavelength calibration solution comprising from about 0.025 to about 0.140 molar neodymium and from about 0.135 to about 0.550 molar samarium, wherein the neodymium is present as a neodymium ionized constituent and the samarium is present as a samarium ionized constituent.A method for checking the wavelength accuracy of spectrometers or spectrophotometers of the type comprising measuring the absorbance (A) or percent transmittance (% T) of a wavelength calibration check solution versus a blank at more than one wavelength. The method is characterized in that the above solution is employed therein as the wavelength calibration check solution.
Abstract:
Gain hysteresis exhibited by the photomultiplier detector of a single beam spectrophotometer is reduced by illuminating the detector and applying dynode voltage thereto during the normal "off" or "idle" interval of the spectrophotometer.
Abstract:
Method and apparatus for authenticating documents such as government notes and currency, stock certificates, and the like by marking the document with an encapsulated dyed liquid crystal material and examining the document for unique optical characteristics of the mark. Reading apparatus for the document measures changes in reflectivity of the liquid crystal mark with changes in an electrical field applied thereto. In other embodiments, reflectivity is measured at a plurality of different wavelengths. In one embodiment, the dye absorbs in regions of the electromagnetic spectrum "invisible" to the human eye and the reading apparatus monitors reflectivity changes at these invisible wavelengths.