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US 5,963,320 AGranted
Active spectrometer
AssigneeGeneral Atomics
InventorsNeil H. Brooks, Sergey N. Tugarinov, Nicolae N. Naumenko, Torkil H. Jensen, Daniel Finkenthal
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Abstract
A grating spectrometer employing digital control of an oscillating component (a mirror) and phase-locked digital recording of the intensity profile within the narrow spectral domain defined by an oscillation frequency. Flexible choice of oscillation frequency permits measurement in a quiet region of the noise spectrum. Reference waveforms acquired with the same insturment can be stored and later used to deconvolute a more complex spectrum. The use of multiple detector/slit combinations along a Rowland circle makes the spectrometer sensitive to specific atomic elements.
Claims33
Apparatus for providing one or more electrical signals representing a measurement of spectral similarity between an emission spectrum from a light source and a reference spectrum, comprising:
- an optical instrument that spectrally disperses an optical signal, in a dispersion direction that lies substantially in a dispersion plane, such that spectral components of the optical signal are projected and imaged onto an image region oriented perpendicular to the dispersion plane with the spectral components resolved along the dispersion direction;
- a template, herein defined as a plurality of transmissive slits which may be individual assemblies or part of a mask, that is located in the image region, wherein the transmissive slits are located along the dispersion direction at (i) positions that encode the reference spectra or (ii) at regularly-spaced intervals that span a continuous portion or the entirety of the image region;
- a driver that induces relative movement in the dispersion direction between the optical signal's imaged components in the image region and the template located in the image region, or visa versa;
- a plurality of electro-optical sensors, less than or equal in number to that of the transmissive slits, which are responsive to light from the spectral components passing through the transmissive slits, each electro-optical sensor providing an electrical signal representing intensity of light passing through respective transmissive slits optically coupled to respective sensors;
- a plurality of signal conditioning circuits which (i) transmit the electrical signals generated by the plurality of electro-optical sensors faithfully over a frequency range .omega.-(N/2).omega., where .omega. is a frequency of relative movement induced by the driver and N.omega. is a sampling frequency with which the electrical signal generated by each electro-optical sensor is converted, respectively, to a digital signal, and (ii) attenuate the electrical signals outside the frequency range;
- a digital control and data acquisition system containing (i) both output channels and input channels, the former of which are used to output a sinusoidal waveform at a frequency .omega. to the driver and the latter of which are used to sample at a frequency N.omega. the electrical signals and store the respective digital signals in memory, (ii) a single master clock to permit setting a ratio of sampling frequency and oscillation frequency, N, to an integral value with high precision, or separate master clocks for the output and input channels in which the period of their beat frequency is long compared with the duration of data collection with the active spectrometer, and (iii) a data processing capability wherein the digitally stored data from successive periods at the frequency of relative movement .omega. is averaged together, thereby reducing a level of noise relative to that of the electrical signals in a spectral interval spanned by the relative movement of the spectral components in the image region and the template located in the image region.
3 more elements
An active spectrometer comprising:
- dispersion device selected from the group of devices consisting of diffraction gratings and prisms;
- a focal plane defined by an emission spectrum dispersed from the dispersion device in response to light directed onto the dispersion device;
- means for defining a target spectrum comprising wavelengths of light associated with at least one target substance;
- means for inducing a relative oscillatory movement in a dispersion direction between the means for defining a target spectrum and the emission spectrum, the relative oscillatory movement being at a first oscillation frequency;
- a detector position receiving light at the focal plane;
- an analog-to-digital converter, coupled to the detector position, sampling light received at the detector position, the sampling being at second oscillation frequency, wherein the second oscillation frequency is an integral multiple of the first oscillation frequency.
3 more elements
A method of active spectrometry comprising:
- dispersing light;
- defining a focal plane with an emission spectrum dispersed from a dispersion device in response to the light;
- defining a target spectrum comprising wavelengths of light associated with at least one target substance;
- inducing a relative oscillatory movement in a dispersion direction between the target spectrum and the emission spectrum, the relative oscillatory movement being at a first oscillation frequency;
- detecting light of the emission spectrum at a detector position at the focal plane;
- and
- sampling light received at the detector position, the sampling being at second oscillation frequency, wherein the second oscillation frequency is an integral multiple of the first oscillation frequency.
4 more elements
Dependencies are inferred from the claim text.