US4948257A
Expired / Lapsed
US
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Laser optical measuring device and method for stabilizing fringe pattern spacing
Assignee: TSI Inc
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Filing: 1989-06-23
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Granted: 1990-08-14
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Expires: 2009-06-23
Abstract
Abstract Methods and apparatus for enhancing the accuracy of laser optical measuring instruments using fringe pattern spacing are disclosed. The apparatus in one embodiment includes a laser beam source 10, a beam splitter 14, and mirrors 22 to deflect the beams 18, 20 emitted from the beam splitter 14 to a sensing volume. Alternative embodiments include prisms 42, 44, gratings 62 or other optical devices in lieu of mirrors 22. Objects passing through the sensing volume scatter light which is detected by the instrument to determine, among other things, the velocity of the object. The emitted beams 18, 20 are automatically deflected in response to wavelength changes of the laser beam 16 such that variations in the fringe spacing, due to variations in laser beam 16 wavelength, are compensated by variations in the closing angle K of the emitted, deflected beams. The fringe pattern spacing is thereby held more nearly constant enhancing the accuracy of the instrument. Methods of enhancing the accuracy of measurements taken with laser optical measuring instruments are also disclosed.
Inventors
- 👤 Stanley L. Kaufman
- 👤 Frank D. Dorman
- 👤 Daniel C. Bjorkquist
- 👤 Miles R. Finn
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 06:59
CPC Classifications
G; G01; G01P; G01P5/00; G01P5/26; G01S; G01S17/00; G01S17/02; G01S17/50; G01S17/58
Claims Analysis
Total Claims: 28
Claim 1
Independent Claim
106 words
A method of stabilizing fringe pattern spacing in a laser optical measuring instrument, wherein the fringe pattern spacing is formed by intersecting laser beams, the beams each having a wavelength and a direction, and wherein the fringe pattern spacing varies with the wavelengths and directions of the beams, comprising the step of: altering the direction of at least one of the beams automatically in response to changes in the wavelength of that beam through use of a dispersive element, whereby variations in the fringe pattern spacing due to the wavelength change are eliminated without movement of said dispersive element to provide a stabilized fringe pattern spacing.
Claim 2
Independent Claim
106 words
A method of stabilizing fringe pattern spacing in a laser optical measuring instrument, wherein the fringe pattern spacing is formed by intersecting laser beams, the beams each having a wavelength and a direction, and wherein the fringe pattern spacing varies with the wavelengths and directions of the beams, comprising the step of: altering the direction of at least one of the beams automatically in response to changes in the wavelength of that beam through use of a dispersive element, whereby variations in the fringe pattern spacing due to the wavelength change are eliminated without movement of said dispersive element to provide a stabilized fringe pattern spacing.
Claim 3
Dependent Claim
93 words
The method of claim 1 wherein the method of altering the laser beam direction comprises the steps of: (a) splitting a generated laser beam into a second beam and a third beam; and (b) deflecting the second and third beams to intersect at a closing angle using optical elements in a fixed spatial relation and orientation, whereby the fringe pattern spacing is represented by the formula: d f =WL/2sin(K), where d f is the fringe pattern spacing, WL is the wavelength of the first laser beam, and K is one-half the closing angle.
Claim 4
Dependent Claim
92 words
The method of claim 2 wherein the laser optical measuring instrument includes a first wedge prism and a second wedge prism, and the distance between the first and second wedge prism and the intersection defines a standoff distance and wherein the deflecting step further comprises varying the first and second wedge prisms by rotating the wedge prisms in relation to one another in response to changes in the standoff distance, whereby compensation for changes in the standoff distance may be made while preserving the stabilized fringe pattern spacing without requiring additional movement.
Claim 5
Dependent Claim
39 words
The method of claim 2 wherein a sensing volume is defined by the intersection of the second and third beams and further comprising the step of detecting a Doppler frequency generated by an object moving through the sensing volume.
Claim 6
Dependent Claim
34 words
The method of claim 4 wherein the number of deflections for each of the second and third beams are odd when the second and third beams do not intersect prior to the sensing volume.
Claim 7
Dependent Claim
32 words
The method of claim 4 wherein the number of deflections for each of the second and third beams are even when the second and third beams intersect prior to the sensing volume.
Claim 8
Dependent Claim
131 words
A laser optical measuring instrument comprising: (a) a laser beam source that generates a first laser beam; (b) a laser beam splitting device that accepts the first laser beam and splits it so that the first laser beam emerges from the laser beam splitting device as a second beam and a third beam, the second and third beams forming an included angle; and (c) means for deflecting at least one of the second and third beams to form a closing angle and a fringe pattern spacing, the deflecting means including dispersive elements which are responsive to variations in the wavelength of the first beam, and wherein the deflecting means stabilize the fringe pattern spacing by varying the closing angle, the deflecting means being fixed in spacial relation and orientation while operative.
Claim 9
Dependent Claim
131 words
A laser optical measuring instrument comprising: (a) a laser beam source that generates a first laser beam; (b) a laser beam splitting device that accepts the first laser beam and splits it so that the first laser beam emerges from the laser beam splitting device as a second beam and a third beam, the second and third beams forming an included angle; and (c) means for deflecting at least one of the second and third beams to form a closing angle and a fringe pattern spacing, the deflecting means including dispersive elements which are responsive to variations in the wavelength of the first beam, and wherein the deflecting means stabilize the fringe pattern spacing by varying the closing angle, the deflecting means being fixed in spacial relation and orientation while operative.
Claim 10
Dependent Claim
14 words
The instrument of claim 7 wherein the laser beam splitting device includes a grating.
Claim 11
Dependent Claim
57 words
The instrument of claim 8 wherein the grating includes grating lines, and wherein the included angle is represented by the formula: K 1 =sin -1 (WL/2A), wherein K 1 is one-half the value of the included angle, WL is the wavelength of the first laser beam, and A is the spacing of (distance between) the grating lines.
Claim 12
Dependent Claim
63 words
The instrument of claim 7 wherein the laser beam splitting device includes an acousto-optic device that creates an acoustic wave, and wherein the included angle is represented by the formula: K 1 =sin -1 (WL/2A), wherein K 1 is one-half the value of the included angle, WL is the wavelength of the first laser beam, and A is wavelength of the acoustic wave.
Claim 13
Dependent Claim
34 words
The instrument of claim 7 wherein the deflecting means includes a pair of plane parallel mirrors, including a first mirror to deflect the second beam and a second mirror to deflect the third beam.
Claim 14
Dependent Claim
32 words
The instrument of claim 7 wherein the deflecting means includes a pair of prisms, including a first prism to deflect the second beam and a second prism to deflect the third beam.
Claim 15
Dependent Claim
12 words
The instrument of claim 12 wherein the prisms have a positive dispersion.
Claim 16
Dependent Claim
12 words
The instrument of claim 12 wherein the prisms have a negative dispersion.
Claim 17
Dependent Claim
11 words
The instrument of claim 12 wherein the prisms are acromatic prisms.
Claim 18
Dependent Claim
16 words
The instrument of claim 7 wherein the deflecting means includes a pair of doublet wedge prisms.
Claim 19
Dependent Claim
12 words
The instrument of claim 7 wherein the deflecting means comprises a grating.
Claim 20
Dependent Claim
19 words
The instrument of claim 7 wherein the measurement of the included angle equals the measurement of the closing angle.
Claim 21
Dependent Claim
16 words
The apparatus of claim 7 wherein the laser optical measuring instrument is a laser Doppler velocimeter.
Claim 22
Dependent Claim
15 words
The apparatus of claim 7 wherein the laser optical measuring instrument is a laser interferometer.
Claim 23
Dependent Claim
17 words
The apparatus of claim 7 wherein the laser optical measuring instrument is a laser particle sizing instrument.
Claim 24
Independent Claim
134 words
A method of stabilizing fringe pattern spacing in a laser optical measuring instrument comprising the steps of: (a) generating a first laser beam having a wavelength; (b) splitting the first laser beam into a second beam and a third beam, wherein the second and third beam form an included angle; and (c) deflecting the second and third beams with dispersive elements, the beams being deflected so as to intersect at a sensing volume with a fringe pattern spacing, the intersection of the second and third beams forming a closing angle, the deflection of the second and third beam, and thereby the closing angle, automatically varying due to the dispersion of the elements as a function of the wavelength, whereby the fringe pattern spacing is held more nearly constant without adjustment of said dispersive elements.
Claim 25
Independent Claim
134 words
A method of stabilizing fringe pattern spacing in a laser optical measuring instrument comprising the steps of: (a) generating a first laser beam having a wavelength; (b) splitting the first laser beam into a second beam and a third beam, wherein the second and third beam form an included angle; and (c) deflecting the second and third beams with dispersive elements, the beams being deflected so as to intersect at a sensing volume with a fringe pattern spacing, the intersection of the second and third beams forming a closing angle, the deflection of the second and third beam, and thereby the closing angle, automatically varying due to the dispersion of the elements as a function of the wavelength, whereby the fringe pattern spacing is held more nearly constant without adjustment of said dispersive elements.
Claim 26
Dependent Claim
37 words
The method of stabilizing fringe pattern spacing as recited in claim 22, wherein said deflecting step utilizes dispersive elements arranged and configured in a fixed spatial relationship, whereby measurement of the change in wavelength is not required.
Claim 27
Dependent Claim
37 words
The method of stabilizing fringe pattern spacing as recited in claim 22, wherein said deflecting step utilizes dispersive elements arranged and configured in a fixed spatial relationship, whereby a change in Bragg cell frequency is not required.
Claim 28
Dependent Claim
41 words
The method of stabilizing fringe pattern spacing as recited in claim 23, wherein said deflecting step utilizes dispersive elements arranged and configured in a fixed spatial relationship, whereby a wavelength measurement or a change in Bragg cell frequency is not required.
References Cited (Backward Citations)
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