Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
  • G01B9/02005—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using discrete frequency stepping or switching
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
  • G01B11/303—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces using photoelectric detection means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
  • G01B9/02003—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using beat frequencies
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02007—Two or more frequencies or sources used for interferometric measurement
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
  • G01B9/02044—Imaging in the frequency domain, e.g. by using a spectrometer

Definitions

• the invention relates to a device for the interferometric detection of surface structures by measuring the phase difference in laser-speckle pairs in the measuring points on this surface.
• the device according to the invention with the characterizing features of the main claim has the advantage that a very simple arrangement of optical fiber lines can be used for beam splitting and frequency change of a beam.
• Optical couplers and dividers for such fiber lines are available as common components.
• the beam guidance is therefore variable and does not require any adjustment, at least in this area.
• the frequency shift is achieved by a certain extension of a fiber line and frequency modulation or wavelength modulation, which makes the "frequency converter” very simple and inexpensive. Since the fiber lines can be guided very close to one another without any accuracy being important, the entire arrangement is not only very inexpensive but also very compact.
• a particular problem with the measurement is that the height differences to be measured on the measuring surface in the known methods must be less than half a wavelength of the measuring beam. Differences in height, which differ by half a wavelength, result in the same signal, namely a phase difference of 360 °.
• the wavelength of the measuring beam must be selected accordingly in the known measuring devices, that is to say certain pre-information or estimates of the roughness and structure of the surface to be measured are required.
• this problem takes a back seat.
• the phase differences are determined in a known form, and then a comparison of the various determined phase differences is carried out.
• a simple design is achieved in that the divider device is provided with an optical coupler for the at least two input-side optical fiber lines.
• the wavelengths of the different laser sources differ only slightly.
• the accuracy of the result increases with a larger number of laser sources.
• the laser sources work at the same time and that a number of photo receivers corresponding to the number of laser sources is provided in the photo receiving device, means in front of these photo receivers being provided with means for splitting the laser beam into its components with different wavelengths and for feeding to the individual photo receivers is.
• the laser sources can be controlled very easily, and a very simple evaluation is possible due to the simultaneous presence of the measurement results.
• several photo receivers and a device for splitting the laser beam are required.
• the laser sources can also work sequentially, in which case only a single photo receiver is required in the photo receiver device.
• a memory device for temporarily storing the measurement results is required for the evaluation, and the laser sources must be controlled sequentially.
• Fig. 1 is a schematic representation of the measurement setup for sequential operation and Fig. 2 shows a detail of the measurement setup for the
• three laser sources 10 to 12 designed as laser diodes are provided, the frequency of which by current modulation, in particular injection current modulation.
• the dotted line between the laser sources 11 and 12 is intended to indicate that the number of laser sources can also be higher.
• at least two laser diodes must be provided.
• the laser beams emerging from these laser diodes are each fed via optical fiber lines 13 to 15 to a coupler and divider device 16, where they are first coupled to form a single beam and then divided again into two identical output beams, namely into a reference beam. and into a measuring beam.
• the reference beam is continued in an optical fiber line 17 and the measuring beam in an optical fiber line 18.
• the optical fiber line 17 has a loop 19 for the reference beam, which extends this fiber line 17 relative to the fiber line 18 by the length of this loop 19.
• the reference beam and the measuring beam leave the fiber lines 17, 18 at their ends, are collimated and fed to a deflection device which consists of a mirror 22 inclined at 45 and a beam splitter 23 which is at an angle of 45 ° is inclined in the opposite direction.
• the reference beam emerging from the end 20 is deflected at right angles at the mirror 22, passes through the beam splitter 23 and arrives at a photo receiver 24 designed as a photodiode in a photo receiver device 25.
• the measuring beam runs from the end 21 through the beam _ _
• the splitter 23 to the surface of an object 26 to be measured is reflected from there and also passed from the beam splitter 23 to the photo receiver 24.
• the two components overlap after the interferometer pr ip and thus illuminate the photo receiver unit.
• the received signal from the photo receiver unit 24 is processed in the photo receiver device 25, if necessary, and fed to an evaluation device 27 which, together with a frequency modulator 28, forms the control and evaluation electronics 29.
• the frequency modulator 28 the laser sources 10 to 12 can be current-modulated to change their frequency or wavelength, in particular inject-current-modulated, and can be switched on sequentially in certain time ranges.
• the measuring device shown in FIG. 1 operates in the so-called monocolor mode, that is, the laser sources 10 to 12 are switched on sequentially in their respective time range, so that only laser light of one wavelength is ever present.
• this laser light of one wavelength is divided into a measuring beam and a reference beam in the coupler and divider device 16.
• the reference beam experiences a relative frequency shift of e.g. a few kHz.
• This reference beam and the measuring beam reflected on the surface of the object 26 are then superimposed after the interferometer principle and illuminate the photoreceiver 24, whose measuring signal thus also has a frequency of e.g. has a few kHz, which corresponds to the frequency difference between the measuring and reference beams
• a phase difference arises which depends on these height differences. This is described in more detail in the prior art specified at the outset. For example, a profile change that corresponds to half a wavelength of the laser light results in a measurement signal shift of 360.
• phase difference angles of 36 and 72 are thus recognized. If, on the other hand, height differences on the object 26 were an entire wavelength of the laser light from the first laser source 10, then phase difference angles of 72 and 144 ° would result. In this way, exact measurements of surface structures are also possible, the height differences of which are multiples of half a wavelength.
• the second exemplary embodiment shown in detail in FIG. 2 largely corresponds to the first exemplary embodiment.
• all three laser sources 10 to 12 work simultaneously, and the correspondingly superimposed laser beams with the three different wavelengths are shortly before the photo receiver device 30 by a prism 34 or another wavelength divider, for example an optical grating, in their individual components different wavelengths split.
• the evaluation can take place here simultaneously, since all three measured values are available simultaneously, while in the first embodiment an intermediate storage is required before the phase differences are can be voted.
• the mode of operation on which FIG. 2 is based can also be referred to as multicolor operation

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Instruments For Measurement Of Length By Optical Means (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=6375049

Family Applications (1)

Country Status (5)

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Family Cites Families (5)

• 1989
  • 1989-02-28 DE DE3906118A patent/DE3906118A1/de not_active Ceased
• 1990
  • 1990-02-01 WO PCT/DE1990/000066 patent/WO1990010195A1/de not_active Application Discontinuation
  • 1990-02-01 EP EP19900902162 patent/EP0461119A1/de not_active Ceased
  • 1990-02-01 US US07/752,597 patent/US5293215A/en not_active Expired - Fee Related
  • 1990-02-01 JP JP2502533A patent/JPH04504615A/ja active Pending

Non-Patent Citations (1)

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