Multi-Wavelength Measurement Techniques
Author(s): HAGEN Karl-Meiners, SCH(O)DEL René, BURGARTH Volker, ZEID Ahmed-Abou
Pages: 46-52
Year: 2005 Issue: 1
Journal: NANOTECHNOLOGY AND PRECISION ENGINEERING
Keyword: multi-wavelength interferometry; surface profile; roundness; diode laser; length measurement; phase shifting interferometry;
Abstract: In this paper, three experimental examples are given for applications of the multi-wavelength measurement technique. A multi-wavelength diode laser interferometer for the measurement of surface profiles has been developed. With three diode lasers emitting in the near infrared (780 nm, 823 nm, and 825 nm) synthetic wavelengths of approximately. 15 μm and 290 μm could be achieved. The injection current of the laser diodes is modulated with different frequencies around 1 MHz which leads to a modulation of the wavelength and therefore the interferometer phase. The three interferometer signals are detected by lock-in amplifiers using only one photo detector. In the second example the same interferometer is used for the measurement of roundness deviations. For this application only two wavelengths were used. The third example describes phase shifting interferometry, where the length of a material sample is expressed as a multiple of the wavelength used as light source. Using only one wavelength would require the exact knowledge of the integer interference orders. The use of different wavelengths, i.e. 532 nm, 633 nm and 780 nm, results in independent lengths, where the integer orders can be varied. It is shown in which way the number of variations can be reduced drastically. Considering a measurement example at PTB's Precision Interferometer, the uncertainty of the individual length measurement is small enough so that the range of unambiguity is about 0.6 mm, i.e. a rough estimate of the length is sufficient for ultra precise length measurements.
Pages: 46-52
Year: 2005 Issue: 1
Journal: NANOTECHNOLOGY AND PRECISION ENGINEERING
Keyword: multi-wavelength interferometry; surface profile; roundness; diode laser; length measurement; phase shifting interferometry;
Abstract: In this paper, three experimental examples are given for applications of the multi-wavelength measurement technique. A multi-wavelength diode laser interferometer for the measurement of surface profiles has been developed. With three diode lasers emitting in the near infrared (780 nm, 823 nm, and 825 nm) synthetic wavelengths of approximately. 15 μm and 290 μm could be achieved. The injection current of the laser diodes is modulated with different frequencies around 1 MHz which leads to a modulation of the wavelength and therefore the interferometer phase. The three interferometer signals are detected by lock-in amplifiers using only one photo detector. In the second example the same interferometer is used for the measurement of roundness deviations. For this application only two wavelengths were used. The third example describes phase shifting interferometry, where the length of a material sample is expressed as a multiple of the wavelength used as light source. Using only one wavelength would require the exact knowledge of the integer interference orders. The use of different wavelengths, i.e. 532 nm, 633 nm and 780 nm, results in independent lengths, where the integer orders can be varied. It is shown in which way the number of variations can be reduced drastically. Considering a measurement example at PTB's Precision Interferometer, the uncertainty of the individual length measurement is small enough so that the range of unambiguity is about 0.6 mm, i.e. a rough estimate of the length is sufficient for ultra precise length measurements.
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