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14 February 2005 Laser interferometer for absolute distance measurement based on a tunable VCSEL laser
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Proceedings Volume 5776, Eighth International Symposium on Laser Metrology; (2005)
Event: Eighth International Conference on Laser Metrology, 2005, Merida, Mexico
In the work, we present the absolute distance interferometer with a narrow-linewidth tunable VCSEL laser (Vertical-Cavity Surface-Emitting Laser) working at &lambda; ≈760 nm. As a detection technique, we use a fast wavelength-scanning interferometry improved by an amplitude division of the interference fringe with using two signals in quadrature. Used VCSEL laser is wide tunable with the mod-hop free tuning range more than 1.2 nm by means of the amplitude modulation of the injection current. We control the stabilization and tuning process of the laser wavelength with using the frequency lock to a Fabry-Perot resonator. We build that resonator as a glass plan-parallel etalon with high-fines. Except the frequency lock, the etalon helps us to measure a wavelength-tuning interval of VCSEL laser during the scanning process. We have stabilized an operating temperature of the VCSEL laser by means of a fast digital temperature controller. The optical set-up of the interferometer begins with a polarizing beam-splitter. It splits the laser beam into the measuring and reference arm of the Michelson interferometer. Two cubic corner cubes reflect beams back to this beam-splitter. It collects reflected beams to the same axis of propagation. Then a detection unit produces the combination of two perpendicularly polarized laser beams with production of two electronic signals that are in the quadrature. A fast analog-to-digital card equipped with the digital signal processor (DSP) samples these signals. DSP also controls the course of the scanning process. After Δλ ≈ 1 nm scan of the wavelength of VCSEL laser we obtain a record of passed interference fringes and passed Fabry-Perot resonance modes at the same time. On basis of these measured quantities we are able to calculate with high precision the instantaneous value of the optical path length difference between the measuring and reference arm of the Michelson interferometer. We experimentally compared the developed absolute interferometer with a conventional - incremental Michelson interferometer based on a single frequency He-Ne laser that has the resolution 1.2 nm. We achieved the relative uncertainty and scale linearity below 8 x 10-5 for range of tested distances L ε < 78; 118 > mm. The interferometer is able to work as the conventional interferometer too in case the wavelength of the VCSEL laser is locked into the selected resonance mode of the Fabry-Perot resonator.
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Ondrej Cip, Bretislav Mikel, and Josef Lazar "Laser interferometer for absolute distance measurement based on a tunable VCSEL laser", Proc. SPIE 5776, Eighth International Symposium on Laser Metrology, (14 February 2005);

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