High-resolution and wide range displacement measurement based on planar grating

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm(-1) microm with off-the-shelf components). Preliminary results show that it can achieve a resolution of approximately 4 cm(-1) even with a ball-bearing translation stage.

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique.

A near UV-near IR Fourier transform spectrometer based on a beam-folding position-tracking method realized by using retroreflectors is reported. The use of retroreflectors maintains all beams in the beam-fold arrangement in parallel with the incident beams. The beam-folding interferometer used for position tracking is arranged to have optical path symmetry with the measurement interferometer in the zero path difference position of the measurement interferometer, and the vertex of the movable retroreflector in the measurement interferometer is arranged very close to the midpoint of the vertices of two movable retroreflectors in the position-tracking interferometer. These measures keep the equivalent optical axis of the position-tracking interferometer well in line with that of the measurement interferometer even with translational misalignments. Therefore, the change in the optical path difference of the position-tracking interferometer is always synchronous to that of the measurement interferometer during the scanning process. That is, the position-tracking error can be suppressed to very small values during a scan. We have demonstrated a UV-near IR Fourier transform spectrometer with a standard quality ball-bearing translation stage achieving a resolution close to the theoretical resolution of approximately 0.28 cm(-1) at the He-Ne laser wavelength when the scan distance reaches the travel distance of over 2 cm. This was achieved without the need for elaborate optics, sophisticated detecting electronics, and high-precision servomotion control.

Near UV-near IR Fourier transform spectrometer using the beam-folding position-tracking method based on retroreflectors

The accuracy of a machine tool is based on the direct position feedback from its built-in encoders which accurately measure displacements of motion axes by moire patterns. However, the posture of a...

An approach to investigate moiré patterns of a reflective linear encoder with application to accuracy improvement of a machine tool

The SPectral and Photometric Imaging REceiver (SPIRE) will be launched in 2007 as one of three instruments on ESA's sub-millimetric space telescope Herschel. It covers the 200-670 micron spectral range with a three-band, 4'x8' field-of-view (FOV) photometer and a dual-band, 2.6' diameter FOV imaging Fourier transform spectrometer. Alignment verification of the instrument is accomplished optically by means of OGSE based on classical alignment telescopes and specially designed equipment. The main purpose of this process is to make sure the internal instrument cold stop is aligned with the telescope exit pupil, and that it stays aligned as the instrument is taken down to its 4K operating temperature. Optical alignment verification also includes measurement of pupil imaging quality and characterisation of the instrument wavefront error. For the latter, a Hartmann test is implemented, allowing estimation of the main aberration terms and comparison with the ideal instrument. This paper describes the philosophy of the alignment plan and presents the main results obtained during alignment of the structural and thermal model.

/pdf/optical-alignment-verification-of-the-herschel-spire-2or4zlof14.pdf

Optical alignment verification of the Herschel-SPIRE instrument

An interferential position sensor for operation in space at a deep cryogenic temperature (4 K) is derived from a commercial sensor. The application is for the Spectral and Photometric Imaging Receiver submillimetric imaging Fourier-transform spectrometer on the Herschel space telescope. This sensor is used to control the displacement of the interferometer's moving mirrors and to sample the interferograms. This development addresses the following points: minimization of the effects of cooling critical optical parts, introduction of a fully redundant focal plane, selection of optoelectronic components efficient at 4 K, and design of a cryogenic preamplifier.

Interferential scanning grating position sensor operating in space at 4 K

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Interferential scanning grating position sensor operating in space at 4 K