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TRIOPTICS GMBH ■ OPTICAL TEST EQUIPMENT High Precision Automatic Spectrometer- Goniometer

Page Overview Measurement Principle Error A naly sis and System Requirements Instrument Description SpectroMaster® Selection

OVERVIEW / MEASUREMENT PRINCIPLE Overview The SpectroMaster® family of instruments has been derived from the renowned TRIOPTICS PrismMaster® series of ultra-accurate prism goniometers and is specifically designed for prism refractometry with highest precision. SpectroMaster® Spectrometer-Goniometers are employed by optical glass manufacturers, national metrology institutes as well as scientific research institutes with highest accuracy demands for the determination of the refractive index and dispersion of optical glass and crystalline materials in the UV, VIS or IR spectral range. The...

MEASUREMENT PRINCIPLE humidity and can be calculated with sufficient accuracy from p and T with the generally approved Edlén equation. In most cases, the humidity can be neglected. Since these calculations are quite complex and error-prone, this is done automatically by the instrument software. Goniometer Error As shown above, the refractive index measurement is based on angle measurements. This is done by a precision goniometer equipped with an autocollimation telescope for measuring both the apex angle α and the minimum deviation angle δ. The figure below shows the dependence of the...

ERROR ANALYSIS/SYSTEM REQUIREMENTS Required angle measurement accuracy for given refractive index uncertainty From this result it becomes evi- dent that the angle measure- ment must be accurate to a frac- tion of an arc second if an accu- racy of about lxlO"6 is required, TRIOPTICS has a long experience in manufacturing prism goniome- ters measuring at this level of ac- TRIOPTICS PrismMaster® HR ultra accuracy class are equipped with specially selected Heiden- hain goniometers of the highest accuracy available. With these cial eccentricity and interpolation error compensation, an angle...

Additionally, the SpectroMaster® measurement procedures are performed in a way as to minimize systematic errors and ambient influences, e.g. all angle measurements are done differentially on both sides of the prism, so that potential offset errors are removed by calculating angle differences only. Furthermore, noise is reduced since all angle results emerge from at least two measurements. For further noise reduction, the system can be configured to per form even more measurements for better averaging. However, the experience shows that in a well-shielded environment noise shows up in the...

The principle measurement setup is shown above. A fixed collimator is projecting the image of a slit target through the sample prism. An autocollimator mounted to the rotary air bearing goniometer is picking up the slit image and measuring the deviation angle of the refracted light passing through the prism. The illumination of the variable target slit is done by exchangeable spectral lamps, so that the measurements are done at precisely known wavelengths of selected spectral lines. For a better identification of certain spectral lines, narrow band interference filters can be moved into the...

INSTRUMENT DESCRIPTION the manual adjustment of the telescope angle. Due to the sophisticated software assistance and alignment indicators, it has been proven that manual operators can reach the same high accuracy of the motorized version but at the cost of reduced measurement speed. Collimator and Autocollimator The mirror collimator and the mirror autocollimator include high performance off-axis parabolic mirrors with sur face quality better λ/10. The focal length is 600 mm and the clear aperture 60 mm. Beam folding mirrors of the same surface and coating quality allow for a compact...

INSTRUMENT DESCRIPTION Mirror autocollimator and collimator unit Detectors The most convenient and fastest measurements are done with the CCD camera in the spectral range between 400..1050 nm. Optionally, a special UV-enhanced CCD camera is available which extends the usable UV range down to 250 nm. The CCD camera is also used for measuring the apex angle in autocollimation mode. A photomultiplier tube allows measurements in the spectral range between 130 and 320 nm. Wavelengths below 193 nm are considered as Vacuum-UV and can- Vacuum-UV photomultiplier-tube (PMT) detector mounted on...

INSTRUMENT DESCRIPTION The signal detection and amplification is performed by a laboratory grade lock-in amplifier for best signal-to-noise ratio and detection of even weakest spectral lines. Illumination Accurate refractive index measurements require the exact knowledge of the measurement wavelength. This is achieved by using low-pressure discharge spectral lamps. Spectral lamps generate a spectrum of discrete spectral lines with precisely known and stable wavelengths. The SpectroMaster ® HR comes with a lamp house for up to 8 different spectral lamps on a rotating turret. It allows the...

MEASUREMENT RESULTS 11: t;m cs CWIM ■ CJITOU II fii i GUIPMI NI Measurement Results Filter wheel with interference filters The instrument is delivered with a set of alignment tools for regular alignment checks of the instrument setup. A set of different spectral lamps and interference filters are provided on customer's order, TRIOPTICS can also provide one or more certified reference prisms for the trace- able calibration of the instrument, Wawlnnglh inmi Example measurement on a K5 glass prism and a The above graph shows typical measure- ment results and the fitted dispersion curve for a...

TRlOPTICS GMBH ■ OPTICAL TEST EQUIPMENT MEASUREMENT RESULTS The below plot shows the comparison of SpectroMaster® results and measurement data from an independent institute in the Measurement results for an S-BAL2 sample prism temperature coefficient of this S-BAL2 glass allows highly accurate measure- ments even in standard laboratory envi- ronment which is reflected by the residuals values over the full measurement range, surement results is guaranteed by the careful final inspection using several PTB certified reference prisms available at TRI- OPTICS. Each SpectroMaster® is delivered...