Instrument Description

Rotary Air Bearing Goniometer

The ultra-precision, high stiffness air bearing table is the key element of the SpectroMaster^®, as it determines the angular resolution and measurement accuracy of the minimum deviation angle and apex angle, and thus the overall accuracy of the refractive index measurement. The axial and radial run-out errors of this bearing are smaller than 0.05 µm. It is supplied with an air control unit including pressure gauge and adjustment, particle filter and air dryer. An oil-free factory air supply net or a dedicated compressor is needed at the input of the air control unit. Further specification of the air supply is available upon request.

The goniometer embodies an ultra-precision Heidenhain goniometer unit with an angular resolution of 0.036 arcsec and a software-enhanced accuracy of better +/- 0.2 arcsec. Specially selected goniometers are used for the SpectroMaster^® HR instrument.

The motorized version of SpectroMaster^® HR is driven by a highly dynamic and ultraprecise backlash free piezo motor drive. The piezo motors generate no significant excess heat for optimum temperature stability at the place of the sample. For the same reason, also the rotary and linear sample table stages are piezo driven. The piezo drive combines both, high measurement speeds and sub-arcsecond positioning accuracy.

The manual version of SpectroMaster^® HR employs a differential micrometer screw for highest sensitivity and accuracy during 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.

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.

Air bearing table with manual rotation and adjusting unit

Air bearing table with ultra-accurate
piezoelectric drive

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- not be measured at standard laboratory conditions; however, experiments in nitrogen atmosphere have shown the possibility of vacuum-UV measurements.

For the infrared range 1000...2500 nm a two-stage thermoelectrically cooled PbSDetector with dedicated low-noise amplifier is employed.

A quick-change mount at the variable detector slit allows for the quick and easy exchange between both detectors and the mount of additional custom specific detectors.

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 quick change of the spectral lamp and the set of spectral lines to be measured.

For optimum illumination of the target slit, the lamp house is equipped with a back reflecting mirror and quartz condensor optics. The standard set of 5 spectral lamps is given in the following table. Additional lamps are available on request.

Standard set of spectral lamps

A manual or (optionally) motorized filter changer wheel can be equipped with up to 18 narrow bandwidth interference filters for the easy selection and identification of the measurement spectral line. A set of standard filters is delivered with the instrument. Additional custom specific filters can be ordered separately.

Table of typical wavelengths for refractive index measurement

Filter wheel with interference filters

Accessories

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 traceable calibration of the instrument.

SpectroMaster^® accessories: Alignment tools,
detectors and reference prism