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Variable Angle Laser Ellipsometer

Model No: HO-VALE-01

Ellipsometry is a very sensitive optical technique which provides unequalled capabilities for thin film metrology. Ellipsometry exploits phase information and polarization state of light and so can achieve angstrom level resolution. The main advantages of ellipsometry are its non-destructive character, high sensitivity and wide measurement range. HO-VALE-01 model is suitable for educational purpose and the optical parameters like thickness and refractive indices of a single layer thin film can be determined precisely. In the ellipsometer model HO-VALE-01, a circularly polarized light is made incident on the test substrate and the reflected light which is linearly polarized is analyzed for polarization changes.

The instrument consists of two concentrically rotating arms around a precisely graduated disc that is fixed to a heavy base. The Laser, Polarizer, and Quarter wave plate are mounted on the laser arm, whereas the analyser and the detector are mounted on the detector arm. The two arms can be positioned to set the incident angle between 30 and 90 degrees with a resolution of 0.1 degree. The Polarizer, Analyzer, and the Quarter-Wave plate are mounted in precision rotary stages that are 360° rotatable with a resolution of 0.1°. Linear glass polarizers are used for both polarizer and analyser. Sample is placed on a precision micrometer driven vertical stage with height adjustment range of 10 mm and resolution 0.01 mm. For null method, detector can be replaced with a miniature screen for visual determination of null point, if required.

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    Measurement Range :     50 nm - 300 nm
    Incident Angle : 30° ~ 90°, Error ≤ 0.1°
    Laser : DPSS (532 nm, 5 mW)
    Detector : Si Photodiode (5.8 mm x 5.8 mm)
    Rotation Range
    Polarizer : 0° - 360°
    Quarter-Wave : 0° - 360°
    Resolution : 0.1 degree
    Source Arm
    Rotation Range : 70 degrees (from horizontal plane)
    Main Scale Division : 1 degree
    Resolution : 0.1 degree
    Detector Arm
    Rotation Range : 70 degrees (from horizontal plane)
    Main Scale Division : 1 degree
    Resolution : 0.1 degree
    Sample Holder
    Height Adjustment Range : 10 mm
    Resolution : 10 microns
    Tilting Range : +/- 2 degree



Fig. Schematic diagram of ellipsometer operation

As shown in the Fig., a randomly polarized laser light (532nm) passes through a polarizer which changes the polarization of light from random polarization to linear polarization. The linearly polarized light then passes through a quarter-wave plate (set the fast axis at 45 degree) which changes the polarization state from linear to circular. After reflection from the sample thin film, the circularly polarized light becomes linearly polarized and an analyzer measures the degree of polarization. A software will be used to find out the thickness and refractive index from the measured data.



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