A point laser interferometer for measuring aspheric optics is developed in this paper. The proposed laser interferometer will be used as a optical probe in optical coordinate measuring machines. The point optical probe is based on homodyne interferometry with frequency stabilized He-Ne laser to provide traceable measurements. The influences of various aspheric surface factors on the performance of point optical probe are analyzed, such as roughness, reflectivity, material, slope angle etc. A compensation method is applied in the signal processing system to reduce the influences. Experimental results show that the measurement resolution is at the nanometer level under various conditions.
In order to develop an aspheric surface measurement standard device to provide reliable and traceable measurement and
calibration, a high resolution aspheric surface measurement technology based on laser interferometer is proposed in this
paper. A laser interferometer with frequency stabilized He-Ne laser is used to provide traceable measurements. The
standard device would provide calibrations for different kinds of aspheric surface, therefore the interferometer used in
the standard device would be influenced by various factors, such as roughness, reflectivity, material and slope angle. The
influences of reflectivity and roughness are analyzed. A compensation method based on the analysis is applied in the
signal processing system to reduce the influences of reflectivity and roughness. An objective lens is used to collect the
measurement beam reflected from the target. The laser interferometer is set up and tested under different conditions: the
reflectivity is 1%~100%, the surface roughness is 0.012~0.8μm. Experimental results show that the measurement
resolution of the developed interferometer is at the nanometer level.
Cone parts are widely used in advanced manufacturing and precision mechanics, providing air proof, torque transmission and so on. The straightness of generatrix is one of the important parameters, and the required accuracy can be up to submicrometers. In order to realize the rapid and high precision generatrix measurement of smooth surface cone, a laser interferometric method is proposed based on the structure of typical Fizeau interferometer. The high precision optical flat is used for reference standard, and the surface of cone is the measured object. Two cylindrical lenses with different focal lengths realize unidirectional expansion of parallel beam, solving the problem of CCD camera fringe resolution. The interference fringes are curved because of the cone angle, and the peak is the basis for accurate determination of the generatrix. Two fringe processing techniques are described in detail, which are single-frame and phase-shifting methods. Single-frame method includes two steps, i.e. the calculation of integral part and decimal part. The advantage of this method is the simple measurement structure. Phase-shifting method needs piezoelectric transducer (PZT) to generate several steps for phase calculation, with the advantage of high accuracy. The experimental results show that the straightness measurement accuracy can be better than 0.2 μm.