The combined optical and x-ray interferometer is an instrument that provides a means for transducer calibrations in terms of the standard of length with subnanometric resolution. In combined optical and x-ray interferometry, the optical interferometer is used as the main ruler and the x-ray interferometer as a linear interpolator for subnanometric accuracy.
To achieve subnanometric accuracy in combined interferometry, there is a need for a optical interferometer with subnanometric resolution and accuracy at reference points that are considered as null points for interpolation. To this end, a laser heterodyne interferometer was developed.
This device is composed of four parts; a laser head, compact optics, phase demodulator electronics including phase sensitive detectors, and a computer for displacement calculation. The optical components stick together and the optics are designed so that the optical paths of two interference beams are equal for high stability. The simulation using a phase lock assembly showed that the phase demodulator resolves optical phase difference up to 0.01˚ corresponding to 0.01 nm displacement and finds reference points with 0.03 nm accuracy(standard deviation).
Experimental results are shown of noises, optics stability, and PZT displacement. Investigation about noises source, the error budget and possible improvements are discussed.