KEYWORDS: Digital signal processing, Sensors, Ferroelectric materials, Fringe analysis, Clocks, Data acquisition, Michelson interferometers, Analog electronics, Signal processing, Digital filtering
Intensity division interferometers have been long used in displacement measurement with resolution down to 0.01 micron. However, commercial multi-frequency laser interferometers are very expensive and difficult to be embedded in motion control experiments. In this paper, a single frequency Michelson interferometer combined with an 128 X 1 intensity integration photodiodes to produce a high resolution and wide range displacement detection is presented. With the digital signal microprocessor, plus signal filtering technique, the displacement changes to wavelength/2 has been measured by using PZT stack with high voltage driver. With the He-Ne laser as the light source, the precision is about 0.3 micron, the change pattern of the peak maximum of the fringes corresponding to the change pattern of the PZT driving signal, and the best results are obtained with sine-wave at different frequencies. This system has the features of high resolution, broadband, non- contact measurement. Because of lower cost, easier implementation, faster DSP processing, it is very likely to be embedded in the concurrent control system.
Ultrashort micropulse characterization of IR-FEL is essential to both FEL development and applications such as terahertz spectroscopy and coherent excitation. Due to wavelength limitation of nonlinear medium, existing techniques of pulse shape measurement are not suitable to the Far IR-FEL of above 100 micron. We present the technique of interferometric cross- correlation in the Fourier space to directly obtain the phase and amplitude information of mid-infrared short optical pulse. By introducing a grating pair as disperser, the interferometric cross-correlation for different spectral components of spectrally expanded pulse is recorded by the 2-D array detector as function of relative delay and spectrum. The relative phases in the pulse spectrum are retrieved from the 2-D interferogram, and the spectrum amplitude is taken from the square root of the power spectrum, the pulse shape can be accurately reconstructed by fast Fourier transform of the complex spectrum field. Without nonlinearity, this technique is very likely to be extended to the Far IR-FEL.
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