ABSTRACT
In the spatial carrier methods described in this chapter, only a single frame is necessary to obtain the wavefront, although, if desired, several wavefronts can be averaged to improve the result. One alternative to a linear carrier is a circular carrier that introduces large defocusing. An interesting point of view is to regard an interferogram with a linear carrier as an off-axis hologram. Interferograms with a spatial linear carrier can be analyzed to obtain the wavefront shape by processing the information in the interferogram plane or in the Fourier plane. The frequency width of the filter is given by the space width of the square function and the frequency position of the filter by the frequency of the sine and cosine functions. The voltage-controlled oscillator (VCO) is an oscillator tuned to produce a sinusoidal reference signal with angular frequency in the absence of a control voltage.
