DYNAMIC FOCUS ADJUSTMENT IN A SCOPHONY SCANNING SYSTEM
Original Publication Date: 1979-Apr-30
Included in the Prior Art Database: 2004-Apr-01
Xerox Disclosure Journal
There are situations where it would be desirable to dynamically adjust the final image plane of a Scophony scanning system. The system described here adjusts the image location anamorphically in the direction of scanning by a dispersive filter of variable, programmable chirp rate processing the electronic drive signal to be applied to the acousto-opticmodulator of the scanning system; no focus shift is accomplished in the orthogonal direction. The programmable chirp rate is accomplished by the circuit of the figure. The first dispersive delay filter has a phase shift which is cubic in frequency, and the second dispersive delay filter has the inverse phase shift so that taken together with no mixing in between, the net result would be no dispersion. With mixing in between the cubic frequency, dependence drops out but a residual quadratic phase dependence remains which is proportional to the frequency shift induced by the second voltage controlled oscillator. This is the desired, programmable linear frequency chirp.