The e x p e r i m e n t a l r e s u l t s on i n t e r f e r om e t r i c B r a g g C e l l Spectrum Analyzer a r e indeed encouraging. An experiment w a s p e r f o r m e d using a 5 mW HeNe l a s e r in Mach-Zehnder i n t e r f e r o m e t r i c Configuration. A l i n e a r c h i r p w a s u s e d to g e n e r a t e the r e f e r e n c e b e a m . W e w e r e a b l e to obserw58 dB Dynamic Range f o r CW and 54 d B DR f o r 5ps pulsed signals with 100% Probability of I n t e r c e p t and less than 1 p s T i m e of A r r i v a l a c c u r a c y . Pseudo Noise Sequence w a s a l s o t r i e d i n a n o t h e r e x p e r i m e n t with good r e s u l t s at reduced s y s t e m bandwidth.

IntroductionThe purpose of this study was to investigate a new heterodyne AO spectrum analyzer configuration and provide preliminary results for possible applications in real -time spectrum analysis.This spectrum analyzer was unique in that it used an interferometric configuration to generate direct channelized RF outputs at the input frequencies.Acoustooptic spectrum analyzers use the acousto -optic interaction to create a Fourier plane of light in space. Simultaneous spectrum analysis of multiple signals is possible in real -time in a configuration that continuously receives all input signals due to the channelization of the acousto -optic cell. In a nonheterodyne configuration, the frequency is read as positions in space1. The interferometric spectrum analyzer floods the frequency plane with coherent light to recover the phase information which is modulated onto the diffracted beam by the Bragg cell.Frequency is read spatially but the signal output by the spectrum analyzer can be retransmitted for phase analysis, relative power readings, and other purposes as well.In addition, and perhaps most importantly, the dynamic range is increased by the heterodyne structure. System designThis spectrum analyzer was designed for laboratory testing, so a visible wavelength was preferred. Helium Neon lasers are common, small, and relatively stable. We chose a 1.2 milliwatt He -Ne laser for this system.The main element of the interferometric spectrum analyzer was the acousto -optic cell. At the operating wavelength of 633 nanometers, several materials were available.

A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power.The moire contours are generated in real time by projecting variable spacing gratings upon the target and filtering the image either optically, in the video signal, or in the computer.The system is designed to compare the surface shape of a test object with a previously stored image of a perfect object, and to display the surface errors superimposed on a video image of the test object. A unique feature of the system is the continuously variable depth resolution which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.

Video technology is applied to the problem of moiré metrology. In the past, moiré metrology seemed a promising yet limited method in the measurement and comparison of surface shape. The use of video technology has widened the area of application of moiré metrology by reducing the complexity of the optical set up and providing real time information on surface shape and deformation. A continuously variable grating projector and analog video circuitry are used to generate real time additive (bright line) and transmissive (dark line) moiré patterns. These patterns are used to compare a test object against a “perfect” reference object. This is done in both real time and through the use of computer image processing. Depth resolutions on the order of 0.3 mm are obtained on a cone 25.4 mm high and 50.8 mm wide. The projection system allows easy expansion to large objects. Because of the use of video technology moiré metrology can now be more readily applied to robotic vision and factory assembly line quality control over a wide range of scales.