The fabrication of Fabry-Perot Etalon Filters with spacer elements of solid fused silica is described. Typically spacer thicknesses of 120pm are used to provide filters with .05nm to .07nm FWHM at 656.3nm centre wavelength. More complex devices having two coherently coupled cavities are described. The effect of optical system parameters on the spectral performance of the solid etalon filters is discussed and suitable operating parameters are suggested. The performance of solid etalon filters is compared with the birefringent filters of the Lyot type.
The use of optical systems for tracking objects, map making, space exploration, etc., is becoming more and more prevalent. Since most of these systems are automatically controlled, a concise mathematical description of the pointing and tracking aspects of such systems is required, not only for derivation of control laws, but also for synthesis of the system and study of pointing and tracking errors which give rise to image motion and consequently, reduced resolution. This paper uses the techniques of kinematics to provide a unified technique for the analysis of pointing and tracking problems of optical tracking systems. The general relationship between the position of an object and its image is first formulated. Next, the relation between the motion of the image and the motion of the object as a function of the motion of the various parts of the optical system is derived. These relationships are then used for obtaining control laws to null image motion on the optical axis. Finally, the equations giving the motion of the image at any point on the detector surface are also derived.
Experiments are described in which a carbon dioxide laser oscillating at 28.4 THz has been modulated simultaneously by three commercial television signals with carriers at 54, 66, and 82 MHz. Signal-to-noise degradation in the system was measured to be less than 1 dB, corresponding to modulator drive power of 1 W. This combination of wide bandwidth and low power consumption was made possible by the application of coupling modulation. This technique employs an intracavity electrooptic crystal to which the modulating fields are applied. Despite the fact that the crystal is positioned inside the laser cavity, the maximum bandwidth attainable is independent of both the cavity Q and the laser transition linewidth, and is limited only by modulator characteristics and optical transit time. Rigrod's method has been adapted to obtain an expression for the power coupled out of the laser. Modulator frequency response and drive power requirements are also summarized. It is seen that the noise bandwidth performance of the system would allow simultaneous modulation by 17 color television channels, or equivalently, more than a 300-megabit/s capacity.
To a large extent, American leadership in science has been based on the wide-spread availability of excellent instrumentation: In an earlier era, scientists could make fundamental discoveries with the equivalent of sealing wax and string. Today an occasional worthwhile observation is made with simple tools, but most significant advances depend on the application of complex instrumentation. In many instances appropriate devices make possible a tenfold or greater speed in data collection. In other instances sophisticated equipment permits measurements and experiments heretofore inaccessible. Current trends indicate that, in the future, leadership in science will be even more contingent on pioneering the use of new and increasingly powerful equipment. American scientists are fortunate in having the support of an innovative instrumentation industry that has been a byproduct of federal support of research.