Properties and applications of fast rotors in dynamical optics (abstract)

The term ‘‘dynamical optics’’ is defined as a set of optical elements at least one of which is nonstationary as seen from the laboratory. Present technology allows the construction of fast rotating mirrors as components in dynamical optical systems. Calculations show that such systems can be used to achieve subpicosecond x-ray pulses and extremely high instantaneous intensities, and, alternatively they can be utilized to saturate the transverse coherence of x-ray beams thereby making possible to perform certain interference experiments. Some properties and additional applications of fast rotating mirrors are discussed: (1) The focusing properties of rotating mirrors can differ significantly from those of stationary reflectors, even though the mirrors are, of course, nonrelativistic. A small (diameter <1 mm) plane mirror when rotating can have a focal length fm down to a few meters. By changing the speed of rotation, the focal length can be altered continuously from its minimum value, fm, through infinity (when the mirror is at rest) to −fm (when it’s rotation is reversed). Thus, mirrors can be constructed which can be made to both focus and defocus with continuously and accurately variable focal length. (2) Rotating mirrors will induce a frequency change Δω in the reflected beam, allowing one in principle to tune across resonance lines, and also ‘‘active monochromatization’’ of x-rays, i.e., increasing the spectral intensity in a selected range, while decreasing it outside that range, all this without any change in the total photon beam intensity. This option is of interest when the total photon intensity cannot be increased beyond a certain limit, high resolution monochromatization is available, and large spectral density is called for in a chosen frequency range. (3) The maximum speed whch a rotor can tolerate is determined by its shape as well as its mechanical properties, such as density, elasticity, and tensile strength. Because of their high intrinsic symmetry, spherical rotors are of interest both theoretically and experimentally, but higher speeds can be achieved by rotors specifically shaped for that purpose. A variety of examples will be given to illustrate the relationship between rotor speed and selected parameters.