Microdifferential holography and the polysarcomeric unit of activation of skeletal muscle.

Unbalanced holographic difference images of contracting skeletal muscle fibers reveal that activation affects the amplitude of the light scattered by individual myofibrils. The results suggest that the unit of activation is not the sarcomeric structural unit, but a monomyofibrillar segment containing 20 to 40 contiguous sarcomeres.

Microdifferential holography.

A novel coherent imaging method analogous to electronic differential amplification is described and analyzed. The method is well suited to highlighting local changes in the optical properties of a dynamic object whose more prominent details are largely static. The object may be examined either in transmitted light or in reflected light. The method discriminates between changes that result from substructural reorganization of object details too fine to be imaged as resolved structures and changes that result from the microdisplacement of optically resolved structures. Substructural reorganization is signaled by changes in the amplitude of the transmitted or reflected light, whereas ordinary displacement is displayed in the usual way through a change in phase. The method is capable of detecting displacements as small as several milliwavelengths. Images of contractile activity in muscle are presented that illustrate the method's sensitivity and analytic power.

Microscopic mapping of subnanometric motion.

The sensitivity of a microscope-based holographic system designed for mapping the motion of components of a living cell is calibrated by means of a simple procedure. Bubbles of air are allowed to drift with known velocity in a nearly horizontal, glycerine-filled capillary observed through the microscope. The ultrafine motion of the bubbles is captured interferometrically by subtractive superposition of a pair of holograms recorded a few milliseconds apart. Stationary portions of the field of view are rendered dimly in images reconstructed from the interferogram, while the brightness of moving portions varies monotonically with their displacement. Displacements as small as 1.1 nm were betrayed in the images. Analysis of the experimental conditions suggests that bubble displacements as small as 0.7 nm will become detectable once minor improvements are made in the apparatus.

Dynamic Structures through Microdifferential Holography.

The principles of microdifferential holography are developed primarily from nonmathematical argument, and the method's capabilities are compared with those of x-ray and optical diffraction. Microdifferential holography is very sensitive to small displacements of strongly scattering elements of a specimen whether or not they can be optically resolved. We present and interpret differential images of electrical activity of neurons and of contractile activity of isolated skeletal fibers. The latter confirm the suggestion of earlier work that the dynamic regions of contracting muscle are organized along myofibrillar segments rather than by sarcomeres.

Coherent Radiation for X-Ray Imaging-The Soft X-Ray Undulator and the X1A Beamline at the NSLS.

An undulator-based beamline was built and commissioned at the National Synchrotron Light Source to provide tunable coherent radiation in the 200-800 eV range. The low emittance of the storage ring means that the undulator source has high brightness so that a large flux of coherent x rays is delivered to experimental stations. The beamline uses a horizontally dispersing bichromator that allows two experiments to run simultaneously, making use of the first and second harmonics of the undulator output. In addition, the use of horizontally deflecting optics enables the beamline alignment to be insensitive to electron beam motion since the horizontal electron beam size is quite large. The beamline and its performance are discussed with emphasis on the optics and on stability, radiation, and vacuum considerations.