The protein substructure of skeletal muscle fibers forms a diffraction grating with repeating units, termed 'sarcomeres'. A laser scanning system is described that maps the lengths of sarcomeres (SL) and the widths of the first-order diffraction lines (DLW) of permeabilized single fibers in real-time. The apparatus translates a laser beam (λ = 670 nm and w0 = ~75 μm) along the length of a fiber segment through 20 contiguous regions per sweep at 500 sweeps/s. The fiber segments (~1 mm long) were obtained from vastus lateralis muscles of humans by needle biopsy. During both passive stretches and maximum fixed-end activations, the mappings of SL and DLW of the fibers were extracted from the diffraction spectra. Heterogeneity of SLs was evaluated by computing the standard deviation ( σSL) of the 20 SLs measured during a single sweep. Compared with the σSL before a passive stretch, the increase of 5±0.5% in σSL after the passive stretch, indicated differences in passive length-tension relationships along the fiber. In contrast, no change, ~0.5±0.1%, was observed in DLW. Within 10s after the fiber was returned to its initial length, the shape of the SL profile returned close to pre-stretch conditions ( σSL = 1± 0.2%). Following maximum Ca2+ - activation of the fiber, the heterogeneity of the steady state SLs increased greatly (DLW up by ~300% and σSL up by ~100%). The scanning system provided high resolution tracking of sarcomere behavior single muscle fibers. Potential applications are for studies of the mechanisms of muscle fiber injury and injury propagation.
A comparison is made of two, laser-induced-damage assessment techniques. The first technique monitors the sample for changes in linear transmission after high-energy laser illumination. With the second technique, an image is transmitted through the sample, after high-energy laser illumination, at the position of incidence. Both single and multiple shot data are considered. Results show the imaging technique to be an efficient method by which to unambiguously discern the onset of image-degrading laser- damage, regardless of detector noise, shot-to-shot variations and sample inhomogeneities. Practically speaking, the imaging technique is relatively easy to incorporate into a laser-based experimental system and is particularly relevant to the assessment of optical systems for imaging.
We carried out systematic experiments to study the effect of solvents on power limiting in zinc meso-tetra (p- methoxyphenyl) tetrabenzoporphyrin (ZnTBP). We used Toluene, pyridine, acetone, dichloromethane (DCM) and a toluene pyridine mixture to evaluate polarity and complex formation of the solvent and solute molecules. Z-scan data were generated using picosecond and nanosecond laser pulses at 532 nm. These data were then curvefit to a 5-level model to obtain excited state and two photon absorption coefficients, and the intersystem crossing rates. An f/5 optical limiting setup was used to determine limiting thresholds. Results indicate that toluene and DCM give the lowest limiting thresholds and that pyridine ligation can be used as a means of molecular modification for future molecular studies.
A series of azulenic compounds are synthesized and their third-order nonlinear optical properties are determined. The compounds are studied in solution using degenerate four wave mixing and z-scan at 532 nm with 30 ps pulses. Extrapolated values for the third-order nonlinear optical susceptibility (chi) (3) of the compounds are in the range 10-9 to 10-8 esu. Z-scan results indicate reverse saturable absorption. Optical power limiting with a f/5 system is demonstrated for all of the compounds studied.
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