532-nm Continuous-wave Laser Research Articles

Imaging Ejecta and Debris Cloud Behavior Using Laser Side-lighting

The Caltech Small Particle Hypervelocity Impact Range (SPHIR Facility) utilizes a two-stage, light gas gun to accelerate Nylon 6/6 right cylinders (d = 1.8mm, L/D=1, 5.5mg) and spheres (d = 1.8mm, 3.6mg) to impact speeds of 5km/s and above. The projectiles impact aluminum 6061-T6 plate targets. An optical technique was employed to produce images of the hypervelocity impact event with short exposure times (20ns) and short inter-frame times (<1μs). The technique uses coherent illumination, orthogonal to the projectile flight direction, to provide a series of shadowgraph images of the impact on the target. An expanded beam from a 532nm continuous wave laser is used as the illumination source. The beam is expanded to illuminate a 10cm diameter area and is then directed to a gated, intensified high-speed CCD camera. The front ejecta and debris clouds created behind the target are simultaneously imaged with this system. An edge-finding algorithm has been developed to provide a consistent method for identifying the position of the debris-front in sequential images. This technique enables a regular method to investigate the debris cloud evolution and to characterize its asymmetrical features. Furthermore, with the Laser Side-lighting system atmospheric waves emanating from the impact site are also visible. Increasing the atmospheric pressure in the target chamber (above the nominal 1.5 Torr) significantly increases the observable features of these shock waves. The behaviour of these waves provides an improved understanding of the temporal sequence of the impact phenomena.

Experimental investigations on fluorescence excitation and depletion of ATTO 390 dye

A novel fluorescent dye named ATTO 390 is tested and verified to be applicable in STED microscopy with great performance. The experimental configuration uses a 405nm continuous wave (CW) laser as excitation beam and a 532nm CW laser as depletion beam. The two collinear beams are focused on the dye using an objective with NA=1.4 and the fluorescence is detected by avalanche photodiode detector. With short wavelength in violet band, high fluorescence quantum yield, good photostability, and relatively low Ps demonstrated in a series of experiments, ATTO 390 is proved to be a potential good choice for fluorescent dye in STED microscopy.

Light-Induced Relaxation of Photolyzed Carbonmonoxy Myoglobin: A Temperature-Dependent X-Ray Absorption Near-Edge Structure (XANES) Study

X-ray absorption near-edge structure (XANES) spectra at the Fe K-edge have been measured and compared on solution samples of horse carbonmonoxy-myoglobin and its photoproducts, prepared by two different photolysis protocols: 1), extended illumination at low temperature (15 K) by white light; and 2), slow-cool from 140 to 10 K at a rate of 0.5 K/min while illuminating the sample with a 532-nm continuous-wave laser source. CO recombination has been followed while increasing the temperature at a rate of 1.2 K/min. After extended illumination at 15 K, a single process is observed, corresponding to CO recombination from a completely photolyzed species with CO bound to the primary docking site (formally B-state, in agreement with previous x-ray diffraction studies). The temperature peak for this single process is ∼50 K. Using slow-cool illumination, data show a two-state recombination curve, the two temperature peaks being roughly assigned to 50 K and 110 K. These results are in good agreement with previous FTIR studies using temperature-derivative spectroscopy. The XANES spectroscopic markers probe structural differences between the photoproduct induced by extended illumination at 15 K and the photoproduct induced by slow-cool illumination. These differences in the XANES data have been interpreted as due to light-induced Fe-heme relaxation that does not involve CO migration from the B-state. A quantitative description of the unrelaxed and relaxed B-states, including the measurements of the Fe-N p, Fe-N His, and Fe-CO distances, and the out-of-plane Fe displacement, has been obtained via a procedure (MXAN) recently developed by us. This work shows that XANES, being able to extract both kinetic and structural parameters in a single experiment, is a powerful tool for structural dynamic studies of proteins.