High-speed structured planar laser illumination for contrast improvement of two-phase flow images

A high-speed method to remove blurring effects caused by multiple scattering in planar laser images of two-phase flows is demonstrated. The technique is based on structured illumination and is for the first time to our knowledge applied on a dynamic medium. As structured illumination requires three successive images to be recorded and to freeze the flow motion in time, a high-speed laser and imaging system is employed. We show that by using a time delay of 55 micros between the images a single-shot representation of a dilute flow of water droplets can be achieved. By having an additional inner stream with known structure and composition, the efficiency of the method is quantitatively evaluated, showing an increase from 58% to 93% in image contrast. Such an improvement allows more accurate analysis and interpretation of scattering two-phase flow images.

New spectroscopic results in Kr VIII

New Kr VIII spectroscopic results between 280 and 2000 A using a theta-pinch and a discharge tube are presented, including one new energy level and two new classified lines. The previous analysis was also revised, and the uncertainty in the resulting level values is now <10 cm(-1).

Light-in-flight recording. 5: Theory of slowing down the faster-than-light motion of the light shutter

Light-in-flight recording by holography uses a picosecond pulse for the reference beam, which like a sheet of light intersects the hologram plate and produces a sensitivity area that with a speed faster than light moves over the plate like a light shutter. If, however, the front of the reference pulse by diffraction in a grating is tilted relative to its direction of motion, the velocity of the light shutter can be slowed down resulting in increased recording time. The practical result using a reflection grating was a true recording that corresponded to a time compression of two to one. To minimize distortions of the recorded pulse shape we studied intersections that are identical for apparent (ellipsoidal) and true (spheroidal) wavefronts.

Light-in-flight recording. 6: Experiment with view-time expansion using a skew reference wave

In normal light-in-flight holography the largest time difference that can be created in the image is when the reference light falls nearly parallel with the photographic plate. In that case, where the pulse front is perpendicular to the direction of propagation, the time scale on the plate is given by the speed of light. Thus the time it takes for the reference light to go from one side of the plate to the other sets the upper limit of the observable time interval. By using a reference light where the pulse front is leaning backward, this view time can be increased several times.