Digital self-aligned focusing schlieren.

In this Letter, a digital self-aligned focusing schlieren (D-SAFS) system is introduced. This system uses a digital transparent micro liquid crystal display (μLCD), in combination with a linear polarizer, to act on the linear polarization state of light transmitted in both the forward and reverse directions, essentially acting as both the source and cutoff grids. The use of the μLCD display allows for on-the-fly changes to the cutoff pattern type, spatial frequency, and orientation.

Colinear focused laser differential interferometry and self-aligned focusing schlieren.

A colinear focused laser differential interferometer (FLDI) and self-aligned focusing schlieren (SAFS) system has been assembled and tested in the laboratory, using a turbulent jet of compressed air issuing from a small needle nozzle to provide a high frequency density object. Measurements verified that the coupling of the SAFS system onto the optical axis of the FLDI system had negligible influence on the FLDI system's data, including tests that assessed the influence of the inclusion of dichroic mirrors, dichroic mirror reflection angle, dichroic mirror positioning relative to the Wollaston prisms of the FLDI system, and SAFS light propagation direction. A qualitative comparison of the focusing ability of the two systems was made, and FLDI power spectral density estimates and SAFS spectral proper orthogonal decomposition were used for quantitative comparisons of the acoustic frequency of the jet, with good agreement between the two.

Projection background-oriented schlieren.

A background-oriented schlieren (BOS) system is developed with two benefits over traditional BOS systems. First, the dot pattern required for BOS is projected onto a retroreflective background instead of being painted/printed onto the material itself, allowing for on-the-fly updates to the size and distribution of the dot pattern. Second, a reference image is acquired for every flow image so that real-time BOS images can be displayed, and a flow-off reference image need not be acquired if the projected dot pattern is changed during a run for BOS signal optimization.

Compact, self-aligned focusing schlieren system.

A novel, to the best of our knowledge, compact, self-aligned focusing schlieren system is presented that eliminates the need for a separate source grid and cutoff grid. A single grid element serves both to generate a projected source grid onto a retroreflective background and act as the cutoff grid for the reflected light. This is made possible by manipulating the polarization of light through the system.

Multi-point line focused laser differential interferometer for high-speed flow fluctuation measurements.

A multi-point focused laser differential interferometer (FLDI) has been developed to measure density fluctuations at 16 points along a line. A pair of cylindrical lenses on the transmitter side of a conventional single-point FLDI instrument form two closely spaced (≤200µ), orthogonally polarized, parallel laser lines at the instrument's focus. On the receiver side of the instrument, the interference of the beams on a 16-element photodiode array results in a single line of measurements.

Two-point, parallel-beam focused laser differential interferometry with a Nomarski prism.

A Nomarski polarizing prism has been used in conjunction with a focused laser differential interferometer to measure the phase velocity of a density disturbance at sampling frequencies ≥10. Use of this prism enables the simultaneous measurement of density disturbances at two closely spaced points that can be arbitrarily oriented about the instrument's optical axis. The orientation is prescribed by rotating the prism about this axis.