Timothy J. McIntyre

Differential interference contrast imaging using a spatial light modulator

Differential interference contrast microscopy, imaging by interferometric superposition of two displaced beams passed through a transparent sample, is one of the most sophisticated methods in classical microscopy. Here we demonstrate a versatile electronically controlled variant using a liquid-crystal spatial light modulator that displays a diffractive optical element and steers the beam separation. The orientation and magnitude of the shear angle and the relative phase of the two interfering beams can all be varied at video rates. The technique is demonstrated by imaging polystyrene beads in immersion oil and a sample of red blood cells. The method expands the capabilities of previous implementations of differential interference contrast microscopy by its nonmechanical control over all imaging parameters.

Nonequilibrium radiation intensity measurements in simulated Titan atmospheres

This paper details the experimental work conducted at the University of Queensland to measure the nonequilibrium radiation intensity behind a shock in simulated Titan atmospheres, as would be seen during planetary entry. Radiation during Titan entry is more important at lower speeds (about 5-6 km/s) than other planetary entries due to the formation of cyanogen in above equilibrium concentrations in the shock layer, which is a highly radiative species. The experiments were focused on measuring the nonequilibrium radiation emitted from cyanogen between the wavelength range of 310-450 nm. This paper includes experimental results for radiation and spectra found in the postshock region of the flow. Experiments have been conducted at various ambient pressures, shock speeds, and chemical compositions. This leads to a comprehensive benchmark data set for Titan entry, which will be useful for validation of theoretical models. Spectra were recorded at various axial locations behind the shock, enabling the construction of radiation profiles for Titan entry. Furthermore, wavelength profiles can also be constructed to identify various radiating species, in this case, predominately cyanogen violet. Furthermore, this paper includes comparisons with experiments performed at NASA Ames Research Center on their electric arc-driven shock tube in Titan compositions. Excellent quantitative agreement has been obtained between the two facilities.

Simultaneous two-wavelength holographic interferometry in a superorbital expansion tube facility

A new variation of holographic interferometry has been utilized to perform simultaneous two-wavelength measurements, allowing quantitative analysis of the heavy particle and electron densities in a superorbital facility. An air test gas accelerated to 12 km/s was passed over a cylindrical model, simulating reentry conditions encountered by a space vehicle on a superorbital mission. Laser beams with two different wavelengths have been overlapped, passed through the test section, and simultaneously recorded on a single holographic plate. Reconstruction of the hologram generated two separate interferograms at different angles from which the quantitative measurements were made. With this technique, a peak electron concentration of (5.5 +/- 0.5) x 10(23) m(-3) was found behind a bow shock on a cylinder.

A method for achieving super-resolved widefield CARS microscopy

We propose a scheme for achieving widefield coherent anti-Stokes Raman scattering (CARS) microscopy images with sub-diffraction-limited resolution. This approach adds structured illumination to the widefield CARS configuration [Applied Physics Letters 84, 816 (2004)]. By capturing a number of images at different phases of the standing wave pattern, an image with up to three times the resolution of the original can be constructed. We develop a theoretical treatment of this system and perform numerical simulations for a typical CARS system, which indicate that resolutions around 120 nm are obtainable with the present scheme. As an imaging system, this method combines the advantages of sub-diffraction-limited resolution, endogenous contrast generation, and a wide field of view.

Experimental expansion tube study of the flow over a toroidal ballute

An experimental investigation of high-enthalpy flow over a toroidal ballute (balloon/parachute) was conducted in an expansion tube facility. The ballute, proposed for use in a number of future aerocapture missions, involves the deployment of a large toroidal-shaped inflatable parachute behind a space vehicle to generate drag on passing through a planetary atmosphere, thus, placing the spacecraft in orbit. A configuration consisting of a spherical spacecraft, followed by a toroid, was tested in a superorbital facility. Measurements at moderate-enthalpy conditions (15-20 MJ/kg) in nitrogen and carbon dioxide showed peak heat transfer rates of around 20 MW/m(2) on the toroid. At higher enthalpies (>50 MJ/kg) in nitrogen, carbon dioxide, and a hydrogen-neon mixture, heat transfer rates above 100 MW/m(2) were observed. Imaging using near-resonant holographic interferometry showed that the flows were steady except when the opening of the toroid was blocked.

Optical and Pressure Measurements in Shock Tunnel Testing of a Model Scramjet Combustor

Experimental measurements are presented of the flow in a model supersonic-combustion ramjet. A rectangular duct with a central streamwise-injected planar hydrogen jet has been tested at various enthalpies in a free-piston-driven shock tunnel. Several optical diagnostic techniques were employed to characterize the flow for a moderate enthalpy condition where pressure measurements indicated that significant combustion was occurring. Shadowgraph and emission images provided qualitative information on the density variations and temperature distributions, respectively. The planar laser-induced fluorescence technique has been used to examine the regions of ignition. Combustion was found to be occurring only in a thin mixing layer present between the air and hydrogen streams. The positions of shock waves within the duct compared well with pressure measurements performed along the floor of the duct.

Quantitative SLM-based differential interference contrast imaging

We describe the implementation of quantitative Differential Interference Contrast (DIC) Microscopy using a spatial light modulator (SLM) as a flexible Fourier filter in the optical path. The experimental arrangement allows for the all-electronic acquisition of multiple phase shifted DIC-images at video rates which are analyzed to yield the optical path length variation of the sample. The resolution of the technique is analyzed by retrieving the phase profiles of polystyrene spheres in immersion oil, and the method is then applied for quantitative imaging of biological samples. By reprogramming the diffractive structure displayed at the SLM it is possible to record the whole set of phase shifted DIC images simultaneously in different areas of the same camera chip. This allows for quantitative snap-shot imaging of a sample, which has applications for the investigation of dynamic processes.

Velocimetry and Thermometry of Supersonic Flow Around a Cylindrical Body

The supersonic flow around a cylindrical body has been studied using two optical techniques. For both sets of measurements, the cylinder was mounted from the side of the tunnel, allowing investigation of the bow shock region as well as in the wake. A new technique, laser-enhanced ionization flow tagging, was used for streamwise velocity determinations behind the body. From these measurements, it was found that the downstream velocity outside the wake was (1.90 +/- 0.06) km/s, whereas inside the wake the velocity was about 0-500 m/s in the upstream direction. Planar laser induced fluorescence of nitric oxide was employed for temperature determinations. It was established that the freestream temperature was (2120 +/- 100) K, decreasing to around (1550 +/- 400) K in the wake.

Student experiences of virtual reality - a case study in learning special relativity

A teaching package has been developed centered around a relativistic virtual reality. It introduces concepts of special relativity to students in a gamelike environment where users experience the effects of traveling at near light speeds. From this perspective, space and time are significantly different from that experienced in everyday life. We explore how students worked with this environment and how they used this experience in their study of special relativity. Students found the simulation to be a positive learning experience and described the subject area as being less abstract after its use. Students were more capable of correctly answering concept questions relating to special relativity, and a small but measurable improvement was observed in the final exam.

Vacuum ultraviolet spectral measurements for superorbital earth entry in X2 expansion tube

Experiments were conducted using the X2 expansion tube at two conditions representative of flight velocities of 10.0 and 12.2  km/s for a vehicle entry into Earth’s atmosphere. Calibrated spectral measurements were made of radiating shock layers across and through the surface of a model. These measurements provided a unique dataset for the validation of computational codes used in the calculation of incident vacuum ultraviolet radiative heat flux. Computational simulations at equilibrium gas chemistry were conducted using the Specair program and showed good agreement with the measurements.