What is shadowgrahy imaging technique?
Shadowgraph technique visualizes inhomogeneities in any transparent medium. Inhomogeneities refract light in proportion to the refractive index gradients.
Explain different types of optical setups for shadowgrahy imaging.
direct shadowgraphy, diverging light:
direct shadowgraphy, parallel light:
focused shadowgraphy, parallel light:
Name advantages of shadowgrahy imaging.
simple setup
adaptable to large fields of view
shadwos can be cast on every surface
“skeleton” of complex phenomenon without
details is created
thin sharp-edged features are resolved best
features with small lateral scales -> high
sensitivity (e.g. shock wave)
Name limitations of shadowgrahy imaging.
no 1:1 correspondence between object and image (not true-to-scale)
expect dark regions -> can yield an undistorted representation of object (mark origin of refracted rays)
light rays can overlap, cross and intersect before forming shadowgram -> caustics
caustics can be confused with other phenomena
minimize distance between object and its shadow for faithful representation
not well-suited to quantitative evaluation of refractive index
Describe the front-light shadowgraphy technique.
Combination of shadowgraphy and diffuse front light illumination imaging technique.
-> the liquid gas interface and the density variation can be seen.
What are the benefits of front-light shadowgraphy?
the liquid gas interface (front light) and the density variation (shadowgraphy) can be seen.
Describe the Schlieren method.
Similar to Shadowgraphy, but a knife edge cuts off a part of the ligh beam. Thus not the ray displacement but the ray angle displacement is made visible.
Name differences between Schlieren method and shadowgraph technique.
How can a Schlieren setup look like?
Toepler’s Schlieren Setup:
Dual field lens arrangement:
Z-type Herschellian 2-mirror setup:
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