Laser schlieren deflectometry (LSD) is a method for a high-speed measurement of the gas temperature in microscopic dimensions, in particular for temperature peaks under dynamic conditions at atmospheric pressure. The principle of LSD is derived from

schlieren photography Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. C ...

: a narrow

laser beam A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

is used to scan an area in a gas where changes in properties are associated with characteristic changes of

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

. Laser schlieren deflectometry is claimed to overcome limitations of other methods regarding temporal and spatial resolution. The theory of the method is analogous to the scattering experiment of Ernest Rutherford from 1911. However, instead of

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...

s scattered by gold atoms, here an

optical ray In optics a ray is an idealized geometrical model of light, obtained by choosing a curve that is perpendicular to the ''wavefronts'' of the actual light, and that points in the direction of energy flow. Rays are used to model the propagation o ...

is deflected by hot spots with unknown temperature. A general equation of LSD describes the dependence of the measured maximum deflection of the ray ''δ''₁ on the local maximum of the neutral gas temperature in the hot spot ''T''₁: :

\frac + \frac = 1,

where ''T''₀ is ambient temperature and ''δ''₀ is a calibration constant depending on the configuration of the experiment. Laser schlieren deflectometry has been used for investigation of the temperature dynamics,

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

and energy balance in a miniaturized kind of atmospheric-pressure plasma.

References

{{reflist Plasma physics Thermodynamics Fluid dynamics

See also

References