When taking water droplets ruptured by laser irradiation at ultrahigh speed, it is like this

Along with the evolution of high-speed cameras, we are able to observe what changes are hidden in the phenomenon that occurs instantaneously. Study on fluidPhysics of Fluids, A movie that shoots a moment to rupture by irradiating a laser beam on a water droplet at 20 thousand frames per second and reproduced in slow motion has been released.

Entry for the 2014 Gallery of Fluid Motion of the APS-DFD conference - YouTube


Capillary tubeThe water droplet hanging from it is 1 mm in diameter.


I irradiate this water drop with a pulsed laser to separate it.


Let's take a picture of water droplets being broken up at an ultra high speed of 20,000 FPS (frame / second).


Water drops slowly falling


For a moment, Psych and Pulse Laser were shot down


The water droplet widely spreads in the direction perpendicular to the radiation direction of the laser.


And into smaller water droplets. It is said that such a change occurs due to the difference in the time scale that the deformation of water droplets occurs in units of milliseconds while the change of laser pulses occurs in units of nanoseconds.


This time shooting with a special technique called "stroboscopic imaging" which obtains a mapping by pulsing the light source.


The frame rate of the image reproduced by stroboscopic imaging is amazingly 10 million FPS. It can be seen that the water droplets where the laser pulse was struck are scattered in the form of mist.


At ultra-fast speed, you can perfectly see how it flies and spreads like a mist (cloud).





Next is an experiment on how the splashing water droplets change as laser pulse is changed.


Observe the state of rupture by changing the distance from the focal point of the laser to the falling position of the water droplet.


The result is this. Scattering appear to change considerably depending on the position where the laser is irradiated.


It is like this when comparing how droplets splash from the left in order of distance from the focal point.






Next, we compare the magnitudes of laser energy.


You can see well that water drops splashfully as energy is larger (than from the right side).




The kinetic energy given to the water droplet by the laser was divided by the surface tensionWeber numberLooking about ......


Almost according to theory.


Let's simulate the deformation of the boundary surface.


The greater the energy of the laser, the deeper the deformation becomes ... ...


It is deformed to line symmetry with such feeling.


By the way, what will happen if you irradiate a laser with enormous energy?


The answer is this. The part where the laser was struck wasplasmaIt changes to a state.


It seems like fireworks appear beautifully scattering.




An experiment to shoot the water droplet by irradiating with a laser pulse at an ultra high speed has been described in detail as a super high speed shooting method "compressed ultrafast photography (CUP)" in a paper published in the scientific journal Nature I will.

Single-shot compressed ultrafast photography at one hundred billion frames per second: Nature: Nature Publishing Group
http://www.nature.com/nature/journal/v516/n7529/full/nature14005.html