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Laser beam casts a shadow in a ruby crystal
- Particles of light – photons – when a laser beam is illuminated by another light through a highly nonlinear medium can cast shadow
- This can happen in media that absorb light in a highly nonlinear way. Most materials become more transparent in presence of a strong laser field and produce an “anti-shadow” that is even brighter than the background.
- To produce “reverse saturation of absorption” or “saturable transmission” four conditions are required to be met.
- Ruby is an aluminium oxide crystal that contains impurities of chromium atoms and is found to absorb more of the illuminating blue light, creating the laser beam's shadow echoing the object's shape.
- This shadow behaves like an ordinary shadow and can be controlled by another laser beam
- A theoretical model predicts the darkness of the shadow will increase as a function of the power of the green laser beam.
- Laser shadow creation is based on the interaction of polaritons and not photons and can be useful in devices where we need to control the transmission of laser beams with another laser beam
- Future research will focus on other materials and combinations of wavelengths that might produce a similar “laser shadow” effect
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