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LADIE - a new coherent light effect

Nature Physics reports on a new optical effect discovered in collaboration btw. University of Kassel and IFA.

Two laser pulses excite a crystal of sapphire causing it to emit coherent light

When shooting a short laser pulse into a dielectric material (that is an electrically insulating matter like water or glass) the optical properties of the material change drastically and very fast. From being transparent, the material suddenly behaves as if it was a metal, acting as a "plasma mirror", causing most of the laser light to be reflected. So much the bigger was the surprise among the researchers when a group from Aarhus University led by professor Peter Balling in cooperation with a group from Kassel University led by Thomas Baumert in a similar experiment experienced a totally surprising result: More light was transmitted from the material than was sent into it. In other words, the energy of the probe-light coming out of the exited sample (in this case a small piece of sapphire) was higher than was sent in! The researchers were able to show also that the amplification preserves the phase of the incoming light (i.e. it is coherent as laser light). This newly discovered effect has been named LADIE - Laser Amplification in exited DIElectrics. In the experiment, ultra-short femtosecond long laser pulses with a wavelength of 800 nm were sent into a sapphire crystal to excite it, followed by a delayed 400 nm pulse, which ought to have been reflected and absorbed; instead it was amplified by up to 50%.

It is too early to start guessing what this new effect could be used for, if at all anything more than making us wiser on the World we live in. However, keep in mind that the laser, when discovered in the mid 60'ies, was also quite unexpected, and in the beginning just considered another interesting aspect of quantum physics - and now we could not sustain our technology without it.

The exciting new discovery was published Monday 18 September 2017 in the well renowned web based publication Nature Physics.