Regenerative amplifier

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Under a regenerative amplifier is meant a special design of an optical amplifier operating at ultra-short laser - pulses (in the picosecond to femtosecond large range) performance increases possible. By repeatedly passing the originally weak pulse (a few nanojoules ) through the amplifier medium (e.g. a Ti: Sa crystal), amplification factors of up to 10 6 can be achieved.

Basic structure

The pulses to be amplified come from a mode-switched laser (often referred to as an oscillator) with a repetition rate of several megahertz . Of these, only a few thousand are then amplified because the pump lasers that generate the population inversion in the amplifier crystal cannot deliver power quickly enough. Typically, pulse rates between one and five kilohertz are used with pulsed amplifiers. With continuously pumped variants, rates of over ten kilohertz are possible, but generally lead to A. to longer pulse lengths.

Pockels cells are used to cut out the pulses that follow each other at a distance of a few nanoseconds from the pulse train . Due to the electro-optical effect used, the direction of polarization of the pulse is rotated so that it is coupled into the amplifier's resonator .

The pulse clears a part of the population inversion with each passage through the crystal and is thereby amplified. If the energy stored in the amplifier crystal as a result of the inversion has been sufficiently reduced, amplification no longer takes place and the pulse is decoupled from the resonator again.

In order to avoid damage to the components of the amplifier from the high pulse energies, the pulse is stretched in time before coupling (so-called chirped pulse amplification ) and compressed again at the amplifier output.

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