Chirped Pulse Amplification

Chirped pulse amplification (CPA ) (German: amplification of chirped pulses ) is a method in laser physics, which allows laser pulses with very high intensity to produce. CPA is also used interchangeably with an optical module that uses the method.

With this method, maximum peak powers in the so-called petawatt range can (meaning more than 1015 W ) can be achieved. Thus, high peak powers can not be generated directly from laser sources, since usually the media of the laser amplifier would be destroyed by non-linear optical effects. Therefore, laser pulses are temporally stretched in an amplifier outside the resonator, thus their energy density decreases, and then run through an amplifier medium. After amplification, they are compressed and then used with the higher power density in experiments or industrial applications.

CPA lasers were constructed with intensities of up to 1022 W / cm ² at a pulse length of a few femtoseconds.

CPA was introduced by Gérard Mourou and Donna Strickland 1985.

Principle

The shorter a light pulse, the wider is the range of frequencies contained. This follows from the description of the light pulse as a wave packet (see Selbiger article). For a Gaussian wave packet following relationship between temporal and spectral width Δω length? T applies:

Light of different frequency can be refracted differently by optical components, or delayed. By arrangement of optical components, used mainly grating and prism, the different frequency components of the ( short ) laser pulse can be delayed differently and pull apart the pulse spectrally and compress again. Figuratively speaking, rushing the red ( low frequency ) units above the pulse, while the blue ( high frequency ) Shares are delayed more (or vice versa, depending on the sign of the dispersion). The total pulse is prolonged and reduced the peak pulse power accordingly. Then the intensity can be increased by increasing again to below the influence of nonlinear optical effects in the gain medium.

The expansion or compression is shown schematically in the figure. A first grid fanned the light to frequency dependent. A second grid is set up so that it paralleled the light, but it also causes an expansion or compression. A mirror reflects the laser light so that the beam passes through the grating again and is thereby further expanded or compressed. With parallel to each other grids obtained a positive dispersion ( the blue end is faster). With a simple lens system between the grids, these tilt to one another and sometimes get a negative dispersion ( the blue end is slower).

• Laser Physics
• Optical component