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Decrease of pulse-contrast in nonlinear chirped-pulse amplification systems due to high-frequency spectral phase ripples

: Schimpf, D.N.; Damian, N.; Seise, E.; Limpert, J.; Tünnermann, A.

Postprint (729 KByte; PDF; )

Optics Express 16 (2008), No.12, pp.8876-8886
ISSN: 1094-4087
Journal Article, Electronic Publication
Fraunhofer IOF ()
femtosecond pulse; optical pulses; laser system; modulation; generation; compression; stretcher; amplifier

It is analytically shown that weak initial spectral phase modulations cause a pulse-contrast degradation at the output of nonlinear chirped-pulse amplification systems. The Kerr-nonlinearity causes an energy-transfer from the main pulse to side-pulses during nonlinear amplification. The relative intensities of these side-pulses can be described in terms of Bessel-functions. It is shown that the intensities of the pulses are dependent on the magnitude of the accumulated nonlinear phase-shift (i.e., the B-integral), the depth and period of the initial spectral phase-modulation and the slope of the linear stretching chirp. The results are applicable to any type of laser amplifier that is based on the technique of chirped-pulse amplification. The analytical results presented in this paper are of particular importance for high peak-power laser applications requiring high pulse-contrasts, e. g. high field physics.