Enhancing the output bandwidth of a chirped-pulse Ti:S multipass amplifier via optical rotatory dispersion

In this paper, we present theoretically a simple and passive method to modulate the output spectrum of a broadband multi-pass Ti:S amplifier by means of polarization-dependent gain and optical rotator dispersion (ORD). By choosing the ORD and two π-polarization wavelengths, we can shape the effective gain section flexibly in order to suppress spectral narrowing and red-shift effects. Our simulations show the amplifier we have designed can scale a 0.4nJ, 10fs seed pulse up to 3.31mJ almost without spectral narrowing and central wavelength-shift. Increasing the difference of the two π-polarization wavelengths can result in the saddle output spectrum with a span of about 149nm, which is very helpful for further laser amplification to avoid spectral narrowing.