Dispersion considerations in ultrafast CPA systems

摘要

A basic assumption underlies many designs for chirped-pulsenamplification (CPA) of ultrashort pulses. This assumption is that anTaylor's series expansion of the dispersive delay is well behaved in thensense that each phase order in the expansion produces an effect on thenpulse that is significantly smaller than the effect of the previousnorder. This work investigates this assumption both qualitatively andnquantitatively. We show quantitatively that the requirements fornachieving sub-20-fs pulses are much more stringent than for 100-fsnpulses. We find that when the basic assumption holds, a chirped pulsenamplification (CPA) system may be designed by zeroing each order innsuccession, but that zeroing may not work well for some systems that arennot well behaved. For these cases minimizing the overall dispersionnbecomes necessary. We discuss some common optical components includingnbulk materials, expanders, and compressors and show that they generallynsatisfy the basic assumption. Finally, we discuss the problem ofnoptimizing a CPA system in the laboratory, and describe a newnpolarization-gate (PC) frequency-resolved optical gating (FROG)narrangement that is based on thin-film polarizers and that allowsnaccurate measurements of the phase as well as the intensity with minimalndispersive effects