Multi-pass cross-polarized wave generation system for efficient cleaning and compression of ultrafast pulses

Abstract

Cross polarized wave generation (XPW) is an effect that occurs in crystals that have an asymmetric third-order nonlinear susceptibility. Because of the cubic intensity dependence of the conversion efficiency, the XPW pulse is shorter in time than the input pulse. For well-compressed pulses, the XPW spectrum will be broader and the temporal profile is cleaner, with better contrast between the pulse peak and the low-intensity background. Shorter, cleaner pulses are desirable for many applications. An example of an application for cleaner pulses like this is for experiments where high intensity pulses hit solid targets. Having better intensity contrast between the pre-pulse and the main pulse allows the main pulse to interact with the unexpanded, high density plasma. In this thesis, a novel method is developed to improve conversion efficiency that should also provide better quality spatial modes than previous methods. An optical system was demonstrated where the pulse is relay-imaged from the crystal to itself for multiple passes. This system allows for efficient conversion of low intensity pulses (low energy or long duration). Also, since chirped mirrors can be placed in the setup, the pulse can be more efficiently compressed to short duration. Conversion efficiencies as good as some previous improvement methods are achieved while using uncoated crystals, with quality output mode shapes. Using anti-reflection coated crystals with this new multiple pass setup will likely lead to significant improvement in conversion efficiencies. This method will be attractive for high repetition rate amplified systems that have modest pulse energy in the microjoule range.