Origin and suppression of back conversion in a phase-matched nonlinear frequency down-conversion process

Abstract

Back conversion is an intrinsic phenomenon in nonlinear frequency down-conversion processes. However, the physical reason for its occurrence is not well understood. Here, we theoretically reveal that back conversion is the result of a π-phase jump associated with the depletion of one interacting wave. By suppressing the idler phase jump through a deliberate crystal absorption, the back conversion can be inhabited, thus enhancing the conversion efficiency from the pump to the signal. The results presented in this Letter will further the understanding of nonlinear parametric processes and pave the way toward the design of highly efficient down-conversion systems.

Optical modification of nonlinear crystals for quasi-parametric chirped-pulse amplification

“…6 b, back conversion can still occur in the efficiency curves of SFG-dissipated QPCPA no matter where the quenching position seeds. This is because the phase jump induced by the depletion of the idler will trigger back conversion of both OPCPA and SFG [14] and the generated idler from the back conversion of the SFG will seed back conversion of the OPCPA. Such behavior is quite different from that in the SHG-dissipated QPCPA, where the depletion of the idler cannot trigger back conversion of SHG under perfect PM conditions.…”

“…Since OPCPA is a parametric process, the back-conversion effect is inevitable [ 14 , 15 ] and poses an intractable limitation on OPCPA efficiency. The OPCPA process (pump → signal + idler) and its back conversion (signal + idler → pump) share the same PM condition, so they can occur in the same nonlinear crystal.…”

A Review of Optical Parametric Amplification at the Vulcan Laser Facility

“…Common issues with OPCPA systems include: operating at degeneracy (wherein the idler pulse propagates in the direction of the signal); back-conversion [62,63]; and parasitic second harmonic generation (SHG) [7,9]. A foreseeable bottleneck to OPCPA is the availability of large-aperture crystals.…”