Measurement of χ(2)components by comparing polarization-resolved second-order cascade processes

Abstract

ABSTRACT Cascade third harmonic generation proves to be a versatile tool to access tensor components. Wherevercascade third harmonic generation allows an interference between two second order processes it will be able to determineratio of tensor components. We give a full account for orthorhombic class min2. Given is a discussion of trigonal classes.Polarization resolved signal of cascade third harmonic generation in LBO crystal has been recorded and analyzed.Keywords: cascade third harmonic generation, mm2, LiB3O5, second order nonlinearity 1. INTRODUCTION Measurement of second order susceptibility tensor components is important from one side for the prediction of theefficiency of different types of second order processes in the investigated crystal and from another side for comparison withthe values obtained by different calculation models. Measurement of (2) components of single crystal can be done byinvestigation both phase matched and nonphase matched single second order processes. Using phase matched processes hasthis advantage that their efficiency is many orders ofmagnitudes higher that the non-phase matched process and that it is notnecessary to be used very high power laser sources (or photon counting systems). The disadvantage of this method is the factthat not all (2) components are involved in the effective second order nonlinearities responsible for single phase matchedsecond order process.In this paper we show that this disadvantage can be overcome by using phase matched cascade second orderprocesses in single crystal. We demonstrate both theoretically and experimentally that the investigation of phase matchedcascade third harmonic generation (CTHG) can be an useful tool for measurement of relative magnitude and sign of all (2)tensor components. Previously CTHG has been investigated in [1 ,2,3] with the purpose to estimate the value of cubicnonlinearity in noncentrosymmetric crystals. in none of these papers are provided the correct expressions for phase matchedthird harmonic generation due to cascade second order processes. In the next paragraph we start with the theoreticalconsiderations for the processes of CTHG for all allowed phase matched directions.