Effect of Laser Linewidths on Nonlinear Optical Processes Exploiting Electromagnetically Induced Transparency

Abstract

We investigate the effects of laser linewidths on the efficiency of sum-frequency generation when electromagnetically induced transparency is exploited in the manner suggested by Harris and his co-workers, which makes use of pump lasers and an intense coupling laser. The linewidths are assumed to be due to phase diffusion. Analytic expressions are obtained which are an excellent approximation when the coupling laser is strong. It is found that increasing the coupling-laser linewidth strongly increases the opacity of the medium; a first consideration is therefore to minimize this linewidth. The relative efficiency of sum-frequency generation is measured by the ratio R of the absolute value of the third-order susceptibility, χ₃, to the imaginary part of the first order susceptibility, χ₁. For large intensities of the coupling field, we show that |χ₃| is independent of the laser linewidths, whereas it increases the value of Im(χ₁).