Degenerate and Non-Degenerate Conical Emission and the transient Kerr nonlinear index in BK-7 glass with femtosecond laser pulses

The angle of Degenerate and Non-Degenerate Conical Emission in BK-7 glass is measured in the emission span of +3000 to -2000 cm(-1 )produced from an 800 nm 50 fs source laser beam. The measured emission angle is compared to three different mathematical models. These models are the Alfano-Shapiro Model, the Luther Model, and the Faccio X-Wave model. Experimental results demonstrate the existence of Degenerate Conical Emission at a frequency shift of zero (delta omega & nbsp;= 0) from the source beam. Of the three tested models this is only predicted by the Alfano-Shapiro model, which relates it directly to the Kerr nonlinear index. The relationship shows that the Kerr index has transitioned to a nearly pure electron cloud response due to the temporal nature of the laser pulse. The experimental methods demonstrated here could be used in the future as a means of measuring the response of the Kerr nonlinear index and studying the importance of pulse duration in nonlinear optics.