Crossing a Critical Threshold (IMAGE) Lehigh University Caption A polarized light field microscope image shows crystal junctions written inside glass with a femtosecond laser. Upon divergence (a), independent lattice orientations develop in each branch and are retained (b) as the branches merge back into a single line. The color wheel indicates the angle of the fast or slow axis of birefringence. Credit Lehigh University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.