1. Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, 900 N 16th St., W342 NH, Lincoln, Nebraska 68588, USA
2. Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, 855 N 16th St, Lincoln, Nebraska 68588, USA
3. Laser Center, University of Latvia, Jelgavas St 3, Riga, LV-1004, Latvia