Syed Sohail Abbas and  Sergei Popov,  Compact Er3+-Doped ZBLAN Green Upconversion Fibre Laser.   journal   = {International Journal of Electronics and Communication Engineering}, [online]. World Academy of Science, Engineering and Technology.
    June 2011, vol. 54(6). 776 - 778
    [viewed 25 May 2022]. Available from: https://publications.waset.org/pdf/10512.