Second harmonic generation imaging microscopy with a high-power ultrafast fiber laser

Abstract

Second harmonic generation (SHG) imaging microscopy is an important emerging technique for biological research, with many advantages over existing one- or two-photon fluorescence techniques. SHG is of growing interest to those in the biomedical community studying structural proteins such as collagen and to those in neuroscience using voltage-sensitive dyes. An important consideration in the application of non-linear phenomena such as SHG to routine microscopy is the complexity of the laser source used for excitation. Almost all applications in ultrafast microscopy currently employ mode-locked Ti:sapphire lasers, and though these systems have improved considerably in recent years, they are still expensive, large and complicated for those with skills outside of ultrafast optics. Here we report on SHG microscopy using a high power femtosecond fiber laser. The Femtopower1060 from Fianium Ltd. is an ultrafast fiber laser operating at 1064nm. With a passively mode-locked master source, a high power fiber amplifier and a built-in pulse compressor, the laser produces high quality pulses shorter than 200fs with a repetition rate of 100MHz and an average power of 1W. The unit is turn-key, air-cooled and maintenance free with a small footprint and proves to be an excellent source for SHG and two-photon microscopy at this wavelength outside the range of most Ti:sapphire systems and without those systems' complexity.