title: Improving femtosecond laser pulse delivery through a hollow core photonic crystal fiber for temporally focused two-photon endomicroscopy.
abstract: In this paper, we present a strategy to improve delivery of femtosecond laser pulses from a regenerative amplifier through a hollow core photonic crystal fiber for temporally focused wide-field two-photon endomicroscopy. For endomicroscope application, wide-field two-photon excitation has the advantage of requiring no scanning in the distal end. However, wide-field two-photon excitation requires peak power that is 10(4)-10(5) times higher than the point scanning approach corresponding to femtosecond pulses with energy on the order of 1-10 μJ at the specimen plane. The transmission of these high energy pulses through a single mode fiber into the microendoscope is a significant challenge. Two approaches were pursued to partially overcome this limitation. First, a single high energy pulse is split into a train of pulses with energy below the fiber damage threshold better utilizing the available laser energy. Second, stretching the pulse width in time by introducing negative dispersion was shown to have the dual benefit of reducing fiber damage probability and compensating for the positive group velocity dispersion induced by the fiber. With these strategy applied, 11 fold increase in the two photon excitation signal has been demonstrated.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Heejin
authors.initials: H
authors.lastname: Choi
authors.affiliation: 1] Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA [2] Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA [3] BioSym, Singapore-MIT Alliance for Research and Technology, Singapore 138602, Singapore [4] Laser Biomedical Research Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Peter T C
authors.initials: PT
authors.lastname: So
mesh_terms: D020811:Biomedical Technology / Q000379:methods; D003952:Diagnostic Imaging; D006801:Humans; D007834:Lasers; D008853:Microscopy / Q000379:methods*; D017785:Photons