Supercontinuum generation for coherent anti-Stokes Raman scattering microscopy with photonic crystal fibers

Pernille Klarskov,Kim P Hansen,Peter E Andersen,Antti Isomäki

doi:10.1364/oe.19.026672

Abstract

Photonic crystal fiber (PCF) designs with two zero-dispersion wavelengths (ZDWs) are experimentally investigated in order to suggest a novel PCF for coherent anti-Stokes Raman scattering (CARS) microscopy. From our investigation, we select the optimum PCF design and demonstrate a tailored spectrum with power concentrated around the relevant wavelengths for lipid imaging (648 nm and 1027 nm). This new PCF is characterized by varying the fiber length, the average power, and the pulse width of the fs pump pulses. It was found that the selected PCF design gave a significantly improved spectral distribution compared to an existing PCF for CARS microscopy. Furthermore, the PCF is designed in a twofold symmetric structure allowing for polarization maintaining propagation. Finally, the pulse propagation is investigated numerically showing good agreement with the measured spectrum. From the numerical analysis, the nonlinear effects responsible for the spectral broadening are explained to be soliton fission processes, dispersive waves, and stimulated Raman scattering.

Highlights

Coherent Anti-Stokes Raman Scattering [1] (CARS) microscopy is a nonlinear imaging technique sensitive to molecular vibrations, where a pump beam and a Stokes beam interact with a sample through the third order susceptibility
We experimentally investigated the six Photonic crystal fiber (PCF) designs by inserting each of them in the setup with 35 mW of average power coupled to the core
We have investigated PCF designs with two zero-dispersion wavelengths (ZDWs) in order to suggest a novel PCF design for generating the second wavelength needed for coherent anti-Stokes Raman scattering (CARS) microscopy

Summary

Introduction

Coherent Anti-Stokes Raman Scattering [1] (CARS) microscopy is a nonlinear imaging technique sensitive to molecular vibrations, where a pump beam and a Stokes beam interact with a sample through the third order susceptibility. By controlling the structural design of the PCF, mainly pitch size and relative hole diameter, it is possible to control the position of the ZDWs and thereby tailor the spectral distribution of the power at the output of the PCF Based on such designs, PCFs that concentrate the power at the desired spectral ranges relevant for CARS microscopy have been developed [12]. The PCFs are pumped using a fs Ti:Sapphire laser at center wavelength 795 nm When this wavelength is used as either the Stokes or the pump beam, we suggest an optimum PCF candidate to generate the second wavelength needed for lipid imaging at either 648 nm or 1027 nm, respectively. The spectral broadening of the optimum PCF is compared to an existing commercially available CARS PCF [19]

Photonic crystal fiber designs

Results

Conclusion