The influence of femtosecond laser wavelength on waveguide fabrication inside glass

We have investigated the permanent refractive index changes inside fused silica glass after laser inscription of waveguides using ultrashort laser pulses at different wavelengths. To this end the laser frequency was detuned using an optical parametric amplifier (OPA) combined with a confocal arrangement (for cleaning the laser Gaussian spatial profile). The suitability for waveguiding and the refractive index changes were inspected by measuring the near- and farfield output profiles of the laser-machined lines using a continuous wave laser at 660 nm. Raman spectroscopy was performed both for tracks of damage and for good optical waveguides. The structural changes were inferred from peak shifts and relative intensity fluctuations associated with representative Raman bands. In fused silica, changes in the 605 cm-1 peak, which is due to 3-membered Si-O ring structures, were monitored. Since the laser photon energy rules the order, k, of the multiphoton absorption in dielectrics, the role of the laser wavelength for waveguide fabrication will be discussed in terms of different powers of the laser intensity (I(r,z)k(λ)) and the Keldysh formalism for strong field ionization (WSFI(λ)).

[1]  J. Hernandez-Rueda,et al.  All-optical characterization of fs-laser induced refractive index changes in bulk and at the surface of zinc phosphate glasses , 2015, Photonics West - Lasers and Applications in Science and Engineering.

[2]  J. J. Witcher,et al.  Direct femtosecond laser waveguide writing inside zinc phosphate glass. , 2011, Optics express.

[3]  G. Mourou,et al.  Femtosecond Optical Breakdown in Dielectrics , 1998 .

[4]  J. J. Witcher,et al.  Fs‐Laser Processing of Glass: Plasma Dynamics and Spectroscopy , 2015 .

[5]  J. Siegel,et al.  Femtosecond laser-induced refractive index changes at the surface of dielectrics: quantification based on Newton ring analysis , 2014 .

[6]  J. Siegel,et al.  Correlation of the refractive index change at the surface and inside phosphate glass upon femtosecond laser irradiation , 2012 .

[7]  Surface structuring of fused silica with asymmetric femtosecond laser pulse bursts , 2013 .

[8]  Thomas R Huser,et al.  Modification of the fused silica glass network associated with waveguide fabrication using femtosecond laser pulses , 2003 .

[9]  Tsuneo Mitsuyu,et al.  Photowritten optical waveguides in various glasses with ultrashort pulse laser , 1997 .

[10]  D. Krol.  Spectroscopic Characterization of Waveguides , 2012 .

[11]  A. Couairon,et al.  Femtosecond laser-induced damage and filamentary propagation in fused silica. , 2002, Physical review letters.

[12]  K. Miura,et al.  Writing waveguides in glass with a femtosecond laser. , 1996, Optics letters.

[13]  L. Keldysh,et al.  IONIZATION IN THE FIELD OF A STRONG ELECTROMAGNETIC WAVE , 1964 .

[14]  G. Gibson,et al.  ULTRAFAST ELECTRON DYNAMICS IN FEMTOSECOND OPTICAL BREAKDOWN OF DIELECTRICS , 1999 .