We report optical characterization of the different optical components fabricated in transparent materials by bulk refractive index modification or surface ablation by femtosecond pulses. The methods used for characterization of the components with refractive index modification fabricated in fused silica by high repetition rate femtosecond KGW:Yb laser were transmission and diffraction measurements at 532 and 632.8 nm wavelengths, and total integrated scattering (TIS) at 532 mn wavelength. The combined characterization methods were sufficient for modification process optimization and allowed creation of the Bragg gratings with diffraction efficiency in range from 55 to 90% and low scattering losses. The forward and backward TIS measurements of the radial polarization converter showed that forward scattering is more than five times as high as backward scattering. Solar cells with modified surface by femtosecond pulse ablation were investigated by TIS and Volt-Ampere measurements. The current increase is registered with growth of the scattering loses in the solar cells.
In this work we present the results on volumetric fused silica modifications using femtosecond Gaussian and Gaussian-Bessel laser beams. We show that for specific photonic device, like volume Bragg grating, fabrication, Bessel beams are more superior to Gaussian, as the recording process is much faster and fabricated devices have better efficiencies. Also Gaussian beam tend to be more efficient in formation of nanogratings that causes the appearance of birefringence in modified zones. This reduces optical quality of fabricated device and limits overall recording velocity. We have successfully fabricated volume Bragg gratings in the bulk of fused silica that had absolute diffraction efficiencies reaching ∼90% using femtosecond Gaussian-Bessel beam, while gratings made with Gaussian beam reached only 60%.
We report on a technique for precise hole drilling in optical fibers using tightly focused femtosecond laser pulses. This direct laser writing approach makes it possible to minimize the amount of waveguide material for uncompromised mechanical performance of the fiber. The proof-of-the-principle of the fiber integration into a microfluidic chip is demonstrated. We show that fabricated holes in the waveguides can be used for measurement of absorption coefficient and refractive index changes at 1x10<sup>-3</sup> refractive index units and 2 cm<sup>-1</sup> for refractive index and absorption changes, respectively. Simple design and integration possibility of laser-fabricated waveguide sensors is prospective for optofluidic applications.