Fiber-format dual-comb coherent Raman spectrometer

We demonstrate a fiber-format system for dual-comb coherent anti-Stokes Raman scattering spectroscopy. The system is based on two ytterbium fiber (Yb) femtosecond lasers at repetition frequencies of 94 MHz, a Yb amplifier, and a photonic crystal fiber for spectral broadening and generation of pulses with a central wavelength of 1040 nm and durations in the sub-20-fs regime. We observed Raman spectra of acetonitrile and ethyl acetate with spectral coverage from 100 to 1300  cm-1, resolution of 8  cm-1, and a signal-to-noise ratio of around 100, when averaging over 10 acquisitions. The design is suitable for implementing portable dual-comb coherent Raman spectrometers

Diamond photonics platform enabled by femtosecond laser writing

We demonstrate the first buried optical waveguides in diamond using focused femtosecond laser pulses. The properties of nitrogen vacancy centers are preserved in the waveguides, making them promising for diamond-based magnetometers or quantum information systems.Comment: 24 pages, 6 figure

Synthesis of transparent Er-doped fluorotellurite glass-ceramics through controlled crystallization

This work presents a detailed study of the preparation and microstructure of transparent glass-ceramics obtained from a TeO2-ZnO-ZnF2 fluorotellurite glass doped with ErF3. The determination of nucleation and crystal growth rate-like curves allows establishing a narrow temperature range (340-350°C) for a controlled crystal- lization. Thereafter, a crystalline phase was grown through a two-step heat treatment: 10-20 h at a temperature slightly above the glass transition temperature, followed by a 2.5-3 h treatment at 340°C. Structural analysis showed the nucleation of ErF3 nanocrystals (NCs) with a typical size of ≈50 nm that were homogeneously distributed in the glass matrix. The resulting glass-ceramic material remains highly transparent, with a small crystalline to amorphous ratio; yet the presence of ErF3 NCs has a large impact on the photoluminescence response of Er3+ ions. Upconverted visible emission is analyzed under 980 nm excitation: red emission from the 4F9/2 level is dramatically enhanced with respect to green 2H11/2, 4S3/2 → 4I15/2 hypersensitive transitions. The observed behaviour is attributed to the presence of Er3+ ions in the NCs, which are sites with lower phonon energy than the glass matrix. Moreover, the shorter interionic distance between Er3+ ions in the NCs eases energy transfer between them.This work has been supported by the Spanish Ministry of Economy & Competitivity (Projects MAT 2013-48246- C2-2-P, TEC 2012-38901-C02-01, and TEC 2015-69916-C2-1-R) and the Basque Country Government (Project IT-943-16). R. Morea acknowledges a FPI grant from the Spanish Government.Peer Reviewe

Control of waveguide properties by tuning femtosecond laser induced compositional changes

© 2014 AIP Publishing LLC. Local compositional changes induced by high repetition rate fs-laser irradiation can be used to produce high performance optical waveguides in phosphate-based glasses. The waveguide refractive index contrast is determined by the local concentration of La, which can be changed by the action of the writing laser pulses. In this work, we have investigated the degree of control that can be exerted using this waveguide writing mechanism over the cross-section of the guiding region, and the local refractive index and compositional changes induced. These variables can be smoothly controlled via processing parameters using the slit shaping technique with moderate Numerical Aperture (NA 0.68) writing optics. The combined use of X-ray microanalysis and near field refractive index profilometry evidences a neat linear correlation between local La content and refractive index increase over a broad Δn interval (>3×10-2). This result further confirms the feasibility of generating efficient, integrated optics elements via spatially selective modification of the glass composition.This work was partially supported by the Spanish Ministry Economy and Competitiveness (MINECO, TEC2011-22422, MAT2012-31959), J.H. and T.T.F. acknowledge funding from the JAE CSIC Program (pre- and post-doctoral fellowships, respectively, co-funded by the European Social Fund). B. Sotillo acknowledges her funding in the frame of CSD2009-00013 (MINECO).Peer Reviewe

Ion migration assisted inscription of high refractive index contrast waveguides by femtosecond laser pulses in phosphate glass

In this Letter, we report on the successful fabrication of low loss, high refractive index contrast waveguides via ion migration upon femtosecond laser writing in phosphate glass. Waveguides were produced in two different phosphate glass compositions with high and low La2O3 content. In the La-rich glass, a large refractive index increase in the guiding region was observed due to the incoming migration of La accompanied by the out-diffusion of K. The much smaller refractive index change in the La-less glass is caused by rearrangements of the glass structure. These results confirm the feasibility of adapting the glass composition for enabling the laser writing of high refractive index contrast structures via spatially selective modification of the glass composition. © 2013 Optical Society of America.This work was partially supported by the Spanish Ministry Economy and Competitiveness (TEC2011- 22422), Spanish Ministerio de Educacion y Ciencia (MAT2010‐16161), MINECO (Projects MAT 2012‐31959 and CSD2009‐00013), and the JAE-CSIC Program (TTF).Peer Reviewe

Controlling plasma distributions as driving forces for ion migration during fs laser writing

10 págs.; 12 figs.© 2015 IOP Publishing Ltd. The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.The authors thank Wren Carr at Lawrence Livermore National Laboratory for providing original data from [24] for the display in figure  3. This work was partially supported by the Spanish Ministry Economy and Competitiveness (MINECO, TEC2011-22422, MAT2012-31959), JH and TTF acknowledge funding from the JAE CSIC Program (pre- and postdoctoral fellowships, respectively, co-funded by the European Social Fund). B Sotillo acknowledges her funding in the frame of CSD2009-00013 (MINECO).Peer Reviewe