Abstract:We report the relationship between the initial glass composition and the resulting microstructural changes after direct femtosecond laser waveguide writing with a 1 kHz repetition rate Ti:sapphire laser system. A zinc polyphosphate glass composition with an oxygen to phosphorus ratio of 3.25 has demonstrated positive refractive index changes induced inside the focal volume of a focusing microscope objective for laser pulse energies that can achieve intensities above the modification threshold. The permanent photo-induced changes can be used for direct fabrication of optical waveguides using single scan writing techniques. Changes to the localized glass network structure that produce positive changes in the refractive index of zinc phosphate glasses upon femtosecond laser irradiation have been studied using scanning confocal micro-Raman and fluorescence spectroscopy.

Changes to the glass network structure after modification with tightly focused 1043nm, 400fs laser pulses have been studied in Er–Yb doped phosphate glass using in situ confocal Raman microscopy. For femtosecond laser writing conditions that result in heat accumulation, the 710 and 1209cm−1 Raman peaks, which are due to the (POP)sym and (PO2)sym network vibration modes, respectively, shift to both higher and lower wavenumbers. The differences in refractive index are shown to correlate spatially with the 1209cm−1 Raman signal shifts. Systematic shifts in this Raman peak to higher and lower wavenumbers indicate an overall expansion and/or contraction of the phosphate network that depends on the femtosecond laser writing conditions.

Nonlinear processing of glass using femtosecond laser pulses has been shown as a reliable method for producing photonic devices. To optimize the writing of optical waveguides and harness the true power of fs-laser modification, it is imperative that we gain a greater understanding of the physical mechanisms behind it. This requires experimental and theoretical studies into the dynamical processes during ultrashort laser-matter interaction. In this study, plasma emission spectroscopy and microscopy are shown as a reliable monitor for predicting the smoothness or roughness of the final laser-induced modification. Spectrally and temporally resolved optical transmission measurements using a supercontinuum probe beam are presented as experimental approach for investigating the transient optical properties of fs-laser-processed glass. The description of the light-plasma interaction is given by a simple model, which is used for inferring the order of magnitude of the electron density under such experimental conditions.

We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting internal gain of 1 dB∕cm at 1.53 μm when pumped with 500 mW at 976 nm, were directly fabricated using a regenerative amplified Ti:sapphire 1 kHz, 180 fs laser system. Optical properties as well as insertion losses and internal gain are reported. [14]. Of all these active glasses, phosphate glass systems offer the best RE solubility without RE clustering and are ideal for the fabrication of compact waveguide amplifiers that operate in the telecommunications window [15,16]. In many of these glasses, particularly phosphate glasses, the type of refractive index change that can be induced using the direct-write technique is determined by a combination of the laser processing conditions and the initial glass composition [8,10,[17][18][19][20][21]. While commercially purchased QX phosphate glass has been engineered to function as a short-gain, solid-state laser medium that operates in the C band, it is not necessarily the optimal material for fs-laser waveguide writing. We have recently reported [21] that fs-laser modification in an undoped zinc polyphosphate glass with an O∕P ratio of 3.25 (molar composition 60ZnO-40P 2 O 5 ) always results in a change to the refractive index that is positive and ideal for the fabrication of optical waveguides over a wide range of fs-laser writing conditions. Using this result, it is possible to design an Er-Yb doped zinc polyphosphate glass with the same O∕P ratio in order to fabricate subsurface single-pass waveguide amplifiers. Optimization of the material composition results in an enhanced degree of flexibility with regards to waveguide processing conditions inside Er-Yb doped phosphate glass systems. In this letter we demonstrate the fabrication of a single-pass 1534 nm signal waveguide amplifier with fslaser inscription inside an Er-Yb doped phosphate glass 0.65Er 2 O 3 -1.30Yb 2 O 3 -56.05ZnO-42.00P 2 O 5 mol% using a 1 kHz repetition rate system. The Er-Yb doped zinc polyphosphate glass used in this study may be a more suitable material for directly fabricating waveguides under single-scan writing conditions over an expanded modification range. Such a unique property makes this glass an attractive substrate to use for fs-laser micromachining of active three-dimensional (3-D) photonic devices.An Er-Yb codoped zinc polyphosphate glass with molar composition of 0.65Er 2 O 3 -1.30Yb 2 O 3 -56.05ZnO-42.00P 2 O 5 (from here on referred to as Er-Yb ZnP) was prepared using reagent-grade ZnO, Er 2 O 3 , Yb 2 O 3 , and NH 4 H 2 PO 4 . A detailed melting procedure is described elsewhere [22]. Annealed samples, approximately 15 mm × 5 mm × 5 mm in size, were polished using SiC paper and diamond pastes to a finish of 0.25 microns.Optical waveguides 1.5 cm in length were fabricated using linearly pola...

Absorption measurements on silver bromide crystals and fibers in the infrared J. Appl. Phys. 113, 043111 (2013) Continuous wave ultraviolet-laser sintering of ZnO and TiO2 nanoparticle thin films at low laser powers J. Appl. Phys. 113, 044310 (2013) Controlling laser emission by selecting crystal orientation Appl. Phys. Lett. 102, 011137 (2013) Impact of wavelength dependent thermo-elastic laser ablation mechanism on the generation of nanoparticles from thin gold films Appl. Phys. Lett. 101, 263107 (2012) Apparatus to measure adsorption of condensable solvents on technical surfaces by photothermal deflection Rev. Sci. Instrum. 83, 114905 (2012) Additional information on J. Appl. Phys. We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices. V C 2012 American Institute of Physics.[http://dx