The direct femtosecond laser writing of phase optical elements in glasses represents a promising technique for controlling light beams and developing new functional devices that operate on the birefringence effect. In this study, phase plates were written in the volume of silica and nanoporous glasses using a laser beam. For the first time, the chromatic dispersion curves of birefringence were measured for such plates using multiple methods. This allows the retardance of birefringent elements fabricated by direct laser writing to be estimated, even when using commercial birefringence analysis systems operating at a specific wavelength.

In this study, we proposed silver-doped nanoporous glass as an advanced medium for archival optical data storage based on ultrafast laser writing. Mesoporous structure of synthesized glass with ink-bottle nanopores allows for efficient doping of durable high-silica matrix with silver. An effect of laser writing conditions on luminescence activity and form birefringence of laser-induced nanostructured patterns inside glass is investigated. A single laser pulse has been shown to produce a submicron pattern with Ag-n nanoclusters which allows encoding one bit of information in a well-detectable luminescence signal. Voxels with silver nanoclusters can be erased by the heat treatment at 300 degrees C and re-written by laser pulses. This opens a way to high-speed, ultra-dense and rewritable data storage. At the same time, in addition to the luminescence activity, a few laser pulses can induce form birefringence. The optical retardance and slow axis orientation of birefringent voxels can be controlled by the number of laser pulses or pulse energy and laser beam polarization, which expand the capacity of data encoding by several bits per dot. A reliable data readout with an accuracy over 99.8% has been demonstrated. The obtained results are significant for the development of long-term optical data storage compacted with multilevel encoding and rewriting ability.

The creation of robust joint among different materials with notably different coefficients of thermal expansion (CTE) is an urgent task for the development of the engineering, laser technology, and aerospace industry. In this regard, femtosecond laser welding is a promising technique for efficient adhesion-free bonding of transparent materials. This paper reports on the laser welding of laser phosphate glass (CTE = 110 x 10(-7) K-1) and spinel-based glass-ceramic (CTE = 50 x 10(-7) K-1) by the Bessel beam. Dependencies of weld geometric parameters on the pulse energy and scanning speed were investigated, and the laser exposure conditions were optimized for durable welding. The weld joints were tested on shear strength, which was shown to be as record high as up to 147 MPa. Atomic force microscopy, Raman spectroscopy, and elemental analysis were used to investigate the structure and morphology of the weld after its fracture, which revealed the laser-induced amorphization of glass-ceramics and the formation of strong interconnection by laser-driven mutual diffusion of two glassy phases. The results demonstrate the prospects for using femtosecond lasers for efficient industrial welding of a wide range of materials.

Space-selective laser-induced crystallization of glass enables direct femtosecond laser writing of crystal-in-glass channel waveguides having nearly single-crystal structure and consisting of functional phases with favorable nonlinear optical or electrooptical properties. They are regarded as promising components for novel integrated optical circuits. However, femtosecond-laser-written continuous crystalline tracks typically have an asymmetric and strongly elongated cross-section, which causes a multimode character of light guiding and substantial coupling losses. Here, we investigated the conditions of partial remelting of laser-written LaBGeO5 crystalline tracks in lanthanum borogermanate glass by the same femtosecond laser beam which had been used for their writing. Exposure to femtosecond laser pulses at 200 kHz repetition rate provided cumulative heating of the sample in the vicinity of the beam waist sufficient to provide space-selective melting of crystalline LaBGeO5. To form a smoother temperature field, the beam waist was moved along the helical or flat sinusoidal path along the track. The sinusoidal path was shown to be favorable for tailoring the improved cross-section of the crystalline lines by partial remelting. At optimized laser processing parameters, most of the track was vitrified, and the residual part of the crystalline cross-section had an aspect ratio of about 1:1. Thermal-induced stress emerging during the tailoring procedure was efficiently eliminated by fine post-annealing. The proposed technique suggests a new way to control the morphology of laser-written crystal-in-glass waveguides by tailoring their cross-section, which is expected to improve the mode structure of the guided light.

The influence of femtosecond laser micromachining in thermal and athermal regimes on the structure of a transparent glass-ceramic based on the ZnO–MgO–Al2O3–SiO2 system, which is characterized by heightened mechanical strength and hardness, was studied. Amorphization of nanosized granite ZnAl2O4 crystals, which occurs under the action of laser pulses, is confirmed by means of electron microscopy and electron diffraction. Quantitative phase microscopy was used to assess the change in the refractive index in the tracks written by a laser beam. In an athermal regime, at pulse repetition frequency 10 kHz, the full amorphization of the crystalline phase in the laser processing region in the bulk of the sitall effects an increase in the refractive index by ∆n = 0.0007. The results obtained expand the potential areas of application of transparent sitalls with heightened strength and open up the possibility of forming channel waveguides in their bulk by means of direct laser writing.

Изучена динамика развития структуры двулучепреломляющих лазерно-индуцированных модификаций в нанопористом стекле в зависимости от количества записывающих фемтосекундных импульсов. Обнаружена трансформация эллиптической полости, вытянутой перпендикулярно поляризации записывающего лазерного пучка, в двулучепреломляющую нанорешетку, которая сопровождается увеличением фазовой задержки. Продемонстрирована возможность перезаписи структур путем изменения ориентации их медленной оси двулучепреломления, что обуславливает перспективность применения высококремнеземистых нанопористых стекол в качестве носителей информации с возможностью перезаписи.

We report an unexpected pulse repetition rate effect on ultrafast-laser modification of sodium germanate glass with the composition 22Na2O 78GeO2. While at a lower pulse repetition rate (~≤250 kHz), the inscription of nanogratings possessing form birefringence is observed under series of 105–106 pulses, a higher pulse repetition rate launches peripheral microcrystallization with precipitation of the Na2Ge4O9 phase around the laser-exposed area due to the thermal effect of femtosecond pulses via cumulative heating. Depending on the pulse energy, the repetition rate ranges corresponding to nanograting formation and microcrystallization can overlap or be separated from each other. Regardless of crystallization, the unusual growth of optical retardance in the nanogratings with the pulse repetition rate starting from a certain threshold has been revealed instead of a gradual decrease in retardance with the pulse repetition rate earlier reported for some other glasses. The repetition rate threshold of the retardance growth is shown to be inversely related to the pulse energy and to vary from ~70 to 200 kHz in the studied energy range. This effect can be presumably assigned to the chemical composition shift due to the thermal diffusion of sodium cations occurring at higher pulse repetition rates when the thermal effect of the ultrashort laser pulses becomes noticeable.

Femtosecond laser writing is a versatile and effective technique for high-precision 3D micromachining of crystals for applications in photonics. Here, we demonstrate the femtosecond laser-assisted control over the structure and phase composition in yttrium aluminum garnet (YAG) single crystal. Increasing the energy of the laser pulse enables achieving extremely high temperature and pressure in the laser beam waist region, which leads to pronounced plastic deformation of the crystal structure and even to its complete amorphization inside forming nanogratings or a phase transition from the garnet phase to the perovskite phase. The main types of laser-induced modifications in YAG single crystal are described using quantitative phase microscopy, quantitative birefringence imaging and transmission high-resolution electron microscopy. For the first time, the mechanism of plastic deformation responsible for the formation of dislocations and amorphous phase is experimentally confirmed. The results obtained contribute to the deeper understanding of fundamentals of the direct laser writing in crystals which are essential for the optimization of selective etching processes and fabrication of photonic crystal waveguides.

This paper presents results of femtosecond laser micromachining of a transparent glass-ceramic in the Li2O–Al2O3–SiO2 system with a near-zero linear thermal expansion coefficient in the thermal and athermal regimes. Electron microscopy and electron diffraction data confirm complete amorphization of nanocrystals of β-eucryptite-like solid solutions under the effect of laser pulses. Using quantitative phase microscopy, we have evaluated refractive index changes in individual laser-written tracks. In the athermal regime at a pulse repetition rate of 10 kHz, complete glass-ceramic amorphization leads to a decrease in the refractive index of the material (Δn = −0.0035) in the laser treatment region, which opens up the possibility of using direct laser writing of channel waveguides in a thermally stable glass-ceramic matrix.

The possibility of creating a stable joint of materials with different values of the linear thermal expansion coefficient (LTEC) was demonstrated by means of femtosecond laser beam welding: phosphate glass and zinc-magnesium-aluminum-silicate sitall (their values of the LTEC lie in the range 20 – 300°C: 120 × 10 –7 K –1 and 62 × 10 –7 K –1 respectively. Optical microscopy and Raman spectroscopy were used to investigate the structural features of welds obtained by different laser welding regimes and to optimize the laser welding regimes.

— The dynamics of the variation in the structure of laser-induced birefringent regions in nanoporous glass have been studied in relation to the number of writing femtosecond laser pulses. We have detected transformation of an elliptical cavity elongated across the writing laser beam polarization into a birefringent nanograting, accompanied by an increase in retardance. The feasibility of rewriting such structures by changing the orientation of their slow axis of birefringence has been demonstrated, which suggests that high-silica nanoporous glasses are potentially attractive for use as data storage media, with the possibility of rewriting.

The formation of stable connection between materials with different CTE via using femtosecond laser writing is demonstrated. The welding of phosphate glass (CTE = 120?10–7 K–7) to zinc-magnesium-alumosilicate glass-ceramics (CTE = 62?10–7 K–7) is realised. Investigation of the structural features of laser-induced welds by means of optical microscopy and Raman spectroscopy enables optimization of the laser welding process.

Представлены результаты фемтосекундной лазерной микрообработки в атермическом и тепловом режимах прозрачного ситалла на основе системы Li 2 O–Al 2 O 3 –SiO 2 со значением температурного коэффициента линейного расширения, близким к нулю. Результаты электронной микроскопии и дифракции электронов подтверждают полную аморфизацию наноразмерных кристаллов β-эвкриптитоподобных твердых растворов под действием лазерных импульсов. Методом количественной фазовой микроскопии проведена оценка изменения показателя преломления в отдельных записанных лазерным пучком треках. При частоте следования 10 кГц в атермическом режиме полная аморфизация ситалла приводит к снижению показателя преломления (Δ n = −0.0035) в области лазерной обработки, что открывает возможности использования прямой лазерной записи канальных волноводов в термостабильной ситалловой матрице.

The influence of the spheroidization process in the flow of high-temperature plasma of glass based on the Li2O–Al2O3–SiO2 (LAS) system doped with 1.0 mol. % Nd2O3 on its crystallization properties is investigated. The resulting microspheres with a size of 32 – 64 ?m are characterized by a significantly higher glass transition temperature Tg compared to the Tg of the initial glass (751 °C and 677 °C, respectively), which may be due to both a change in chemical composition during spheroidization and a fundamentally different thermal history of microspheres and glass. Despite the delayed crystallization kinetics, the glass-ceramic structure based on ?-eucryptite-like solid solutions of LixAlxSi1 – xO2 is formed in microspheres, as in the initial glass, under the action of heat treatment, indicating the possibility of both obtaining microspheres with the glass-ceramic structure and varying their coefficient of thermal expansion near zero values.

The formation of polarization-dependent birefringence, apparently due to the formation of nanogratings, in the bulk of lithium silicate and lithium aluminosilicate glasses under the action of a series of femtosecond laser pulses was demonstrated. The phase shift in the light passing through the modified regions was determined as a function of the parameters of the laser radiation and the chemical composition of the glass. It is shown that Al 2 O 3 content growth due to the presence of an alkaline component in the glass composition effects an increase in the minimum number of pulses required for the formation of a birefringent region as well as an increase in the retardance.

In this study, we investigated the structure of microdomains directly laser-written in the bulk of glass and containing CdS nanoparticles by transmission electron microscopy. The CdS nanocrystals have a multidisperse size distribution while quantum dots with a minimal size of 3-4 nm are registered near the edge of a microdomains. The size of CdS nanocrystals sweepingly increases up to-340 nm from the periphery to the center of the laser-written microdomain. It has been found that microdomains possess laser polarization-sensitive optical properties providing opportunities for the development of advanced optical data encoding and security tagging.

Optical data writing and rewriting with a 10.8 GB/cm(3) capacity based on the formation of luminescent silver nanoclusters inside silver-doped sodium aluminoborate glass by ultrafast laser pulses are demonstrated. Even a single laser pulse with an energy of only 60 nJ enables writing a submicron-sized domain yielding a well-detectable photoluminescence signal due to laser-induced silver nanoclustering. We showed the possibility of reducing the distance between luminescent domains to 0.6 mu m, which does not affect the reliable readout and multilayer capabilities of optical data storage. The investigation of the thermal stability of laser-written domains showed that they could survive at temperatures up to the glass transition point. Thermal annealing of glass with the recorded data has been shown to erase the information together with the laser-written domains. The possibility of subsequent rewriting of new data is also confirmed. Single-pulse laser-induced nanoclustering paves the way to fast and ultradense 3D data writing in glass media for robust long-lasting rewritable data storage based on luminescent nanomaterials.

In this study, a simple one-stage laser-assisted metallization technique based on laser-induced backside wet etching and laser-induced chemical liquid-phase deposition is proposed. It allows for the fabrication of gold micropatterns inside the laser-written trace on a glass substrate. The reduction and deposition of gold inside and outside the laser-ablated channel were confirmed. The presence of Au nanoparticles on the surface of the laser-written micropattern is revealed by atomic force microscopy. The specific resistivity of the gold trace formed by ultrafast light-assisted metal micropatterning on a dielectric glass substrate is estimated as 0.04 ± 0.02 mΩ·cm. The obtained results empower the method of the selective laser-assisted deposition of metals on dielectrics and are of interest for the development of microelectronic components and catalysts, heaters, and sensors for lab-on-a-chip devices.

The method of two-stage formation of hollow channels in glass by direct laser writing and subsequent selective etching is profitably used in the manufacture of microfluidics devices. In the present work, the influence of the concentration of the etching solution, the velocity of the laser beam, and the energy of laser pulses on the etching rate, selectivity, and roughness of hollow channels in quartz glass were investigated. For hollow channels, an etching rate 300 μm/h can be achieved together with very high selectivity (680) by using a 1M NaOH solution.

We study the process of femtosecond laser-induced growth of a single-crystal channel waveguide in oxide glasses and point out the challenges that must be overcome on the way to the high performance of laser-written crystal architectures.