Ultrashort-pulse laser calligraphy

Control of structural modifications inside silica glass by changing the front tilt of an ultrashort pulse is demonstrated, achieving a calligraphic style of laser writing. The phenomena of anisotropic bubble formation at the boundary of an irradiated region and modification transition from microscopic bubbles formation to self-assembled form birefringence are observed, and the physical mechanisms are discussed. The results provide the comprehensive evidence that the light beam with centrosymmetric intensity distribution can produce noncentrosymmetric material modifications

Microscopic mechanism of structural and volume relaxation below glass transition temperature in a soda-lime silicate glass revealed by Raman spectroscopy and its first principle calculations

To elucidate the atomistic origin of volume relaxation in soda-lime silicate glass annealed below the glass transition temperature (Tg), the experimental and calculated Raman spectra were compared. By decomposing the calculated Raman spectra into a specific group of atoms, we found that the Raman peak at 1050 cm-1 corresponds to bridging oxygen with a small Si-O-Si bond angle. The experimental Raman spectra indicated that, during annealing below Tg, a homogenization reaction Q2+Q4->2Q3 proceeds in the early stage of structural relaxation. Then, the Si-O-Si units with relatively small angles decrease even in the later stages, which is first evidence of ring deformation causing volume relaxation of soda-lime silicate glass because decreasing small Si-O-Si angles corresponds to the reduce of acute O-O-O angle in a ring and can expand the space inside the rings, and Na can be inserted into the ring center. In conclusion the ring deformation and Na displacement is the origin of the volume relaxation of soda-lime silicate glass below Tg.Comment: 15 figures and 1 table for main text, 8 figures and 1 table for supplemental inf

Ultra-high temperature Soret effect in a silicate melt: SiO2 migration to cold side

The Soret effect, temperature gradient driven diffusion, in silicate melts has been investigated intensively in the earth sciences from the 1980s. The SiO2 component is generally concentrated in the hotter region of silicate melts under a temperature gradient. Here, we report that at ultra-high temperatures above approximately 3000 K, SiO2 becomes concentrated in the colder region of the silicate melts under a temperature gradient. The interior of an aluminosilicate glass (63.3SiO2-16.3Al2O3-20.4CaO(mol%)) was irradiated with a 250 kHz femtosecond laser pulse for local heating. SiO2 migrated to the colder region during irradiation with an 800 pulse (3.2 ms irradiation). The temperature analysis indicated that migration to the colder region occurred above 3060 K. In the non-equilibrium molecular dynamics (NEMD) simulation, SiO2 migrated to the colder region under a temperature gradient, which had an average temperature of 4000 K; this result supports the experimental result. SiO2 exhibited a tendency to migrate to the colder region at 2400 K in both the NEMD and experimental study. The second-order like phase transition was observed at ~ 2000-3400 K when calculated using MD without a temperature gradient. Therefore, the second-order phase transition could be related to the migration of SiO2 to colder region. However, the detailed mechanism has not been elucidated

Low temperature deformation mechanism of semiconductor single crystal and molding of Ge microlens array by direct electrical heating

Although deforming a silicon single crystal at a temperature of about 600 °C lower than its melting point (1414 °C) by direct electrical heating was successfully demonstrated, the mechanism has still not been fully clarified. In this paper, we propose a model for the low temperature deformation of a semiconductor single crystal by direct electrical heating. The thermographic observation during direct electrical heating reveals that the local temperature is higher at the region where dense dislocation occurred in the semiconductor single crystal by uniaxial pressing. This is interpreted in terms of the scattering of an electron by the dislocation leading to an increase in the electrical resistivity. Finally, the deformation temperature of the semiconductor single crystal apparently becomes low due to the occurrence of such hot spots. We have also demonstrated an application to mold a microlens array composed of a germanium single crystal with a focal length of 25 µm

Multilayer aberration correction for depth-independent three-dimensional crystal growth in glass by femtosecond laser heating

Focused femtosecond lasers are known for their ability to modify transparent materials well below the surface with 3D selectivity, but spherical aberration causes degraded focal intensity and undesirable absorption conditions as focal depth increases. To eliminate such effects we have implemented an aberration correction procedure that accounts for multiple refracting layers in order to crystallize LaBGeO5 glass inside a temperature-controlled microscope stage via irradiation through a silica glass window. The correction, applied by a spatial light modulator, was effective at removing the focal depth-dependent degradation and achieving consistent heating conditions at different depths, an important consideration for patterning single-crystal architecture in 3D. Additional effects are noted, which produce a range of crystal cross-section shapes and varying degrees of partial crystallization of the melt

Efficient generation of nitrogen-vacancy center inside diamond with shortening of laser pulse duration

We investigated the effect of laser pulse duration on nitrogen-vacancy (NV) center generation inside a single crystal diamond. We compared pulse durations of 40 fs (femtosecond laser) and 1 ps (picosecond laser). We found that in both cases, ensemble NV centers could be generated inside the diamond. However, the maximum photoluminescence intensity of the NV center without graphitization for the 40 fs duration was higher than that for the 1 ps duration. This indicated that the femtosecond laser was harder to graphitize diamond and could generate more NV centers without graphitization. This difference may be due to the difference in the photo-absorption process and the resulting lattice dynamics

Avant-garde femtosecond laser writing

Recently discovered phenomena of quill and non-reciprocal femtosecond laser writing in glasses and crystals are reviewed. Common beliefs that laser writing does not change when reversing beam scan or propagation direction are challenged

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

Direct laser-writing of ferroelectric single-crystal waveguide architectures in glass for 3D integrated optics

Direct three-dimensional laser writing of amorphous waveguides inside glass has been studied intensely as an attractive route for fabricating photonic integrated circuits. However, achieving essential nonlinear-optic functionality in such devices will also require the ability to create high-quality single-crystal waveguides. Femtosecond laser irradiation is capable of crystallizing glass in 3D, but producing optical-quality single-crystal structures suitable for waveguiding poses unique challenges that are unprecedented in the field of crystal growth. In this work, we use a high angular-resolution electron diffraction method to obtain the first conclusive confirmation that uniform single crystals can be grown inside glass by femtosecond laser writing under optimized conditions. We confirm waveguiding capability and present the first quantitative measurement of power transmission through a laser-written crystal-in-glass waveguide, yielding loss of 2.64 dB/cm at 1530 nm. We demonstrate uniformity of the crystal cross-section down the length of the waveguide and quantify its birefringence. Finally, as a proof-of-concept for patterning more complex device geometries, we demonstrate the use of dynamic phase modulation to grow symmetric crystal junctions with single-pass writing