Adam Stone

Directionally controlled 3D ferroelectric single crystal growth in LaBGeO5 glass by femtosecond laser irradiation

Laser-fabrication of complex, highly oriented three-dimensional ferroelectric single crystal architecture with straight lines and bends is demonstrated in lanthanum borogermanate model glass using a high repetition rate femtosecond laser. Scanning micro-Raman microscopy shows that the c-axis of the ferroelectric crystal is aligned with the writing direction even after bending. A gradual rather than an abrupt transition is observed for the changing lattice orientation through bends up to approximately 14 degrees. Thus the single crystal character of the line is preserved along the bend through lattice straining rather than formation of a grain boundary.

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.

Laser fabrication of semiconducting ferroelectric single crystal SbSI features on chalcohalide glass

This paper demonstrates a laser direct-write method to form single crystal semiconductor ferroelectric SbSI features on chalcogenide glasses for integration into infrared devices. The method overcomes a major limitation of thin-film deposition techniques, viz. the uncontrolled stoichiometry of SbSI due to very different vapor pressure of its constituents. It promises advantages of selective single-crystal formation and control on the morphology of the crystal. Mechanism of and control parameters for laser crystallization are explored.

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.

Unexpected influence of focal depth on nucleation during femtosecond laser crystallization of glass

Three-dimensional (3D) space-selective crystallization by femtosecond laser irradiation was investigated in LaBGeO5 glass. Heat modification could be induced space-selectively, but crystal nucleation showed an unexpected sensitivity to focal depth. Laser-induced heat modification profiles were inspected with optical microscopy and Raman spectroscopy in order to explain this phenomenon. We propose a mechanism based on heterogeneous nucleation at the surface of laser-induced defects and suggest strategies for achieving space-selective crystal nucleation.

Optical properties and structure of Er:LaBGeO 5 laser-induced crystals-in-glass

Three-dimensional laser-induced crystallization of glass via localized heating by focused femtosecond laser irradiation promises the ability to create photonic integrated circuits. However, little work thus far has been done to demonstrate the feasibility of this technique to create crystals in rare earth-doped glasses that may serve as active elements of the circuit, such as lasers. To that end, crystals were grown in ErxLa1−xBGeO5 (x = 0.0, 0.01, 0.04) glasses via this technique and characterized using Raman and fluorescence spectroscopy. Erbium was found to be primarily incorporated within the crystal at the lanthanum site and its energy levels were quantified. The influence of different glass compositions and laser irradiation parameters on the strain gradient within the crystal cross-section as well as the erbium fluorescence is discussed.