It is challenging to store the exponentially increasing amount of data in the information age. The multiplexed optical data storage with merits of high data density (hundreds of terabytes/disk), low energy consumption, and long lifetime could open a new era in data storage technology. The recent progress in five-dimensional (5D) optical data storage based on anisotropic nanostructures written by femtosecond (fs) laser pulses in transparent materials reveals its potential for real-world applications, but high writing speed and density remain a major challenge. Here, we propose a method for rapid and energy-efficient writing of highly localized anisotropic nanostructures in silica glass by energy modulated megahertz-rate fs pulses. An isotropic nanovoid is initially generated with pulse energy above the microexplosion threshold and then elongated to an anisotropic nanolamella-like structure via the near-field enhancement effect by lower energy pulses, minimizing the unwanted thermal effects from megahertz-rate fs pulses. The anisotropic nanostructures are exploited for 5D data storage with a rate of 10 6 v o x e l s / s , corresponding to a demonstrated fast information recording of ∼ 225 k B / s and a potentially high-density data storage of ∼ 500 T B / d i s k .

Photosensitivity in nature is commonly associated with stronger light absorption. It is also believed that artificial optical anisotropy to be the strongest when created by light with linear polarization. Contrary to intuition, ultrafast laser direct writing with elliptical polarization in silica glass, while nonlinear absorption is about 2.5 times weaker, results in form birefringence about twice that of linearly polarized light. Moreover, a larger concentration of anisotropic nanopores created by elliptically polarized light pulses is observed. The phenomenon is interpreted in terms of enhanced interaction of circularly polarized light with a network of randomly oriented bonds and hole polarons in silica glass, as well as efficient tunneling ionization produced by circular polarization. Applications to multiplexed optical data storage and birefringence patterning in silica glass are demonstrated.

High-intensity pulse-beams are ubiquitous in scientific investigations and industrial applications ranging from the generation of secondary radiation sources (e.g., high harmonic generation, electrons) to material processing (e.g., micromachining, laser-eye surgery). Crucially, pulse-beams can only be controlled to the degree to which they are characterized, necessitating sophisticated measurement techniques. We present a reference-free, full-field, single-shot spatiospectral measurement technique called broadband single-shot ptychography (BBSSP). BBSSP provides the complex wavefront for each spectral and polarization component in an ultrafast pulse-beam and should be applicable across the electromagnetic spectrum. BBSSP will dramatically improve the application and mitigation of spatiospectral pulse-beam structure.

It is demonstrated that ultrafast laser writing in silica glass depends on the grade of silica glass associated with the method of its manufacture. Moreover, laser‐written modifications, in particular birefringent modifications, reveal a dependence on the geometry of writing, that is, the modification strength of voxels is smaller than that of single line structures and multi‐line scanned areas, which can be explained by free carrier diffusion and reduced electric field in scanning writing. The retardance of scanned birefringent region produced in the regime of anisotropic nanopores formation in silica glass manufactured by vapor axial deposition (VAD) is about five times higher than that in an electrically fused sample at the same laser writing parameters, while the difference in retardance of a nanograting based modification in synthetic and fused silica is only about 10%. The phenomenon is interpreted in terms of the higher concentration of oxygen deficient centers in the electrically fused silica glass, which can confine self‐trapped holes and prevent the nanopores formation. Improvement of high transmission optical elements is demonstrated in the VAD sample, and low cost multiplexed optical data storage with higher capacity and readout accuracy is realized in the electrically fused silica glass.

Birefringent patterning by ultrafast laser nanostructuring in silica glass has been used for space-variant birefringent optics with high durability and high optical damage threshold. We demonstrate that the oblate-shaped birefringent modification (type X) with ultrahigh optical transmission has higher optical damage resistance, comparable to pristine silica glass. The lower damage threshold of nanogratings based modification (type 2) following thermal annealing at 900°C for an hour is improved from 0.96 J/cm² to 1.62 J/cm² for 300 fs laser pulses and approaches the optical damage threshold of type X (1.56 J/cm²). This opens the door to utilize these optical elements for high power laser applications where optical transmission and damage threshold are the key parameters. The lower damage threshold of type 2 modification is related to the relatively high concentration of defects, such as E’ centers and oxygen-deficiency centers (ODCs).