Design and fabrication of multiplexed volume Bragg gratings as angle amplifiers in high power beam scanning system

Optical vortex switch based on multiplexed volume gratings with high diffraction efficiency

Systems of controllable orbital angular momentum (OAM) require more compact, higher conversion efficiency and more tolerable wavelength or polarization. We introduce an optical vortex switch based on a multiplexed volume grating (MVG). The MVG recorded in a piece of photo-thermo-refractive (PTR) glass exhibits high diffraction efficiency (DE, also known as conversion efficiency in transporting), sensitive angular selectivity, and polarization-insensitivity. The effects of the incident divergence angle and polarization on the DE and the far-field diffraction profiles are demonstrated and investigated. It turns out that the divergence angle of the probe beam can greatly affect the DE. The fluctuation of the DE caused by polarization variation is less than 1.59%. This switch can be potentially applied in vortex tweezers, optical communication, and high power systems.

Effects of CeO2 and Sb2O3 on the Nonlinear Photochemical Process in Ultrashort Laser Gaussian-Bessel Beams Irradiated Photo-Thermo-Refractive Glass

Microfluidic chips and optical elements can be fabricated based on the nonlinear photosensitivity in photo-thermo-refractive (PTR) glass by controlling the growth of nanocrystals in the femtosecond (fs) laser-irradiated region. Here, we focus on CeO₂ and Sb₂O₃ that play important roles in UV irradiation, experimentally investigate the effects of the dopants on the nonlinear photochemical process in PTR glass triggered by fs Gaussian-Bessel beams. The results show that the generation of Ag⁰ atoms and the Ag nanoparticles can be improved by CeO₂ and Sb₂O₃ co-doping. Besides, each multivalent ion in PTR glass possibly participates in the electron transfer processes and contributes to the generation of Ag⁰ atoms. Finally, X-ray diffraction analysis reveals the precipitation of NaF nanocrystals with an average size of 10 to 12 nm after laser irradiation and thermal treatment, which is unrelated to the dopants.

Non-Mechanical Beam Steering with Polarization Gratings: A Review

Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining characteristics of this beam steering architecture and highlight several applications of the technology.

Photochemical response triggered by ultrashort laser Gaussian-Bessel beams in photo-thermo-refractive glass

Photosensitivity in photo-thermo-refractive (PTR) glass can be triggered by UV and near-infrared fs laser irradiation. Here we focus on the nonlinear photochemical process triggered by ultrashort laser Gaussian-Bessel beams. The transmission and absorption spectra show that the primary difference between UV and fs laser exposure is the formation of color centers and kinetic process of silver nanoparticles growth. It is contributed to the nonlinear ionization of PTR glass matrix and thermal effects during interaction of glass matrix and ultrashort laser pulses. Transmission electron microscopy verifies the generation of nanoscale crystals in the irradiated region, and X-ray diffraction shows the existence of quartz crystal and NaF after laser irradiation and thermal treatment. Moreover, the dependence of photochemical reaction on laser parameters is investigated, as well as the tailoring of silver nanoparticles. On this basis, volume Bragg gratings with ultrashort laser Gaussian-Bessel beams are inscribed as an application which possess good diffraction characteristics.

Fabrication of high-precision reflective volume Bragg gratings

Reflecting Bragg gratings (RBGs) recorded in photo-thermo-refractive (PTR) glasses have been widely used in narrowing and stabilization of the laser emission spectrum. As the center wavelength of RBGs determines the final output wavelength of lasers, it is necessary to carefully control the center wavelength of RBGs during the fabrication process. In this paper, the fabrication process of high-precision RBGs was investigated. We developed a two-step method and demonstrated both theoretically and experimentally that it is effective and can be used to guide the fabrication process of high-precision RBGs. The experimental results show that the center wavelength of the fabricated RBG deviates from the target center wavelength within ±10  pm.