BaMgF₄: An Ultra‐Transparent Two‐Dimensional Nonlinear Photonic Crystal with Strong χ⁽³⁾ Response in the UV Spectral Region

Abstract

Ferroelectric patterning is often used in advanced photonics and optoelectronic devices to increase their operational bandwidth and functionality, providing novel and unique performances. However, the extension of the ferroelectric structures to two‐dimensional geometries is currently limited to very few oxides and phosphates systems, which constrains its current and future applications. Here, careful processing based on e‐beam lithography and poling is employed to fabricate the first example of a two‐dimensional nonlinear photonic crystal in Barium Magnesium Fluoride, BaMgF4, a ferroelectric fluoride crystal with an extraordinary transparency ranging from the deep ultraviolet (≈126 nm) to the mid infrared (≈13 μm). The optical characterization shows the possibility of obtaining simultaneously up to three different Cerenkov‐type second harmonic generation processes distributed in a conical geometry via χ(2)‐quasi‐phase‐matching technique. Additionally, the remarkably high χ(3) nonlinear response of BaMgF4 crystal in the UV spectral region is exploited to demonstrate what is believed to be the highest direct UV‐third harmonic generation conversion efficiency in a solid state system via pure χ(3) nonlinear process. Together, the results highlight the outstanding opportunities offered by nonlinear photonic structures as innovative avenues to manipulate the light generation and control with reliable multifunctional optical character.

Hybrid Plasmonic–Ferroelectric Architectures for Lasing and SHG Processes at the Nanoscale

“…In all the cases, the photodeposition parameters are adjusted to obtain metallic arrangements supporting plasmonic resonances to enhance different optical processes generated by the ferroelectric substrates. The ferroelectric domains are obtained either during the crystal growth process, as it is the case of PPLN crystals, or by using direct electron beam writing, which enables shaping periodical domain structures in a controlled way without the need of any mask …”

Nonlinear Diffuse fs-Pulse Reflectometry of Harmonic Upconversion Nanoparticles

“…An alternative to the direct third harmonic generation can be achieved in polar media through cascaded second-order processes where SHG is sum-frequency mixed with the remainder of the pump wave [25][26][27]:…”

VUV–UV 5d–4f interconfigurational transitions of Nd3+ in BaMgF4 ferroelectric crystals

“…The potential use of Nd 3 þ -doped BMF single crystals for self-frequency-doubling lasers has already been documented in a recent paper [10], where the spectroscopy properties of this material have been thoroughly investigated under excitation in the near IR region. However, to the best of our knowledge the spectroscopic characteristics of the interconfigurational 5d-4f transitions of Nd 3 þ ion in BMF have not been reported in literature so far, although the Nd 3 þ laser action in VUV-UV spectral region based on the 5d-4f transitions has already been demonstrated in other similar fluoride single crystals such as LaF 3 and LiYF 4 [11,12].…”

“…Namely, a collinear second harmonic generation (SHG) as well as conical Cerenkov SHG processes have been recently achieved by using 1D and 2D ferroelectric domain structures, respectively. Further, a very efficient UV third harmonic generation (THG) at 385 nm has been also demonstrated by means of a χ (3) process [2,3]. In this context, the use of this BMF ferroelectric crystal as a host matrix for optically active ions appears as a very interesting subject [4][5][6].…”