Designing an Excellent Deep-Ultraviolet Birefringent Material for Light Polarization

Abstract

Owing to their vital role in creating and controlling polarized light, birefringent materials are used extensively in various advanced optical systems which in turn impact a large, rapidly increasing range of applications in science and technology. Currently, the fairly small birefringence of MgF 2 and the low transmittance of α-BaB 2 O 4 (α-BBO) hinder their efficient application for wavelength below 200 nm. For example, deepultraviolet (DUV) birefringent materials for light polarization are urgently needed for DUV lithography. Here we demonstrate based on computational and experimental results that parallel chains of corner-connected planar sp 2 -hybridized BO 3 groups found in Ca(BO 2 ) 2 effectively produce large birefringence. Ca(BO 2 ) 2 achieves three vital "best" properties including the shortest UV cutoff edge, the largest birefringence, and the highest laser-induced damage threshold (LIDT) compared to all the reported borate birefringent materials. On the basis of a Ca(BO 2 ) 2 single crystal, a DUV Glan polarizer has been realized and is more efficient than one constructed with commercially available MgF 2 .

An Exceptional Peroxide Birefringent Material Resulting from d–π Interactions

“…0.105 at 1064 nm) and Rb 3 VO(O 2 ) 2 CO 3 (calc. 0.075 at 1064 nm), as well as the recently reported Li 2 Na 2 B 2 O 5 (0.095 at 532 nm), Ca(BO 2 ) 2 (0.1355 at 546 nm), Sn 2 B 5 O 9 Cl (0.168 at 546 nm), NaCa 4 V 5 O 17 (calc. 0.1 at 1064 nm), and LiHgPO 4 (calc.…”

“…Large anisotropic polarizability in crystals will give rise to large birefringence. Some strategies have been developed to enhance the birefringence of a crystal: 1) Introducing second‐order Jahn–Teller distorted polyhedra with d 0 cation (V 5+ , Mo 6+ ) centers; related compounds include YVO 4 (Δ n =0.225 at 633 nm) and NaCa 4 V 5 O 17 (Δ n =0.1 at 1064 nm); 2) introduction or condensation of delocalized π‐conjugated planar groups such as BO 3 groups; for example, Pan and co‐authors recently reported two borates, Li 2 Na 2 B 2 O 5 and CaB 2 O 4 , which are composed of condensed B 2 O 5 dimers and [B 2 O 4 ] ∞ infinite chains and exhibit large birefringences of Δ n =0.095 at 532 nm and Δ n =0.1355 at 546 nm, respectively; 3) introducing highly polarizable cations such as Hg 2+ with d 10 ‐configuration or Pb 2+ , Sn 2+ , I 5+ with lone pair electrons as in LiHgPO 4 (Δ n =0.068 at 1064 nm), Pb 2 (IO 3 )(PO 4 ) (Δ n =0.060 at 1064 nm), and Sn 2 B 5 O 9 Cl (Δ n =0.168 at 546 nm) . In particular, Sn 2 B 5 O 9 Cl exhibits a remarkable enhancement of 16 times as compared with the isostructural Ba 2 B 5 O 9 Cl.…”

Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

“…It is reported that the π‐conjugated planar groups of BO 3 and B 3 O 6 made the largest contribution to the birefringence compared with the other borate groups . An excellent birefringent crystal, Ca(BO 2 ) 2 , consisting of [BO 2 ] n infinite chains, and exhibiting a large birefringence, short UV cut‐off edge and high laser‐induced damage threshold, was reported by Pan et al in 2018 . Transition metal with d 0 electronic configuration (d 0 ‐TM), such as Ti 4+ , Nb 5+ and Mo 6+ , are beneficial to the birefringence because they are susceptible to second‐order Jahn–Teller (SOJT) distortions, and the intensity of birefringence may be related to the distortion degree of the d 0 ‐TM polyhedron .…”

An Unprecedented Antimony(III) Borate with Strong Linear and Nonlinear Optical Responses

“…Guided by this theory, scientists have discovered a great variety of borate NLO materials in which optical properties are mainly attributable to the B−O anionic groups, including the commercially available LiB 3 O 5 and β‐BaB 2 O 4 , as well as KBe 2 BO 3 F 2 , NaBeB 3 O 6 , NaSr 3 Be 3 B 3 O 9 F 4 , Li 4 Sr(BO 3 ) 2 , and CsB 4 O 6 F . Meanwhile, scientists also discovered a variety of borates of large birefringence, including the commercially used birefringent crystal α‐BBO, as well as the newly emerged Ca(BO 2 ) 2 and Li 2 Na 2 B 2 O 5 . In these borates, the π‐conjugated B−O anionic groups possess either large polarizability and/or anisotropy of polarizability and give rise to relatively large SHG and/or birefringence, but the cations (such as alkaline and alkaline earth cations) contribute only a little to SHG and/or birefringence.…”