Circularly polarized vacuum ultraviolet coherent light generation using a square lattice

This document provides supplementary information to “Circularly polarized vacuum ultraviolet coherent light generation using a square lattice photonic crystal nanomembrane,”


Polarization selection rule of the third-order nonlinear response
As shown in ref. [1], the relation between the electric fields of the fundamental and second harmonic beams in the far field can be generally described in the circular basis using a nonlinear response tensor A ν μρ as follows:    (S13) that is, both LCP and RCP TH components are allowed.
Under the LCP fundamental beam, the ratio γ /β can be obtained from the measured intensities of the LCP and RCP components of the TH beam. According to the experimental data in Fig. 2 In the Cartesian basis, the relation between the electric fields of the fundamental and TH beams in the far field can be described as follows [2]: Isotropic: Four-fold (4 mm): Two-Fold (2 mm): 3 , , xxxx xxyy xxxx yyyy xxyy yyxx The relation between electric fields in the circular and Cartesian planes is 1 ( ) . 2 x y E E iE ± = ± (S17) Thus, equation (S16) can be converted to  1  1  3  2  2  1  2  1  2  1  1 3  2  2  1  1  3  ,  2  2 x y x y Isotropic: Four-fold (4 mm): Two-Fold (2 mm): 1 Equation (S18) is consistent with (S11).

Sample fabrication
A 48 nm epitaxially grown γ-Al 2 O 3 thin film was deposited onto a 525 μm-thick Si substrate by chemical vapour deposition [4]. The Si substrates were cleaned using SC-1, SC-2 and diluted HF solutions. The dry substrates were loaded into a CVD chamber, and an epitaxial γ-Al 2 O 3 film was grown on the Si (100) substrates by pyrolysis of N 2 -bubbled trimethyl aluminium and O 2 gas for 10 min at 960°C and a pressure of 500 Pa. The crystallinity of the epitaxial film was analysed using reflection high-energy electron diffraction. Then, the epitaxial γ-Al 2 O 3 thin film was coated with an electron beam (EB) resist (ZEP520A) by spin coating (4000 rpm, 60 s) and baked at 180°C for 5 min. Photonic crystal structures with a total area of 300 × 300 μm 2 were patterned using a rapid EB lithography system (F7000S-VD02, Advantest). ZEP520A was developed with ZED-N50; the photonic crystal structures were then transferred to the epitaxial γ-Al 2 O 3 thin film by inductively coupled plasma reactive ion etching (ICP-RIE, NE-550, ULVAC) using an O 2 :CF 4 mixture (4 SCCM:40 SCCM ratio) for 75 s. The remaining resist was removed after 25 min of O 2 plasma ashing using an RIE system (RIE-10NR, SAMCO). Then, the epitaxial γ-Al 2 O 3 photonic crystal layer was protected with JSR PFR 7790G photoresist (3000 rpm, 30 s spin coating followed by 2 min baking on a 120°C hotplate). The backside of the Si substrate was spin coated with the photoresist AZ P4620 (3000 rpm, 60 s) and baked for 2 min at 110°C. Square 300 × 300 μm 2 hole patterns were fabricated on the backside of the photonic crystal using backside-alignment photolithography (MA6 Mask Aligner, Süss Microtech), developed in 2.38% tetramethylammonium hydroxide (TMAH) for 4 min and baked for 2 min at 120°C. The Si substrate under the photonic crystal structure was removed by deep RIE (DRIE, MUC-21 ASE-Pegasus, SPP Technologies) using a high-etching-rate recipe. To avoid damaging the epitaxial γ-Al 2 O 3 thin film, etching was stopped when a few microns of Si remained. The sample was then submerged in acetone to remove the photoresists. Finally, the sample was dipped into TMAH at 80°C for approximately 1 h to remove the remaining Si and cleaned with 2-propanol (IPA). 3 3

Obs with t
The V highes corresp arrow is on th

served THG the highest int
VUV THG sp st intensity is ponds to the in Fig. 4 If the intensity of the LCP and RCP components of the detected light is expressed as I L and I R , respectively, then CD signal can be expressed as [6] ( ) 0 log / 2cos sin , where 0 A Δ is the CD signal when θ=±π/4.
When the LCP and RCP components of elliptically polarised light are expressed as E L and E R , respectively, is expressed as The graph of ( )  From Fig. 2( Fig. S6. This result means that, when CD measurements were performed using the VUV THG obtained in this experiment as the probe light, a signal intensity of 69% with respect to CD spectroscopy with perfectly circularly polarised VUV light was obtained.