Top-Performance Transmission Gratings with Haloalkanes-Based Polymeric Composite Materials

Abstract

We report on highly transparent holographic phase transmission volume gratings recorded in the visible region at λ = 532 nm. The maximum measured diffraction efficiency is higher than 80% with a grating pitch of Λ≈ 300 nm and a refractive index modulation Δn ≈ 0.018. To obtain these results, we used a holographic mixture based on multi-reticulated acrylate and haloalkanes (1-bromo-butane and 1-bromo-hexane) and a synergic combination of camphore-quinone, which has a maximum absorbance at c.a. 470 nm, and R6G, here used as co-initiator, to efficiently initiate the photo-polymerization process. High transparent and high efficient holographic structures based on polymers can find applications in many research fields including integrated optics, sensors, high density data storage and security.

Keywords: acrylate; halo-alkanes; holographic gratings; polymers.

Figure 1

Schematic representation of the writing setup used to record the holographic one dimensional structures. $\lambda$/2 = half wavelength plate; M = mirror; P = polarizer; S = sample; 2 × BE = 2 × beam expander; t and d = transmitted and diffracted beams, respectively. The recorded periodic structure inside the sample is reported in black.

Figure 2

Best diffraction efficiency value measured using an incoherent white light source impinging at 56° with respect to the normal to the glasses.

Figure 3

Angular selectivity measurement taken at $\lambda$ = 632 nm. The experimental data fit, reported in red, is made by using Equation (1).

Figure 4

Typical transmission spectra as a function of the external rotation angles. The reflection peaks show a FWHM of ≈8 nm.

Figure 5

Diffraction efficiency values reported as a function of the wavelength. Each wavelength corresponds to a different Bragg angle for the diffracted signal. The continuous line represents the experimental data fit.