Spectrometer‐free Optical Hydrogen Sensing Based on Fano‐like Spatial Distribution of Transmission in a Metal−Insulator−Metal Plasmonic Doppler Grating

Abstract

However, its properties of odorless, colorless, high flammable, wide explosive range (4-75 Vol.%), and low spark ignition energy (0.02 mJ) also arise critical safety concerns due to potential explosion risks. [3] Safety protocol implementation and real-time monitoring are essential for its application. Sensitive, accurate, and fast leakage detection, especially for detecting hydrogen below the explosive limit (<4%), is critical.Various hydrogen sensing strategies have been proposed, including microelectromechanical, [4] catalytic, [5] thermal, [6] electrochemical, [7] mechanical, [8] optical, [9] and acoustic [10] detection schemes. The core element for all these sensing systems is the hydrogen sensitive materials, such as metal oxides (In 2 O 3 , [11] ZnO, [12] TiO 2 , [13] and W 18 O 49 [14] ) and hydride-forming metals (Pd, [15] Mg, [16] Y, [17] alloys [18] ). Among various sensing materials, metal oxides are less applicable because they require a high working temperature of over 400 °C to maintain optimal sensitivity. Therefore, hydride-forming metals, which can work at room temperature with high sensitivity and selectivity, have been commonly used in optical hydrogen sensors. In particular, Pd has been widely used in many works because of its fully reversible hydride formation properties under ambient conditions. When Pd is exposed to hydrogen gas, hydrogen Optical nanosensors are promising for hydrogen sensing because they are small, free from spark generation, and feasible for remote optical readout. Conventional optical nanosensors require broadband excitation and spectrometers, rendering the devices bulky and complex. An alternative is spatial intensity-based optical sensing, which only requires an imaging system and a smartly designed platform to report the spatial distribution of analytical optical signals.

Broadband Four‐Wave Mixing Enhanced by Plasmonic Surface Lattice Resonance and Localized Surface Plasmon Resonance in an Azimuthally Chirped Grating

“…In our previous studies, the ACG works in the regime, where its optical response can be well described analytically by considering only the periodicity. [25][26][27][28] We showed that the ACG could be designed to have grating sections simultaneously supporting photon-to-surface plasmon polaritons (SPP) coupling at various frequencies relevant for the nonlinear optical processes. The suitable sector areas of the ACG could be predicted solely by considering the photon-SPP momentum-matching condition.…”

Nonlinear Optical Signal Generation Mediated by a Plasmonic Azimuthally Chirped Grating

“…The grating periodicity ( P ) at a certain in-plane azimuthal angle (φ) is given by P normalΔ r , d ( φ ) = | d cos ⁡ φ ± false( d 2 .25em cos nobreak0em.25em⁡ 2 φ + 2 normalΔ r 2 − d 2 false) / 2 | As the in-plane azimuthal angle increases from 0° to 180°, the periodicity of ACG varies continuously from Δ r + d to Δ r – d , as illustrated in Figure a. By choosing suitable Δ r and d , the range of grating periodicities can be easily designed for any desired application. , In this work, the Δ r and d were chosen to be 0.7 and 0.4 μm, respectively, corresponding to the minimum and maximum grating periodicities of 0.3 and 1.1 μm. A graphical representation of this azimuthal angle-dependent periodicity is given in the Supporting Information (Figure S1).…”

“…The mirror symmetry of the images from the two halves of the ACG thus serves as an indicator for optical setup optimization. Slight asymmetry due to elliptical polarization of the illumination can be corrected with simple post-data processing …”

“…By choosing suitable Δr and d, the range of grating periodicities can be easily designed for any desired application. 32,33 In this work, the Δr and d were chosen to be 0.7 and 0.4 μm, respectively, corresponding to the minimum and maximum grating periodicities of 0.3 and 1.1 μm. A graphical representation of this azimuthal angle-dependent periodicity is given in the Supporting Information (Figure S1).…”

“…Slight asymmetry due to elliptical polarization of the illumination can be corrected with simple post-data processing. 33 The ACG was mounted on a three-axis piezo nanopositioning stage (Nano-PDQ series, Mad City Laboratories), allowing a raster scan over the grating structure. The generated SHG and TPPL spectra were then collected by the same objective and aligned through two short-pass filters (FF01-770/SP-25, Semrock) to spectrally filter out the fundamental excitation beam before being focused by an achromatic lens to the entrance slit of the spectrometer (Kymera 193i, Andor) equipped with a CCD camera (DU920P-BEX2-DD, Newton920 CCD, Andor).…”