C R Lawrence's research while affiliated with QinetiQ and other places

Publications (30)

Article
A metamaterial surface formed by three slot gratings at 60° to each other has two possible high-symmetry arrangements. One forms equilateral triangular metal patches, the other a combination of hexagons and small equilateral triangles. When spaced above a ground plane with a thin dielectric spacer both structures give strong microwave absorption at...
Article
The resonant absorption of microwave radiation by thin, two-dimensional microcavity arrays has been studied. Resonant modes associated with these structures, formed from copper-clad FR4 laminates, exhibit both an azimuthal and polar angle independent electromagnetic response. The experimental data agree well with the predictions of a finite element...
Article
Full-text available
Selective transmission of radiation through a two-dimensional array of subwavelength slits in an otherwise opaque thin metal film is presented at microwave frequencies. Individual slits are modified with the addition of perpendicular cuts, which interestingly and perhaps counterintuitively leads to resonant transmission when the incident radiation...
Article
Full-text available
Resonant transmission of microwaves through a hexagonal array of holes in a very thin aluminium layer is studied. The array of holes, with diameter much less than the incident wavelength, leads to a strong transmission peak at a frequency just lower than the diffraction limit of the array. The results are well-modelled using a finite element packag...
Article
Full-text available
The resonant transmission of microwaves polarized perpendicular to a single subwavelength slit of finite length is presented in detail. It is shown that the resonant frequency rises monotonically as slit length is reduced. Increasing confinement of the resonant fields within the slit is shown to cause the frequency rise. Angle dependence of the tra...
Article
Full-text available
A slit in a thick metal plate that is extremely subwavelength will not transmit microwaves polarized parallel to it. It is shown here that cuts perpendicular to the slit allow parallel polarized radiation to resonantly transmit. Furthermore, a zero-order mode may be excited within the slit, the frequency of which, to first order, is independent of...
Article
Full-text available
It is well established that much more radiation may be transmitted through a set of apertures in a metallic screen than a simple calculation from the transmission through the aperture area alone would predict. There has been substantial debate regarding the exact cause of this enhanced transmission, and confusion over the difference between the beh...
Article
Full-text available
Surfaces of low reflectance are ubiquitous in animate systems. They form essential components of the visual appearance of most living species and can explicitly influence other biological functions such as thermoregulation. The blackness associated with all opaque surfaces of low reflectivity has until now been attributed to strongly absorbing pigm...
Article
Full-text available
Fabry-Perot-like resonant transmission of microwave radiation through a single subwavelength slit in a thick aluminum plate is quantified for a range of slit widths. Surprisingly, and in contrast to previous studies [e.g., Phys. Rev. Lett. 86, 5601 (2001)]], the resonant frequency exhibits a maximum as a function of slit width, decreasing as the sl...
Article
A reflection grating demonstrating extraordinarily broad-band polarization conversion in a nondiffractive regime has been studied at microwave frequencies. This single-element structure has been fabricated by electrolessly plating a metallic layer onto a stereo-lithographically produced resin profile. Angle-dependent microwave reflectivity data col...
Article
Remarkably enhanced transmission of microwave radiation through a single subwavelength slit in a thick metallic substrate surrounded by just a pair of parallel deep and narrow grooves is recorded. By also patterning the output face of the metal slab with two grooves there is strong exit beam confinement. There are no gratings in this structure and,...
Article
It is shown that microwave radiation can be transmitted through a wall of aluminum-alloy bricks even though the width of the gaps between the metallic elements is less than 5% of the radiation wavelength. Up to 90% of the radiation made incident upon the wall is transmitted, with both linear polarizations being passed. Experimental results are comp...
Article
A nondiffracting metallic lamellar grating formed from three equally spaced grooves per repeat period, with one being slightly shallower than the other two is examined at microwave frequencies. When filled with a slightly lossy dielectric, this structure supports a remarkably nondispersive surface plasmon polariton mode, which exhibits strong selec...
Article
Full-text available
Few mechanisms exist in nature that effect colour reflectivity, simultaneously high in spectral purity and in intensity, over a strictly limited portion of solid angle above a surface. Fewer still bring about such colour reflectivity with an angle dependence that is distinct from the colour transition associated with conventional multilayer interfe...
Article
The Troides magellanus butterfly exhibits a specialized iridescence that is visible only when its hind wings are both illuminated and viewed at near-grazing incidence. The effect is due to the presence of a constrained bigrating structure in its wing scales that has been previously observed in only one other species of butterfly (Ancyluris meliboeu...
Article
Some beetles in the Namib Desert collect drinking water from fog-laden wind on their backs. We show here that these large droplets form by virtue of the insect's bumpy surface, which consists of alternating hydrophobic, wax-coated and hydrophilic, non-waxy regions. The design of this fog-collecting structure can be reproduced cheaply on a commercia...
Conference Paper
The Troides magellanus butterfly exhibits iridescence when both viewed and illuminated at near grazing incidence. The effect derives from a complex bigrating structure that provides exquisite control over both the viewing angles and colour observed.
Article
The dazzling iridescence seen in some hummingbirds1 and tropical butterflies2 arises from natural optical phenomena, the brightest of which originate in nanoscale structures that produce ultra-high reflectivity and narrow-band spectral purity3. Here we investigate the coloration of male Ancyluris meliboeus Fabricius butterflies4, which have patches...
Article
Zero-order metal grating structures are found to give extraordinary selective transmission at microwave frequencies through the resonant excitation of coupled surface waves. The metal slat structures with dielectric spacings as small as 250 μm strongly transmit wavelengths of several millimeters. A simple interpretation of these novel results which...
Article
A dielectric grating on top of a planar metal substrate is shown to couple near-grazing microwave photons to surface plasmon polaritons (SPPs). It is shown that when the grating grooves are oriented such that they are parallel to the plane of incidence (phi = 90 degrees), coupling to SPPs with both s- and p-polarized photons is possible at three di...
Article
Green coloration in the animal kingdom, as seen in birds' feathers and reptile integument, is often an additive mixture of structurally effected blue and pigmentary yellow. Here we investigate the origin of the bright green coloration of the wing scales of the Indonesian male Papilio palinurus butterfly, the microstructure of which generates an ext...
Article
It is shown that an absorbing dielectric layer, sinusoidally modulated in height, on top of a planar metal substrate, may be used to provide coupling between both s- and p-polarized incident microwave photons and surface plasmon polaritons, which propagate along the metal–dielectric interface. The study is carried out using paraffin wax as the diel...
Article
This work presents a detailed investigation of electromagnetic coupling to the surface plasmon-polariton (SPP) at microwave frequencies. We have recorded the wavelength-dependent reflectivity from a metallic sinusoidal diffraction grating of pitch 15 mm. In order to minimize the problems associated with nonplanar incident wavefronts, we have develo...
Article
Full-text available
Brilliant iridescent colouring in male butterflies enables long-range conspecific communication and it has long been accepted that microstructures, rather than pigments, are responsible for this coloration. Few studies, however, explicitly relate the intra-scale microstructures to overall butterfly visibility both in terms of reflected and transmit...
Article
We compare two methods for characterizing the profile of surface relief diffraction gratings. First a Talystep and an atomic force microscope (AFM) are used to sense the surface and generate profiles that are a convolution of the stylus and the shape of the grating's surface. Second the reflectivity of the grating is scanned as a function of the an...
Article
In this work, we have used a new technique to characterize optically a periodically modulated metal–dielectric interface involving the measurement of the azimuthal-angle-dependent specular reflectivity. This method presents advantages over the conventional polar angle scan experiment since it requires no moving signal detector. The data recorded ha...
Article
A few-monolayer zwitterionic, non-centrosymmetric Langmuir-Blodgett film has been sandwiched between two electrodes, one of which is transparent. Curves of dark current density as a function of applied bias were observed to exhibit rectifier-like behaviour and to follow closely the dependences measured from junctions using two metallic electrodes....
Article
The influence on the near critical angle reflectivity of a thin film deposited on the face of a glass prism is used to optically characterize a zwitterion Langmuir-Blodgett film.
Article
In this study, surface plasmon resonance studies of Langmuir-Blodgett multilayers have been used to characterize an optically highly absorbing zwitterionic material which would be difficult to otherwise analyse. By fitting reflectivity data with Fresnel theory for a range of wavelengths it has been possible to obtain the real and imaginary parts of...

Citations

... [20] While the wrinkles in these examples present one degree of structural order, nature offers optimization strategies for designing hierarchical structures that have multilayer reflectance yet can achieve low angular dependence in most Morpho butterfly species, the striking iridescent blue color of the wing scales does not change over a wide range of viewing angles. [21][22][23] Through the modeling of the Morpho optical properties, it is understood that by introducing an alternating multilayer with heightvaried separation in the carriers of multilayers, the angular range is uniformized and angular dependence suppressed. [24][25][26] The height variation and tilt angle difference between ridges induces an interference/diffraction effect that provides constructive interference in the observation direction and destructive interference in the normal direction when observed at non-normal angles. ...
... The composite SiO 2 -Teflon coatings [14] , SiO 2 /TiO 2 particles layer [15,16] , TiO 2 AR coatings [16] , SiO 2 polymer composite coatings [17] , spirooxaize-polystyrene coatings [18] , SiO 2 mesoporous e-ISSN: 2321-6212 p-ISSN: 2347-2278 nanoparticles [19] or polymer AR coatings [20] are common examples of monolayer AR coatings which minimize reflectance at broader region without focusing on other properties such as mechanical thermal or non-wetting properties. Single layer AR coatings are applicable and desirable in different laser applications [21,22] , photodiodes [23] , light emitting diodes [24][25][26] or solar cell [27][28][29][30][31] applications. Due to the limited band width and reflectance minima at a smaller spectral region, these are not applicable to display devices, screens or eye wear optical equipment. ...
... In addition, it is also worth noting that there are many applications of SPPs in the perpendicular direction, which focus on the transmission of electromagnetic energy through the thin metallic film. Since Ebbesen first reported the extraordinary optical transmission (EOT) phenomena through a two-dimensional (2-D) hole array perforated on a silver screen in 1998 [4], considerable researches on the optical properties of this periodic subwavelength structure have been conducted [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The transmittance of light passing through the periodic structure surrounded by surface corrugation has been studied extensively. ...
... Metal subwavelength apertures surrounding a given power source have been shown to improve its transmission properties [44], by taking advantage of the fact that grooved structures act as secondary sources and re-radiate the surface wave energy in phase with the primary electromagnetic wave, to realize the improvement in the gain. This is true for grooved-structures whose aperture width is less than the freespace wavelength (w r « λ 0 ), depth (h r ) is approximately equal to an integer multiple λ 0 /4, and distance (d s ) among adjacent structures and primary source around λ 0 [44], [45]. ...
... It is generally accepted that blazed, compound, and complex gratings can be harnessed for the design of spectral and spatial distribution of transmitted, reflected, and guided light modes with improved desired properties such as enhancement or improved coherence of emitted radiation [150]. These kinds of grating can be used for beam shaping [151,152], spectroscopy [153], and spectral filtering [154]. Coherent SP radiation, generated by the passage of relativistic short-bunched electrons across the surface of a metallic grating, has been observed in the wavelength region from 0.5 to 4.0 mm [155]. ...
... Further studies indicate that the surface plasmon is not necessary, and the EOT can be interpreted by means of the full-wave diffraction model [10,18] and the equivalent circuit model [20]. Although the transmission through a single subwavelength aperture of radius r scales with (r∕ ) 4 according to Bethe's diffraction theory [8], there are many approaches to break though this limit, such as decorating the metal surface with periodic groves or some special patterns [3,17], sandwiching the holes with dielectric slabs [19], filling the holes with high dielectric permittivity materials [1,26], placing subwavelength metamaterial in front of or at the back of the apertures [5], and utilizing split ring resonators in the vicinity of the apertures [4]. In general, these methods stated above to achieve transmission enhancement rely on the enhancement of coupling efficiencies between the corresponding resonance modes and plane wave in free space near the small apertures. ...
... 16,17) It has been shown that by placing a dielectric or semiconductor grating adjacent to a homogeneous metal film or metal substrate, surface plasmon polaritons (SPPs) can be excited. [18][19][20][21][22] Quite recently, a thermal emitter that consists of one silicon RWG positioned above a SiC substrate was proposed and studied. 23) Incident light could be absorbed via the evanescent waves coupling between the guided mode and the surface phonon polaritons (SPhPs) mode. ...
... Several experimental works have investigated TE and TM transmission through 2D metallic gratings. 13,14 In Ref. 13, transmission was measured only at normal incidence, while in Ref. 14 its angular dependence was investigated. EOT was observed due to the excitation of resonant modes along the aperture length, which may be coupled to spoof surface plasmon modes. ...
... Since the first address of the extraordinary optical transmission (EOT) [1], a plethora of new research dedicated to the subject of enhanced transmission through one-dimensional (1-D) [2][3][4][5][6][7][8] and two-dimensional (2-D) [9][10][11][12][13][14][15] periodic arrays of sub-wavelength slits and holes was initiated. Therefore, a lot of complementary (and sometimes contradictory) explanations exists regarding the origin of that effect. ...
... To excite SPP at the interface between the silver grating and dielectric medium, it is necessary to match the projection of the light's wave vector (k 0 = 2/,  is the wavelength of the incident radiation) upon the surface of the sample, with the wave vector of SPP (k SPP ), and the grating vector (G = 2/a, a is the grating period). When the plane of incidence of the exciting radiation is oriented along the perpendicular to grating grooves, this matching condition can be written in the scalar form [23]: ...