Photonic systems are an excellent platform for experimenting with fundamental aspects of waves in disordered systems. We will review recent progress, ranging from Anderson localization and disorder-enhanced transport to hypertransport and disordered photonic topological insulators.

Multiple scattering is of critical importance in controlling light and has the potential to improve light harvesting in solar cell applications. This research aims to observe multiple scattering and absorption enhancement in dense nanoparticle assemblies. It is hypothesized that multiple scattering events can enhance light absorption in dense absorptive media by increasing photon-matter interactions. While this enhancement has been shown theoretically, few experimental efforts have demonstrated it. To test this hypothesis, dense nanoparticle stacks were assembled by a solution casting method. In this method dispersed nanoparticle solutions of either functionalized gold or alumina were added dropwise to glass substrates, then allowed to dry at ambient conditions. With each addition of nanoparticles to the stack, absorbance, transmission and reflectivity were measured using both UV-visible spectrophotometry and a customized optical apparatus.
UV-visible absorption data show an enhancement in the gold surface plasmon peak with increasing stack volume. Absorbance of gold nanoparticle stacks as a function of nanoparticle count shows distinct regimes in the absorption, with a distinct change in the increase of absorption with particle drops. These two regimes of lower and higher slope provide experimental evidence of enhanced absorption above a critical nanoparticle count. In contrast, absorption data for alumina nanoparticle stacks show no enhanced absorption and a single linear increase of absorption with number of nanoparticles. To show that the gold nanoparticle stack absorbance is a result of multiple scattering, absorbance data was fit to a multiple scattering model. The fit provides further evidence of multiple scattering resulting in enhanced absorption.

Ceramic photonic glasses, which consist of a disordered arrangement of monodisperse ceramic spheres with diameters in the wavelength range of the incident light, are novel materials with a wide range of applications, including broadband reflectors for thermal radiation barrier coatings (TBCs) and high temperature stable structural colorants. Given that heat transfer is to a significant part radiative at higher temperatures (>1000 °C), photonic glass TBCs offer a substantial increase in performance over conventional non-photonic coatings for applications such as in jet turbine engines by providing broadband reflection of thermal radiation.
Here, we introduce a concept for the fabrication of novel photonic structures with a high, broadband reflectance in the infrared using zirconium dioxide microspheres. We present a straightforward sol-gel approach to the synthesis of zirconium dioxide particles for use as primary building blocks in photonic glasses and crystals. By altering synthetic variables such as the water content, zirconium precursor, solvent composition and organic stabilizer, we were able to reproducibly yield particles with diameters ranging from 0.4 to 4.3 µm with consistently small standard deviations of between 5 and 10%. Suspensions of these particles were successfully employed for the deposition of disordered photonic films. These films exhibited broadband reflection in a wavelength range of 1 to 6 µm for particles with a diameter of ~3 µm. Additionally, the thermal stability and the phase transitions of the particles was investigated at temperatures up to 1500 °C. It was found that larger microparticles, which were synthesized using zirconium n-propoxide and a higher stabilizer concentration, crystallized at lower temperatures and consisted of smaller grains. This was accompanied by a better high temperature stability.
Lastly, in order to further improve the high temperature stability by inhibiting the destructive tetragonal-to-monoclinic phase transformation in zirconium dioxide, the particles were doped with yttrium oxide. Microparticles containing between 3 and 6% yttrium oxide were successfully prepared and they displayed an enhanced stability up to 1200 °C.

In their inverse forms, photonic crystals and glasses are composed of ordered and disordered arrangements of monodisperse porosity. These structures owe their photonic properties to their engineered features. Emerging applications of photonic structures in high-temperature applications, such as in thermal barrier coatings, structural coloration, and thermophotovoltaics, require the stability of these features at operating temperatures. However, in high-temperature environments (>1000 °C), these structures can exhibit significant undesired microstructural changes (phase changes, sintering, grain growth, etc.) that result in a loss of the desired photonic properties. Strategies to control these phenomena will be explored. As a model system for ordered, monodisperse porosity, alumina inverse opal films were prepared from templates of vertically self-assembled polystyrene (PS) monospheres by atomic layer deposition (ALD) infiltration and subsequent calcination. The effects of introducing dopants (Cr, Nd) by solution nitrate-based infiltration on the transformation into the α-alumina phase and on grain growth instabilities will be presented. Additionally, alumina inverse photonic glass films were prepared in a similar fashion using a destabilized suspension of PS monospheres. The sintering behaviour of the ordered, monodisperse pore structures in the form of the inverse opal photonic crystal will be contrasted with the disordered, monodisperse pores in the form of the inverse photonic glass.

The efficiency of a frequency conversion process in a nonlinear crystal depends crucially on the phase matching condition. Typically one can modulate the nonlinearity of a crystal periodically in one or two dimensions to achieve quasi-phase matching for certain parametric processes. However, as only some discrete wavelengths are phase-matched in these periodic nonlinear structures, random nonlinear photonic crystals have gained a lot of interest during the last years [1]. Thy possess an inherent disordered nonlinearity and therefore a large set of reciprocal grating vectors which can compensate for any phase mismatch making them suitable for broadband frequency conversion.
We have examined the frequency conversion of infrared ultrashort laser pulses in strontium barium niobate (SBN) and barium titanate (BaTio3) crystals exhibiting domain structures with different degrees of disorder. While SBN can be considered as a random two dimensional nonlinear photonic crystal, the domain structure in BaTiO₃ is modulated in three dimensions because the domains are oriented either at an angle of 180 or at 90 degrees to each other. Furthermore, the refractive index in BaTiO₃ is also modulated which leads to characteristic emission patterns of the second harmonic. We can induce a random domain structure in both types of crystals by heating them up above the Curie temperature and subsequently cooling them down to room temperature. In SBN the disorder of the nonlinearity can also be controlled by a combination of electrical field poling and structured illumination.
We have analyzed the polarization and angular distribution of the second harmonic in dependence of the polarization, wavelength, and angle of incidence of the fundamental wave. This k-spectroscopy allows us to determine the spectrum of reciprocal grating vectors as well as the effective nonlinear coefficients [2]. All measurements of second harmonic generation (SHG) in the far field are compared with Cerenkov-type SHG microscopy images of the ferroelectric domains [3]. In Cerenkov SHG the longitudinal phase mismatch is zero and the second harmonic is emitted at a characteristic angle which is only determined by the refractive indices of the fundamental and harmonic wave, respectively. The intensity of Cerenkov SHG depends on the transverse Fourier spectrum of the emitted part of the nonlinear structure. When a diffraction limited laser spot for instance hits a domain wall a Cerenkov-phase matched second harmonic wave is emitted whereas there is no SHG in regions with a homogeneous nonlinearity. With this technique we are able to image any complex nonlinear photonic structure in three dimensions like the ferroelectric domains in SBN with a tailored disorder for efficient broadband second harmonic and cascaded third harmonic generation.
[1] M. Baudrier-Raybaut et al., Nature 432, 374 (2004)
[2] M. Ayoub et al., Opt. Express 21, 8220 (2013)
[3] Y. Sheng et al, Opt. Express 18, 16539 (2010)

Introducing tailored disorder into three-dimensional photonic structures allows for studying the disorder-related change of the underlying transport mechanisms. Here, we introduce deterministic aperiodic disorder in periodic photonic crystals. Deterministic aperiodic structures offer the possibility to reproducibly create specific potential landscapes whose Fourier components are determined by the underlying aperiodic sequence. In accordance with Lebesgue&’s spectral theorem the Fibonacci, Thue-Morse and Rudin-Shapiro sequences are examples of the three basic spectral measures, namely pure-point, singularly-continuous and absolutely-continuous, respectively. Especially, the Rudin-Shapiro series is found to be indiscernible from randomly disordered samples concerning their diffraction patterns/properties [1]. Varying the structural parameters, e.g., the lattice spacing, according to the aperiodic sequences allows us to introduce deterministic aperiodic disorder into the photonic crystals [2,3].
Samples are fabricated via direct laser writing in negative-tone photoresist. Using a dip-in lithography approach, samples of considerable height (> 70 unit cells) are prepared with constant high quality throughout the volume. We measure reflectance and transmittance spectra as well as time-resolved photonic transport and correlate the results with mode patterns to deduce the underlying transport mechanism [2]. The different types of aperiodic disorder show characteristic transport properties well reproduced in numerical calculations.
References
[1] M. Baake and U. Grimm, J. Phys. Conf. Ser. 226, 012023 (2010)
[2] Michael Renner and Georg von Freymann, Advanced Optical Materials 2, 226 (2014)
[3] 3D Photonic Quasicrystals and Deterministic Aperiodic Structures, A. Ledermann, M. Renner, and G. von Freymann, in “Light Localization and Lasing”, Mher Ghulinyan, and Lorenzo Pavesi, editors, Cambridge University Press (2015).

In this study, we investigate a low-cost and scalable fabrication of an opal structure via self-assembly of colloidal silica microspheres and propose a model describing a relationship between assembly parameters. To fabricate an opal structure, silica microspheres with a diameter of ~900 nm are first functionalized with allyltrimethoxysilane and dispersed in chloroform. Langmuir-Blodgett (LB) method is then used to self-assemble silica microspheres onto Si(100) substrates. By optimally adjusting the pulling speed of the substrate and surface pressure within the trough, a hexagonally closed-packed opal structure is achieved. Scanning electron microscopy (SEM) images have shown domain size of the monolayer assembly to be approximately 10 mu;m by 10 mu;m. The light diffraction pattern and intensity distribution from the opal structure also support the average domain size. By repeating LB coating processes for n number of times, an n-multilayer assembly is formed, creating an opal template structure. An analytical model is also derived from material flux balance and a 2D equation of state of silica spheres on water surface to describe the relationship between pulling speed, surface pressure, barrier speed, number of layers, and sphere&’s diameter. This model allows us to predictably manipulate the crystal domain size and therefore the level of order in the assembly.

Recently, quasi-random nanostructures have been of great interest for photon management. Typically, such patterns require expensive fabrication processes in order to create these pre-designed, sub-wavelength nanostructures. Interestingly, these patterns exist in Blu-ray movie discs, a consumer product that is already mass-produced and readily available. Here we discover that the patterns on Blu-ray discs are surprisingly well suited for light trapping applications due to their quasi-random nature. The algorithms that encode data found on Blu-ray discs were developed to optimize data compression and error-tolerancing; coincidentally, these algorithms also create a quasi-random arrangement of islands and pits on the final media discs. These nanopatterns are near-optimized for photon management over the entire solar spectrum, regardless of the information stored on the discs. As a proof-of-concept, we imprint polymer solar cells with the Blu-ray patterns, which increases their efficiencies. Further, simulation suggests that Blu-ray patterns could be applied broadly, enhancing solar cells made of many other materials.

Unlike graphene multilayer, the colors of graphene oxide (GO) multilayer were found to produce periodical changes as their thickness increased due to changing light interference when light passes through their layers. In addition, the spacing between the interlayer in GO sheets creates water trap state under water, which allows water permeation through GO membrane. However, in dry state, GO sheets are completely impermeable. These optical properties of 2D GO multilayer could transfer to interesting optical phenomenon since the structure is expected to produce multiple light interference as the environment changed (i.e. humidity). If the GO structure is three dimensional (3D), it may result in more dramatic optical property changes and show unique optical behavior which cannot be observed in 2D structures. To prove our hypothesis, we fabricated a 3D hollow structure with both vertical and horizontal free-standing GO membrane, which does not have additional support or substrate, using origami like self-folding approaches. This approach can preserve the intrinsic properties of GO membrane. In this presentation, we introduce our current observation of dynamic adjustments of optical transparency in 3D GO as environment changes. The adaptive behaviors of the 3D GO are based on the combination of water permeable multilayer structure and 3D geometrical effects. The optical behavior was not seen in 2D planar GO multilayers as we expected and it was also not observed in 3D reduced graphene oxide (RGO). Based on our observation, we present our current understanding of the phenomenon and discuss opportunity for a new class of 3D graphene applications.

The highly elaborate technique of optical induction is an exceptionally suitable tool to create a manifold line-up of photonic structures. Thus, the examination of propagation effects in 2d and 3d photonic structures of almost arbitrary configuration has led to remarkable results in the last decade, ranging from Rabi oscillations, and Zener tunneling in the linear as well as solitons in the nonlinear regime [1]. These are just a few examples that illustrate the noticeable benefit of using artificially generated photonic structures as model systems to investigate intriguing wave propagation effects.
Since the beginning times of inquiring gap solitons in periodic photonic lattices a prevalent medium used for the optical induction is the photorefractive strontium barium niobate (SBN) crystal. Its properties allow a relatively fast and reversible index modulation offering a versatile platform for generating various photonic potentials. By implementing proper writing light fields - our particular expertise are so called nondiffracting beams - the induction of complex light potentials is readily to achieve. In addition, operating computer controlled spatial light modulators affords in a flexible way to generate these specific light fields.
To generally get deeper insight into wave propagation in complex random media it turned out that it is again necessary to find proper model systems [2]. Thus, beyond inducing well researched regular patterns that bear band gap features, especially the possibility to introduce disorder is an appealing perspective of our optical induction scheme.
A specific nondiffracting beam that holds transversely random intensity is thereby an indispensable tool to establish disorder. Since the spectrum of the resulting random structures is intrinsically low pass filtered, a crucial dependency of the propagation behavior on the direction of the light is significant. This in turn allows for addressing the two different regimes of wave localization - strong and weak - simply by controlling the direction of the probe. The first one is identical to Anderson localization where the latter one often is referred to coherent backscattering. Adapted from wave propagation in a bulk system of irregularity, it is of further general interest to explore the influence of disorder on wave propagation at surfaces. As nondiffracting Mathieu beams offer such interfaces, we combined them with the mentioned random light field to receive variably disordered potential configurations.
In our experimental realizations of all of these potentials we could consistently recover fascinating light localization effects and hence introduce a proper model system for disorder [3]. Due to the universal nature of strong and weak localization our results are relevant for all wave systems containing randomness.
[1] F. Lederer et al., Phys. Rep. 463, 1 (2008)
[2] L. Levi et al., Nat. Phys. 8, 912 (2012)
[3] M. Boguslawski et al., Opt. Express 21, 31713 (2013)

Aluminum is a material that is readily compatible with silicon complementary metal oxide semiconductor (CMOS) processes and optical properties of Aluminum has been recently studied to highlight the effect of incorporated aluminum oxide (Al₂O₃) within and on the surface of aluminum. Moreover, Al₂O₃ is transparent over a wide wavelength range, from the ultraviolet to about 10 mu;m. Here, we demonstrate the use of Aluminum and native Al₂O₃ for the fabrication of plasmonic nanostructures that exhibit resonances spanning a wide
spectral range, from the visible to mid-infrared (MIR) region of the spectrum. We use the native Al₂O₃ to fabricate periodic metal-insulator-metal (MIM) resonators with various structures, and simultaneous presence of visible and IR resonances are shown to be possible.
For the infrared resonances with measured insulator thickness of 5 nm and absorption peaks at 8 mu;m, the cavity size is on the order of lambda;³/100000. The IR resonances are used in surface enhanced infrared absorption spectroscopy (SEIRA), enabling the detection of self-assembled monolayers of DDT. Through fabrication of silver nanoislands on aluminum surfaces and MIM plasmonic surfaces with a thin native Al₂O₃ layer, hierarchical plasmonic structures are formed. Such hierarchical plasmonic surfaces are shown to enhance the spectroscopic signals to levels that exhibit monolayer sensitive SEIRA demonstrating the versality of aluminum as a Plasmonic material.

Disordered optical media are ubiquitous in nature, and a proper description of light propagation in such materials is crucial for a number of applications ranging from the characterization of these materials to the fabrication of new types of lasers [1].
Here, we describe studies on light diffusion in disordered meso-macroporous materials with a cylindrical shape [2]. High Internal Phase Emulsion (HIPE)-based silica foam samples are realized. To quantify the effect of a finite lateral size on measurable quantities, an analytical model for diffusion in finite cylinders is developed and validated by Monte Carlo random walk simulations. Steady-state and time-resolved transmission experiments are performed and the transport parameters are successfully retrieved owing to the proposed model. The scattering losses on the lateral sides of the samples are responsible for a lowering of the transmission signal and a shortening of the photon lifetime. The recognition of this geometrical effect is essential since its wrong attribution to material absorption could be detrimental in various applications, such as biological tissue diagnosis or conversion efficiency in dye-sensitized solar cells.
In a second step, we show the light diffusion behaviour in (HIPE)-based isodense polystyrene foams [3]. Optical measurements combining steady-state and time-resolved detection are used to characterize the photon transport parameters. Very interestingly, a clear scalability of the transport mean free path l_t with the average size of the pores S is observed, featuring a constant velocity of the transport energy in these isodense structures. This study strongly motivates further investigations into the limits of validity of this scalability as the scattering strength of the system increases.
Finally, we recently predicted the coexistence and competition of random lasing (RL) and stimulated Raman scattering (SRS) in active disordered random media [4]. We develop a simple model which includes both mechanisms coupled to diffusion equation. We find that the prevalence of a nonlinear mechanism over the other is determined by the degree of scattering. This is confirmed experimentally in dye-infiltrated 3-dimensional porous silica-based disordered samples, with controllable pore size and transport properties. Experimentally, random lasing dominates in sample with large transport mean free path, l_t asymp; 100 mu;m, while it gives way to SRS for l_t asymp; 25 mu;m. The competition is explained in terms of disorder-dependent pump depletion and fluorescence saturation.
[1] D. S. Wiersma, Nat. Phys. 4, 359 (2008); B. Redding, M.A. Choma, H. Cao, Nat. Photonics 6, 355 (2012); D. S Wiersma, Nat. Photonics, 7, 188 (2013).
[2] P. Gaikwad, S. Ungureanu, R. Backov, K. Vynck and R.A.L. Vallée, Opt. Express 22, 7, 7503, (2014).
[3] S. William Reginald, V. Schmitt and R.A.L. Vallée, EPL 107, 64003, (2014).
[4] N. Bachelard, P. Gaikwad, R. Backov, P. Sebbah and R. A. L. Vallée, ACS Photonics, in press.

The search of unique materials exhibiting efficient emission in aggregated states is nowadays the one of the most interesting and important issue of material sciences. Such unique molecular systems shows increasing luminescence efficiency with increasing concentration, opposite to common and well known luminescent dyes obeying rule of concentrational quenching.
In our work we focused our attention on 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecule, a pyrazoline derivative which can form non-centrosymetric crystals capable to emit the light. Our detailed spectroscopic studies performed in cryogenic temperatures confirm the existence of trap states in emission spectrum. Moreover the performed experiments concerning the DCNP as a dopant for polymeric matrices have confirmed the occurrence of stimulated emission exactly at the same spectral position as trap state emission is located. The measurements of emission decay times show directly that excitonic states lifetime is approximately 250 ps whereas trap states emits in time scale of several nanoseconds and thus trap states can be thought as metastable states for laser emission. The Raman spectroscopy of DCNP dissolved in n-nonane matrix, shows in cryogenic temperatures specific vibrational modes characteristic for the DCNP molecule. Comparison of Raman spectra with low temperature emission shows good coincidence of vibrational modes and therefore indicates that nature of the traps is rather structural. Therefore the crystallization of DCNP is necessary for light amplification.
The doping procedure of polymers in high concentration of DCNP dye, constitutes not only gain but also the disorder. Both results in random lasing, for which light localization occurs inside DCNP microcrystals. Non-crystalized molecules can provide more efficient optical pumping as their emission overlaps absorption spectra of excitonic and trap states of the DCNP crystal.
Complex photo-physics of DCNP makes this system unique and very interesting for further studies especially in a context of chemical modification that can result in different wavelength of emission. Moreover, despite efficient random lasing occurring in polymeric layers containing DCNP microcrystals, it is possible to couple well defined distributed feedback resonator with the random resonator and therefore obtain precise mode selection.
The authors would like to acknowledge the National Science Centre of Poland for financial support, grant decision number: DEC-2013/09/D/ST4/03780

We investigate the mechanism of structural coloration by quasi-ordered nanostructures in bird feather barbs. Small-angle X-ray scattering (SAXS) data reveal the structures are isotropic and have short-range order on length scales comparable to optical wavelengths. We perform angle-resolved reflection and scattering spectrometry to fully characterize the colors under directional and omni-directional illumination of white light. Under directional lighting, the colors change with the angle between the directions of illumination and observation. The angular dispersion of the primary peaks in the scattering/reflection spectra can be well explained by constructive interference of light that is scattered only once in the quasi-ordered structures. Using the Fourier power spectra of structure from the SAXS data we calculate optical scattering spectra and explain why the light scattering peak is the highest in the backscattering direction. Under omni-directional lighting, colors from the quasi-ordered structures are invariant with the viewing angle. The non-iridescent coloration results from the isotropic nature of structures instead of strong backscattering.
Inspired by nature, we fabricated the self-assembly of biomimetic isotropic films which display structural color that is amenable to potential applications in coatings, cosmetics, and textiles. We find that isotropic structures with a characteristic length-scale comparable to the wavelength of visible light can produce structural color when wavelength-independent scattering is suppressed.
We also achieved lasing in photonic amorphous structures that mimic the isotropic nanostructures which produce non-iridescent color in nature. Our experimental and numerical studies reveal that lasing becomes most efficient at certain frequencies, due to enhanced optical confinement by short-range order. The optimal lasing frequency can be tuned by adjusting the structure factor. Therefore, lasing in nanostructures may be effectively improved and manipulated by short-range order.

An amazing range of complex optical structures exists in nature. Such structures have been optimised by at least 500 million years of evolution [1] and they are assembled of mainly two basic materials: Chitin/keratin and melanin [2]. These are found in various parts of animal bodies that often result in intriguing optical effects ranging from matte to iridescent colours, and from black to extremely white [3]. These structural colours arise from complex nanostructures such as ordered and quasi-ordered photonic crystals and random assemblies.
While the most dazzling displays are due to ordered photonic structures with a strong selective reflection of single colours, whiteness arises from diffuse and broadband reflection of light. Whiteness, which is less explored than coloured structures, is typically achieved through optical scattering in randomly structured media. A white surface appearance generally requires a relatively thick material system comprising randomly positioned high refractive-index scattering centres. This is in strong contrast to structural colour where colouration originates in coherent scattering.
Here, we demonstrate how the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles is provided by a remarkably optimised polydispersity and anisotropy of intra-scale chitin networks that act as scattering elements [4]. Using time-resolved measurements, we show that light propagating in the scales of the beetles undergoes strong multiple scattering that is associated with the lowest transport mean free path and diffusion constants reported to date for low-refractive-index systems.
Our experimental findings are complemented by advanced finite-difference time-domain modelling on three-dimensional networks with controlled anisotropy ratios to understand the important parameters in the design of efficient scattering media. The systems extracted optical parameters suggest new designs for efficient strongly-scattering 3D bio-inspired photonic structures.
References
[1] 515 million years of structural colour. J Opt A Pure Appl Opt 2, R15-R28 (2000).
[2] A protean palette: colour materials and mixing in birds and butterflies J. R. Soc. Interface 6, S221-S231 (2009)
[3] Brilliant whiteness in ultrathin beetle scales, Science 315, 5810 (2007)
[4] Bright-White Beetle scales Optimise Multiple Scattering of Light, Sci. Rep. 4, 6075 (2014)

Animate natural systems achieve spectacular properties with limited resources through complex structuring. Due to lineage and evolutionary adaptation, common features on various levels of hierarchy are combined and tailored to achieve widely differing external properties in related species. Comparison with industrial production strategies illustrates that the abstracted underlying economics and technical solutions of an animal, fungus or plant are mirrored in human applications. Therefore, looking towards nature for inspiration has again become a major focus of research.
In particular, photonic structures from nature show unexpected external properties such as diffuse reflection, control of polarization, externally-induced color changes or brilliant whiteness. At the same time, photonic structures for technical applications are rapidly being developed, leading to breakthrough successes in many fields, e.g. sensing, information transfer or photovoltaics. It is reasonable to become inspired by nature in order to explore possibilities, determine applicable structuring and overcome processing limitations. This can be achieved by employing biological design strategies, hierarchical structures or processing solutions for advanced engineering and the formation of functional materials. One possible strategy is the direct replication of a biological structure as an engineering material, termed biotemplating [1]. Another is the use of natural polymers with self-assembly capabilities [2] for the fabrication of optical materials. Accordingly, periodically ordered three-dimensional biological structures have been used as unique blueprints for semiconducting and metallic photonic crystals [3].
A more recent research issue in natural-, basic- and technical application research are the properties of photonic materials with seemingly irregular or disordered structures. They were regarded as defective and useless, until several unique optical properties of such materials were discovered. These include Anderson localization of modes, multiplied path lengths, random lasing and spatially diffuse, broad- or narrowband reflectivity. An example from nature can be found in the cuticle of the long-horn beetle Anoplophora elegans, Figure 1c [4]. Despite containing randomly organized features with no long-range order, it selectively reflects yellow light in a very narrow reflection band, which is nearly insensitive to changes in the angle of incidence. These two features are not attainable by periodically ordered structures of the same dielectric composition.
The properties of disordered photonic materials, which have been discovered so far, are already of high value for applications from imaging over miniaturization to laser design. Since nature is still providing us with new examples of correlated structures and properties, it is expected that the field of bioinspired optical materials design will open up new research and application avenues.
[1] D. Van Opdenbosch, M. Johannes, X. Wu, H. Fabritius, C. Zollfrank, Photonics Nanostruct. - Fund. Appl. 2012, 10, 516-522.
[2] C. Zollfrank, Scripta Materialia 2014, 74, 3-8
[3] M.R. Jorgensen, M.H. Bartl, J. Mater. Chem. 2011, 21, 10583-10591.
[4] J.W. Galusha, L.R. Richey, M.R. Jorgensen, J.S. Gardner, M.H. Bartl, J. Mater. Chem. 2010, 20, 1277-1284.

Currently the great effort is being put into biological materials for random lasing application. It has been developed an idea for generation of laser action coming from fully biologically originated system. In our work we present that not only widely used DNA, and its modifications exploited in various systems are suitable as a material for embedding laser dyes but also such materials like polysaccharides and especially starch [1]. Due to temperature originated sol-gel transition starch can be obtained in two forms showing various optical properties. Gelatinization lead to obtainment of anisotropic transparent material. The opposite process results in increase of sample scattering due to formation of starch granules of approximate weight ~10⁵ Da. For random lasing applications we have investigated Rhodamine 6G doped starch systems. We show that oxygen permeability of starch layers is significantly lower than similar made of DNA and modifications [2], increasing the dye photodegradation time. It has been reported a feature of Rhodamine, which forms H, J and higher order aggregates, having shifted fluorescence emission [3]. This fact give us an possibility to design tunable random laser based on aggregation of Rhodamine, in range 580 - 605 nm of emitted light. Moreover due to phase transitions of starch and caused changes in optical properties we were able to manipulate light scattering regime in order to acquire stimulated emission from Rhodamine doped starch gel and random lasing from highly scattering dye doped starch granules deposited on glass slide.
This work was supported from National Science Centre, decision number DEC-2013/09/D/ST4/03780 and DEC-2013/11/N/ST4/01488
[1] K. Cyprych, L. Sznitko, J. Mysliwiec, Starch: Application of biopolymer in random lasing, Organic Electronics, Volume 15, Issue 10, October 2014, Pages 2218-2222,
[2] P. Forssell, R. Lahtinen, M. Lahelin, P. Myllarinen, Oxygen permeability of amylose and amylopectin films, Carbohyd. Polym., 47 (2002), pp. 125-129,
[3] V.M. Martinez, F.L. Arbeloa, J.B. Prieto, I.L. Arbeloa, Characterization of rhodamine 6G aggregates intercalated in solid thin films of laponite clay. 2 - fluorescence spectroscopy, J. Phys. Chem. B, 109 (2005), pp. 7443-7450.

The skin structure of cephalopods endows them with remarkable dynamic camouflage capabilities. Consequently, much research effort has focused on understanding and emulating these animals&’ color changing abilities in the visible region of the electromagnetic spectrum. In contrast, despite the importance of infrared signaling and detection for many industrial and military applications, few studies have attempted to translate the principles underlying cephalopod adaptive coloration to infrared camouflage. We have drawn inspiration from nanostructures implicated in cephalopods&’ camouflage abilities and developed strategies for the self-assembly of unique cephalopod structural proteins into dynamically tunable biomimetic camouflage coatings on both transparent and flexible substrates.^1,2 Our substrates can adhere to arbitrary surfaces, and their reflectance can be reversibly modulated from the visible to the near-infrared regions of the electromagnetic spectrum with both chemical and mechanical stimuli.^1,2 Thus, we can endow common objects with any shape or form factor with tunable camouflage capabilities.^1,2 Our work represents a key step toward the development of wearable biomimetic color and shapeshifting technologies for stealth applications.
1. Phan, L.; Walkup IV, W. G.; Ordinario, D. O.; Karshalev, E.; Jocson, J.-M.; Burke, A. M.; Gorodetsky, A. A. Adv. Mater.2013, 25, 5621-5625.
2. Phan, L.; Ordinario, D. O.; Karshalev, E.; Shenk, M.; Gorodetsky, A. A. 2014, Submitted.