Ultralow threshold laser action from toroidal polymer microcavity

Cataloged from PDF version of article.We report laser action from a toroidal microcavity coated with pi-conjugated polymer. An ultralow threshold value of similar to 200 pJ/pulse is achieved by free space excitation in ambient conditions. This is the lowest threshold energy obtained in microtoroid lasers by free space excitation. The effective refractive index of the polymer, extracted from Fourier analysis of emission spectra, is 1.787, which is very close to measured value of 1.790 indicating that laser modes are located around the circumference of the cavity as whispering gallery resonances

Being close to far away

In 1948 my great-grandfather was imprisoned in a Russian forced labor camp known as the Gulag, an acronym for the title Chief Administration of Corrective Labor Camps and Colonies Surviving this life event pushed my great-grandfather beyond the limits of civil society, rationality, and empathy into a world that author Aleksandr Solzhenitsyn called, an unassimilable spiritual earthquake which not every person can cope with. Like millions of others, my great grandfather took a journey into the Gulag country, a place beyond vision or understanding. In the fall of 2012, I too traveled to the Gulag country, in order to trace the footsteps of my great-grandfather. Being Close to Far Away explores a post-traumatic environment in Vorkuta, Russia, a former location of the Gulag, and the camp where my great-grandfather was imprisoned. The Gulag was shrouded in secrecy by the Soviet Government until the death of Stalin, and my great-grandfather disappeared behind this shroud for seven years (1948-1955). This thesis project is in part to reclaim those years; for him, for myself, and for my family. I photographed the prison sites extensively. I did so in order to explore the traces and scars of the Gulag

Biomineral Amorphous Lasers through Light-Scattering Surfaces Assembled by Electrospun Fiber Templates

New materials aim at exploiting the great control of living organisms over molecular architectures and minerals. Optical biomimetics has been widely developed by microengineering, leading to photonic components with order resembling those found in plants and animals. These systems, however, are realized by complicated and adverse processes. Here we show how biomineralization might enable the one-step generation of components for amorphous photonics, in which light is made to travel through disordered scattering systems, and particularly of active devices such as random lasers, by using electrospun fiber templates. The amount of bio-enzymatically produced silica is related to light-scattering capacity and the resulting organosilica surfaces exhibit a transport mean free path for light as low as 3 micron, and lasing with linewidth below 0.2 nm. The resulting, complex optical material is characterized and modelled to elucidate scattered fields and lasing performance. Tightly-controlled nanofabrication of direct biological inspiration establishes a new concept for the additive manufacturing of engineered light-diffusing materials and photonic components, not addressed by existing technologies.Comment: 37 pages, 11 figure

Designing coupled microcavity lasers for high-Q modes with unidirectional light emission

We design coupled optical microcavities and report directional light emission from high-$Q$ modes for a broad range of refractive indices. The system consists of a circular cavity that provides a high-$Q$ mode in form of a whispering gallery mode, whereas an adjacent deformed microcavity plays the role of a waveguide or collimator of the light transmitted from the circular cavity. As a result of this very simple, yet robust, concept we obtain high-$Q$ modes with promising directional emission characteristics. No information about phase space is required, and the proposed scheme can be easily realized in experiments.Comment: 3 pages, 3 figure

Unidirectional laser emission from ∏-conjugated polymer microcavities with broken symmetry

Journal ArticleWe report unidirectional laser emission from ∏-conjugated polymer microcavities with broken symmetry geometries such as spiral and microdisk containing a "line defect," in comparison with plain microdisk cavity having isotropic emission. We found that the laser emission directionality contrast ratio is 8-10 and far field lateral divergence angle is 12°-15° for both broken symmetry geometries, with no significant increase in the laser threshold intensity. Fourier transform analysis of the laser emission spectra shows that unlike microdisks with line defect, the variation of light trajectories in the spiral microcavities leads to less defined laser modes

Threshold excitation statistics and imaging of random lasers in ?-conjugated polymer films; evidence for random resonators

ManuscriptRandom lasing is laser action that consists of a sequence of narrow, coherent spectral lines observed when stimulated emission in a disordered gain medium is excited above threshold excitation intensity, Ith. We studied three Ith distribution functions, F(n)(Ith) in ?-conjugated polymer films, where n (= 1-3) is the number of lasing random resonators in the excited film area; including their evolution with respect to the excitation area size, and polymer mixture with various concentrations of TiO2 nanoparticles. Optical images of the excited film area support the Ith measurements; since the sharp laser lines in the emission spectrum are accompanied by the appearance of lasing random resonators in the picture. At Ith, where a single dominant random lasing resonator appears in the accompanying picture, we found good agreement between the cavity diameter extracted from the emission power Fourier transform analysis, and the cavity size in the picture. This was directly confirmed by a novel technique of space/spectrum cross-correlation of the laser emission lines with 10x10 ?m2 spatial resolution; where we show that the laser modes are indeed localized within the respective lasing resonator. We found that F(1)(Ith) has both a marked asymmetry with respect to the mean threshold, (Ith)ave, and decreases with the area size. We also found that upon increasing the TiO2 nanoparticles density, ? in the polymer/TiO2 mixture the light mean free path decreases, F(1)(Ith) broadens, and (Ith)ave linearly increases with ?, indicating that the addition of extrinsic scatterers to the polymer matrix is not beneficial to random lasing. Our results provide strong evidence for the model of random resonators in the gain medium for explaining random lasing in ?-conjugated polymer films

Investigation of cultural ecosystem services supply in a river landscape: a case study in the Lower Rhine area using social media images

River landscapes have an important function in the landscape in terms of coastal use and the opportunities they provide and they offer different cultural ecosystem services (CES). CES have a significant impact on human welfare in terms of the recreational, aesthetic and spiritual benefits these generate for people. However, the modelling and analysis of these services is more limited versus other ecosystem services due to their intangibility and subjectivity which creates unique challenges. Recently, social media data have provided an opportunity to generate spatial models of CES, offering significant cost and time advantages. Nevertheless, the usefulness of these novel data sources still requires more investigation versus more traditional survey techniques. This study aims to understand the variety of information provided by the images that users upload publicly on a daily basis to social media in a urban/rural setting. Specifically, CES provided by the open and green spaces around the Lower Rhine (Nederrijn) in Wageningen were studied using images uploaded to the social media platform Flickr. A photographic survey was then conducted to compare the utility and accuracy of these new data versus traditional techniques. In doing so, spatial data, ratings and survey evaluations related to the photographs were digitised, classified and integrated with land cover features. The results show that there is a good consistency between the two sources of data and that a wide range of CES measures can be established using these novel data sources. More work is now needed in developing spatial indicators of CES relevant to local assessments, such as the one carried out in this study.Focusing on the Lower Rhine region as a case study, we used the Flickr digital platform to address the following three key questions:(1) What is the spatial distribution of CES?(2) Do users who post on the Flickr platform fully represent the cultural identity of the community and visitors in the region?(3) Which land-cover types of the Lower Rhine region are most appreciated for CES and what are the aesthetic preferences of visitors and experts that correspond to this