Harnessing ultraconfined graphene plasmons to probe the electrodynamics of superconductors.

We show that the Higgs mode of a superconductor, which is usually challenging to observe by far-field optics, can be made clearly visible using near-field optics by harnessing ultraconfined graphene plasmons. As near-field sources we investigate two examples: graphene plasmons and quantum emitters. In both cases the coupling to the Higgs mode is clearly visible. In the case of the graphene plasmons, the coupling is signaled by a clear anticrossing stemming from the interaction of graphene plasmons with the Higgs mode of the superconductor. In the case of the quantum emitters, the Higgs mode is observable through the Purcell effect. When combining the superconductor, graphene, and the quantum emitters, a number of experimental knobs become available for unveiling and studying the electrodynamics of superconductors.

Disentangling Cathodoluminescence Spectra in Nanophotonics: Particle Eigenmodes vs Transition Radiation.

Cathodoluminescence spectroscopy performed in an electron microscope has proven a versatile tool for analyzing the near- and far-field optical response of plasmonic and dielectric nanostructures. Nevertheless, the transition radiation produced by electron impact is often disregarded in the interpretation of the spectra recorded from resonant nanoparticles. Here we show, experimentally and theoretically, that transition radiation can by itself generate distinct resonances that, depending on the time-of-flight of the electron beam inside the particle, can result from constructive or destructive interference in time. Superimposed on the eigenmodes of the investigated structures, these resonances can distort the recorded spectrum and lead to potentially erroneous assignment of modal characters to the spectral features. We develop an intuitive analogy that helps distinguish between the two contributions. As an example, we focus on the case of silicon nanospheres and show that our analysis facilitates the unambiguous interpretation of experimental measurements on Mie-resonant nanoparticles.

Quantum surface effects in the electromagnetic coupling between a quantum emitter and a plasmonic nanoantenna: time-dependent density functional theory vs. semiclassical Feibelman approach.

We use time-dependent density functional theory (TDDFT) within the jellium model to study the impact of quantum-mechanical effects on the self-interaction Green's function that governs the electromagnetic interaction between quantum emitters and plasmonic metallic nanoantennas. A semiclassical model based on the Feibelman parameters, which incorporates quantum surface-response corrections into an otherwise classical description, confirms surface-enabled Landau damping and the spill out of the induced charges as the dominant quantum mechanisms strongly affecting the nanoantenna-emitter interaction. These quantum effects produce a redshift and broadening of plasmonic resonances not present in classical theories that consider a local dielectric response of the metals. We show that the Feibelman approach correctly reproduces the nonlocal surface response obtained by full quantum TDDFT calculations for most nanoantenna-emitter configurations. However, when the emitter is located in very close proximity to the nanoantenna surface, we show that the standard Feibelman approach fails, requiring an implementation that explicitly accounts for the nonlocality of the surface response in the direction parallel to the surface. Our study thus provides a fundamental description of the electromagnetic coupling between plasmonic nanoantennas and quantum emitters at the nanoscale.

Anisotropic second-harmonic generation from monocrystalline gold flakes.

Noble metals with well-defined crystallographic orientation constitute an appealing class of materials for controlling light-matter interactions on the nanoscale. Nonlinear optical processes, being particularly sensitive to anisotropy, are a natural and versatile probe of crystallinity in nano-optical devices. Here we study the nonlinear optical response of monocrystalline gold flakes, revealing a polarization dependence in second-harmonic generation from the {111} surface that is markedly absent in polycrystalline films. Our findings confirm that second-harmonic microscopy is a robust and non-destructive method for probing the crystallographic orientation of gold, and can serve as a guideline for enhancing nonlinear response in plasmonic systems.

Detection of the Faraday Chiral Anisotropy.

The connection between chirality and electromagnetism has attracted much attention through the recent history of science, allowing the discovery of crucial nonreciprocal optical phenomena within the context of fundamental interactions between matter and light. A major phenomenon within this family is the so-called Faraday chiral anisotropy, the long-predicted but yet unobserved effect which arises due to the correlated coaction of both natural and magnetically induced optical activities at concurring wavelengths in chiral systems. Here, we report on the detection of the elusive anisotropic Faraday chiral phenomenon and demonstrate its enantioselectivity. The existence of this fundamental effect reveals the accomplishment of envisioned nonreciprocal electromagnetic metamaterials referred to as Faraday chiral media, systems where novel electromagnetic phenomena such as negative refraction of light at tunable wavelengths or even negative reflection can be realized. From a more comprehensive perspective, our findings have profound implications for the general understanding of parity-violating photon-particle interactions in magnetized media.

On the applicability of quantum-optical concepts in strong-coupling nanophotonics.

Rooted in quantum optics and benefiting from its well-established foundations, strong coupling in nanophotonics has experienced increasing popularity in recent years. With nanophotonics being an experiment-driven field, the absence of appropriate theoretical methods to describe ground-breaking advances has often emerged as an important issue. To address this problem, the temptation to directly transfer and extend concepts already available from quantum optics is strong, even if a rigorous justification is not always available. In this review we discuss situations where, in our view, this strategy has indeed overstepped its bounds. We focus on exciton-plasmon interactions, and particularly on the idea of calculating the number of excitons involved in the coupling. We analyse how, starting from an unfounded interpretation of the term N/V that appears in theoretical descriptions at different levels of complexity, one might be tempted to make independent assumptions for what the number N and the volume V are, and attempt to calculate them separately. Such an approach can lead to different, often contradictory results, depending on the initial assumptions (e.g. through different treatments of V as the-ambiguous in plasmonics-mode volume). We argue that the source of such contradictions is the question itself-How many excitons are coupled?, which disregards the true nature of the coupled components of the system, has no meaning and often not even any practical importance. If one is interested in validating the quantum nature of the system-which appears to be the motivation driving the pursuit of strong coupling with small N-one could instead focus on quantities such as the photon emission rate or the second-order correlation function. While many of the issues discussed here may appear straightforward to specialists, our target audience is predominantly newcomers to the field, either students or scientists specialised in different disciplines. We have thus tried to minimise the occurrence of proofs and overly-technical details, and instead provide a qualitative discussion of analyses that should be avoided, hoping to facilitate further growth of this promising area.

Importance of substrates for the visibility of "dark" plasmonic modes.

Dark plasmonic modes have interesting properties, including longer lifetimes and narrower linewidths than their radiative counterpart, and little to no radiative losses. However, they have not been extensively studied yet due to their optical inaccessibility. In this work, we systematically investigated the dark radial breathing modes (RBMs) in monocrystalline gold nanodisks, specifically their outcoupling behavior into the far-field by cathodoluminescence spectroscopy. Increasing the substrate thickness resulted in an up to 4-fold enhanced visibility. This is attributed to breaking the mirror symmetry by the high-index substrate, creating an effective dipole moment. Furthermore, the resonance energy of the dark RMBs can be easily tuned by varying the nanodisk diameter, making them promising candidates for nanophotonic applications.

Management of pouch-vaginal fistulas - experience from our institution.

AIM: Pouch-vaginal fistula (PVF) is an uncommon but serious complication of ileo-anal pouch reconstruction. This study aimed to review the recent management of PVF, in particular the role of anti-tumour necrosis factor (anti-TNF) drugs. METHOD: All patients presenting for management of PVF to our surgical service between 2007 and 2016 were studied. The median duration of follow-up from diagnosis of PVF was 6 years. Details of the original pouch surgery, timing of presentation of PVF, management and final outcome were recorded. Primary outcome was gastrointestinal (GI) continuity (as defined by the presence or absence of a stoma). RESULTS: A total of 23 patients were identified (median age 45 years) of whom nine had pelvic sepsis at the time of original pouch surgery. Management included local surgical repair, defunctioning ileostomy, pouch excision and anti-TNF therapy. GI continuity was achieved in 12 patients (52%). Healing of the PVF was achieved in 12 patients (52%). Pelvic sepsis was significantly associated with the need for a long-term ileostomy (P = 0.009). Biological therapy was used in 12 patients, of whom seven maintained GI continuity. Patients with late presentation PVF (60 months or longer postsurgery) and those with clinical features of Crohn's disease appeared to benefit from anti-TNF treatment. CONCLUSION: PVF remains a challenging problem with overall healing rates and GI continuity rates of just over 50%. Anti-TNF therapy may have a role in patients with late presentation PVF and those with features suggestive of Crohn's disease.

Development and early outcomes of the national training initiative for transanal total mesorectal excision in the UK.

AIM: Transanal total mesorectal excision (TaTME) has attracted substantial interest amongst colorectal surgeons but its technical challenges may underlie the early reports of visceral injuries and oncological concerns. The aim of this study was to report on the feasibility, development and the outcome of the national pilot training initiative for TaTME-UK. METHODS: TaTME-UK was successfully launched in September 2017 in partnership with the healthcare industry and endorsed by the Association of Coloproctology of Great Britain and Ireland. This multi-modal training curriculum consisted of three phases: (i) set-up; (ii) selection of pilot sites; and (iii) formal proctorship programme. Bespoke Global Assessment Scoring (GAS) forms were designed and completed by both trainees and mentors. Data were collected on patient demographics, tumour characteristics and perioperative clinical and histological outcomes. RESULTS: Twenty-four proctored cases were performed by 10 colorectal surgeons from five selected pilot sites. Median operative time was 331 ± 90 (195-610) min which was reduced to 283 ± 62 (195-340) min in the final case. Independent performance (GAS score of 5) was achieved for most operative steps by case 5. There was one conversion (4.2%), but no visceral injuries. Pathological data confirmed no bowel perforation and intact quality of the mesorectal TME specimens with clear distal margin in all cases and circumferential margins in 23/24 cases (96%). CONCLUSION: This exploratory study demonstrates acceptable early outcomes in a small cohort suggesting that a competency-based multi-modal training programme for TaTME can be feasible and safe to implement at a national level.

Short- and long-term outcomes of strictureplasty for obstructive Crohn's disease.

AIM: To evaluate the frequency and outcome of strictureplasty in the era of biologicals and to compare patients operated on by strictureplasty alone, resection alone or a combination of both. METHOD: A retrospective review of all patients undergoing strictureplasty for obstructing jejunoileal Crohn's disease (CD) in Oxford between 2004 and 2016 was conducted. For comparison, a cohort of CD patients with resection only during 2009 and 2010 was included. RESULTS: In all, 225 strictureplasties were performed during 85 operations, 37 of them in isolation and 48 with simultaneous resection. Another 82 procedures involved resection only; these patients had shorter disease duration, fewer previous operations and longer bowel preoperatively. The frequency of strictureplasty procedures did not alter during the study period and was similar to that in the preceding 25 years. There was no postoperative mortality. One patient required re-laparotomy for a leak after strictureplasty. None developed cancer. The 5-year reoperation rate for recurrent obstruction was 22% (95% CI 12-39) for resection alone, 30% (17-52) for strictureplasty alone and 42% (27-61) for strictureplasty and resection (log rank P = 0.038). Young age was a risk factor for surgical recurrence (log rank P = 0.006). CONCLUSION: The use of strictureplasty in CD has not changed significantly since the widespread introduction of biologicals. Surgical morbidity remains low. The risk of recurrent strictures is high and young age is a risk factor. In this study, strictureplasty alone was associated with a lower rate of reoperation compared with strictureplasty with resection.

Ultraviolet Interband Plasmonics With Si Nanostructures.

Although Si acts as an electrical semiconductor, it has properties of an optical dielectric. Here, we revisit the behavior of Si as a plasmonic metal. This behavior was previously shown to arise from strong interband transitions that lead to negative permittivity of Si across the ultraviolet spectral range. However, few have studied the plasmonic characteristics of Si, particularly in its nanostructures. In this paper, we report localized plasmon resonances of Si nanostructures and the observation of plasmon hybridization in the UV (∼250 nm wavelength). In addition, simulation results show that Si nanodisk dimers can achieve a local intensity enhancement greater than ∼500-fold in a 1 nm gap. Lastly, we investigate hybrid Si-Al nanostructures to achieve sharp resonances in the UV, due to the coupling between plasmon resonances supported by Si and Al nanostructures. These results will have potential applications in the UV range, such as nanostructured devices for spectral filtering, plasmon-enhanced Si photodetectors, interrogation of molecular chirality, and catalysis. It could have significant impact on UV photolithography on patterned Si structures.

Radiotherapy after local excision of rectal cancer may offer reduced local recurrence rates.

AIM: Early rectal cancer can be managed effectively with local excision, which is now the standard of care for many T1 lesions. However, the presence of unexpected adverse histopathological factors may indicate an increased risk of local recurrence, prompting consideration of completion radical surgery. Many patients are unfit or prefer to avoid radical surgery, relying instead on surveillance and early detection of recurrent disease. Recently, radiotherapy has shown promise as an adjuvant therapy in this group. This study assesses local recurrence rates after local excision with adjuvant radiotherapy at a single centre. METHOD: This was a retrospective review of a prospective database of all patients undergoing transanal endoscopic microsurgery (TEM) in a single institution. Data covering a 10-year period were analysed. RESULTS: Of 197 patients undergoing TEM for rectal cancer, 33 (17%) had adjuvant radiotherapy because of adverse histopathological features. At 3.2 years' median follow-up, there were three instances of local recurrence (9.1%). Estimated local recurrence at 1 and 3 years was 0% and 6.9%, compared to 16.8% and 21.2% in a propensity-score-matched group who were followed by surveillance alone. Local recurrence was diagnosed at a median of 23 months post-TEM in the radiotherapy group, compared to 8 months in the matched group. CONCLUSION: Radiotherapy after TEM is associated with a trend towards a reduced rate of local recurrence, even for high-risk disease. Radiotherapy would appear to offer a viable alternative to radical completion surgery in the presence of unforeseen adverse histopathological features, as long as a meticulous surveillance programme is in place.

Direct Characterization of Near-Field Coupling in Gap Plasmon-Based Metasurfaces.

Metasurfaces based on gap surface-plasmon resonators allow one to arbitrarily control the phase, amplitude, and polarization of reflected light with high efficiency. However, the performance of densely packed metasurfaces is reduced, often quite significantly, in comparison with simple analytical predictions. We argue that this reduction is mainly because of the near-field coupling between metasurface elements, which results in response from each element being different from the one anticipated by design simulations, which are commonly conducted for each individual element being placed in an artificial periodic arrangement. In order to study the influence of near-field coupling, we fabricate meta-elements of varying sizes arranged in quasi-periodic arrays so that the immediate environment of same size elements is different for those located in the middle and at the border of the arrays. We study the near-field using a phase-resolved scattering-type scanning near-field optical microscopy (s-SNOM) and conducting numerical simulations. By comparing the near-field maps from elements of the same size but different placements we evaluate the near-field coupling strength, which is found to be significant for large and densely packed elements. This technique is quite generic and can be used practically for any metasurface type in order to precisely measure the near-field response from each individual element and identify malfunctioning ones, providing feedback to their design and fabrication, thereby allowing one to improve the efficiency of the whole metasurface.

Multicentre phase II trial of near-infrared imaging in elective colorectal surgery.

BACKGROUND: Decreasing anastomotic leak rates remain a major goal in colorectal surgery. Assessing intraoperative perfusion by indocyanine green (ICG) with near-infrared (NIR) visualization may assist in selection of intestinal transection level and subsequent anastomotic vascular sufficiency. This study examined the use of NIR-ICG imaging in colorectal surgery. METHODS: This was a prospective phase II study (NCT02459405) of non-selected patients undergoing any elective colorectal operation with anastomosis over a 3-year interval in three tertiary hospitals. A standard protocol was followed to assess NIR-ICG perfusion before and after anastomosis construction in comparison with standard operator visual assessment alone. RESULTS: Five hundred and four patients (median age 64 years, 279 men) having surgery for neoplastic (330) and benign (174) pathology were studied. Some 425 operations (85·3 per cent) were started laparoscopically, with a conversion rate of 5·9 per cent. In all, 220 patients (43·7 per cent) underwent high anterior resection or reversal of Hartmann's operation, and 90 (17·9 per cent) low anterior resection. ICG angiography was achieved in every patient, with a median interval of 29 s to visualization of the signal after injection. NIR-ICG assessment resulted in a change in the site of bowel division in 29 patients (5·8 per cent) with no subsequent leaks in these patients. Leak rates were 2·4 per cent overall (12 of 504), 2·6 per cent for colorectal anastomoses and 3 per cent for low anterior resection. When NIR-ICG imaging was used, the anastomotic leak rates were lower than those in the participating centres from over 1000 similar operations performed with identical technique but without NIR-ICG technology. CONCLUSION: Routine NIR-ICG assessment in patients undergoing elective colorectal surgery is feasible. NIR-ICG use may change intraoperative decisions, which may lead to a reduction in anastomotic leak rates.

Modern management of T1 rectal cancer by transanal endoscopic microsurgery: a 10-year single-centre experience.

AIM: Minimally invasive, organ-sparing surgery has been used increasingly for early rectal cancer in recent years. However, local recurrence remains a concern. This study presents a 10-year single-centre experience of recurrence after local excision for T1 rectal cancer. METHOD: Data were collected prospectively on all patients undergoing local excision by transanal endoscopic microsurgery (TEM) in a single institution. Data covering a 10-year period were analysed. RESULTS: In all, 192 patients underwent TEM for rectal cancer; 70 of these had T1 tumour in the TEM specimen and did not have preoperative radiotherapy. Four were managed with completion surgery following TEM and a further six had radiotherapy; 60 underwent surveillance alone. Local recurrence occurred in six patients; three underwent salvage surgery. Estimated local recurrence at 3 years was 7.2% for the surveillance alone group. CONCLUSIONS: Local recurrence rates were lower than previous studies. Better preoperative assessment, more effective local excision surgery and postoperative radiotherapy may be contributory factors to a better-than-predicted outcome. Local excision should be offered as part of standard of care for T1 rectal cancer in the presence of good preoperative selection and meticulous surveillance.

Session 3: Many ways to organ preserve the rectum but which is correct?

From the patient's perspective, cancer cure with full preservation of function is a crucial goal. There are many advances that have emerged which may make this possible in a greater proportion of patients without compromising oncological outcomes. Professor Tekkis reviews the options and evidence to date for 'organ preservation' and the expert panel discuss the implications for current and future patient care.

Optical Observation of Plasmonic Nonlocal Effects in a 2D Superlattice of Ultrasmall Gold Nanoparticles.

The advances in recent nanofabrication techniques have facilitated explorations of metal structures into nanometer scales, where the traditional local-response Drude model with hard-wall boundary conditions fails to accurately describe their optical responses. The emerging nonlocal effects in single ultrasmall silver nanoparticles have been experimentally observed in single-particle spectroscopy enabled by the unprecedented high spatial resolution of electron energy loss spectroscopy (EELS). However, the unambiguous optical observation of such new effects in gold nanoparticles has yet not been reported, due to the extremely weak scattering and the obscuring fingerprint of strong interband transitions. Here we present a nanosystem, a superlattice monolayer formed by sub-10 nm gold nanoparticles. Plasmon resonances are spectrally well-separated from interband transitions, while exhibiting clearly distinguishable blueshifts compared to predictions by the classical local-response model. Our far-field spectroscopy was performed by a standard optical transmission and reflection setup, and the results agreed excellently with the hydrodynamic nonlocal model, opening a simple and widely accessible way for addressing quantum effects in nanoplasmonic systems.

Quantum Corrections in Nanoplasmonics: Shape, Scale, and Material.

The classical treatment of plasmonics is insufficient at the nanometer-scale due to quantum mechanical surface phenomena. Here, an extension of the classical paradigm is reported which rigorously remedies this deficiency through the incorporation of first-principles surface response functions-the Feibelman d parameters-in general geometries. Several analytical results for the leading-order plasmonic quantum corrections are obtained in a first-principles setting; particularly, a clear separation of the roles of shape, scale, and material is established. The utility of the formalism is illustrated by the derivation of a modified sum rule for complementary structures, a rigorous reformulation of Kreibig's phenomenological damping prescription, and an account of the small-scale resonance shifting of simple and noble metal nanostructures.

The role of a defunctioning stoma for colonic and perianal Crohn's disease in the biological era.

OBJECTIVE: A defunctioning stoma is a therapeutic option for colonic or perianal Crohn's disease. In the pre-biologic era the response rate to defunctioning in our unit was high (86%), but intestinal continuity was only restored in 11-20%. Few data exist on the outcome of defunctioning since the widespread introduction of biologicals. MATERIAL AND METHODS: All patients undergoing a defunctioning stoma for colonic/perianal Crohn's disease since 2003-2011 were identified from a prospective database. Indications for surgery, medical therapy, response to defunctioning and long-term clinical outcome were recorded. Successful restoration of continuity was defined as no stoma at last follow up. RESULTS: Seventy-six patients were defunctioned (57 with biologicals) and at last follow up, 20 (27%) had continuity restored. Early clinical response rate (<3 months) was 15/76 (20%) and overall response 31/76 (41%). Complex anal fistulae/stenosis were associated with a very low chance of restoring continuity (10% and 0%, respectively), while colitis was associated with a higher chance of restoring continuity (48%). Endoscopic or histological improvement in colitis after defunctioning was associated with a higher rate of restoring continuity (10/16, 63%) compared to no such improvement (4/15, 27%, p = 0.05). Those failing biologics had similar chance of restoration as those not receiving biologics, 15/57 (26%) and 5/19 (26%), respectively. CONCLUSION: Overall response to colonic defunctioning was 41%. Successful restoration of continuity occurred in 27%, but 48% in the absence of perianal disease. Response is appreciably less in the pre-biologic era, so patient and physician expectations need to be managed appropriately.

Subtotal colectomy for ulcerative colitis: lessons learned from a tertiary centre.

AIM: Subtotal colectomy (STC) is a well-established treatment for complicated and refractory ulcerative colitis (UC). A laparoscopic approach offers potentially improved outcomes. The aim of the study was to report our experience with STC for UC in a single large centre. METHOD: From January 2007 to May 2015, all consecutive patients undergoing STC for UC were retrospectively analysed from a prospectively managed database. Patients with known Crohn's disease or those undergoing one-stage procedures were excluded. Demographics, perioperative outcomes and second-stage procedures were analysed. RESULTS: During the study period, 151 STCs were performed for UC [100 emergency (66%) and 51 elective (34%)]. Acute severe colitis refractory to therapy was the most common indication (62%). Overall, 117 laparoscopic (78%) and 34 open STCs were performed, with a conversion rate of 14.5%. Mortality and morbidity rates were 0.7% and 38%, respectively. Whilst operative time was shorter for open STC (by 75 min; P = 0.001), there were fewer complications (32% vs 62%; P = 0.002) and a shorter hospital stay (by 6.9 days; P = 0.0002) following laparoscopic STC. Fewer complications and shorter hospital stay were also observed after elective STC. Patients undergoing laparoscopic STC were more likely to undergo a restorative second-stage procedure than those having open STC (75% vs 50%; P = 0.03). CONCLUSION: Laparoscopic STC for UC is feasible and safe, even in the emergency situation. A laparoscopic approach may offer advantages in terms of lower morbidity and reduced length of stay. Elective resection may offer similar advantages and is best performed whenever possible.