Safety and efficacy of direct oral anticoagulants in patients with atrial fibrillation on concomitant treatment with dronedarone

Funding Acknowledgements

Type of funding sources: None.

Introduction

The use of direct oral anticoagulants (DOACs) in patients with atrial fibrillation (AF) is associated with bleedings. Interactions with dronedarone may increase this risk, but data on concomitant treatment of DOACs with dronedarone are limited.

Purpose

The primary endpoint was to compare the survival free from the composite endpoint of clinically relevant bleeding, thromboembolic event and all-cause death, between AF patients on treatment with dronedarone and different DOACs. The secondary endpoints were to compare the survival free from i) clinically relevant bleeding and ii) clinically relevant major bleeding.

Methods

A retrospective study was conducted at our Local Health Unit, from January 1st 2016 to December 31st 2020. The population included AF patients with concomitant prescriptions of DOACs and dronedarone. Patients were divided into 4 groups (rivaroxaban, apixaban, edoxaban, dabigatran). Clinically relevant major bleedings were defined as fatal bleeding or bleeding leading to transfusion of ≥2 units of blood. Clinically relevant non-major bleedings were defined as any sign of hemorrhage that does not fit the criteria for major bleeding but does lead to hospitalization or emergency room admission. Thromboembolic events were defined as ischemic stroke, transient ischemic attack (TIA), and systemic embolism.

Results

165 patients were included: 46/165 (28%) on rivaroxaban, 66/165 (40%) on apixaban, 45/165 (27%) on edoxaban, and 8/165 (5%) on dabigatran (Fig.1). Over a median follow-up of 339 days, 14/165 (8%) met the primary composite endpoint: 8/165 (5%) had clinically relevant bleedings, of which 1/165 (0.6%) was a clinically relevant major bleeding (i.e., fatal spontaneous intracerebral hemorrhage), 2/165 (1%) had TIAs, and 5/165 (3%) died. We found no difference in survival free from the primary composite endpoint and from clinically relevant bleeding between groups (p=0.19 and p=0.69, respectively) (Fig. 2A-B). However, survival free from clinically relevant major bleeding was significantly lower in dabigatran users (p=0.003) (Fig. 2C). At a secondary analysis, DOACs contraindicated by 2015 EHRA guide (dabigatran, edoxaban 60 mg), and not by 2018/2021 EHRA guides (rivaroxaban, dabigatran, edoxaban 60 mg), were associated with lower survival from either clinically relevant bleeding or clinically relevant major bleeding (p=0.03 and p<0.001, respectively).

Conclusions

In our study on patients on concomitant treatment with DOACs and dronedarone, there was no difference in survival free from the primary composite endpoint and from clinically relevant bleeding between groups of coadministration. However, survival free from clinically relevant major bleeding was significantly lower in dabigatran users. DOACs contraindicated by 2015 EHRA guide (and not by the latest 2018/2021 EHRA guides) are associated with lower survival from either clinically relevant bleeding or clinically relevant major bleeding.

C51 SAFETY AND EFFICACY OF DIRECT ORAL ANTICOAGULANTS IN PATIENTS WITH ATRIAL FIBRILLATION ON CONCOMITANT TREATMENT WITH DRONEDARONE

Background

The use of direct oral anticoagulants (DOACs) in patients with atrial fibrillation (AF) is associated with bleedings. Interactions with dronedarone may increase this risk, but data on concomitant treatment of DOACs with dronedarone are limited.

Aim

The primary endpoint was to compare the survival free from the composite endpoint of clinically relevant bleeding, thromboembolic event and death, between AF patients on treatment with dronedarone and different DOACs. The secondary endpoints were to compare the survival free from i) clinically relevant bleeding and ii) clinically relevant major bleeding.

Methods

A retrospective study was conducted at the Local Health Unit “Ulss3 Serenissima” of Venice, Italy, from January 1st 2016 to December 31st 2020. The eligible population included AF patients with concomitant prescriptions of DOACs and dronedarone. Patients were divided in 4 groups (rivaroxaban, apixaban, edoxaban, dabigatran).

Results

165 patients were included: 46/165 (28%) on rivaroxaban, 66/165 (40%) on apixaban, 45/165 (27%) on edoxaban, and 8/165 (5%) on dabigatran (Fig.1). Over a median follow–up of 339 days, 14/165 (8%) met the primary composite endpoint: 8/165 (5%) had clinically relevant bleedings, of which 1/165 (0.6%) was a clinically relevant major bleeding, 2/165 (1%) had TIAs, and 5/165 (3%) died. We found no difference in survival free from the primary composite endpoint and from clinically relevant bleeding between groups (log–rank test p = 0.19 and p = 0.69, respectively) (Fig. 2A–B). However, survival free from clinically relevant major bleeding was significantly lower in dabigatran users (p = 0.003) (Fig. 2C). At a secondary analysis, DOACs contraindicated by 2015 EHRA guide (dabigatran, edoxaban 60 mg), and not by 2018/2021 EHRA guides (rivaroxaban, dabigatran, edoxaban 60 mg), were associated with lower survival from either clinically relevant bleeding or clinically relevant major bleeding (log–rank test p = 0.03 and p < 0.001, respectively) (Fig. 3).

Conclusions

In our study, there was no difference in survival free from the primary composite endpoint and from clinically relevant bleeding between groups of coadministration. However, survival free from clinically relevant major bleeding was significantly lower in dabigatran users. DOACs contraindicated by 2015 EHRA guide (and not by the latest 2018/2021 EHRA guides) are associated with lower survival from either clinically relevant bleeding or clinically relevant major bleeding.

P202 PRETREATMENT WITH ANTAGONISTS OF P2Y12 PLATELETS RECEPTORS IN ST–ELEVATION MYOCARDIAL INFARCTION: CLINICAL AND ANGIOGRAPHIC OUTCOMES

Background

The use of antagonists of P2Y12 platelets receptors as antiplatelets drugs is a cornerstone in the treatment of ACS. Many efforts are made to understand the right timing of beginning this therapy with the purpose to reduce intra– and periprocedural complications (stent thrombosis, no reflow phenomenon). The rationale behind “pretreatment” (administration of antagonists of P2Y2 platelet receptor before the coronarography) is valuable but the evidences are lacking, also in the setting of ACS–STEMI.

Method and Objectives

We conduct an observational, monocentric (Ospedale dell’Angelo – Venezia Mestre), retrospective study including patients with STEMI (1st January 2016 – 9th august 2018). We compared two strategies of administration of clopidogrel, ticagrelor and prasugrel (pretreatment vs no pretreatment). Primary endpoints were bleeding BARC 3–5, acute or subacute stent thrombosis and TIMI flow grade > 0 in the culprit coronary. Secondary endpoints were cardiovascular and no cardiovascular in–hospital mortality and in–hospital neurological complications.

Results

We studied 501 patients (199 in the group pretreated and 302 in the group no pretreated). The median time from first medical contact to PCI was 70,5 minutes in the pretreated group and 60 minutes in the no pretreated group (p = 0.022). No significant differences between the two groups were observed in terms of acute or subacute stent thrombosis (OR 3.72 [0.82–14.20], p = 0.09) e TIMI flow grade > 0 in the culprit coronary (OR 1.11 [0.77–1.58], p = 0.58). In the multivariate analysis we observed that bleeding BARC 3–5 significantly were increased in the pretreated group (adjusted OR 2.78 [1.13–6.83, p = 0.025). In the subgroup analysis, the pretreated subjects with age > 75 were at augmented risk of bleeding BARC 3–5.

Conclusions

Pretreatment in the setting of ACS–STEMI is not associated with benefits in terms of acute or subacute stent thrombosis and perfusion of culprit coronary but may cause clinically relevant bleedings, in particular in the elderly (age > 75).

P2 IMPACT OF CATHETER ABLATION ON ARRHYTHMIC STORM: A SINGLE–CENTER EXPERIENCE

Background

Arrhythmic storm (AS) is a medical emergency whom management is multidisciplinary and includes antiarrhythmic medications, sedation and mechanical circulatory support, as well as catheter ablation, a procedure that is gaining growing relevance in clinical practice, supported by guidelines.

Methods and Aims

It is a retrospective observational study of patients admitted to Cardiology Department of Ospedale dell’Angelo for AS from 2016 to 2021. The primary endpoint was the rate of arrhythmic recurrences and their clinical predictors; the secondary endpoint was a composite of all– cause death, LVAD or cardiac transplant. Successful CA was defined as no inducibility of any VT at the end of the procedure.

Result

We evaluated 74 patients. Catheter ablation (CA) was performed in 56 patients, while in the other 18 patients, the treatment of the arrhythmic emergency was limited to medical therapy. At a median follow–up of 10 months (range 4–36 months), the overall arrhythmic recurrence rate was 39.1% and AS recurrence occurred in 11% of patients; the incidence of the composite end–point of all–cause death, LVAD implant or cardiac transplant was 20.2%. B–blockers (85% vs 100%, p = 0.025) and successful CA (60% vs 88.6%, p = 0.021) were associated with less arrhythmic recurrences. At multivariate analysis, a successful CA was an independent predictor of arrhythmic recurrence free survival (HR 0.32, [0.11–0.94], p = 0.039), and of ICD shocks free survival (HR 0.087, [0.02–0.37], p = 0.001). ICD shocks at admission (8.06 ± 9.8 vs 3.18 ± 4.24, p = 0.005), NYHA class III–IV (46.6% vs 5%, p = 0.001), medical treatment (53.3% vs 83%, p = 0.031), ICD shocks during follow–up (53.3% vs 18,6%, p = 0.004) and AS recurrence (33.3% vs 10.1%, p = 0.039) were associated with an increased rate of the secondary endpoint.

Conclusions

In our real world experience of patients admitted for AS, CA was a predictor of arrhythmic recurrence free survival and may have a role in improving quality of life and prognosis by reducing ICD shocks. CA was an independent predictor of the reduced incidence of all–cause death, LVAD implant or cardiac transplant, although this finding might reflect a more severe cardiac disease of the medically treated patients than a real benefit of CA on mortality.

P146 A CASE OF TYROSINE–KINASE INHIBITOR INDUCED CARDIOTOXICITY

This case is about a 69 years–old woman with no prior cardiovascular disease and a history of rheumatoid arthritis;in 2017 underwent right nephrectomy for renal cancer. A few weeks before admission, due to evidence of secondary bone lesions at a follow–up CT–scan, a single dose of the tyrosine kinase inhibitor (TKI) Nivolumab was administered. On the same evening she suffered from a severe reacutization of arthritic symptoms, that led her Oncologist to suspend treatment with nivolumab, and oral corticosteroid therapy was initiated. The following weeks remained though characterized by intense persistent asthenia, severe arthralgias, profuse diarrhea and a syncopal episode; no chest pain was reported. Given the persistence of symptoms, she went to the Emergency Room. Initial work–up revealed a complete heart block, with a previously unknown right bundle branch block (see Figure 1). At blood tests there was a significant increase of troponin I to 7616 ng/L (Normal<12ng/L), BNP 1113 pg/mL (NR < 100 pg/mL), creatinine 2.34 mg/dL (NR 0.55–1.02mg/dL), CPK 1681 U/L (NR 10–145 U/L) and D–dimer 17780 mcg/L (NR < 600). She was immediately transferred to our Cardiologic Intensive Care Unit, where an echocardiogram showed normally functioning ventricular chambers and no valvulopathies. Due to the ongoing acute kidney injury and the history of right nephrectomy, a coronary angiography was not immediately performed, considering the low probability of ACS (no typical symptoms, no regional wall motion abnormalities).Suspecting nivolumab–induced myocarditis, high–dose glucocorticoids were initiated. After a few days we observed persistence of bradycardia and complete AV block despite isoprenaline infusion, and due to signs of peripheral malperfusion (acute kidney injury, hypotension) a definitive leadless pace–maker Micra was implanted (this choice given the need of immunosuppressive therapy that could predispose her to device infections). After normalization of renal function, we performed a coronary angiography that showed normal coronary arteries. Despite the initial improvement of the clinical conditions, the patient suffered a fatal cardiac arrest due to electromechanical dissociation 3 weeks after admission. This case report is an important example showing the significant mortality of cardiotoxicity induced by tyrosine–kinase inhibitors, a side effect that every Cardiologist must be aware of in order to recognize it and immediately intervene with the appropriate therapy.

On the equilibrium bifurcation of axially deformable holonomic systems: solution of a long-standing enigma

The stability of equilibrium is a fundamental topic in mechanics and applied sciences. Apart from its central role in most engineering fields, it also arises in many natural systems at any scale, from folding/unfolding processes of macromolecules and growth-induced wrinkling in biological tissues to meteorology and celestial mechanics. As such, a few key models represent essential benchmarks in order to gain significant insights into more complex physical phenomena. Among these models, a cornerstone is represented by a structure made of two straight axially deformable bars, connected by an elastic hinge and simply supported at the ends, which are capable of buckling under a compressive axial force. This classical example has been proposed and analysed in some depth by Feodosyev but the attention is here focused on an apparently paradoxical result given by this model, i.e. the existence of a lower bound for the axial-to-flexural stiffness ratio in order for the bifurcation to take place. This enigma is solved theoretically by showing that, differently from other classical stability problems, constitutive and geometric nonlinearities cannot be a priori disconnected and an ideal linearized axial constitutive law cannot be employed in this case. The theory is validated with an experiment, and post-buckling and energy extrema of the proposed solution are discussed as well, highlighting possible snap-back and snap-through phenomena. Finally, the results are extended to the complementary case of tensile buckling.

Bulky auxeticity, tensile buckling and deck-of-cards kinematics emerging from structured continua

Complex mechanical behaviours are generally met in macroscopically homogeneous media as effects of inelastic responses or as results of unconventional material properties, which are postulated or due to structural systems at the meso/micro-scale. Examples are strain localization due to plasticity or damage and metamaterials exhibiting negative Poisson’s ratios resulting from special porous, eventually buckling, sub-structures. In this work, through ad hoc conceived mechanical paradigms, we show that several non-standard behaviours can be obtained simultaneously by accounting for kinematical discontinuities, without invoking inelastic laws or initial voids. By allowing mutual sliding among rigid tesserae connected by pre-stressed hyperelastic links, we find several unusual kinematics such as localized shear modes and tensile buckling-induced instabilities, leading to deck-of-cards deformations—uncapturable with classical continuum models—and unprecedented ‘bulky’ auxeticity emerging from a densely packed, geometrically symmetrical ensemble of discrete units that deform in a chiral way. Finally, after providing some analytical solutions and inequalities of mechanical interest, we pass to the limit of an infinite number of tesserae of infinitesimal size, thus transiting from discrete to continuum, without the need to introduce characteristic lengths. In the light of the theory of structured deformations, this result demonstrates that the proposed architectured material is nothing else than the first biaxial paradigm of structured continuum —a body that projects, at the macroscopic scale, geometrical changes and disarrangements occurring at the level of its sub-macroscopic elements.

Towards a patient-specific estimation of intra-operative femoral fracture risk

Total Hip Arthroplasty requires pre-surgical evaluation between un-cemented and cemented prostheses. A Patient with intra-operative periprosthetic fracture and another with a successful outcome were recruited, and their finite element models were constructed by processing CT data, assuming elastic-plastic behavior of the bone as function of the local density. To resemble the insertion of the prosthesis into the femur, a fictitious thermal dilatation is applied to the broach volume. Strain-based fracture risk factor is estimated, depicting results in terms of the total mechanical strain expressed using a simple "traffic lights" color code to provide immediate, concise, and intelligible pre-operative information to surgeons.

Microgel assisted Lab-on-Fiber Optrode

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.

Novel Approaches for the Treatment of Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal disorder characterized by increased levels of total cholesterol and low density lipoprotein (LDL) cholesterol.The extent of underdiagnosis and undertreatment of individuals with FH is largely unknown.The LDL-lowering capacity of statins in combination with other lipid-lowering drugs is maximally around 50-60%. FH patients have a strongly elevated LDL-C and in most cases maximal current treatment is not sufficient to reach the desired LDL targets.Therefore, FH patients have a large residual cardiovascular risk despite the use of statins and there is a medical need for new additional drugs to further lower LDL-C in patients with FH to improve their prognosis.PCSK9 inhibitors have shown great efficacy in lowering lipids with very few side effects. No synergism between statins and PCSK9 inhibition was observed in many trials, allowing clinicians to select a statin dose before considering the initiation of PCSK9-inhibitor therapy.In patients with FH, who are at risk for markedly accelerated atherosclerosis and premature cardiovascular death, also treatment with lomitapide or mipomersen has the potential to reduce the risk of atherosclerotic cardiovascular disease and premature mortality.These new drugs will be probably reserved for the most severely affected FH patients and could help clinicians to reduce their residual cardiovascular risk.

Disputes in the Treatment of Diabetic Nephropathy: The Dual Blockade of Renin-Angiotensin System

The prevention and the treatment with drugs interacting with the renin-angiotensin system (RAAS) are one of the greatest successes of the pharmacological research in the last years. Many trials demonstrated the efficacy of ARBs and ACEi in preventing or reducing the progression of albuminuria, the loss of kidney function and the mortality in diabetic population.The rationale for applying a dual RAAS blockade is based on data showing that ACEi mono-therapy produces an incomplete RAAS blockade with angiotensin I and renin accumulation and the subsequent angiotensin II 'escape' production by non-ACE pathways. The use of ARBs and ACEi in combination could lead to a stronger RAAS block and consequently to a more effective nephroprotection. Years ago, some studies performed in small groups of patients with diabetic nephropathy confirmed the effectiveness of this pharmacological approach.In contrast recent important trials, like ONTARGET, ALTITUDE and VA NEPHRON-D failed to demonstrate the effectiveness of this therapeutic strategy, suggesting that probably not all the diabetic patients with nephropathy should be considered equal as regard the response to this therapy. These 3 long-term studies showed that the dual blockade of RAAS may bring cardiovascular and renal adverse events, even in presence of a reduction of albuminuria. Dual blockade of RAAS is not currently feasible in patients with diabetic nephropathy, but we consider that the effort to try to apply a complete RAAS blockade should be pursued and that probably through an accurate selection of patients in the future we could reconsider this kind of therapy.

The role of viscoelasticity and stress gradients on the outcome of conductive keratoplasty

A mechanical analysis of the conductive keratoplasty on hyperopic eyes has been carried out, and the attention has been focused on incorporating the actual viscoelastic properties of the human corneal tissue and on the stress gradients induced by the intervention. By avoiding unnecessary complications which may obscure the essential behaviour of the model, the results are in very good agreement with the clinical and experimental findings and suggest that the major role in the commonly observed decrease of the initial degree of the refractive correction might be played by the stress gradients at the intervention spots, which are likely to influence the wound-healing. The study aims to contribute some firm mechanical roots to the predictability of the outcome of an increasingly popular technique that, notwithstanding several advantages with respect to ablative interventions, at present cannot be considered completely satisfactory.

Long period grating working in transition mode as promising technological platform for label-free biosensing

We present the development of a platform for label-free biosensing based on overlayered Long Period Gratings (LPGs) working in transition mode. Nano-scale layers of Polystyrene (PS) with different thicknesses were deposited onto the same LPG to test the performances of the device in different working points of its modified sensitivity characteristic. Adsorption dynamic of biotinylated bovine serum albumin (BBSA) onto the PS overlays was on-line monitored as well as a subsequent streptavidin (SA) binding dynamic on the biotinylated sites of the protein ad-layer. Experimental results show that overlayered LPGs are among the most sensitive refractive index transducers to be employed in label-free biochemical detection and that wide margins of further optimization exist.

Micro-structured fiber Bragg gratings: optimization of the fabrication process

This work has been devoted to present and demonstrate a novel approach for the fabrication of micro-structured fiber Bragg gratings (MSFBGs) with enhanced control of the geometric features and thus of the spectral properties of the final device. The investigated structure relies on the localized stripping of the cladding layer in a well defined region in the middle of the grating structure leading to the formation of a defect state in the spectral response. In order to fully explore the versatility of MSFBGs for sensing and communications applications, a technological assessment of the fabrication process aimed to provide high control of the geometrical features is required. To this aim, here, we demonstrate that the optimization of this device is possible by adopting a fabrication process based on polymeric coatings patterned by high resolution UV laser micromachining tools. The function of the polymeric coating is to act as mask for the HF based chemical etching process responsible for the cladding stripping. Whereas, UV laser micromachining provides a valuable method to accurately pattern the polymeric coating and thus obtain a selective stripping along the grating structure. Here, we experimentally demonstrate the potentiality of the proposed approach to realize reliable and cost efficient MSFBGs enabling the prototyping of advanced photonics devices based on this technology.

Immediate- and late-hemodynamic coronary effects of tadalafil in men with erectile dysfunction and coronary artery disease

We investigated whether coronary flow reserve (CFR) can be modified by tadalafil, a long-acting phosphodiesterase 5 (PDE5) inhibitor, in patients with documented coronary artery disease (CAD). CFR was non-invasively evaluated in 12 men with a positive history for erectile dysfunction (ED) and angiographically documented CAD, in the distal portion of the left anterior descending coronary artery, free from critical stenosis, with contrast enhanced echocardiography at time zero (T0). Then, after 20 mg tadalafil was orally administered CFR measurement was repeated after 2 h (T1) and after 24 h (T2). Doppler curves suitable for the analysis were obtained in all patients (CFR feasibility: 100%). The peak diastolic velocity after adenosine infusion increased from 71.3+/-14.3 cm/s at T0 to 82.5+/-24.0 at T1 (P=NS) and to 89.5+/-21.1 at T2 (P=0.0010). CFR after tadalafil increased significantly from 2.6+/-0.3 at T0 to 3.1+/-0.7 at T1 (P=0.0078) and a further increment was found at T2 (3.5+/-0.9; P=0.0010 vs T0). Our study shows that oral administration of tadalafil exerts a long standing, potentially beneficial effect on coronary microvasculature in patients with ED.

Near field behavior of SnO(2) particle-layer deposited on standard optical fiber by electrostatic spray pyrolysis method

We report the emergent optical near field profiles from standard single mode optical fibers on the cleaved end of which were deposited particle layers of SnO(2). The layers, composed of micron and sub-micron sized particles, were deposited by means of Electrostatic Spray Pyrolysis (ESP) technique. Powerful analytical tools such as Atomic Force Microscopy (AFM) and Scanning Near-field Optical Microscopy (SNOM) were used to obtain simultaneously the SnO(2) layers topography and the related optical near field intensity distribution, when the fiber-substrate is illuminated by a light radiation in NIR range. We show that isolated microstructures, positioned in correspondence of the fiber core, reveal highly unusual capability of locally enhancing the collected optical near field. The observed phenomenon leads to new concepts of fiber optic chemical sensors and in fiber microsystems as well.

Mode transition in high refractive index coated long period gratings

In this work, the numerical and experimental investigation of the cladding modes re-organization in high refractive index (HRI) coated Long Period Gratings (LPGs) is reported. Moreover, the effects of the cladding modes re-organization on the sensitivity to the surrounding medium refractive index (SRI) have been outlined. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness) and on the SRI. In particular, if layer parameters are properly chosen, the transition of the lowest order cladding mode into an overlay mode occurs. As a consequence, a cladding modes re-organization can be observed leading to relevant improvements in the SRI sensitivity in terms of wavelength shift and amplitude variations of the LPGs attenuation bands.

Contactless optoelectronic technique for monitoring epoxy cure

We describe a novel noninvasive optical technique to monitor the refractive-index variation in an epoxy-based resin that is due to the polymerization process. This kind of resin is widely used in polymer matrix composites. It is well known that the process of fabricating a thermoset-based composite involves mass and heat transfer coupled with irreversible chemical reactions that induce physical changes. To improve the quality and the reliability of these materials, monitoring the cure and optimization of the manufacturing process are of key importance. We discuss the basic operating principles of an optical system based on angle deflection measurements and present typical cure-monitoring results obtained from optical characterization. The method provides a flexible, high-sensitivity, material-independent, low-cost, noninvasive tool for monitoring real-time refractive-index variation.

Effect of fabrication errors in channel waveguide Bragg gratings

The spectral performances of nonideal rectangular Bragg gratings, integrated in a rib waveguide, are analyzed by a multilayer approach based on the effective-index method. The effects of errors on the photolithographic definition of the grating, that is, period and shape, and of errors on the control of etching depth are investigated. Also the influence of the stitching error, which is unavoidable when the grating is realized by means of electron-beam photolithography, is addressed. A novel analytical approach that extends coupled-mode theory to the analysis of real gratings is also presented.

Real-time measurement of transverse-mode-mixing effects in a Q-switched Nd:YAG laser

We describe a novel apparatus for the real-time characterization of transverse-mode-mixing effects by monitoring the fluctuations of the M(2) factor defined by Siegman [Proc. Soc. Photo-Opt. Instrum. Eng. 1224, 2 (1990)]. A comparison between the results provided by our approach and those obtained by the use of a standard measurement apparatus has shown a satisfactory agreement within the experimental uncertainty.

Transverse mode analysis of a laser beam by near- and far-field intensity measurements

A quantitative measurement of laser-beam quality can be performed by determination of the presence of multiple transverse modes of the laser oscillator and by calculation of their power content. Along this line of argument, we discuss a new approach that, starting from near-field and far-field intensity measurements, can evaluate the complex excitation coefficients of the transverse modes in a laser beam. The exploitation of near-field measurements sharply improves the performances of the technique in those cases in which only far-field measurements are used. The validity of the method is confirmed by several accurate numerical simulations and by some experimental results relative to a multimode Q-switched Nd:YAG laser.

Characterization of the transverse modes in a laser beam: analysis and application to a Q-switched Nd:YAG laser

We have developed a numerical code that, starting from far-field intensity measurements, is able to evaluate the excitation coefficients of the transverse modes in a laser system.Both the coherent and incoherent mode cases are addressed, and, while the incoherent case is shown to be equivalent to a linear problem, the coherent case is discussed through its equivalence to the phase-retrieval problem. Problems arising from both ill posedness and the nonlinearity are discussed in detail.The validity of our approach is confirmed by several numerical simulations and some experimental results on the characterization of a Q-switched Nd:YAG laser.

Tapered and inhomogeneous dielectric light concentrators

A detailed analysis of tapered and inhomogeneous dielectric light collectors was worked out for both illumination and solar energy applications. In particular, tapered dielectric guides have been investigated both theoretically and experimentally together with their capability to collect and transmit high fluxes of light energy. Furthermore, GRIN rods are considered as matching devices, to improve the collecting performance of tapered guides.

Optoelectronic technique for the characterization of high concentration gas-solid suspension

We describe a simple technique for measuring high (up to 0.16) time-averaged solids volumetric concentration in a two-phase flow. The technique is based on a properly modified version of the forward scattering of laser light. It is useful in a variety of practical configurations, and, in particular, it is instrumental in the diagnostics of particle flow in the free board of bubbling fluidized beds and in the circulating fluidized beds. A fallout of this work is the measurement of the extinction coefficient of the solid material tested.

Cavity dumping for free electron lasers

The cavity dumping technique, applied to free electron lasers (FEL), is described. Taking advantage of both numerical simulations and experimental results on the Mark III FEL, a fairly exhaustive analysis is reported. In particular, we show that the output peak power can be increased by a factor even higher than one hundred. The cavity dumping experiment, under way on the Mark III FEL, is discussed in some detail.

Mode size and time duration fluctuations in a picosecond Nd:YAG laser

A new technique is successfully used to analyze in real time the pulse-to-pulse fluctuations of mode size and time duration in a picosecond Nd:YAG laser. In particular we show that the pulse length (30 psec) of our active-passive mode-locked Nd:YAG laser is stable to within 10% when the cavityis perfectly tuned and the saturable absorber is fresh. This technique is experimentally shown to be effective and reliable for real-time analysis of the stability of ultrashort laser pulses undera broad range of experimental conditions.

Mode characterization, autocorrelation measurements, and harmonic conversion with pico- and femtosecond pulses delivered by the Mark III free-electron laser

After briefly reporting on the present status of the infrared free-electron laser now operating at the Stanford Photon Research Laboratory and powered by the linear accelerator Mark III, we discuss the results of using nonlinear optical techniques for both the characterization of its output radiation and the enhancment of its tunability range. In particular, to show the evidence of possible self-guiding effects, a new and reliable technique has been devised and successfully tested for real-time monitoring of the micropulse evolution during the buildup of radiation. Finally, we discuss the main problems connected with the damage threshold of optical materials.

Acoustooptical suppression of sideband instabilities in free electron lasers

We describe an electronically tunable intracavity filter, based on the acoustooptic effect, that suppresses the sideband instabilities in a free electron laser. Different configurations are analyzed, and the problems encountered in the design and construction of a broadband acoustic transducer are discussed in some detail. In addition, some preliminary experimental results on the construction of broadband acoustic transducers are reported. The main advantages of this device are high damage threshold, low insertion losses, good tunability, and easy handling.

Tunable electrooptic intracavity filter for sideband suppression in free electron lasers

We describe a tunable intracavity filter, which, taking advantage on the electrooptic effect, limits the growth of the sidebands in a free electron laser and even suppresses them in some cases.

Absorptance enhancement for laser metal processing: application to steel samples

We describe a reliable technique that noticeably increases the absorptance of a metal surface without any change in its chemical and physical properties, obtained through a chemically induced enhancement of the surface roughness. The main advantages of this method are low cost, easy handling, and low tolerances. A set of optical and mechanical measurements was performed to gain a detailed knowledge of the technique.

Alignment and performance of almost concentric resonators for low gain free-electron lasers

The propagation of mismatched and misaligned laser beams bouncing back and forth between the mirrors of an almost concentric resonator is investigated with reference to the alignment of the cavities used for low gain free-electron lasers. In addition, the excitation of the cavity modes by the spontaneous radiation of a linear undulator is analyzed by considering the reduction of their coupling factors due to the misadjustment of the optical cavity with respect to the axis and the center of the undulator. In particular, analytical expressions are given for the coupling coefficients of two misaligned sets of Gauss-Laguerre or Gauss-Hermite modes and for the coupling factors between the cavity modes and the spontaneous radiation.