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1.
J Neurol Neurosurg Psychiatry ; 95(2): 142-150, 2024 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-37775266

RESUMO

BACKGROUND: The assessment of treatment response is a crucial step for patients with relapsing-remitting multiple sclerosis on disease-modifying therapies (DMTs). We explored whether a scoring system developed within the MAGNIMS (MRI in Multiple Sclerosis) network to evaluate treatment response to injectable drugs can be adopted also to oral DMTs. METHODS: A multicentre dataset of 1200 patients who started three oral DMTs (fingolimod, teriflunomide and dimethyl fumarate) was collected within the MAGNIMS network. Disease activity after the first year was classified by the 'MAGNIMS' score based on the combination of relapses (0-≥2) and/or new T2 lesions (<3 or ≥3) on brain MRI. We explored the association of this score with the following 3-year outcomes: (1) confirmed disability worsening (CDW); (2) treatment failure (TFL); (3) relapse count between years 1 and 3. The additional value of contrast-enhancing lesions (CELs) and lesion location was explored. RESULTS: At 3 years, 160 patients experienced CDW: 12% of them scored '0' (reference), 18% scored '1' (HR=1.82, 95% CI 1.20 to 2.76, p=0.005) and 37% scored '2' (HR=2.74, 95% CI 1.41 to 5.36, p=0.003) at 1 year. The analysis of other outcomes provided similar findings. Considering the location of new T2 lesions (supratentorial vs infratentorial/spinal cord) and the presence of CELs improved the prediction of CDW and TFL, respectively, in patients with minimal MRI activity alone (one or two new T2 lesions). CONCLUSIONS: Early relapses and substantial MRI activity in the first year of treatment are associated with worse short-term outcomes in patients treated with some of the oral DMTs.


Assuntos
Esclerose Múltipla Recidivante-Remitente , Esclerose Múltipla , Humanos , Esclerose Múltipla/tratamento farmacológico , Imunossupressores/efeitos adversos , Esclerose Múltipla Recidivante-Remitente/diagnóstico por imagem , Esclerose Múltipla Recidivante-Remitente/tratamento farmacológico , Cloridrato de Fingolimode/uso terapêutico , Recidiva
2.
Mult Scler ; : 13524585241274600, 2024 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-39263885

RESUMO

BACKGROUND: Evidence on the impact of dimethyl fumarate (DMF) during pregnancy in women with multiple sclerosis (MS) is limited. OBJECTIVES: To investigate disease activity and pregnancy outcomes in a retrospective cohort of women exposed to DMF in early pregnancy. METHODS: Women discontinuing DMF after pregnancy confirmation were identified from 29 Italian MS Centers. Disease activity 12 months before conception, during pregnancy, and 12 months postpartum were recorded, exploring reactivation predictors. Pregnancy and fetal outcomes were assessed. RESULTS: The study analyzed 137 pregnancies (12 pregnancy losses, 125 live births) from 137 women (mean age 32.9 ± 4.7 years), discontinuing DMF within a median (interquartile range (IQR)) interval of 4.9 (3.7-5.7) weeks from conception. In live birth pregnancies, annualized relapse rate (ARR) significantly decreased during pregnancy (ARR = 0.07, 95% confidence interval (CI): 0.03-0.14, p = 0.021) compared to pre-conception (ARR = 0.21 (95% CI: 0.14-0.30)) and increased postpartum ((ARR = 0.22 (95% CI: 0.15-0.32), p = 0.006). Median time to first relapse (TTFR) was 3.16 (IQR: 1:87-5.42) months. Higher pre-conception relapse number (hazard ratio (HR) = 2.33, 95% CI: 1.08-5.02) and Expanded Disability Status Scale (EDSS; HR = 1.81, 95% CI: 1.17-2.74) were associated with shorter TTFR, while treatment resumption with longer TTFR (HR = 0.29, 95% CI: 0.11-0.74). Fetal outcomes were unaffected by DMF exposure. CONCLUSION: DMF discontinuation does not increase relapse risk during pregnancy. Early therapy restart prevents postpartum relapses. Early DMF exposure shows no adverse fetal outcomes.

3.
Rheumatol Int ; 2024 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-38976028

RESUMO

Currently, standardized magnetic resonance imaging (MRI) scoring systems and protocols for assessment of idiopathic inflammatory myopathies (IIMs) in children and adults are lacking. Therefore, we will perform a scoping review of the literature to collate and evaluate the existing semi-quantitative and quantitative MRI scoring systems and protocols for the assessment and monitoring of skeletal muscle involvement in patients with IIMs. The aim is to compile evidence-based information that will facilitate the future development of a universal standardized MRI scoring system for both research and clinical applications in IIM. A systematic search of electronic databases (PubMed, EMBASE, and Cochrane) will be undertaken to identify relevant articles published between January 2000 and October 2023. Data will be synthesized narratively. This scoping review seeks to comprehensively summarize and evaluate the evidence on the scanning protocols and scoring systems used in the assessment of diagnosis, disease activity, and damage using skeletal muscle MRI in IIMs. The results will allow the development of consensus recommendations for clinical practice and enable the standardization of research methods for the MRI assessment of skeletal muscle changes in patients with IIMs.

4.
Int J Mol Sci ; 25(8)2024 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-38674141

RESUMO

A few cases of multiple sclerosis (MS) onset after COVID-19 vaccination have been reported, although the evidence is insufficient to establish causality. The aim of this study is to compare cases of newly diagnosed relapsing-remitting MS before and after the outbreak of the COVID-19 pandemic and the impact of COVID-19 vaccination. Potential environmental and genetic predisposing factors were also investigated, as well as clinical patterns. This is a single-centre retrospective cohort study including all patients who presented with relapsing-remitting MS onset between January 2018 and July 2022. Data on COVID-19 vaccination administration, dose, and type were collected. HLA-DRB1 genotyping was performed in three subgroups. A total of 266 patients received a new diagnosis of relapsing-remitting MS in our centre, 143 before the COVID-19 pandemic (until and including March 2020), and 123 during the COVID-19 era (from April 2020). The mean number of new MS onset cases per year was not different before and during the COVID-19 era and neither were baseline patients' characteristics, type of onset, clinical recovery, or radiological patterns. Fourteen (11.4%) patients who subsequently received a new diagnosis of MS had a history of COVID-19 vaccination within one month before symptoms onset. Patients' characteristics, type of onset, clinical recovery, and radiological patterns did not differ from those of patients with non-vaccine-related new diagnoses of MS. The allele frequencies of HLA-DRB1*15 were 17.6% and 22.2% in patients with non-vaccine-related disease onset before and during the COVID-19 era, respectively, while no case of HLA-DRB1*15 was identified among patients with a new diagnosis of MS post-COVID-19 vaccine. In contrast, HLA-DRB1*08+ or HLA-DRB1*10+ MS patients were present only in this subgroup. Although a causal link between COVID-19 vaccination and relapsing-remitting MS cannot be detected, it is interesting to note and speculate about the peculiarities and heterogeneities underlying disease mechanisms of MS, where the interactions of genetics and the environment could be crucial also for the follow-up and the evaluation of therapeutic options.


Assuntos
Vacinas contra COVID-19 , COVID-19 , Cadeias HLA-DRB1 , Haplótipos , SARS-CoV-2 , Humanos , Feminino , Masculino , Cadeias HLA-DRB1/genética , Adulto , COVID-19/genética , COVID-19/prevenção & controle , COVID-19/imunologia , COVID-19/epidemiologia , Vacinas contra COVID-19/efeitos adversos , Vacinas contra COVID-19/imunologia , Estudos Retrospectivos , SARS-CoV-2/genética , SARS-CoV-2/imunologia , Pessoa de Meia-Idade , Vacinação , Esclerose Múltipla Recidivante-Remitente/genética , Esclerose Múltipla Recidivante-Remitente/imunologia , Esclerose Múltipla/genética , Predisposição Genética para Doença
5.
Clin Exp Rheumatol ; 41(2): 370-378, 2023 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-36762744

RESUMO

OBJECTIVES: Sporadic inclusion body myositis (IBM) is a debilitating idiopathic inflammatory myopathy (IIM) which affects hand function, ambulation, and swallowing. There is no approved pharmacological therapy for IBM, and there is a lack of suitable outcome measure to assess the effect of an intervention. The IBM scientific interest group under IMACS reviewed the previously used outcome measures in IBM clinical studies to lay the path for developing a core set of outcome measures in IBM. METHODS: In this systematised review, we have extracted all outcome measures reported in IBM clinical studies to determine what measures were being used and to assess the need for optimising outcome measures in IBM. RESULTS: We found 13 observational studies, 17 open-label clinical trials, and 15 randomised control trials (RCTs) in IBM. Six-minute walk distance, IBM-functional rating scale (IBM-FRS), quantitative muscle testing, manual muscle testing, maximal voluntary isometric contraction testing, and thigh muscle volume measured by MRI were used as primary outcome measures. Twelve different outcome measures of motor function were used in IBM clinical trials. IBM-FRS was the most used measure of functionality. Swallowing function was reported as a secondary outcome measure in only 3 RCTs. CONCLUSIONS: There are inconsistencies in using outcome measures in clinical studies in IBM. The core set measures developed by the IMACS group for other IIMs are not directly applicable to IBM. As a result, there is an unmet need for an IBM-specific core set of measures to facilitate the evaluation of new potential therapeutics for IBM.


Assuntos
Miosite de Corpos de Inclusão , Miosite , Humanos , Músculo Esquelético , Miosite/complicações , Avaliação de Resultados em Cuidados de Saúde , Caminhada
6.
Int J Mol Sci ; 24(13)2023 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-37446317

RESUMO

BACKGROUND: Sporadic inclusion body myositis (s-IBM) represents a unique disease within idiopathic inflammatory myopathies with a dual myodegenerative-autoimmune physiopathology and a lack of an efficacious treatment. Circulating miRNA expression could expand our knowledge of s-IBM patho-mechanisms and provide new potential disease biomarkers. To evaluate the expression of selected pre-amplified miRNAs in the serum of s-IBM patients compared to those of a sex- and age-matched healthy control group, we enrolled 14 consecutive s-IBM patients and 8 sex- and age-matched healthy controls. By using two different normalization approaches, we found one downregulated and three upregulated miRNAs. hsa-miR-192-5p was significantly downregulated, while hsa-miR-372-3p was found to be upregulated more in the s-IBM patients compared to the level of the controls. The other two miRNAs had a very low expression levels (raw Ct data > 29). hsa-miR-192-5p and hsa-miR-372-3p were found to be significantly dysregulated in the serum of s-IBM patients. These miRNAs are involved in differentiation and regeneration processes, thus possibly reflecting pathological mechanisms in s-IBM muscles and potentially representing disease biomarkers.


Assuntos
MicroRNA Circulante , MicroRNAs , Miosite de Corpos de Inclusão , Miosite , Humanos , MicroRNA Circulante/genética , Miosite de Corpos de Inclusão/genética , MicroRNAs/metabolismo , Biomarcadores
7.
Rep Prog Phys ; 85(6)2022 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-35294930

RESUMO

Since the first demonstration of the generation of attosecond pulses (1 as = 10-18s) in the extreme-ultraviolet spectral region, several measurement techniques have been introduced, at the beginning for the temporal characterization of the pulses, and immediately after for the investigation of electronic and nuclear ultrafast dynamics in atoms, molecules and solids with unprecedented temporal resolution. The attosecond spectroscopic tools established in the last two decades, together with the development of sophisticated theoretical methods for the interpretation of the experimental outcomes, allowed to unravel and investigate physical processes never observed before, such as the delay in photoemission from atoms and solids, the motion of electrons in molecules after prompt ionization which precede any notable nuclear motion, the temporal evolution of the tunneling process in dielectrics, and many others. This review focused on applications of attosecond techniques to the investigation of ultrafast processes in atoms, molecules and solids. Thanks to the introduction and ongoing developments of new spectroscopic techniques, the attosecond science is rapidly moving towards the investigation, understanding and control of coupled electron-nuclear dynamics in increasingly complex systems, with ever more accurate and complete investigation techniques. Here we will review the most common techniques presenting the latest results in atoms, molecules and solids.

8.
Opt Express ; 30(8): 12248-12267, 2022 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-35472864

RESUMO

The first step to gain optical control over the ultrafast processes initiated by light in solids is a correct identification of the physical mechanisms at play. Among them, exciton formation has been identified as a crucial phenomenon which deeply affects the electro-optical properties of most semiconductors and insulators of technological interest. While recent experiments based on attosecond spectroscopy techniques have demonstrated the possibility to observe the early-stage exciton dynamics, the description of the underlying exciton properties remains non-trivial. In this work we propose a new method called extended Ptychographic Iterative engine for eXcitons (ePIX), capable of reconstructing the main physical properties which determine the evolution of the quasi-particle with no prior knowledge of the exact relaxation dynamics or the pump temporal characteristics. By demonstrating its accuracy even when the exciton dynamics is comparable to the pump pulse duration, ePIX is established as a powerful approach to widen our knowledge of solid-state physics.

9.
Artigo em Inglês | MEDLINE | ID: mdl-35477891

RESUMO

OBJECTIVE: To explore whether age at onset increased over time despite a shortened interval from the initial clinical demyelinating event to the diagnosis of multiple sclerosis (MS), as promoted by updated diagnostic criteria. METHODS: This was an independent, multicentre, retrospective study based on data from 4345 patients with relapsing-onset MS attending three tertiary MS Clinics in Italy. After stratifying the year of MS onset into four periods (<1991, 1991-2000, 2001-2010, 2011-2021), we analysed the temporal trends in age at onset and interval from onset to diagnosis; we then explored the female-to-male ratio and onset location across different classes of age at onset. RESULTS: We observed an increased mean age at onset, and a shortened mean interval to diagnosis over time (p<0.0001). Accordingly, there were more MS onsets at the older age classes of 40-49, 50-59 and ≥60 years (p<0.0001). In cases with age at onset ≥40 years, we also found an increased female-to-male ratio (p=0.007), more frequent spinal cord (p=0.0004) and less frequent supratentorial onset (p=0.008). CONCLUSION: Our study shows a forward shift towards an older age at onset of MS, thus suggesting considerable thought on the place-in-therapy of most currently used disease-modifying treatments, and on the standard of care to an older population.

10.
Opt Express ; 29(7): 9711-9722, 2021 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-33820125

RESUMO

Recent development of spectroscopic techniques based on attosecond radiation has given the community the right tools to study the timing of the photoelectron process. In this work we investigate the effect of Fano resonances in attosecond streaking spectrograms and the application of standard phase-reconstruction algorithms. We show that while the existence of the infrared coupling (ac-Stark shift) hinders the applicability of FROG-like methods, under certain conditions it is still possible to use standard reconstruction algorithms to retrieve the photoemission delay of the bare resonance. Finally, we propose two strategies to study the strength of IR coupling using the attosecond streaking technique.

11.
Neurourol Urodyn ; 40(6): 1500-1508, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34082481

RESUMO

AIMS: Lower urinary tract symptoms are common in multiple sclerosis (MS) and have a great impact on quality of life. We evaluated prevalence and characteristics of urological symptoms in a cohort of patients with MS. METHODS: This is a cross-sectional study conducted on consecutive patients with MS attending our Center in 2018. We evaluated prevalence, clinical features, and response to symptomatic treatments of lower urinary tract disorders; we investigated the relationship between them and clinical and demographic features. Data of urodynamic studies were also collected. RESULTS: In our cohort of 806 patients, the overall prevalence of urological symptoms was 52.9% and urgency was the most frequent symptom (59.4%). Symptomatic patients had a higher disability, a longer disease duration, a later age at onset, and a greater mean age at the time of evaluation. Urinary disorders were more frequent in patients with progressive disease and in women. About 41.8% of patients were under treatment for the urological disorder and 81.5% of them reported an improvement of symptoms. CONCLUSION: Urinary disorders in patients with MS have a high prevalence. An early and correct characterization of types of symptoms and an early and targeted therapeutic strategy are essential to improve the patient's quality of life and avoid future complications.


Assuntos
Sintomas do Trato Urinário Inferior , Esclerose Múltipla , Estudos Transversais , Feminino , Humanos , Sintomas do Trato Urinário Inferior/diagnóstico , Sintomas do Trato Urinário Inferior/epidemiologia , Sintomas do Trato Urinário Inferior/etiologia , Esclerose Múltipla/complicações , Esclerose Múltipla/epidemiologia , Esclerose Múltipla/terapia , Prevalência , Qualidade de Vida , Bexiga Urinária
12.
Opt Express ; 28(7): 10210-10224, 2020 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-32225611

RESUMO

Frequency-resolved optical gating for the complete reconstruction of attosecond bursts (FROG-CRAB) is a well-known technique for the complete temporal characterization of ultrashort extreme ultraviolet (XUV) pulses, with durations down to a few tens of attoseconds. Recently, this technique was extended to few-femtosecond XUV pulses, produced by high-order harmonic generation (HHG) in gases, thanks to the implementation of a robust iterative algorithm: the extended ptychographic iterative engine (ePIE). We demonstrate, by using numerical simulations, that the ptychographic reconstruction technique is characterized by an excellent degree of convergence and robustness. We analyse the effects on pulse reconstruction of various experimental imperfections, namely, the jitter of the relative temporal delay between the XUV pulse and a suitably delayed infrared (IR) pulse and the noise of the measured FROG-CRAB spectrograms. We also show that the ePIE approach is particularly suitable for the reconstruction of incomplete FROG-CRAB spectrograms (i.e., spectrograms with a reduced number of measured time delays) and of spectrograms acquired with a reduced spectral resolution, particularly when relatively high-intensity IR pulses are employed.

13.
Phys Chem Chem Phys ; 21(33): 18380-18385, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31403645

RESUMO

The ultrafast nuclear dynamics of the acetylene cation C2H2+ following photoionization of the neutral molecule is investigated using an extreme-ultraviolet pump/infrared probe setup. The observed modulation of the C2H+ fragment ion yield with pump-probe delay is related to structural changes induced by the extreme-ultraviolet pump pulse taking place on the femtosecond timescale. High-level simulations suggest that the trans-bending and C-C bond stretching motion of the C2H2+ cation govern the observed interaction with the infrared pulse. Depending on the molecular configuration at arrival of the infrared pulse, it either transfers population to higher-lying states or to the C2H2+ ground state, thereby enhancing or lowering the C2H+ yield. Our ultrafast pump-probe scheme can thus be used to track excited state nuclear dynamics with a resolution of a few femtoseconds, leading the way to studying fast dynamics also in larger hydrocarbon molecules.

14.
Opt Express ; 26(6): 6771-6784, 2018 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-29609365

RESUMO

Sub-10-fs pulses tunable in the extreme-ultraviolet (XUV) spectral region are particularly important in many research fields: from atomic and molecular spectroscopy to the study of relaxation processes in solids and transition phase processes, from holography to free-electron laser injection. A crucial prerequisite for all applications is the accurate measurement of the temporal characteristics of these pulses. To fulfill this purpose, many phase retrieval algorithms have been successfully applied to reconstruct XUV attosecond pulses. Nevertheless, their extension to XUV femtosecond pulses is not trivial and has never been investigated/reported so far. We demonstrate that ultrashort XUV pulses, produced by high-order harmonic generation, spectrally filtered by a time-delay compensated monochromator, can be fully characterized, in terms of temporal intensity and phase, by employing the ptychographic reconstruction technique while other common reconstruction algorithms fail. This allows us to report on the generation and complete temporal characterization of XUV pulses with duration down to 5 fs, which constitute the shortest XUV pulse ever achieved via a time-delay compensated monochromator.

15.
Opt Express ; 26(7): 8364-8374, 2018 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-29715804

RESUMO

The precise knowledge of the electric field in close proximity to metallic and dielectric surfaces is a prerequisite for pump-probe experiments aiming at the control of dynamic surface processes. We describe a model to reconstruct this electric field in immediate surface proximity from data taken in photoelectron THz-streaking experiments with an angle-resolved electron analyzer. Using Monte-Carlo simulations we are able to simulate streaking experiments on arbitrary surfaces with a variety of initial electron momentum distributions and to reconstruct the effective electric field at the surface. Our results validate the approach and suggest energy regimes for optimal pulse reconstruction.

16.
Hum Mol Genet ; 22(23): 4748-55, 2013 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-23847048

RESUMO

Mutations in the gene encoding fused-in-sarcoma (FUS) have been identified in a subset of patients with sporadic and familial amyotrophic lateral sclerosis (ALS). Variants in the 3' untranslated region (3'UTR) of FUS have also been reported in ALS patients, but their pathogenic role has not been assessed. We sequenced the whole 3'UTR of FUS in 420 ALS patients who were negative for mutations in the currently known ALS genes and in 480 ethnically matched controls. We detected four 3'UTR variants (c.*48 G>A, c.*59 G>A, c.*108 C>T and c.*110 G>A) in four sporadic and in one familial ALS patients compared with none in controls (P = 0.02).We investigated whether these variants impaired FUS expression in primary fibroblast cultures from three patients harbouring the c.*59 G>A, c.*108 C>T and c.*110 G>A variants, respectively. The pattern of FUS expression was also investigated in fibroblasts from one ALS patient with FUS R521C mutation, in two ALS patients without mutations in the known ALS genes and in four control individuals. By immunostaining and immunoblotting, large amounts of FUS were observed in both the cytoplasm and nuclei of mutant 3'UTR FUS fibroblasts. In FUS R521C mutant fibroblasts, we observed a slight increase of FUS in the cytoplasm associated with a remarkable loss of detection in nuclei. Our findings show that mutations in 3'UTR of FUS are overrepresented in ALS patients and result into translation de-regulation of FUS. Overexpression and mislocalization of wild-type FUS likely contribute to ALS pathogenesis in these cases.


Assuntos
Regiões 3' não Traduzidas , Esclerose Lateral Amiotrófica/genética , Proteína FUS de Ligação a RNA/genética , Proteína FUS de Ligação a RNA/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Esclerose Lateral Amiotrófica/metabolismo , Esclerose Lateral Amiotrófica/patologia , Estudos de Casos e Controles , Núcleo Celular/genética , Núcleo Celular/metabolismo , Células Cultivadas , Citoplasma/metabolismo , Feminino , Regulação da Expressão Gênica , Variação Genética , Humanos , Masculino , Pessoa de Meia-Idade , Mutação , Análise de Sequência de DNA , Adulto Jovem
18.
ACS Photonics ; 11(4): 1673-1683, 2024 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-38645995

RESUMO

High-order harmonic generation (HHG) arising from the nonperturbative interaction of intense light fields with matter constitutes a well-established tabletop source of coherent extreme-ultraviolet and soft X-ray radiation, which is typically emitted as attosecond pulse trains. However, ultrafast applications increasingly demand isolated attosecond pulses (IAPs), which offer great promise for advancing precision control of electron dynamics. Yet, the direct generation of IAPs typically requires the synthesis of near-single-cycle intense driving fields, which is technologically challenging. In this work, we theoretically demonstrate a novel scheme for the straightforward and compact generation of IAPs from multicycle infrared drivers using hollow capillary fibers (HCFs). Starting from a standard, intense multicycle infrared pulse, a light transient is generated by extreme soliton self-compression in a HCF with decreasing pressure and is subsequently used to drive HHG in a gas target. Owing to the subcycle confinement of the HHG process, high-contrast IAPs are continuously emitted almost independently of the carrier-envelope phase (CEP) of the optimally self-compressed drivers. This results in a CEP-robust scheme which is also stable under macroscopic propagation of the high harmonics in a gas target. Our results open the way to a new generation of integrated all-fiber IAP sources, overcoming the efficiency limitations of usual gating techniques for multicycle drivers.

19.
Struct Dyn ; 11(4): 044303, 2024 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-39175799

RESUMO

Understanding photoinjection in semiconductors-a fundamental physical process-represents the first step toward devising new opto-electronic devices, capable of operating on unprecedented time scales. Fostered by the development of few-femtosecond, intense infrared pulses, and attosecond spectroscopy techniques, ultrafast charge injection in solids has been the subject of intense theoretical and experimental investigation. Recent results have shown that while under certain conditions photoinjection can be ascribed to a single, well-defined phenomenon, in a realistic multi-band semiconductor like Ge, several competing mechanisms determine the sub-cycle interaction of an intense light field with the atomic and electronic structure of matter. In this latter case, it is yet unclear how the complex balance between the different physical mechanisms is altered by the chosen interaction geometry, dictated by the relative orientation between the crystal lattice and the laser electric field direction. In this work, we investigate ultrafast photoinjection in a Ge monocrystalline sample with attosecond temporal resolution under two distinct orientations. Our combined theoretical and experimental effort suggests that the physical mechanisms determining carrier excitation in Ge are largely robust against crystal rotation. Nevertheless, the different alignment between the laser field and the crystal unit cell causes non-negligible changes in the momentum distribution of the excited carriers and their injection yield. Further experiments are needed to clarify whether the crystal orientation can be used to tune the photoinjection of carriers in a semiconductor at these extreme time scales.

20.
Light Sci Appl ; 13(1): 197, 2024 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-39164239

RESUMO

Isolated attosecond pulse (IAP) generation usually involves the use of short-medium gas cells operated at high pressures. In contrast, long-medium schemes at low pressures are commonly perceived as inherently unsuitable for IAP generation due to the nonlinear phenomena that challenge favourable phase-matching conditions. Here we provide clear experimental evidence on the generation of isolated extreme-ultraviolet attosecond pulses in a semi-infinite gas cell, demonstrating the use of extended-medium geometries for effective production of IAPs. To gain a deeper understanding we develop a simulation method for high-order harmonic generation (HHG), which combines nonlinear propagation with macroscopic HHG solving the 3D time-dependent Schrödinger equation at the single-atom level. Our simulations reveal that the nonlinear spatio-temporal reshaping of the driving field, observed in the experiment as a bright plasma channel, acts as a self-regulating mechanism boosting the phase-matching conditions for the generation of IAPs.

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