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Spatial coherence of electrically pumped random terahertz lasers

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Photonics Research 2022年第2期10卷 524-534页

作者： eva A.A.Pogna Alessandra Di Gaspare Kimberly Reichel Chiara Liberatore harvey e.beere David A.Ritchie Miriam S.Vitiello NeST CNR-Istituto Nanoscienze-Scuola Normale Superiore56127 PisaItaly Cavendish Laboratory University of CambridgeCambridge CB3 OHEUK

Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz(THz) spectral regions, which host a large variety of molecular absorptions and distinctive fingerprints to be exploited for sensing and tomography. Here, we characterize the spatial coherence of random multimode THz quantum cascade lasers(QCLs) emitting > m W optical power per mode and showing low divergence(10°–30°), performing a modified Young’s double-slit experiment. Partial spatial coherence values ranging between 0.16 and 0.34 are retrieved, depending on the specific degree of disorder. These values are significantly lower than those(0.82) of conventional Fabry–Perot THz QCLs exploiting an identical active region quantum design. We then incorporate the devised low spatial coherence random lasers into a confocal imaging system with micrometer spatial resolution and demonstrate notable imaging performances, at THz frequencies,against spatial cross talk and speckles.

关键词： pumped random quantum

Frequency-tunable continuous-wave random lasers at terahertz frequencies

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Light(Science & Applications) 2019年第1期8卷 828-840页

作者： Simone Biasco harvey e.beere David A.Ritchie Lianhe Li AGiles Davies edmund H.Linfield Miriam S.Vitiello NeST CNR-Istituto Nanoscienze and Scuola Normale SuperiorePiazza San Silvestro 1256127 PisaItaly Cavendish Laboratory University of CambridgeCambridge CB30HEUK School of electronic and electrical engineering University of LeedsLeeds LS29JTUK

Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence.However,for many applications ranging from sensing and spectroscopy to speckle-free imaging,it is essential to have high-radiance sources operating in continuous-wave(CW).In this paper,we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional(2D)random distribution of air holes is patterned into the top metal waveguide.We obtain a highly collimated vertical emission at ~3 THz,with a 430 GHz bandwidth,device operation up to 110 K,peak(pulsed)power of 21 mW,and CW emission of 1.7 mW.Furthermore,we show that an external cavity formed with a movable mirror can be used to tune a random laser,obtaining continuous frequency tuning over 11 GHz.

关键词： tunable tuning pumped

Graphene-loaded metal wire grating for deep and broadband THz modulation in total internal reflection geometry

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Photonics Research 2018年第12期6卷 1151-1157页

作者： YIWeN SUN RICCARDO DeGLJINNOCeNTI DAVID A.RITCHIe harvey e.beere LONG XIAO MICHAeL RUGGIeRO J.AXeL ZeITLeR RAYKO I.STANTCHeV DANNI CHeN ZHeNGCHUN PeNG eMMA MACPHeRSON XUDONG LIU National-Regional Key Technology engineering Laboratory for Medical Ultrasound Guangdong Key Laboratory for Biomedical Measurements and Ultrasound ImagingDepartment of Biomedical EngineeringSchool of MedicineShenzhen UniversityShenzhen 518060China Cavendish Laboratory University of CambridgeJ J Thomson AvenueCambridge CB30HEUK Department of electrical engineering and Computer Science Massachusetts Institute of TechnologyCambridgeMassachusetts 02139USA Department of Chemistry University of Vermont82 University PlaceBurlingtonVermont 05405USA Department of Chemical engineering and Biotechnology University of CambridgePembroke StreetCambridge CB2 3RAUK Department of electronic engineering The Chinese University of Hong KongHong KongChina Key Laboratory of Ministry of education for Optoelectronic Devices and Systems College of Optoelectronic EngineeringShenzhen University Shenzhen 518060China Department of Physics University of WarwickGibbet Hill RoadCoventry CV4 7ALUK

We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO_2∕Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.

关键词： modulation depth (MD) graphene Wire grating

Continuous-wave laser operation of a dipole antenna terahertz microresonator

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Light(Science & Applications) 2017年第1期6卷 512-516页

作者： Luca Masini Alessandro Pitanti Lorenzo Baldacci Miriam S Vitiello Riccardo Degl’Innocenti harvey e.beere David A Ritchie Alessandro Tredicucci NeST CNR-Istituto Nanoscienze and Scuola Normale SuperiorePiazza San Silvestro 1256127 PisaItaly Cavendish Laboratory University of CambridgeJJ Thomson AvenueCambridge CB30HEUK NeST CNR-Istituto Nanoscienze and Dipartimento di Fisica‘E.Fermi’Universitàdegli studi di Pisa56127 PisaItaly

Resonators and the way they couple to external radiation rely on very different concepts if one considers devices belonging to the photonic and electronic worlds.The terahertz frequency range,however,provides intriguing possibilities for the development of hybrid technologies that merge ideas from both fields in novel functional designs.In this paper,we show that high-quality,subwavelength,whispering-gallery lasers can be combined to form a linear dipole antenna,which creates a very efficient,lowthreshold laser emission in a collimated beam pattern.For this purpose,we employ a terahertz quantum-cascade active region patterned into two 19-μm-radius microdisks coupled by a suspended metallic bridge,which simultaneously acts as an inductive antenna and produces the dipole symmetry of the lasing mode.Continuous-wave vertical emission is demonstrated at approximately 3.5 THz in a very regular,low-divergence(±10°)beam,with a high slope efficiency of at least 160 mWA^(−1) and a mere 6 mA of threshold current,which is ensured by the ultra-small resonator size(VReS/λ^(3)≈10^(−2)).The extremely low power consumption and the superior beam brightness make this concept very promising for the development of miniaturized and portable THz sources to be used in the field for imaging and sensing applications as well as for exploring novel optomechanical intracavity effects.

关键词： microresonators optical antennas quantum cascade laser terahertz whispering-gallery

Kaoline-based catalyst for a high stability desulfurization of sour heavy naphtha in a three-phase oscillatory baffled reactor

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Particuology 2024年第1期84卷 249-260页

作者： Hassan M.Hmood Saba A.Gheni Safaa M.R.Ahmed Mudheher M.Ali Hamid Yonis Saleh Mohammed H.Mohammed Awad e.Mohammed Marwan A.Mahomood Hiba R.Mohammed Ahmed A.Hassan Adam harvey North Refineries Company Ministry of OilIraq Chemical engineering Department Tikrit UniversityIraq Ministry of Oil Iraq AL-Hawija Technical Institute Northern Technical UniversityMoselIraq School of engineering Newcastle UniversityUK

To meet the rapidly increasing demand for energy and the dramatic depletion of conventional crude oil,it is imperative to utilize sour naphtha.With no coke being produced,oxidative desulfurization(ODS)of naphtha lowers its sulfur content and average molecular weight.In this article,we outline a method for heavy naphtha non-extractive ODS using a very stable catalyst.The technique involves the use of a solid catalyst with oxygen gas as the oxidant.This necessitated relatively high mixing intensities;hence a three-phase Oscillatory Baffled Reactor(OBR)was used.The catalyst was based on the zeolite ZSM-5,prepared from natural kaolin by a series of delamination and activation steps and impregnated with Fe.A TiO2 nanolayer was applied,using the sol-gel method,to prevent rapid deactivation.The reactor performance was evaluated to minimize the sulfur content in the naphtha fuel.Due to the protective coating,the sulfur conversion stabilized at 90%.The results of this work establish the use of natural clay-based catalysts in a continuous,three-phase ODS,particularly with regard to proving long-term stability.It also showed that modest ODS can be achieved using an environmentally friendly oxidant,at mild operating conditions,whilst maintaining stability.

关键词： Natural kaoline Desulfurization Three-phase Oscillatory baffled reactor

Differentiation and functional connectivity of fetal tectal transplants

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Neural Regeneration Research 2023年第11期18卷 2325-2331页

作者： Alan R.harvey School of Human Sciences The University of Western AustraliaLions Eye Instituteand Perron Institute for Neurological and Translational ScienceNedlandsWAAustralia

Data from studies analyzing the differentiation and functional connectivity of embryo nic neural tissue grafted into the mammalian nervous system has led to the clinical testing of the fetal graft approach in patients with neurodegenerative disease.While some success has been achieved,ethical concerns have led to a search for alternative therapeutic strategies,mostly exploring the use of neural precursors or neurons derived from pluripotent stem cells to replace damaged host neurons and restore lost circuitries.These more recent studies address questions of graft viability,differentiation,and connectivity similar to those posed by researchers in earlier fetal transplant work,thus reviews of the fetal graft literature may inform and help guide ongoing research in the stem cell/organoid field.This brief review describes some key observations from research into the transplantation of neural tissue into the rat visual syste m,focusing on grafts of the fetal supe rior colliculus(tectal grafts) into neonatal or adult hosts.In neonate hosts,grafts quickly develop connections with the underlying host mid b rain and attain a morphology typical of mature grafts by about 2 weeks.G rafts consistently contain numerous localized regions which,based on neurofibrillar staining,neuronal morphology(Golgi),neurochemistry,receptor expression,and glial architecture,are homologous to the stratum griseum supe rficiale of normal superior colliculus.These localized "patches" are also seen after explant culture and when donor tectal tissue is dissociated and reaggregated prior to transplantation.In almost all circumstances,host retinal innervation is restricted to these localized patches,but only those that are located adjacent to the graft surfa ce.Synapses are formed and there is evidence of functional drive.The only exception occurs when Schwann cells are added to dissociated tecta prior to reaggregation.In these co-grafts,the peripheral glia appear to compete with local target fa ctors and host retinal ingrowth is more widespread.Othe

关键词： axon regeneration differentiation embyronic grafts fetal tissue neural precursors retinotectal stem cells superior colliculus synaptogenesis transplantation

Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns

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Light(Science & Applications) 2020年第1期9卷 1498-1508页

作者： Simone Biasco Andrea Ciavatti Lianhe Li AGiles Davies edmund H.Linfield harvey beere David Ritchie Miriam S.Vitiello NeST CNR-Istituto Nanoscienze and Scuola Normale SuperiorePiazza San Silvestro 1256127 PisaItaly School of electronic and electrical engineering University of LeedsLeeds LS29JTUK Cavendish Laboratory University of CambridgeCambridge CB30HEUK

Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation.Once implemented on the top surface of a semiconductor laser,a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature.Therefore,this methodology offers the possibility to achieve efficient emission,combined with tailored spectra and controlled beam divergence.Here,we apply this concept to a onedimensional quantum cascade wire laser.By lithographically patterning a series of air slits with different widths,following the Octonacci sequence,on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies,we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth,achieving a maximum peak optical power of 240mW(190 mW)in multimode(single-frequency-mode)lasers,with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η≈1%.

关键词： lasers surface quantum

A route to enhanced performance for the petawatt beamlines of the Orion laser facility

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High Power Laser Science and engineering 2022年第3期10卷 11-18页

作者： e.J.harvey AWe AldermastonReadingRG74PRUK

The Orion laser facility at AWe provides multiple beams to target delivering synchronized pulses at both nanosecond and sub-picosecond duration.In the latter,the peak power approaches the petawatt level.This paper presents a conceptual design for potential development of these beamlines.This would deliver a significant enhancement of performance at the fundamental level.In addition,a new approach is described for the management of frequency conversion at high intensity,which may allow significantly enhanced performance at the second harmonic also.

关键词： chirped pulse amplification frequency doubling temporal contrast

Generation and Regulation of CD8^+ Regulatory T Cells

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Cellular & Molecular Immunology 2008年第6期5卷 401-406页

作者： Linrong Lu harvey Cantor Department of Cancer Immunology ＆ AIDS Dana-Farber Cancer Instituteand Department of Pathology Harvard Medical School Boston MA 02115USA Institute of Immunology Zhejiang University School of MedicineHangzhou China Corresponding to： Dr. harvey Cantor Department of Cancer Immunology ＆ AIDS Dana-Farber Cancer Institute and Department of Pathology Harvard Medical School 44 Binney Street Boston MA 02115 USA

Research into the suppressive activity of CD4＋FoxP3＋ T regulatory cells （Treg） has defined a sublineage of CD4＋ cells that contribute to self-tolerance and resistance to autoimmune disease. Much less attention has been given to the potential contribution of regulatory sublineages of CD8＋ cells. Analysis of a small fraction of CD8＋ cells that target autoreactive CD4＋ cells through recognition of the MHC class Ib molecule Qa-1 in mouse and HLA-e in human has revitalized interest in CD8＋ Treg. Here we summarize recent progress and future directions of research into the role of this CD8＋ sublineage in resistance to autoimmune disease. Cellular ＆ Molecular Immunology. 2008; 5（6）：401-406.

关键词： CD8＋ regulatory T cell self-tolerance autoimmune disease eAe Qa-1 NKG2A