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Nonlinear optical susceptibility of atomically thin WX2 crystals
摘要： We have studied tungsten diselenide (WSe2) and tungsten disulfide (WS2) monolayer materials in second harmonic generation spectroscopy and microscopy experiments. Ultra-broadband continuum pulses served as the fundamental beam while its second harmonic spectrum in the visible and ultraviolet (UV) range was detected and analyzed with a better than 0.3 nm spectral resolution (< 2 meV). We provide dispersion data and absolute values for χ(2) for the materials within a photon energy range of 2.3–3.2 eV. Fine spectral features that were detected within the dispersion data for the optical nonlinearities indicate the impact of near bandgap exciton transitions. The fundamental bandgap of 2.35 eV and exciton binding energy of 0.38 eV were determined from the measurements for WS2 monolayers while the corresponding values in WSe2 monolayers were 2.22 eV and 0.71 eV. Ranges for the absolute values of the sheet nonlinearity for WS2 and WSe2 are shown to be 0.58–1.65 × 10?18 m2/V and 0.21–0.92 × 10?18 m2/V, correspondingly.
关键词： Nonlinear spectroscopy and microscopy,Transition metal dichalcogenides,Two-dimensional semiconductors,Second harmonic generation,Optical nonlinearity in semiconductors,Monolayer crystals,Optics at interfaces
更新于2025-09-09 09:28:46
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Theory of interacting cavity Rydberg polaritons
摘要： Photonic materials are an emerging platform to explore quantum matter (Carusotto and Ciuti 2013 Rev. Mod. Phys. 85 299; Sommer et al 2015 arXiv:1506.00341) and quantum dynamics (Peyronel et al 2012 Nature 488 57). The development of Rydberg electromagnetically induced transparency (Weatherill et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 201002; Petrosyan et al 2011 Phys. Rev. Lett. 107 213601) provided a clear route to strong interactions between individual optical photons. In conjunction with carefully designed optical resonators, it is now possible to achieve extraordinary control of the properties of individual photons, introducing tunable gauge ?elds (Schine et al 2016 Nature 534 671) whilst imbuing the photons with mass and embedding them on curved spatial manifolds (Sommer et al 2016 New J. Phys. 18 035008). Building on work formalizing Rydberg mediated interactions between propagating photons (Gorshkov et al 2011 Phys. Rev. Lett. 107 133602; Gullans et al 2016 Phys. Rev. Lett. 117 113601), we develop a theory of interacting Rydberg polaritons in multimode optical resonators, where the strong interactions are married with tunable single particle properties to build and probe exotic matter. In the presence of strong coupling between the resonator ?eld and a Rydberg-dressed atomic ensemble, a quasiparticle called the ‘cavity Rydberg polariton’ emerges. We investigate its properties, ?nding that it inherits both the fast dynamics of its photonic constituents and the strong interactions of its atomic constituents. We develop tools to properly renormalize the interactions when polaritons approach each other, and investigate the impact of atomic motion on the coherence of multi-mode polaritons, showing that most channels for atom-polariton cross-thermalization are strongly suppressed. Finally, we propose to harness the repeated diffraction and refocusing of the optical resonator to realize interactions which are local in momentum-space. This work points the way to ef?cient modeling of polaritonic quantum materials in properly renormalized strongly interacting effective theories, thereby enabling experimental studies of photonic fractional quantum Hall ?uids and crystals (Sommer et al 2015 arXiv:1506.00341; Umucal?lar et al 2014 Phys. Rev. A 89 023803; Grusdt and Fleischhauer 2013 Phys. Rev. A 87 043628), plus photonic quantum information processors and repeaters (Jaksch et al 2000 Phys. Rev. Lett. 85 2208; Saffman et al 2010 Rev. Mod. Phys. 82 2313; Han et al 2010 Phys. Rev. A 81, 052311).
关键词： quantum gases,Rydberg polaritons,quantum optics
更新于2025-09-09 09:28:46
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Efficient excitation of dye molecules for single photon generation
摘要： A reliable single photon source is required for many aspects of quantum technology. Organic molecules are attractive for this application because they can have high quantum yield and can be photostable, even at room temperature. To generate a photon with high probability, a laser must excite the molecule efficiently. We develop a simple model for that efficiency and discuss how to optimise it. We demonstrate the validity of our model through experiments on a single dibenzoterrylene (DBT) molecule in an anthracene crystal. We show that the excitation probability cannot exceed 75% at room temperature, but can increase to over 99% if the sample is cooled to liquid nitrogen temperature. The possibility of high photon generation efficiency with only modest cooling is a significant step towards a reliable photon source that is simple and practical.
关键词： single molecules,photon anti-bunching,single photon source,quantum optics,confocal microscopy
更新于2025-09-09 09:28:46
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A new calibration strategy for adaptive telescopes with pyramid WFS
摘要： Several telescopes include large deformable mirrors (DM) located directly inside the telescope. These adaptive telescopes trigger new constraints for the calibration of the adaptive optics (AO) systems as they usually offer no access to an artificial calibration source for the interaction matrix measurement. Moreover, the optical propagation between the DM and the wavefront sensor (WFS) may evolve during the operation, resulting in misregistrations that highly affect the AO performance and thus the scientific observation. They have to be measured and compensated, for instance by updating the calibration. A new strategy consists of estimating the misregistrations and injecting them into synthetic models to generate noise-free interaction matrices. This pseudo-synthetic approach is the baseline for the adaptive optics facility working with a Shack–Hartmann WFS and seems particularly suited for the future Extremely Large Telescope as the calibration will have to be regularly updated, for a large numbers of actuators. In this paper, the feasibility of a pseudo-synthetic calibration with pyramid WFS at the Large Binocular Telescope (LBT) is investigated. A synthetic model of the LBT AO systems is developed, and the procedure to adjust the misregistrations parameters is introduced, extracting them from an experimental interaction matrix. We successfully tested an interaction matrix generated from the model on the real system in high-order AO mode. We recorded a slightly better performance with respect to the experimental one. This work demonstrates that a high-accuracy calibration can be obtained using the pseudo-synthetic approach with pyramid WFS.
关键词： telescopes,instrumentation: adaptive optics
更新于2025-09-09 09:28:46
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Detection and Treatment Systems based on Optics and Photonics in New Age Healthcare Management
摘要： The world is becoming smaller in the means of communication and information but we are yet short to make basic medical needs deliverable universally. There have been many breakthroughs and advancements in the field of medical and healthcare but they fall scant in stature, in terms of taking care of major healthcare problems across the globe. If we look closely, major healthcare problems can be classified as primary and secondary. Accurate diagnosis, treatment and therapies for severe diseases and disorders which are prolonged threat to life form the primary healthcare problems. Secondary health care problems include conditions like trauma, or accidents, or mishaps in daily life. The latter healthcare conditions demand for quick and immediate medical attention for stabilizing the victims and then initiate recovery. Human population is advancing in terms of medical technologies with respect to diagnostic and treatment modalities to tackle serious healthcare issues, but most of the latest medical technologies are available in established centres which are formed by a high economic investment. The high cost makes the technology unavailable to a majority of the population residing in developing countries. In cases of road trauma several factors need to be considered within a small time frame to provide immediate medical supervision, also medical procedures to be provided simultaneously in no time. The loss in time in such cases eventually leads to loss of life or loss of functionality of organs. Excessive losses of blood or internal injuries are most common but are involved with most time consumption for proper attention and diagnosis leading to irreversible lethality to important organs like brain, heart, liver or kidneys. Thus researchers are continuously developing diagnostic and therapeutic systems which are affordable in resource poor settings. Optical technologies provide most suitable approach for deployment in resource poor settings. Optical technologies are continuously evolving and advancing our healthcare systems. Proper utilization and conditioning of light spectrum and exploring optical properties of novel materials have shown promising results for development of medical techniques. Modification, assembly and combination of optical equipment’s can be easily integrated to form dedicated instruments for health anomalies. As a requirement to increase deliverability, solutions need to rely on new components which travel and transfer information faster. Use of light for above purpose can solve all the above mentioned perils and also provide non-invasive and harmless method of diagnosis and treatment. Diagnostic and scanning techniques like PET, X-ray, CT etc. have already employed optical techniques for in vivo imaging and surgery. Endoscopic examination of GIT involves use of light and camera inserted using a flexible tube and a colour TV monitor is the basic example of use of optics for imaging and visualization of disease manifestations [1]. On the other hand, lasers are part of helpful optical instruments in the medical sector from deep vein thrombosis (DVT) to sutures and vessels sealing from time to time [2,3] In case of DVT by ‘Laser Thrombolysis’ (Use of laser pulses to remove the clots) using different sets of lasers and intensity, timings are used to disintegrate the clot without making unnecessary incisions [2-4]. Lasers are also deployed in sensitive surgical procedures for vision impairment owing to its precision, reach, and less invasive properties. Apart from proven aesthetic uses like tattoo and pigmentation removal, optical instruments are also to be utilized in the field of non-invasive patient monitoring systems as optical pulse and oxygen saturation analyser for uninterrupted patient recovery and observation. Various skin diseases are being tested by scope of optical scanning including skin cancer, chronic pain using ‘photo-dynamic therapy’ [2,3]. The scope of optical techniques in diagnostic and therapeutic usage has been described in the adjoining (Figure 1). The use of optics is not restricted to one property or one field but it appears as vast as its extension in spectrum thus the same source and property of light can also be used in other objectives with few changes, establishing its integration compactly and low energy tool developments. These prospects are greatest and most desirable cues for using optical technology in almost every field where portability and ambulatory utilization is very high in demand. Recently, a healthcare company ‘THERANOS’ developed 140 types of testing and analysis with a single drop of blood and has been well received in scientific community [5]. The product signifies the precision, reaching ability, less invasive nature and adaptability to different needs of the system. Similarly, optical characteristic profiling gives strong hope for testing other soft or hard tissue like bone and density and bodily samples as well on the basis of signal processing internally or by sampling them out in very fewer quantities than the existing procedures. In another application of pulse oximetry red and infra-red light is utilized to get the absorbance of dissolved gasses and saturation level of biological carriers like haemoglobin. Continuous monitoring systems like pulse oximetry capable to detect pulse rates, O2 and CO2 gasses saturation level can be deployed [1-2,6-12]. Infrared thermometers or pulse laser thermometers or temperature guns working on the principle of capturing and measuring infrared emittance of a heated body by focusing it to a particular spot; which is not only applicable in medical field but serves very vast field of applications and industrial areas. Lasers and optics make another robust base for telemedicine and remote analysis prospective in healthcare field with appropriate placements and counter check with other indicative and suggestive parameters. Telemedicine and remote analysis can provide a huge possibility for screening by non-invasive method and remote execution. Development of analytic tools in movement and body structure related disorders with added benefit of being non-invasive as in GAIT and posture analysis [2-7]. Different types of lasers are being combined for the therapies like CO2 lasers are used to make incisions in tissues with low vascularity (mostly used in neurosurgery for precision), while on the other hand with Nd-YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) lasers are applicable in high vascular areas and tumour shrinkage, or surgical removal without leaving scars owing to energy dependent concentration where tumours can be thermally destroyed by concentrating the laser beam. This strategy also prevents undue toxicity to normal cells in comparison to other chemotherapeutic methods [2]. It also allows separation of tumours from vital structures minimizing low risk to surrounding tissues in the removal of tumours with surgeries. Use of monochromatic light absorption property different levels of tissues within internal layers can be operated with success [3,4]. Another example is maintenance of secretory activity of small glands glands can be maintained by using a catheter to remove over-secretory regions by flashing laser pulses. Above mentioned properties surely give an upper hand to practitioners and surgeons for performing highly complex procedures in critical areas like brain where collateral damage can lead to severe implications. Needless to mention that these procedures save a lot of time, effort, risk of collateral damage to surrounding tissues, and manage blood loss in comparison to normal surgical procedure subsequently leading to early and sound recovery without any scar formation or associated complications. Conditions associated with brain are most susceptible and irreversible to collateral damage owing to non-repairable nature of brain structures. Cerebral hypoxia associated with trauma cases due to low blood pressure or clot formation and subsequent fall in essential nutrition is one such process which is not completely understood by researchers and physicians. The neurons are dependent for supplies on the blood flow to the brain and other parts of nervous system, and these constant supplies are utilized in the energy production to carry out different duties, most primarily conduction of impulses via interneuron junctions called synapse in a vast interconnected complex network lying all across the brain tissue. Whenever brain is exposed to resource scanty conditions the important physiological responses are hampered as brain doesn’t have any kind of storage facility for energy produced. The brain does not have pain receptors or physical warning signs for indicating ongoing damage which ultimately leads to brain tissue death [1,2-15]. Cerebral hypoxia causes a partial/complete loss of functionality of brain tissues due to degeneration [12-18]. The most alarming part is that the function of that part cannot be restored by any present therapeutic manner as brain tissue doesn’t inhabit the power of regeneration, surgical and chemotherapeutic treatments are also less effective due to complexity of the organ and the presence of blood brain barrier. Invasive procedures for brain trauma treatment are associated with vulnerabilities to damage of other parts of brain. In response to detrimental conditions, at times the brain activates and alters different control mechanisms of normal physiological factors and bodily conditions under its command; towards the values, which are of opposite effect on present danger in order to nullify its further negative effect on neural tissue. The Brain raises cerebral blood pressure and breathing rates by neural control centre to fulfil elevated demand of oxygen or nutrient. Along with these parameters neural activity at brain also increases several folds to prepare and release more counter measures for present dangerous situation, as biochemical messengers responsible to initiate vascularisation and elevate blood pressure at cellular level by constricting blood vessels, are released in bloodstream returning from cerebral region to increase blood vessels [11,14,15-17]. We believe that research in mapping of cerebral hypoxia can be a new prospective area of research to be dealt using optical methodologies. It is also interesting to see the enthusiasm of national and international organizations who are supporting this initiative by financial and resources aid. It will be astonishing if in near future we can develop a whole automated setup based on optical and electrical components capable to capture whole body scans at once without any human intervention especially in remote and resource poor healthcare settings [3,5,19].
关键词： Optical technologies,Diagnostics,Healthcare,Telemedicine,Remote analysis,Therapeutics,Photonics,Lasers,Non-invasive methods,Optics
更新于2025-09-09 09:28:46
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Controllable generation of second-harmonic vortex beams through nonlinear supercell grating
摘要： Lithium niobate (LiNbO3) nonlinear photonic crystals have been widely used in nonlinear wave front modulation for the p-phase difference between the second-harmonic (SH) waves from positive and negative domains. Aided by optimizing algorithms, we can control the diffraction patterns of SH vortex beams by designing nonlinear fork gratings with supercell structures in LiNbO3 crystals. In experiment, we demonstrate that the diffraction energies can be equally distributed in each order or concentrated on certain orders, in agreement with theoretical designs. Potential applications include controllable vortex beam generation, nondestructive parallel vortex detection, and so on.
关键词： quantum information processing,Lithium niobate,optical communication,nonlinear photonic crystals,supercell grating,second-harmonic vortex beams,nonlinear optics
更新于2025-09-09 09:28:46
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Modified physical optics algorithm for near field scattering
摘要： A novel modi?ed physical optics algorithm is proposed to overcome the dif?culties of near ?eld scattering prediction for classical physical optics. The method is applied to calculating the near ?eld radar cross section of electrically large objects by taking into account the in?uence of the distinct wave propagation vector, the near ?eld Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is re?ned both in amplitude and phase terms and allows for near ?eld calculation. The scattered characteristics of the near ?eld targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.
关键词： physical optics,scattering,near ?eld
更新于2025-09-09 09:28:46
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Generation of sustained optimal entropy squeezing of a two-level atom via non-Hermitian operation
摘要： We investigate the entropy squeezing of a two-level atom in the Jaynes–Cummings model, and provide a scheme to generate the sustained optimal entropy squeezing of the atom via non-Hermitian operation. Our results show that the squeezing degree and the persistence time of entropy squeezing of atomic polarization components greatly depend on the non-Hermiticity intensity in non-Hermitian operation. Especially, under a proper choice of non-Hermiticity parameters, the sustained optimal entropy squeezing of the atom can be generated even though the atom is initially prepared in a no entropy squeezing state.
关键词： Jaynes–Cummings model,entropy squeezing,non-Hermitian dynamics,quantum optics
更新于2025-09-09 09:28:46
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Network Topology Reconfiguration for FSO-based Fronthaul/Backhaul in 5G+ Wireless Networks
摘要： Using free space optics (FSO) in the mobile fronthaul/backhaul networks is a promising solution that can potentially enhance the capacity of mobile networks. The main challenge of establishing FSO-based fronthaul/backhaul networks is the dynamic feature of the networks, i.e., the fragile links under adverse weather conditions and the dynamic traf?c demands among small cells. Topology recon?guration is proposed to dynamically rearrange the FSO links. In this paper, two types of network recon?gurations are investigated, in which the proactive network recon?guration is to proactively optimize the topology of the FSO-based fronthaul/ backhaul networks for each speci?c time period based on the statistics of the network, and the reactive recon?guration is to actively adjust the topology when traf?c demands and link states are changed. The proactive network recon?guration is formulated as a mixed integer nonlinear programming (MINLP) problem, which jointly optimizes the network throughput and power consumption of FSO-based fronthaul/backhaul networks. A greedy algorithm is proposed to derive the solution of the proposed problem. After the network topology having been recon?gured by solving the MINLP problem, two reactive recon?guration algorithms are designed to optimally adjust the network topology once a link failure and demand explosion occur, respectively, to further enhance the network throughput and reduce the power consumption. The performance of the algorithms is demonstrated via extensive simulations.
关键词： FSO-based fronthaul/backhaul,multi-criteria optimization,topology recon?guration,free space optics (FSO)
更新于2025-09-09 09:28:46
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Vernier effect of cascaded dual microring sensor
摘要： We demonstrate a Vernier microring sensor consisting of a traditional cascaded dual microring resonator and an additional measurement range unit. The sensor’s performance is simulated for different concentrations of aqueous solutions of ethylene glycol (C2H6O2). The theoretical sensitivity of our system is as high as 7386 nm/RIU, an order of magnitude much larger than that of the traditional cascaded dual microring sensor (562 nm/RIU), 13.1 times more than the traditional cascaded dual microring sensor. At the same time, the measurement range can reach as high as 2.49 × 10?2 RIU.
关键词： measurement range,Integrated optics,Vernier effect,microring sensor
更新于2025-09-09 09:28:46