- 标题
- 摘要
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- 实验方案
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Plaid Detectors in Macaque V1 Revealed by Two-Photon Calcium Imaging
摘要： Neuronal responses to one-dimensional orientations are combined to represent two-dimensional composite patterns; this plays a key role in intermediate-level vision such as texture segmentation. However, where and how the visual cortex starts to represent composite patterns, such as a plaid consisting of two superimposing gratings of different orientations, remains neurophysiologically elusive. Psychophysical and modeling evidence has suggested the existence of early neural mechanisms specialized in plaid detection [1–6], but the responses of V1 neurons to an optimally orientated grating are actually suppressed by a superimposing grating of different orientation (i.e., cross-orientation inhibition) [7, 8]. Would some other V1 neurons be plaid detectors? Here, we used two-photon calcium imaging [9] to compare the responses of V1 super?cial-layer neurons to gratings and plaids in awake macaques. We found that many non-orientation-tuned neurons responded weakly to gratings but strongly to plaids, often with plaid orientation selectivity and cross-angle selectivity. In comparison, most (～94%) orientation-tuned neurons showed more or less cross-orientation inhibition, regardless of the relative stimulus contrasts. Only a small portion (～8%) of them showed plaid facilitation at off-peak orientations. These results suggest separate subpopulations of plaid and grating responding neurons. Because most of these plaid neurons (～95%) were insensitive to motion direction, they were plaid pattern detectors, not plaid motion detectors.
关键词： Neuronal Responses,Macaque V1,Cross-Orientation Inhibition,Plaid Detectors,Two-Photon Calcium Imaging
更新于2025-09-16 10:30:52
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Two-photon excited luminescence in POPOP under pulse-periodic laser excitation
摘要： The spectra of two-photon-excited luminescence were registered in a polycrystalline aromatic compound POPOP. The two-photon luminescence in this substance was excited by the second optical harmonic of a solid-state neodymium-doped yttrium lithium fluoride laser (λ = 527 nm) and a copper vapor laser (λ = 510.6 nm). It is shown that the intensity of two-photon-excited luminescence depends nonlinearly on the intensity of an exciting radiation. It has been established that the intensity of the two-photon-excited luminescence is comparable to the intensity of Raman scattering under certain excitation conditions.
关键词： Raman scattering,two-photon excited luminescence,POPOP,laser
更新于2025-09-16 10:30:52
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Modeling and analysis for the position and posture errors of laser focal spot in large-scale fabrication via two photon polymerization
摘要： The position and posture errors of laser focal spot significantly affect the fabrication quality and functionality of microstructures in two photon polymerization, especially over a large area. These errors can be greatly reduced by using ultra-precision positioning device, such as piezoelectric stage and scanning galvanometer. However, the position and posture errors cannot be neglected in large-scale fabrication using large stroke linear stages which are necessary tools in most instances. In the present work, the relationship between the geometric errors of large stroke positioning platform and the position and posture of laser focal spot were revealed and modeled by homogeneous transformation matrix. Key errors affecting on the position and posture of focal spot were found out by sensitivity analysis and compensated during the construction of machine tool. Proof-of-concept experiments were performed in a millimeter-level (1 mm × 1 mm) fabrication of microfluidic whose surface was measured by an optical profiler. The measuring results showed that arithmetical mean height (Sa) and root mean square height (Sq) of the measured surface were less than 100 nm and maximum height (Sz) of the measured surface was less than 500 nm. The compensated machine tool demonstrated a high precise performance within a large continuous area. This work was expected to provide references for the rational layout of optical components in optical system or error compensation in laser process equipment over a large area.
关键词： Laser beam delivery,Position and posture error,Error analysis,Large-scale fabrication,Two photon polymerization
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Time-Energy Entangled Photon Pairs from Doppler-Broadened Atomic Ensemble Via Collective Two-Photon Coherence
摘要： We experimentally demonstrate two-photon interference between a time-energy entangled photon pair generated from Doppler-broadened cascade-type 87Rb atoms using an unbalanced Michelson interferometer. In our system, the CW-mode time-energy entangled photon-pair sources are generated via the SFWM process and the collective two-photon coherence effect of a Doppler-broadened cascade-type atomic ensemble. The coherence time of the two-photon state from the Doppler-broadened atomic ensemble is more than 100 times longer than that of the single-photon state. We investigate two-photon interference (TPI) by means of highly time-resolved coincidence detection and determine the two-photon coherence length of a photon pair from the Doppler-broadened atomic ensemble. We observed fourth-order interference with visibility as high as 97% with the time-energy entangled CW-mode photon pairs from the atomic ensemble for the first time.
关键词： Doppler-Broadened Atomic Ensemble,Quantum Optics,Time-Energy Entangled Photon Pairs,Collective Two-Photon Coherence,Two-Photon Interference
更新于2025-09-12 10:27:22
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GaAs Quantum Dot in a Parabolic Microcavity Tuned to <sup>87</sup> Rb D <sub/>1</sub>
摘要： We develop a structure to efficiently extract photons emitted by a GaAs quantum dot tuned to Rubidium. For this, we employ a broadband microcavity with a curved gold backside mirror which we fabricate by a combination of photoresist reflow, dry reactive ion etching in an inductively coupled plasma and selective wet chemical etching. Precise reflow and etching control allows us to achieve a parabolic backside mirror with a short focal distance of 265 nm. The fabricated structures yield a predicted (measured) collection efficiency of 63 % (12 %), an improvement by more than one order of magnitude compared to unprocessed samples. We then integrate our quantum dot parabolic microcavities onto a piezoelectric substrate capable of inducing a large in-plane biaxial strain. With this approach, we tune the emission wavelength by 0.5 nm/kV, in a dynamic, reversible and linear way, to the Rubidium D1 line (795 nm).
关键词： two-photon resonance fluorescence,strain tuning,microcavity,single-photon source,extraction efficiency,semiconductor quantum dots
更新于2025-09-12 10:27:22
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Two-photon absorption in a two-level system enabled by noise
摘要： We address the textbook problem of dynamics of a spin placed in a dc magnetic field and subjected to an ac drive. If the drive is polarized in the plane perpendicular to the dc field, then the drive photons are resonantly absorbed when the spacing between the Zeeman levels is close to the photon energy. This is the only resonance when the drive is circularly polarized. For a linearly polarized drive, additional resonances corresponding to absorption of three, five, and multiple odd numbers of photons is possible. Interaction with the environment causes the broadening of the absorption lines. We demonstrate that the interaction with environment enables the forbidden two-photon absorption. We adopt a model of the environment in the form of random telegraph noise produced by a single fluctuator. As a result of the synchronous time fluctuations of different components of the random field, the shape of the two-photon absorption line is non-Lorentzian and depends dramatically on the drive amplitude. This shape is a monotonic curve at strong drive, while, at weak drive, it develops a two-peak structure reminiscent of an induced transparency on resonance.
关键词： environment interaction,absorption spectrum,noise,two-photon absorption,telegraph noise,Floquet description,two-level system
更新于2025-09-12 10:27:22
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New Approach for Pulsed-Laser Testing That Mimics Heavy-Ion Charge Deposition Profiles
摘要： A novel approach for two-photon absorption (TPA) pulsed-laser testing produces extended charge deposition profiles that are analogous to those produced by heavy ions. In this approach, which utilizes an axicon rather than a spherical lens, the conventional Gaussian beam is replaced by a quasi-Bessel beam. The key feature of a quasi-Bessel beam, relevant to pulsed-laser single-event effects (PL-SEE) studies, is that its radial size (~1 μm) remains constant over the axial length of the beam (several 100s of μm) resulting in a charge-deposition profile that more closely mimics that produced by a heavy ion. This elongated charge distribution directly lends itself to a simple and intuitive description in terms of linear-energy transfer, or LET, facilitating laser/ion correlation studies. Experimental results comparing a conventional TPA PL-SEE focusing geometry and the axicon focusing geometry are presented for three different test vehicles: a 45-nm SOI nFET, a bulk silicon photodiode, and an LM 124 operational amplifier. Using the axicon approach, strong laser/ion correlation is observed in the silicon photodiode for single-event transients (SET) across a wide range of LETs. The correlation is achieved by “tuning” the laser to the desired LET rather than relying on pre-existing heavy-ion data and therefore this approach holds promise as a predictive tool.
关键词： single-event effect (SEE),silicon,Correlation methods,single-event transient (SET),heavy-ion testing,pulsed-laser,two-photon absorption,linear energy transfer (LET)
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Soliton-Plasma Interactions and Dispersive-Wave Emission Beyond Two-Photon Resonances in Gas-Filled Hollow Capillary Fibres
摘要： Recently we have demonstrated soliton effects at high energy (0.3 mJ) in helium- and neon-filled hollow capillary fibres (HCF) [1]. We observed pulse self-compression to single-cycle durations and the generation of deep (DUV) and vacuum ultraviolet (VUV) radiation at record energy levels for a tunable source. Here, we demonstrate that soliton dynamics in capillary fibres can also be accessed with argon- and krypton-filled HCF, although ionisation effects then start to play a larger role. We also find that the DUV and VUV generation through resonant dispersive-wave (RDW) emission can be achieved at wavelengths considerably shorter than the two-photon resonances in each gas—something surprising, given previous work in gas-filled photonic crystal fibres HC-PCF [2], where soliton-related effects have been previously extensively explored at μJ pulse energy levels [3].
关键词： two-photon resonances,soliton-plasma interactions,dispersive-wave emission,gas-filled hollow capillary fibres
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Increasing Two-Photon Polymerization Fabrication Speed of 3D Structures for Cell Interaction Studies
摘要： Expanding cell studies and tissue engineering from a 2D platform to a 3D mimic of their natural environment demands fabrication methods capable of creating scaffolds covering large volumes with feature sizes down to a few μm. Two-photon polymerization (TPP) is a direct writing method capable of fabricating free-form 3D structures with sub-wavelength features and is therefore well-suited for template fabrication for cell motility and tissue engineering. We demonstrate 9 times increased fabrication speed for 3D periodic structures using a diffractive optical element (DOE) that creates 9 beamlets from one femtosecond laser beam. The parallelized method maintains fabrication quality and each beamlet is used for the fabrication of the base structures that form the periodic pattern. Two 3D designs were fabricated from bio-compatible SZ2080 polymer, where the distance between structures are accurately matching the distance between beamlets. Both of the fabricated structure arrays consists of 3x3 patterns with 9 individual structures in each pattern and covers an area of 450x450 μm. The first design contains unsupported interconnections between individual structures and field-of-views (FOV’s). The second design contains additional supporting structures that stabilize those interconnections between individual structures and FOV’s. For the first design high similarity is observed between the individual base structures inside each FOV, while at the stitching positions between different FOV’s discrepancies are observed leading to gaps in the overall periodic pattern. The gaps arise from contraction of the polymer material during the development process and subsequently drying process. It is related to large leapfrog movement of the stage system (>150 μm) between FOV’s. In the second design, additional support was added between individual one voxel thin structures to overcome this problem. Using this strategy, no gaps are observed and any remaining mismatch is less than 100 nm for stitching of structures. Additional studies were performed where HeLa-cells were incubated for 24 hours on both scaffolds and cell affinity is studied. We observe in both cases that HeLa-cells attach to wall and corner segments of the periodic designs and furthermore HeLa-cells are seen stretching the full length of the individual wall segments. In summary, we show that parallelization of the fabrication process has the potential to make TPP a fast method for large volume periodic 3D structure.
关键词： Two-photon polymerization,cell interaction studies,fabrication speed,diffractive optical element,3D structures
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Photon Correlations in PT-Symmetric Waveguide Systems
摘要： Parity-Time (PT)-symmetric systems have been intensely studied since their first description by Bender & Boettcher in 1998 [1]. Especially in photonics, numerous PT-symmetric effects and systems were investigated [2]. However, all of these experiments used classical light or single photons. Here, we present the first observation of two-photon interference in a lossy directional coupler and its associated Hong-Ou-Mandel (HOM) dip. In optics, PT symmetric potentials can be realized by enforcing a symmetric real part of the refractive index and an antisymmetric imaginary part (gain/loss) [3]. Notably, the transition to the quantum-optical regime precludes one from deploying gain [4], thus, we make use of entirely passive systems: By choosing an appropriate loss distribution, the behaviour of the system can be separated into a global loss factor and the desired non-Hermitian dynamics [5]. In this vein, the object of our following considerations is a passive PT-symmetric coupler in which two waveguides interact over a distance z, see Fig. 1 A. Rapid microscopic undulations of the waveguide trajectory serve to introduce effectively constant Markovian losses, resulting in the desired complex index distribution (B). Fig. 1. (A) In a pair of coupled waveguides, rapid undulations introduce bending losses and the (B) effective complex index distribution. (C) Dependence of the two-photon coincidence on the propagation length in the coupler. In contrast to the Hermitian case, PT-symmetry systematically displaces the dip minimum towards shorter propagation lengths, as indicated by the vertical dashed red line. In the experiment (D), corresponding coincidence data were obtained for Hermitian and PT-symmetric couplers. We achieved a dip with a visibility of 87±2 % and the minimum at 3 cm in the Hermitian case, and in the PT case 90±4 % at a position of 2.75 cm. We theoretically describe light propagation in the lossy directional coupler by a quantum master equation in Lindblad form. Our rigorous approach provides information on the full quantum state of the system. It is based on a Lie algebra treatment that provides us with an eigen-decomposition of the density matrix. The analytical solution holds for the unbroken PT-symmetry case, i.e. for losses that do not exceed twice the coupling. The resulting coincidence function for a |1,1> input state is plotted in Fig. 1 C: In the Hermitian case, the HOM dip occurs at exactly half the coupling length. In contrast, the interference minimum occurs after a shorter propagation length in the PT-symmetric system, as the vertical dashed line indicates. For the experiment, a set of lossy directional couplers of identical couplings with different propagation lengths was implemented to sample light at different z positions. A corresponding set of conventional Hermitian couplers served as baseline reference. Our measurements were executed with pairs of indistinguishable photons obtained by type-I spontaneous parametric down conversion, the coincidences at the sample output were recorded by avalanche photo detectors. In conclusion, our theoretical and experimental findings indicate that the asymmetric loss distribution in the PT-symmetric case can systematically accelerate the quantum interference dynamics in comparison to the Hermitian case.
关键词： PT-symmetric systems,two-photon interference,quantum optics,non-Hermitian dynamics,Hong-Ou-Mandel dip
更新于2025-09-12 10:27:22