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A dynamical symmetry triad in high-harmonic generation revealed by attosecond recollision control
摘要： A key element of optical spectroscopy is the link between observable selection rules and the underlying symmetries of an investigated physical system. Typically, selection rules arise from the interaction of its constituents. In light-matter interaction, emergent phenomena are particularly prominent in strongly driven states of matter, as evident in light-induced variants of superconductivity, the Hall effect, and topological insulators in the condensed phase, as well as exceptional points in molecules, Kramers–Henneberger states in gases, and time-crystals in isolated many-body systems. Such emergent states are often governed by novel symmetry properties and topologies, which may be probed by external or emitted radiation fields. Here, we report on the experimental observation of an emergent class of symmetries in the electromagnetic field emitted by a strongly driven atomic system. Specifically, we analyze the sets of allowed and forbidden harmonic orders in high-harmonic generation from tailored bi-circular and bi-elliptical fields. Corroborated by theoretical modeling, the identified selection rules correspond to a complete triad of dynamical symmetries. We believe that the general principles underlying our observations will be equally relevant for other systems, including crystalline solids.
关键词： bi-elliptical fields,optical spectroscopy,high-harmonic generation,dynamical symmetries,selection rules,bi-circular fields,symmetries
更新于2025-09-19 17:13:59
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Alternation of the Mode Synchronization and Desynchronization in Ultrafast Fiber Laser
摘要： Ultrafast fiber lasers offer a unique opportunity to implement optically a Poincaré mapping in the phase space of a variety of complex dissipative dynamical systems operating far from the equilibrium. Understanding of such complex optical dynamical systems revealing, for instance, ultrafast dynamics of the dissipative solitons (DSs) and more complex regimes is important for advancing specification and performance of the mode-locked lasers used in a vast number of applications ranging from spectroscopy and medicine to metrology and telecom. Here, using the mode-locked fiber laser as a test-bed, the Shilnikov-type ultrafast dynamics taking the form of randomly switching between noise-like pulsing and quasi-continuous-wave regimes is experimentally demonstrated. The transient coherence recovery is revealed, during which the noise-like pulse (NLP) is transformed into a coherent DS state and then returned to an incoherent NLP state. The demonstrated alternation of mode synchronization and desynchronization is both of practical importance for developing new types of partially mode-locked lasers and of the fundamental interest for the nonlinear science in the context of revealing routes to the turbulence in distributed nonlinear systems.
关键词： optical spectroscopy,nonlinear optics,fiber laser
更新于2025-09-19 17:13:59
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Optical spectroscopy studies of atom intermixing in the core versus growth temperature of the claddings in MOCVD-grown quantum cascade lasers
摘要： Here we present optical spectroscopy studies to examine structural and optical properties of active region of quantum cascade lasers grown fully by MOCVD technique. The active part is InGaAs/AlInAs based multilayer structure nominally lattice matched to InP substrate. In this communication we study a set of structures with different growth temperature of the cladding layers and its influence on the properties of active core. The x-ray spectroscopy (XRD) allowed to determine the widths of constituent layers and compare obtained values with nominal ones. Fourier-transformed photoluminescence (FTPL) and photoreflectance (PR) measurements provided high signal to noise spectra, proving good optical and structural properties of investigated samples. A model of atoms interdiffusion processes was presented to explain observed small energy shifts of the transitions energies within the investigated multilayer structures.
关键词： MOCVD,optical spectroscopy,semiconductors,mid infrared,atoms interdiffusion,quantum cascade lasers
更新于2025-09-16 10:30:52
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Optical characterization of low temperature amorphous MoOX, WOX, and VOX prepared by pulsed laser deposition
摘要： Transition metal oxides are materials combining properties of electrical conductivity, optical transparency, and catalytical function. They are widely used in applications including solar cells, flat panel displays, and detectors. In particular, high work function oxides such as MoO3, WO3, and V2O5 have become popular. In many applications, low deposition temperatures are required, leading to amorphous structure. In this study, thin films of amorphous MoOX, WOX, and VOX were prepared by pulsed laser deposition, and their optical properties and work function were determined. Samples of polycrystalline ZnO were also prepared for comparison. Substrate temperature was varied in the range of 25 °C – 100 °C and oxygen pressure was varied in the range of 10 – 20 Pa during the process and also during the following sample cool-down and chamber venting. Optical characterization was based on photothermal deflection spectroscopy, which is a non-contact and non-destructive method for measuring directly absorptance spectra with sensitivity down to 10–4. Absorptance in the band gap serves as an indication of the presence of defects such as oxygen vacancies or metallic phases. Our optimized films achieved a sub-bandgap absorption coefficient as low as 103 cm-1 for MoOX, VOX, and 102 cm-1 in the case of the WOX. From the gradient of the absorption edge, Urbach energy was obtained, evaluating disorder in the semiconductor material. The work function of each material was obtained by Kelvin probe, and a slight correlation with Urbach energy was found. X-ray photoelectron spectroscopy indicated successful stochiometric transfer mainly for the lowest pressure and highest temperature samples.
关键词： work function,Urbach energy,optical spectroscopy,pulsed laser deposition,transparent metal oxide,photothermal deflection spectroscopy
更新于2025-09-12 10:27:22
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Double line waveguide amplifiers written by femtosecond laser irradiation in rare-earth doped germanate glasses
摘要： We report the production of active double waveguides in Er/Yb doped GeO2-PbO glasses, by direct femtosecond laser writing. The glasses were produced using the melt-quenching technique and the active waveguides were written using 30 fs laser pulses, at 800 nm, with writing speed of 0.06 mm/sec and pulse energy of 32 μJ. The photo-induced negative refractive index change was of -7.4x10-3. The Er/Yb doped sample showed a relative gain (signal enhancement of 7.5 dB/cm, for 105 mW of 980 nm pump power. The relative gain compensates both, the propagation losses and the absorption losses, and a positive maximum internal gain of 4.6 dB/cm can be obtained at the signal wavelength of 1550 nm. The results obtained in present work demonstrate that Er/Yb glasses are promising materials for the fabrication of integrated amplifiers, lossless components and lasers based on germanate glasses.
关键词： Optical materials,Laser processing,Optical spectroscopy,Amorphous materials
更新于2025-09-12 10:27:22
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A Comparative Investigation of Plasmonic Properties between Tunable Nanoobjects and Metallized Nanoprobes for Optical Spectroscopy
摘要： In order to evaluate the optical efficiency of tip-based probes for future tip-enhanced optical spectroscopy applications, we have developed an experimental setup based on the coupling of an achromatic inverted microscope equipped with a total internal reflection objective and an atomic force microscopy (AFM) head. This spectroscopic tool has been validated using individual nanofabricated antennas (gold nanodisks/nanocones) on a glass substrate, which act as nanoresonators based on localized surface plasmons. Spectrally tunable transverse electric and magnetic plasmonic resonances are identified and are in excellent agreement with numerical calculations performed as a function of the nano-antenna geometry and size. We have investigated a series of state-of-the-art gold-coated AFM probes, which are commonly used for tip-enhanced (Raman spectroscopy) optical experiments. Their scattering spectrum consists of resonances depending on the tip sharpness or granularity superimposed on a broad emission spectrum due to semi-infinite metal layer acting as a non-resonant antenna. From the comparison between the plasmonic response of both types of optical antennas, a new generation of probes for tip-enhanced optical spectroscopy is proposed, in which single plasmonic nano-antennas are engineered at the apex of a non-metallic AFM tip. As from numerical simulation results, such tips would ensure a spectral tunability as a function of the material, size, and geometry, together with expected high enhancement factors. Such features would allow the design of spectrally tunable surface enhanced Raman spectroscopy substrates, and should be a reliable and efficient alternative to tips commonly used in tip-enhanced optical spectroscopy experiments such as tip-enhanced Raman spectroscopy.
关键词： Optical Spectroscopy,Plasmonics,TERS,Nano-antennas,AFM
更新于2025-09-12 10:27:22
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Dark sub-gap states in metal-halide perovskites revealed by coherent multidimensional spectroscopy
摘要： Metal-halide perovskites show excellent properties for photovoltaic and optoelectronic applications, with power conversion efficiencies of solar cell and LEDs exceeding 20%. Being solution processed, these polycrystalline materials likely contain a large density of defects compared to melt-grown semiconductors. Surprisingly, typical effects from defects (absorption below the bandgap, low fill factor and open circuit voltage in devices, strong non-radiative recombination) are not observed. In this work, we study thin films of metal-halide perovskites CH3NH3PbX3 (X = Br,I) with ultrafast multidimensional optical spectroscopy to resolve the dynamics of band and defect states. We observe a shared ground state between the band-edge transitions and a continuum of sub-bandgap states, which extends at least 350 meV below the band edge). We explain the comparatively large bleaching of the dark sub-bandgap states with oscillator strength borrowing from the band-edge transition. Our results show that upon valence to conduction band excitation such sub-gap states are instantaneously bleached for large parts of the carrier lifetime and conversely, that almost dark sub-bandgap states can be populated by light excitation. This observation helps unraveling the photophysical origin of the unexpected optoelectronic properties of these materials.
关键词： photovoltaic,defect states,metal-halide perovskites,optoelectronic,ultrafast multidimensional optical spectroscopy
更新于2025-09-12 10:27:22
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Anharmonicity of Bi <sub/>2</sub> Se <sub/>3</sub> revealed by fs transient optical spectroscopy
摘要： We investigate the anharmonic effects in Bi2Se3 crystals using femtosecond transient optical spectroscopy at 5–280 K. The re?ectivity time series consist of exponential decay due to hot carriers and decaying oscillations due to the A1 1g phonon vibration. Vibration frequency and dephasing time of this optical phonon mode are obtained as a function of temperature, decreasing with increasing temperature; both the red shift in frequency and the increased dephasing rate induced by heating can be well described using the anharmonicity model including lattice thermal expansion and phonon-phonon coupling.
关键词： Bi2Se3,femtosecond transient optical spectroscopy,phonon dynamics,anharmonicity,thermal expansion,phonon-phonon coupling
更新于2025-09-11 14:15:04
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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) - UV Luminescence in Ho:ZBLAN Glasses
摘要： Compact, short-wavelength lasers are continuously considered as one of the most attractive among all coherent light sources. A very wide range of applications such as data storage, photolithography, medical diagnostics and sterilization motivates research and development on new active materials which can efficiently emit light in the UV spectral range. There are three general methods to achieve UV and visible light emission. The first are semiconductor-based LEDs and laser diodes - in the recent years a rapid progress in the field of semiconductor lasers has been observed resulting in a variety of commercially available short-wavelength laser diodes. These impressive devices, however, are not free from some disadvantages, like poor quality of the beam and limited output power. That’s why other sources continue to attract researchers’ attention. The second method deploys nonlinear crystals, which enable obtaining short wavelength emission by the frequency multiplication. The third way to achieve UV and visible light is to directly use the optical transitions within rare earth ions in solid state media [1-2]. This work is focused on this last method.
关键词： short-wavelength emission,Ho:ZBLAN glasses,optical spectroscopy,rare earth ions,UV luminescence
更新于2025-09-11 14:15:04
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Influence of the Anatase and Rutile phases on the luminescent properties of rare-earth-doped TiO2 films
摘要： For a long time, the development of new and more efficient light-emitting materials has been the driving force to investigate the presence of trivalent rare-earth (RE3+) ions into solid hosts. It happens because RE3+ ions provide efficient and well-defined optical transitions whose intensities are determined by phenomena regarding excitation-recombination mechanisms or, ultimately, by the RE3+ atomic surroundings. Motivated by these aspects, this paper presents a comprehensive study of the influence exerted by TiO2 (under the amorphous and crystalline forms) onto the light emission due to Sm3+ and Tm3+ ions. To this end, Sm-, Tm-, and SmTm-doped TiO2 films were prepared and their structural-electronic properties were investigated by optical spectroscopic techniques - following appropriate thermal annealing treatments. As a result of the deposition method and conditions, the as-deposited (stoichiometric) TiO2 films present an amorphous structure and single RE concentrations around 0.5 at.%. Also, whereas thermal annealing the films at increasing temperatures resulted in almost no changes in their elemental composition, extensive variations were observed in their atomic structure and RE3+-related light emission characteristics. Based on the experimental results, it became clear the role played by the amorphous or crystalline (Anatase or Rutile) structures of the TiO2 films onto the RE3+-related luminescence features, and the likely mechanisms behind the phenomenon are presented and discussed in detail.
关键词： Vapor deposition (IBAD),Optical spectroscopy,Optical properties,Oxide materials (TiO2)
更新于2025-09-10 09:29:36