High Harmonic Generation from Multiple Orbitals in N2 MCFARLAND, Brian K; FARRELL, Joseph P; BUCKSBAUM, Philip H ...
Science (American Association for the Advancement of Science),
11/2008, Letnik:
322, Številka:
5905
Journal Article
Recenzirano
Molecular electronic states energetically below the highest occupied molecular orbital (HOMO) should contribute to laser-driven high harmonic generation (HHG), but this behavior has not been observed ...previously. Our measurements of the HHG spectrum of N2 molecules aligned perpendicular to the laser polarization showed a maximum at the rotational half-revival. This feature indicates the influence of electrons occupying the orbital just below the N2 HOMO, referred to as the HOMO-1. Such observations of lower-lying orbitals are essential to understanding subfemtosecond/subangstrom electronic motion in laser-excited molecules.
Ultrathin metasurfaces with record‐high nonlinear optical response of 1.2 × 106 pm V−1 for second harmonic generation are experimentally demonstrated in the mid‐infrared spectral range. A second ...harmonic power conversion efficiency of 0.075% is achieved in a 400‐nm‐thick (λ/25) metasurface at a pump intensity of only 15 kW cm−2.
Recent studies have reported electromagnetic ion cyclotron (EMIC) waves with nonlinear second harmonics (SHs) whose frequency and wave number are twice those of the fundamental waves (FWs). In this ...paper, we provide detailed analyses of the cross‐band SH generation of EMIC waves in a multi‐ion plasma. In the presence of heavy ions, EMIC wave modes can be divided into distinct wave bands according to heavy ion gyrofrequencies, and the SH can exist in a wave band different from that of the FW. The SH can be generated around or even exactly on the normal modes of the plasma system, leading to a more efficient energy transfer than that in H+‐only plasmas. The detailed parametric analysis also manifests the vital role of heavy ions in promoting SH's amplitude. Further, multiple 1‐D hybrid simulations are performed to investigate the cross‐band SH generation and validate the theoretical results. The SHs are well reproduced in simulations and the quantitative relation of frequency and wave number between the FW and the SH is well satisfied. The variations of the amplitude ratios (the SH to the FW) with fundamental frequencies are well consistent with those obtained from theoretical calculations in magnitude. Therefore, our results demonstrate the significant roles of heavy ions in the SH generation.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) waves have recently been observed to have nonlinear second harmonics (SHs) with frequencies twice those of the fundamental waves (FWs). With the existence of heavy ions (He+ and O+), EMIC waves are categorized into three distinct wave bands in terms of heavy ion gyrofrequencies, i.e., H+ band, He+ band, and O+ band. In this situation, the FW in the He+ band could generate the SH in the H+ band. The cross‐band energy transfer would be expected to be more efficient than that in a singular H+ plasma, leading to larger amplitudes of the SH. But such effects of heavy ions on the SH generation have not been studied and verified in detail yet. In this letter, we provide theoretical analyses of the EMIC wave cross‐band energy transfer and utilize hybrid simulations to reproduce the SH generation and verify the theoretical results. Heavy ions are found to play significant roles in the SH excitation.
Key Points
The theoretical amplitude ratio of the fundamental to the second harmonic (SH) for electromagnetic ion cyclotron (EMIC) waves is obtained in cold multi‐ion plasmas
The cross‐band SHs of EMIC waves in multi‐ion plasmas are successfully reproduced by 1‐D hybrid simulations
Heavy ions can promote the cross‐band energy transfer efficiency from the fundamental waves to the SHs
A new nonlinear optical (NLO) oxysulfide, Sr6Cd2Sb6O7S10, which contains the functional groups SbOxS5−x7− (x=0, 1) with a 5s2 electron configuration, is synthesized by a solid‐state reaction. This ...compound displays a phase‐matchable second harmonic generation (SHG) response four times stronger than AgGaS2 (AGS) under laser irradiation at 2.09 μm. Single‐crystal‐based optical measurements reveal a SHG intensity that can be tuned by temperature and novel photoluminescence properties. Theoretical analyses demonstrate that tetragonal SbOS47− and SbS57− pyramids make the predominant contribution to the enhanced SHG effect. Among those, the SbOS47− units with mixed anions make a larger contribution. This work proposes that oxysulfide groups with an ns2 electron configuration can serve as new functional building units in NLO materials and opens a new avenue for the design of other optoelectronic materials.
A new nonlinear‐optical oxysulfide Sr6Cd2Sb6O7S10 containing multitype 5s2‐electron SbOxS5−x7− (x=0, 1) tetragonal pyramids displays a four‐times stronger phase‐matchable SHG response than AgGaS2 under 2.09 μm laser irradiation. Theoretical analyses demonstrate that the oxysulfide SbOS47− make predominate contribution to the enhanced SHG effect rather than sulfide SbS57−.
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•Amorphous ZnO thin films were grown using sol–gel technique.•X-Ray and AFM images were measured to investigate the structural properties.•Photoluminescence spectra and decay lifetime ...curves have been measured.•The SH and TH spectra were measured to investigate the NLO properties.•Second and third order nonlinear susceptibilities were calculated.
This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz and glass substrates at temperature equal to 350K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190–1100nm. Measurement of the polarized optical properties was shows a high transmissivity (80–99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films.
Plasmonic nanoantennas are efficient devices to concentrate light in spatial regions much smaller than the wavelength. Only recently, their ability to manipulate photons also on a femtosecond time ...scale has been harnessed. Nevertheless, designing the dynamical properties of optical antennas has been difficult since the relevant microscopic processes governing their ultrafast response have remained unclear. Here, we exploit frequency-resolved optical gating to directly investigate plasmon response times of different antenna geometries resonant in the near-infrared. Third-harmonic imaging is used in parallel to spatially monitor the plasmonic mode patterns. We find that the few-femtosecond dynamics of these nanodevices is dominated by radiative damping. A high efficiency for nonlinear frequency conversion is directly linked to long plasmon damping times. This single parameter explains the counterintuitive result that rod-type nanoantennas with minimum volume generate by far the strongest third-harmonic emission as compared to the more bulky geometries of bow-tie-, elliptical-, or disk-shaped specimens.
Microresonator-Based Optical Frequency Combs Kippenberg, T. J.; Holzwarth, R.; Diddams, S. A.
Science (American Association for the Advancement of Science),
04/2011, Letnik:
332, Številka:
6029
Journal Article
Recenzirano
The series of precisely spaced, sharp spectral lines that form an optical frequency comb is enabling unprecedented measurement capabilities and new applications in a wide range of topics that include ...precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. A new optical frequency comb generation principle has emerged that uses parametric frequency conversion in high resonance quality factor (Q) microresonators. This approach provides access to high repetition rates in the range of 10 to 1000 gigahertz through compact, chip-scale integration, permitting an increased number of comb applications, such as in astronomy, microwave photonics, or telecommunications. We review this emerging area and discuss opportunities that it presents for novel technologies as well as for fundamental science.
Second harmonic generation (SHG) of 2D crystals has been of great interest due to its advantages of phase‐matching and easy integration into nanophotonic devices. However, the polarization‐dependence ...character of the SHG signal makes it highly troublesome but necessary to match the laser polarization orientation relative to the crystal, thus achieving the maximum polarized SHG intensity. Here, it is demonstrated a polarization‐independent SHG, for the first time, in the van der Waals Nb3SeI7 crystals with a breathing Kagome lattice. The Nb3 triangular clusters and Janus‐structure of each Nb3SeI7 layer are confirmed by the STEM. Nb3SeI7 flake shows a strong SHG response due to its noncentrosymmetric crystal structure. More interestingly, the SHG signals of Nb3SeI7 are independent of the polarization of the excitation light owing to the in‐plane isotropic arrangement of nonlinear active units. This work provides the first layered nonlinear optical crystal with the polarization‐independent SHG effect, providing new possibilities for nonlinear optics.
Normally, the SHG signal intensity of nonlinear optical crystals is highly dependent on the angles between polarized light and crystal axis, resulting in big challenges in matching the laser polarization orientation. Hence, the polarization‐independent SHG effect discovered for the first time in layered Kagome Nb3SeI7 crystals is of great significance for nonlinear optics.
Optical Harmonic Generation in 2D Materials Khan, Ahmed Raza; Zhang, Linglong; Ishfaq, Kashif ...
Advanced functional materials,
01/2022, Letnik:
32, Številka:
3
Journal Article
Recenzirano
2D materials are emerging as ideal candidates for fundamental investigations and new technologies due to their unique optoelectronic properties. Giant nonlinear susceptibility and perfect phase ...matching in 2D materials lead to extraordinary nonlinear light matter interactions, thus enabling several potential applications and fundamental scientific discoveries in nonlinear optics. For instance, second harmonic generation in 2D materials play an important role in optical devices such as, lasers, tunable waveguides, electro‐optic modulators, and switches. This review will discuss optical harmonic generation (OHG) processes, various characterization modes, and tuning techniques in 2D materials. The future prospectives for OHG in 2D materials is discussed. The extremely promising attributes of combining nonlinear optics and 2D materials is becoming a highly important multidisciplinary field.
Optical harmonic generation (OHG) is reviewed in 2D materials. First, 2D materials are introduced with respect to their optical harmonic properties. Second, various types of characterization modes and tuning techniques in 2D materials are reviewed using their OHG properties. Finally, a review of 2D materials based device applications is presented based on their OHG properties.
Transition metal dichalcogenides (TMDs) have provided a fundamental stage to study light–matter interactions and optical applications at the atomic scale due to their ultrathin thickness and their ...appropriate band gap in the visible region. Here, we report the strong nonlinear optical effects, including second-harmonic generation (SHG) and third-harmonic generation (THG) in spiral WS2 structures. SHG intensity quadratically increases with layer numbers, other than diminishing the oscillation of 2H stacking TMDs. The contrary SHG behavior is attributed to the broken symmetry from twisted screw structures, revealed by aberration-corrected transmission electronic microscope observation. Furthermore, the twist angle of the screw structure (5 degrees) was obtained by high-resolution transmission microscope measurements and confirmed by polarization tests of SHG output. Moreover, we roughly estimate the effective second-order nonlinear susceptibility. The discovery and understanding of the accumulation of nonlinear susceptibility of spiral structures with increasing thickness will extend the nonlinear applications of TMDs.
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