Optical Harmonics Research Articles

Exciton Spectroscopy of Semiconductors by the Method of Optical Harmonics Generation (Review)

Nonlinear optical phenomena are widely used for the study of semiconductor materials. The paper presents an overview of experimental and theoretical studies of excitons by the method of optical second and third harmonics generation in various bulk semiconductors (GaAs, CdTe, ZnSe, ZnO, Cu$_2$O, (Cd,Mn)Te, EuTe, EuSe), and low-dimensional heterostructures ZnSe/BeTe. Particular attention is paid to the role of external electric and magnetic fields that modify the exciton states and induce new mechanisms of optical harmonics generation. Microscopic mechanisms of harmonics generation based on the Stark effect, the spin and orbital Zeeman effects, and on the magneto-Stark effect specific for excitons moving in an external magnetic field are considered. This approach makes it possible to study the properties of excitons and to obtain new information on their energy and spin structure that is not available when the excitons are investigated by linear optical spectroscopy. As a result of these studies, a large amount of information was obtained, which allows us to conclude on the establishing of a new field of research - exciton spectroscopy by the method of optical harmonics generation.

A Fluorimeter on the Basis of a Femtosecond Cr+4: Forsterite Laser

An apparatus for measuring luminescence lifetimes using the femtosecond up-conversion method is presented. A laser system based on a chromium–forsterite crystal with a lasing wavelength of 1250 nm is used to generate ultrashort pulses. Luminescence is excited in a sample by optical harmonics that are generated in nonlinear optical crystals. The width of the instrument function of the system is 200 fs. Methods for optimizing the signal-to-noise ratio in measurements are discussed. The results of measurements of the fluorescence- decay dynamics and the anisotropy of aqueous solutions of an inclusion complex of the 4-DASPI styrene dye in cucurbit[6]uril on short (5 ps) and long (500 ps) time scales are presented.

Crystal Structure and Properties of Levofloxacinium 2-Thiobarbiturate Trihydrate

The structure of levofloxacinium 2-thiobarbiturate trihydrate LevoH 2 + Htba–·3H2O (I) (LevoH is levofloxacin, H2tba is 2-thiobarbituric acid) is determined (CIF file CCDC No. 1547466); its thermal decomposition and IR spectrum are studied. The crystals of I are triclinic: a = 8.670(1) A, b = 9.605(1) A, c = 15.786(2) A, α = 89.144(5)°, β = 88.279(5)°, γ = 76.068(5)°, V = 1275.4(3) A3, space group P1, Z = 2. The unit cell of I contains two LevoH 2 + ions, two Htba– ions, and six H2O molecules. The absolute structure of the crystal and the configuration of the chiral center in a levofloxacin molecule S are determined. Experiments for generating the second optical harmonics gave a positive result. Intermolecular hydrogen bonds (HBs) N–H···O and O–H···O in I form a bilayer system along the ab diagonal with hydrophilic moieties within a layer and hydrophobic moieties directed outward. The structure is stabilized by multiple HBs and the π–π interaction between the Htba–and LevoH 2 + ions and between the LevoH 2 + ions.

Enhancement of Nonlinear Optical Effects in Porous Composite Plasmonic Structures

A method for formation of bulk plasmonic structures based on porous quartz with silver nanoparticles in pores has been proposed and implemented. The spectroscopy of their optical and nonlinear optical properties has been performed by methods of second harmonic generation and two-photon absorption. A significant increase in the nonlinear absorption coefficient has been detected in the plasmon resonance region. The enhancement of the second optical harmonic has been observed with the shift by tens of nanometers from the plasmon resonance position toward the long-wavelength region.

Transmission Spectra and Optical Properties of a Mesoporous Photonic Crystal Based on Anodic Aluminum Oxide

Optical properties of a one-dimensional photonic-crystal film with a lattice period of ≈380 nm formed by electrochemical etching of an aluminum foil are investigated. Experimental data on the spectra of transmission and reflection in the region of the first, second, and third stop bands of anodic photonic crystal of aluminum oxide are compared with a theoretical dependence obtained from the well-known dispersion relation. The possibility of creating selective narrow-band optical filters based on mesoporous one-dimensional photonic crystals is analyzed. The conditions of enhancement of an electromagnetic field of laser radiation at 532 nm under normal incidence on a photonic-crystal surface are established. The possibility of generation of optical harmonics under the conditions of sharp increase in the effective field of the driving radiation in a mesoporous photonic crystal of anodic aluminum oxide filled with lithium iodate is analyzed.

Международная школа-семинар Экситоны в кристаллах и полупроводниковых наноструктурах", посвященная 120-летию со дня рождения Е. Ф. Гросса, Санкт-Петербург 10-12 октября 2017 года Экситонная спектроскопия полупроводников методом генерации оптических гармоник [1mm] (О б з о р)

AbstractNonlinear optical phenomena are widely used for the study of semiconductor materials. The paper presents an overview of experimental and theoretical studies of excitons by the method of optical second and third harmonics generation in various bulk semiconductors (GaAs, CdTe, ZnSe, ZnO, Cu_2O, (Cd,Mn)Te, EuTe, EuSe), and low-dimensional heterostructures ZnSe/BeTe. Particular attention is paid to the role of external electric and magnetic fields that modify the exciton states and induce new mechanisms of optical harmonics generation. Microscopic mechanisms of harmonics generation based on the Stark effect, the spin and orbital Zeeman effects, and on the magneto-Stark effect specific for excitons moving in an external magnetic field are considered. This approach makes it possible to study the properties of excitons and to obtain new information on their energy and spin structure that is not available when the excitons are investigated by linear optical spectroscopy. As a result of these studies, a large amount of information was obtained, which allows us to conclude on the establishing of a new field of research—exciton spectroscopy by the method of optical harmonics generation.

Highly efficient optical parametric amplifier tunable from near- to mid-IR for driving extreme nonlinear optics in solids.

We have developed a robust optical parametric amplifier (OPA) based on three-AgGaS2-crystal pumping by a Cr:Forsterite GW femtosecond laser system, generating 150fs pulses in dual bands of 1.6-2.0μm (signal wave) and 3.5-5.5μm (idler wave). By introducing a negative prechirp to the pump, a combined efficiency in two waves of greater than 10% was achieved, with signal energy up to 110μJ and idler energy up to 43μJ. Operation parameters of the system (intensity up to 90 TW/cm2) make OPA a promising tool for driving nonlinear optical phenomena, including generation of optical harmonics and laser-induced extreme states of matter in solids and liquids. As a proof of principle, we generated harmonics up to the sixth order and sum frequencies in 5mm thick polycrystalline ZnSe.

Optical properties of mesoporous photonic crystals, filled with dielectrics, ferroelectrics and piezoelectrics

At present, it is very important to create new types of mirrors, nonlinear light frequency transformers and optical filters with controlled optical properties. In this connection, it is of great interest to study photonic crystals. Their dielectric permittivity varies periodically in space with a period permitting Bragg diffraction of light. In this paper, we have investigated the optical properties of mesoporous three-dimensional (3D) opal-type and one-dimensional (1D) anodic alumina photonic crystals, filled with different dielectrics, ferroelectrics and piezoelectrics. We have compared the optical properties of initial mesoporous photonic crystals and filled with different substances. The possibility of mesoporous photonic crystals using selective narrow-band light filters in Raman scattering experiments and nonlinear mirrors has been analyzed. The electromagnetic field enhancing in the case of exciting light frequency close to the stop band edges has been established. The optical harmonics and subharmonics generation in mesoporous crystals, filled with ferroelectrics and piezoelectrics was proposed.

Multiphoton Effects Enhanced due to Ultrafast Photon-Number Fluctuations.

The rate of an n-photon effect generally scales as the nth order autocorrelation function of the incident light, which is high for light with strong photon-number fluctuations. Therefore, "noisy" light sources are much more efficient for multiphoton effects than coherent sources with the same mean power, pulse duration, and repetition rate. Here we generate optical harmonics of the order of 2-4 from a bright squeezed vacuum, a state of light consisting of only quantum noise with no coherent component. We observe up to 2 orders of magnitude enhancement in the generation of optical harmonics due to ultrafast photon-number fluctuations. This feature is especially important for the nonlinear optics of fragile structures, where the use of a noisy pump can considerably increase the effect without overcoming the damage threshold.

Parametric Amplification of Phase‐Locked Few‐Cycle Pulses and Ultraviolet Harmonics Generation in Solids at High Repetition Rate

AbstractA high‐power femtosecond Yb:fiber system is seeded by a phase‐locked Er:fiber source and drives an ultra‐broadband optical parametric amplifier that operates at 10 MHz repetition rate. The resulting pulses display precise control of the carrier‐envelope phase. Their 8.3 fs temporal duration corresponds to 2.3 optical cycles of the 1100 nm carrier wavelength. Focusing 200 nJ of pulse energy into widegap materials generates optical harmonics up to fifth order. Even in a perturbative regime, strong effects of the carrier‐envelope phase on the emitted spectra are observed.

Development of a virtual metrology method using plasma harmonics analysis

A virtual metrology technique based on plasma harmonics is developed for predicting semiconductor processes. From a plasma process performed by 300 mm photoresist stripper equipment, a strong correlation is found between optical plasma harmonics intensities and the process results, such as the photoresist strip rate and strip non-uniformity. Based on this finding, a general process prediction model is developed. The developed virtual metrology model shows that the R-squared (R2) values between the measured and predicted process results are 95% and 64% for the photoresist strip rate and photoresist strip non-uniformity, respectively. This is the first research on process prediction based on optical plasma harmonics analysis, and the results can be applied to semiconductor processes such as dry etching and plasma enhanced chemical vapor deposition.

Population Dynamics of Ground State Sublevels: Influence on Polarization Properties of High Harmonics

Within the framework of the non-perturbative light–atom interaction theory, we consider the population dynamics of the ground-state sublevels corresponding to the different values of the orbital quantum number (l) projections and its influence on the high optical harmonics. We study the problem of high optical harmonics generation in two geometries: (1) two linearly polarized fields at frequencies ω and 2ω for different angles of azimuthal projection difference and arbitrary orientation with respect to the angular momentum of the atom direction; (2) two elliptically polarized fields at frequencies ω and 2ω rotating in opposite directions with variable mutual ellipticity. We show that the unequal population dynamics of the levels with different projections of the atom angular momentum (magnetic quantum number) has a significant impact on the value of the ellipticity of the generated radiation.

Stabilized chip-scale Kerr frequency comb via a high-Q reference photonic microresonator.

We stabilize a chip-scale Si3N4 phase-locked Kerr frequency comb via locking the pump laser to an independent stable high-Q reference microresonator and locking the comb spacing to an external microwave oscillator. In this comb, the pump laser shift induces negligible impact on the comb spacing change. This scheme is a step toward miniaturization of the stabilized Kerr comb system as the microresonator reference can potentially be integrated on-chip. Fractional instability of the optical harmonics of the stabilized comb is limited by the microwave oscillator used for a comb spacing lock below 1 s averaging time and coincides with the pump laser drift in the long term.

Angle-resolved multioctave supercontinua from mid-infrared laser filaments

Angle-resolved spectral analysis of a multioctave high-energy supercontinuum output of mid-infrared laser filaments is shown to provide a powerful tool for understanding intricate physical scenarios behind laser-induced filamentation in the mid-infrared. The ellipticity of the mid-infrared driver beam breaks the axial symmetry of filamentation dynamics, offering a probe for a truly (3+1)-dimensional spatiotemporal evolution of mid-IR pulses in the filamentation regime. With optical harmonics up to the 15th order contributing to supercontinuum generation in such filaments alongside Kerr-type and ionization-induced nonlinearities, the output supercontinuum spectra span over five octaves from the mid-ultraviolet deep into the mid-infrared. Full (3+1)-dimensional field evolution analysis is needed for an adequate understanding of this regime of laser filamentation. Supercomputer simulations implementing such analysis articulate the critical importance of angle-resolved measurements for both descriptive and predictive power of filamentation modeling. Strong enhancement of ionization-induced blueshift is shown to offer new approaches in filamentation-assisted pulse compression, enabling the generation of high-power few- and single-cycle pulses in the mid-infrared.

Side-Mode Excitation in Single-Mode Laser Diodes

A double-peaked spectrum in some distributed feedback laser diodes is demonstrated to relate to axially confined catastrophic optical damage (COD), followed by the excitation of a transversal optical mode. The melting-regrowth kinetics of CODs also reveal another possibility of COD-induced side optical modes in a fiber distributed Bragg reflector pump laser diode. A third case completely reverses the cause-effect relationship between CODs and lateral optical harmonics.

Spectra of secondary emission during generation of optical harmonics in globular photonic crystals

Secondary emission spectra of globular silica photonic crystals when their surfaces were exposed to laser pulses 250 fs long at a power density to 1 TW/cm2 have been studied. Optical harmonics and plasma emission were detected in this case. For the opal matrix containing pores filled with air, in the reflection mode, the third optical harmonic with a conversion efficiency of ∼10% arises. The highest conversion efficiency for exciting radiation with wavelengths of 1026 or 513 nm is implemented when the frequencies of the exciting radiation or the second harmonic are near the stop band edge. In globular photonic crystals filled with sodium nitrite or barium titanate ferroelectrics, the second optical harmonic is observed. The exciting radiation conversion efficiency to the second optical harmonic was a few percent and depended on the frequency of exciting radiation and photonic crystal globule diameters. It is found that the plasma emission intensity increases with the exciting radiation power density. The dependences of the intensity of the second and third optical harmonics on the pump intensity are constructed for various photonic crystal globule diameters.

Mid-infrared-to-mid-ultraviolet supercontinuum enhanced by third-to-fifteenth odd harmonics.

A high-energy supercontinuum spanning 4.7 octaves, from 250 to 6500nm, is generated using a 0.3-TW, 3.9-μm output of a mid-infrared optical parametric chirped-pulse amplifier as a driver inducing a laser filament in the air. The high-frequency wing of the supercontinuum spectrum is enhanced by odd-order optical harmonics of the mid-infrared driver. Optical harmonics up to the 15th order are observed in supercontinuum spectra as overlapping, yet well-resolved peaks broadened, as verified by numerical modeling, due to spatially nonuniform ionization-induced blue shift.

High-order optical vortex harmonics generated by relativistic femtosecond laser pulse**Project supported by the National Basic Research Program of China (Grant Nos. 2013CBA01501 and 2013CBA01504), the National Key Scientific Instrument and Equipment Development Project, China (Grant No. 2012YQ120047), CAS Key Program and National Natural Science Foundation of China (Grant Nos. 11135012 and 11375262), and a Project of Higher Educational Science and

Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional (2D) particle-in-cell (PIC) simulation, we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape. This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics.

Preface to the second special issue on Terahertz Wave Science, Technology, and Application

Terahertz (THz) frequency region has attracted considerable interest, due to its unique nature and promising applications. A number of breakthroughs were achieved by the worldwide research groups in this field, including high-performed sources, detectors, functional devices, interaction with materials as well as applications. Previously, the first special issue on “Terahertz Wave Science, Technology, and Application” was presented (June 2014). This is the second special Issue with 3 review articles and 8 research articles, which introduce and discuss recent developments of relevant subjects. These papers can be divided into such categories: nonlinear optical response of grapheme, semiconductor activated metamaterials, superconducting metamaterials, THz generation with air and GaAs photoconductive antenna, double-probe-pulse THz detection, applications in sensing, imaging and spectroscopy, and so on. Prof. Chao Zhang and coworkers of University of Wollongong reviewed the recent developments of nonlinear optical response of graphene in THz and near-infrared frequency regime. Prof. Hou-Tong Chen of Los Alamos National Laboratory reviewed the recent progresses on semiconductor activated THz metamaterials. Prof. Weili Zhang and coworkers of Tianjin University reviewed the recent results on tailoring electromagnetic responses in THz superconducting metamaterials. In the research articles, Prof. Kun Zhao’s group of China University of Petroleum reported the detection of nheptane, n-octane and nitrate solutions with THz time-domain spectroscopy. Prof. Zhi Hong and coworkers of China Jiliang University investigated a high Q THz asymmetrically coupled resonator and its sensing performance. Prof. Alexander Shkurinov’s group of Lomonosov Moscow State University demonstrated the simultaneous generation of nonlinear optical harmonics and THz radiation in air: polarization discrimination of various nonlinear contributions. Prof. J. Bianca Jackson and coworkers of Ecole Polytechnique applied THz pulse imaging in archaeology. Dr. Haiwei Du of RIKEN investigated optical ionization evolution effect on photocurrent produced from two-color femtosecond laser pulses. Prof. Jinsong Liu’s group presented the studies on the behavior of GaAs photoconductive antenna. The articles in this special issue have certain significance for promoting the development of THz technology. It is hoped that the second special issue will benefit THz applications. On behalf of the editorial committee, we express our sincere thanks to all the authors and reviewers for their great contribution to this special issue. Also, we thank the editorial committee members for their excellent assistance. Finally, we are grateful to the editorial staff for their help, also thanks for my research assistants Dr. Pengxiang Liu, Dr. Lanju Liang and Yating Zhang. Without all of the contributions of these hard-working, dedicated people, it would have been impossible to produce this second special issue.

Miniature multioctave light source based on a monolithic microcavity

Optical microresonators are ideal tools for the reduction of the threshold of optical parametric oscillation based on four-wave mixing. Usually, the efficiency and bandwidth of the resonant process are interdependent due to stringent phase matching requirements leading to limitation of the bandwidth of the spectrum generated for a given pump power. We demonstrate a continuous-wave low-threshold resonant optical parametric oscillator with optical spectral span ranging from 0.36 to 1.6 μm. Harmonic generation is observed when a MgF2 microresonator characterized by quality factor approaching 1010 is pumped either at 780 nm, with a standard distributed-feedback semiconductor laser, or at 698 nm, with a reflective amplifier. Pump power does not exceed 25 mW. The nonlinear process is phase matched due to χ(3)-facilitated interaction of different mode families of the resonator. The optical harmonics generated can be used to seed high-power visible lasers, generate correlated photon pairs, and perform spectroscopy measurements.